MSOP-MGS Aerobraking Status Reports for 1999

Tuesday, December 29 (DOY 357/19:00:00 to DOY 363/19:00:00 UTC)

Last Orbit Covered by this Report = 953

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 380

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 4648 km
Apoapsis altitude decrease since start of aerobraking = 49378 km

Periapsis altitude = 111.1 km

Current Orbit Period = 03:41:40
Orbit Period decrease since start of aerobraking = 41:17:53

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues excellent aerobraking performance. Each periapsis pass reduces the orbit period by about 21 seconds which continues to under perform the current reset target but removes some excess margin that must be deleted prior to ending Phase 2. Currently, the period is about 3.5 minutes ahead of the baseline. The dynamic pressure 8-orbit running mean is now 0.132 N/m2 which is within the desired corridor, 0.11 N/m2 to 0.17 N/m2. No periapsis raise maneuvers were required this period.

Currently, sequence P948 is controlling the S/C activities. It will be replaced later this afternoon with P955 which will control activities starting with orbit 955 through orbit 960. No backup orbits were executed this period. All sequences built this period had 7 primary orbits and 3 backups to maintain a primary shift build schedule. Periapsis timing predictions have been slightly off due to higher dynamic pressure estimations than actual. An interim sequence, P953, was built following the results of orbit 951 by applying a timing bias to the current solution in use. The uplink of this sequence was aborted due to realization the bias was applied in the wrong direction. An ISA will be opened to document the event. The periapsis timing data received by later orbits show the expected timing errors to be high but not beyond the S/C performance capability. Another interim sequence, P954 was prepared but not used.

The backup SCP remains in contingency mode this period. A recovery sequence that runs only on SCP2, has been prepared and tested in the STL. The final version will be built today to target SCP2 recovery for tomorrow right after the periapsis pass of orbit 960, DOY 364/20:31:00 SCET. During this period the S/C will be in Inertial Slew Hold (ISH), Earth pointed. The Load & Go sequence running in SCP2 will configure its flight parameters to be identical to those running in the primary processor. This sequence and the drag sequence running in SCP1 will command their processors to Array Normal Spin at precisely the same time, returning SCP2 to nominal operation.

Having SCP2 operating the aerobraking sequence along with the control SCP provides redundancy in case a processor hardware failure occurs on SCP1 without invoking contingency mode. The capability for a seamless transition to the backup SCP will once again be possible.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Because of the new S/C orientation during the drag pass, sun sensor data is no longer available on the -Y solar array panel. Therefore, no peak deflection data is retrieved during drag. The new orientation was required for power generation on the +Y panel before, during and immediately following the pass as well as payload sun avoidance concerns. While the backup SCP is in contingency mode, the high rate data from the accelerometers has been cut in half. This has affected the calculations for the structural frequency, which now registers a little higher than before.

Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with battery discharge depths now only 4 to 5% each drag pass with 35 minutes of re-charge margin. Battery 2 charge rate periodically is being set to a lower level by software and sometimes results in 2% charge shortfall. This is caused by a software conflict between tasks that control different power tasks. The under charge is always recovered later in the orbit and there is no concern for hardware health. When the eclipse season begins in the next few days, the charge rate will be set correctly and this feature will go away. Commands have been sent to manually set the V/T curve settings to level 6. The minimum MOLA laser temperature observed this period was 13.0 °C now being warmed by the Earth pointed power generation maneuver that’s being performed each orbit. The telecommunications subsystem continues solid performance.

System Test Lab (STL) validation of 2 am flight software changes continue. The SCP2 contingency mode recovery has been tested. The updated aerobraking parameters and new contingency mode script have also been validated.

UPCOMING EVENTS:

Periapsis for Orbit 954 DOY363/21:40:02 UTC Through
Periapsis for Orbit 972 DOY001/15:30:40 UTC

(Note: MST = UTC-7 hours DOY363=12/29)

SPACECRAFT COMMANDING:

There were 24 command files radiated to the S/C during this period. The total files radiated since launch is now 3104. These commands were sent in support of the following activities:

Nominal drag pass sequences (P917, P923, P929, P935, P942, P948)

Nominal corridor control maneuver sequences (none)

Command loss timer resets

Nominal star catalogs and ephemeris file updates

Set SCP2 C’Mode’Active’Flag

Express engineering data playback

Battery VT-Curve commands

KaBLE experiment off

Aborted attempt for interim sequence P953

Last Orbit Covered by this Report = 879

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 306

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 5493 km
Apoapsis altitude decrease since start of aerobraking = 48532 km

Periapsis altitude = 115.3 km

Current Orbit Period = 04:06:46
Orbit Period decrease since start of aerobraking = 40:52:47

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues excellent aerobraking performance. Each periapsis pass reduces the orbit period by about 27 seconds which prevents increasing the margin against the baseline. Eventually, the margin will need to be removed to assure the 1.9 hour target period is not reached before the 2:00 am LST can be achieved. For now, being ahead of the plan allows for a short interruption in aerobraking without giving up final orbit targets. Currently, the period is about 12 minutes ahead of the baseline. The dynamic pressure 7-orbit running mean is now 0.121 N/m2 which is within the desired corridor, 0.11 N/m2 to 0.17 N/m2. A periapsis raise maneuver was executed on orbit 873 to lower the drag force to the lower part of the desired corridor. This will assure no increase in the margin from the baseline plan. The orbit-to-orbit dynamic pressure variability has been has been much lower the past three days with variations over the entire reporting period registering 46%, following a periapsis raise maneuver.

Currently, sequence P875 is controlling the S/C activities. It will be replaced later this afternoon with P881 which will control activities starting with orbit 881 through orbit 886. No backup orbits were executed this period. All sequences built this period had 6 primary orbits and 3 backups to maintain a primary shift build schedule. Periapsis timing predictions by the Nav team continue to be outstanding, enabling prime shift sequence builds. The aerobraking weekly reset meeting was held on Wednesday. Starting with P875, all sequences will no longer contain the third engineering data playback due to the receding orbit period.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. The structural stiffness data is becoming more reliable now that the sun sensor on the -Y array is being illuminated during peak deflection. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with battery discharge depths ranging from 11.4% to 14.3%. Sun avoidance maneuvers occur about every third orbit and contribute the higher DoD. There are 8 minutes of primary charger margin following the deeper discharges. The minimum MOLA laser temperature observed this period was 12.0 °C using a 30 minute warming maneuver each orbit. The telecommunications subsystem continues solid performance.

System Test Lab (STL) validation of 2 am flight software changes continue. Commands to re-pressurize the propulsion system were built and tested successfully. Preparations are underway to test the fixed HGA mapping sequence and an aerobraking sequence with eclipse parameters included, featuring the post-periapsis roll-out to Earth-pointed power generation / MOLA warming maneuver.

UPCOMING EVENTS:

Periapsis for Orbit 880 DOY351/21:21:47 UTC Through
Periapsis for Orbit 903 DOY355/18:12:15 UTC

(Note: MST = UTC-7 hours DOY351=12/17)

SPACECRAFT COMMANDING:

There were 10 command files radiated to the S/C during this period. The total files radiated since launch is now 3061. These commands were sent in support of the following activities:

Nominal drag pass sequences (P869, P875)

Nominal corridor control maneuver sequences (A873)

Command loss timer resets

Nominal star catalogs and ephemeris file updates

Last Orbit Covered by this Report = 862

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 289

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 5745 km
Apoapsis altitude decrease since start of aerobraking = 48281 km

Periapsis altitude = 113.8 km

Current Orbit Period = 04:14:14
Orbit Period decrease since start of aerobraking = 40:45:19

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft maintains excellent performance as Phase 2 aerobraking operations continue. Each periapsis pass reduces the orbit period by about 30 seconds which keeps the period reduction profile even with the planned period reduction for the week. Currently, the period is about 12 minutes ahead of the baseline. The dynamic pressure 7-orbit running mean is now 0.131 N/m2 which is within the desired corridor, 0.11 N/m2 to 0.17 N/m2. A periapsis raise maneuver was executed on orbit 845 to lower the drag force and to assure Phobos avoidance. Phobos was missed by about 300 km on orbit 849 and future encounters will not be any closer since the MGS orbit is now totally within the Phobos orbit. The orbit-to-orbit dynamic pressure variability has been as high as 55% during this period.

Currently, sequence P858 is controlling the S/C activities. It will be replaced later this afternoon with P863 which will control activities starting with orbit 863 through orbit 869. No backup orbits were executed this period. All sequences built this period had 6 primary orbits and 3 backups to maintain a primary shift build schedule. Periapsis timing predictions by the Nav team continue to be outstanding enabling prime shift sequence builds.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with battery discharge depths ranging from 11.4% to 14.3%. Sun avoidance maneuvers occur about every third orbit and contribute the higher DoD. There are 8 minutes of primary charger margin following the deeper discharges. The minimum MOLA laser temperature observed this period was 12.0 °C using a 30 minute warming maneuver each orbit. The telecommunications subsystem continues solid performance. The uplink for the P847 sequence failed due to a missing message. This occurred over DSS-34 on 98-345/20:27:31. The sequence was re-radiated in whole and was successful the second time.

System Test Lab (STL) validation of 2 am flight software changes continue. Preparations are underway to test the fixed HGA mapping sequence and an aerobraking sequence with eclipse parameters included, featuring the post-periapsis roll-out to Earth-pointed power generation / MOLA warming maneuver.

UPCOMING EVENTS:

Periapsis for Orbit 863 DOY348/22:33:21 UTC Through
Periapsis for Orbit 873 DOY350/16:25:31 UTC

(Note: MST = UTC-7 hours DOY348=12/14)

SPACECRAFT COMMANDING:

There were 14 command files radiated to the S/C during this period. The total files radiated since launch is now 3051. These commands were sent in support of the following activities:

Nominal drag pass sequences (P836, P841, P847, P852, P858, P863)

Nominal corridor control maneuver sequences (A845)

Command loss timer resets

Last Orbit Covered by this Report = 834

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 261

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 6203 km
Apoapsis altitude decrease since start of aerobraking = 47822 km

Periapsis altitude = 112.1 km

Current Orbit Period = 04:28:10
Orbit Period decrease since start of aerobraking = 40:31:23

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

Excellent spacecraft performance continues as Phase 2 aerobraking operations continue. Each periapsis pass reduces the orbit period by about 36.5 seconds with 30 seconds per pass required to maintain the baseline glide slope. Currently, the period is about 11 minutes ahead of the baseline. The dynamic pressure 7-orbit running mean is now 0.183 N/m2 which is higher than the new desired corridor which is 0.11 N/m2 to 0.17 N/m2. A periapsis raise maneuver was executed on orbit 834 to lower the drag force and to assure Phobos avoidance. Because the uncertainty in future period reduction, the Phobos encounters must be monitored regularly. The orbit-to-orbit dynamic pressure variability is still high but lower than last period. The lowest drag force of 0.08 N/m2 was experienced on orbit 820 and the high was 0.28 N/m2 recorded on orbit 830.

Currently, sequence P831 is controlling the S/C activities. It will be replaced later this evening with P836 which will control activities starting with orbit 836 through orbit 840. No backup orbits were executed this period. Future sequences, starting with P836, will have 6 primary orbits and 3 backups to maintain a primary shift build schedule. Periapsis timing predictions by the Nav team have been excellent, which continues to allow prime shift builds.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with battery discharge depths ranging from 12% to 17%. Sun avoidance maneuvers cost about 5% extra DoD when they occur. The primary charger connect duration has been increased by 15 minutes to accommodate these maneuvers. The minimum MOLA laser temperature observed this period was 9.6 °C using a 20 minute warming maneuver each orbit. Due to the Array Normal Spin (ANS) Earth pointing angle phasing, the MOLA laser does not receive quite as much heating as observed earlier. The warming maneuver duration has been increased by 10 minutes to assure higher temperatures. The largest temperature increase due to aero-heating was 58°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

Mapping preparations continue with STL checkout of the 2 am mapping profile. Final SCT preparations have been made for the MCO launch, now scheduled for Friday. The MCO status reports will be published separately starting with launch.

UPCOMING EVENTS:

Periapsis for Orbit 835 DOY343/21:06:17 UTC Through
Periapsis for Orbit 862 DOY348/17:28:32 UTC

(Note: MST = UTC-7 hours DOY343=12/9)

SPACECRAFT COMMANDING:

There were 13 command files radiated to the S/C during this period. The total files radiated since launch is now 3037. These commands were sent in support of the following activities:

Nominal drag pass sequences (P816, P821, P826, P831)

Nominal corridor control maneuver sequences (A834)

Command loss timer resets

Nominal star catalog and ephemeris file updates

Last Orbit Covered by this Report = 813

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 240

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 6617 km
Apoapsis altitude decrease since start of aerobraking = 47409 km

Periapsis altitude = 112.6 km

Current Orbit Period = 04:40:56
Orbit Period decrease since start of aerobraking = 40:18:37

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft maintains excellent performance during Phase 2 aerobraking operations. The orbit period has been reduced more than 10.0 minutes over the past 15 orbits. The rate of period reduction has been reduced to maintain the planned slope. The dynamic pressure 7-orbit running mean is now 0.145 N/m2 which is near the low end of the 0.14 to 0.20 N/m2 desired corridor. A small periapsis raise maneuver has been built and loaded that will lower the drag force for the following orbits, especially 819 which was predicted to peak at about 0.36 N/m2 without the maneuver. The orbit-to-orbit dynamic pressure variability has remained high for this period. The lowest drag force of 0.10 N/m2 was experienced on orbit 807 and the high was 0.38 N/m2 recorded on orbit 803.

Currently, sequence P811 is controlling the S/C activities. It will be replaced later this evening with P816 which will control activities starting with orbit 816 through orbit 820. Another orbit, 806, was executed using the backup commands this period. Orbit timing was good and no excessive fuel use was noted.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. The stiffness calculation, when available, continues to show no further structural degradation. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with battery discharge depths ranging from 10.5% to 15%. The larger DoD occurs when the attitude control system performs a Sun avoidance maneuver following the drag pass. Except for orbits with Sun avoidance maneuvers, there continues to be positive re-charge margin each orbit. The minimum MOLA laser temperature observed this period was 9.9 °C using a 20 minute warming maneuver each orbit. Due to the Array Normal Spin (ANS) Earth pointing angle phasing, the MOLA laser does not receive quite as much heating as observed earlier. The largest temperature increase due to aero-heating was 61°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

UPCOMING EVENTS:

Periapsis for Orbit 814 DOY339/21:04:36 UTC Through
Periapsis for Orbit 829 DOY342/18:00:00 UTC

(Note: MST = UTC-7 hours DOY339=12/5)

SPACECRAFT COMMANDING:

There were 6 command files radiated to the S/C during this period. The total files radiated since launch is now 3024. These commands were sent in support of the following activities:

Nominal drag pass sequences (P801, P807, P811)

Nominal corridor control maneuver sequences (A804, A814)

Command loss timer resets

Last Orbit Covered by this Report = 798

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 225

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 6940 km
Apoapsis altitude decrease since start of aerobraking = 47086 km

Periapsis altitude = 111.7 km

Current Orbit Period = 04:51:03
Orbit Period decrease since start of aerobraking = 40:08:30

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft maintains excellent performance during Phase 2 aerobraking operations. The orbit period has been reduced by about 8.7 minutes over the past 10 orbits. The current period maintains about 9 minutes margin on the baseline plan. At today’s reset meeting, the desired dynamic pressure corridor was lowered and is now bounded by 0.14 N/m2 and 0.20 N/m2. It was lowered to follow the baseline plan. The dynamic pressure 7-orbit running mean is 0.222 N/m2 which is above the new trigger limit. A 0.45 m/s periapsis raise maneuver was ordered and will execute on the apoapsis portion of orbit 804 to lower the drag pass forces to about the middle of the new corridor. The orbit-to-orbit dynamic pressure variability has remained high for this period. The lowest drag force of 0.11 N/m2 was experienced on orbit 794 and the high was recorded on the last orbit, 798, registering 0.36 N/m2.

Currently, sequence P795 is controlling the S/C activities. It will be replaced early tomorrow morning with P801 which will control activities starting with orbit 801 through orbit 805. At the reset meeting held today, the decision was made to continue to use 5 primary orbit sequences, but start the builds using the third predicted orbit from the navigation team. Due to Earth occultation and shrinking orbit period, there is no longer sufficient time to build, review and load sequences before they are needed unless this change is made. This requires the Nav team to generate 7 orbit predictions. In order to transition to this strategy, orbit 800 is being allowed to execute as a backup orbit from sequence P795. The program set, ABGEN, was re-delivered today which removes the ‘send’two’word’ command from the drag sequences. This was done in response to last week’s unintentional cancellation of drag sequence P771.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with battery discharge depths ranging from 10.5% to 13.2%. There continues to be positive re-charge margin each orbit. The minimum MOLA laser temperature observed this period was 11.2 °C using a 25 minute warming maneuver each orbit. The largest temperature increase due to aero-heating was 61°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

UPCOMING EVENTS:

Periapsis for Orbit 799 DOY336/21:46:40 UTC Through
Periapsis for Orbit 808 DOY338/19:10:56 UTC

(Note: MST = UTC-7 hours DOY336=12/2)

SPACECRAFT COMMANDING:

There were 8 command files radiated to the S/C during this period. The total files radiated since launch is now 3018. These commands were sent in support of the following activities:

Nominal drag pass sequences (P791, P795)

Nominal corridor control maneuver sequences (none)

Command loss timer resets

Nominal star catalog and ephemeris file updates

Last Orbit Covered by this Report = 788

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 215

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 7215 km
Apoapsis altitude decrease since start of aerobraking = 46811 km

Periapsis altitude = 111.8 km

Current Orbit Period = 04:59:44
Orbit Period decrease since start of aerobraking = 39:59:49

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The spacecraft health and performance remains excellent as the orbit period is now below 5 hours. The orbit period has been reduced by about 19.5 minutes over the past 23 orbits, close to the baseline schedule. The current period maintains about a 9 minute lead on the baseline. The dynamic pressure 7-orbit running mean is 0.228 N/m2 which is close to the trigger limit of 0.23 N/m2. A periapsis raise maneuver was ordered and will execute on the apoapsis portion of orbit 789 to lower the drag pass forces. The orbit-to-orbit dynamic pressure variability has increased over the past 2 weeks. For this period, the lowest drag force of 0.11 N/m2 was experienced on orbit 773. The high was recorded on the last orbit, 788, registering 0.33 N/m2.

Currently, sequence P785 is controlling the S/C activities. It will be replaced early tomorrow morning with P791 which will control activities starting with orbit 791 through orbit 794. P785 was to be replaced by P790 but because of DSN station gaps, navigation data will not be available for the P790 build. The decision was made to allow the first backup orbit from P785 to control activities for orbit 790 and start the next sequence with orbit 791. Early this reporting period, P771 encountered an error and halted, leaving the current sequence (P767) the responsibility of executing orbit 771 as backup. The error, execution of a ‘Send-Two-Word’ command in the same second as another command, has been encountered before. Automated tools discovered the error, but the warnings were misinterpreted by ground personal allowing the error to propagate. Once loaded, the error canceled the sequence early in its startup. A replacement sequence, P772, was generated and loaded. A timing error of 320 seconds was experienced on the backup orbit, which is high but within backup orbit tolerances. The S/C processed a Sun avoidance maneuver following the 771 drag pass which resulted in over 20 grams of fuel used. An ISA has been initiated to document the event. Removal of the ‘Send-Two-Word’ from future sequences was approved by MCR. This fix will be installed on Wednesday.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with battery discharge depths ranging from 10.5% to 13.2%. A larger 15.2% DoD was experienced during the Sun avoidance maneuver on orbit 771. There continues to be positive re-charge margin each orbit. The minimum MOLA laser temperature observed this period was 11.2 °C using a 25 minute warming maneuver each orbit. The largest temperature increase due to aero-heating was 61°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

Earth occultations occur each orbit starting just before apoapsis and lasting about 1 hour. The MOLA warming maneuver is executed within the occultation period allowing for maximum ground communication time each orbit.

UPCOMING EVENTS:

Periapsis for Orbit 789 DOY334/20:35:38 UTC Through
Periapsis for Orbit 798 DOY336/16:52:03 UTC

(Note: MST = UTC-7 hours DOY334=11/30)

SPACECRAFT COMMANDING:

There were 10 command files radiated to the S/C during this period. The total files radiated since launch is now 3010. These commands were sent in support of the following activities:

Nominal drag pass sequences (P767, P771, P772, P775, P780, P785)

Nominal corridor control maneuver sequences (A789)

Command loss timer resets

Last Orbit Covered by this Report = 765

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 192

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 7787 km
Apoapsis altitude decrease since start of aerobraking = 46239 km

Periapsis altitude = 115.3 km

Current Orbit Period = 05:18:12
Orbit Period decrease since start of aerobraking = 39:41:21

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues successful phase 2 aerobraking operations with no concerns. The past 13 drag passes have provided about 11 minutes of orbit period reduction. The current period maintains about a 9 minute lead on the baseline. The dynamic pressure 7-orbit running mean is 0.185 N/m2 which is below the 0.23 N/m2 corridor control trigger limit. There was 1 corridor control maneuver executed on the apoapsis portion of orbit 764 to raise periapsis and lower the drag force.

Currently, sequence P762 is controlling the S/C activities. It will be replaced early this evening with P767 which will control activities starting with orbit 767 through orbit 770. P762 was to be replaced by P766 but because of a sequence build error, the P766 product could not be built and verified in time to radiate to the S/C. The decision was made to allow the first backup orbit from P762 to control activities for orbit 766 and start the next sequence with orbit 767. Each sequence continues to be built with 5 primary orbits even though, in order to maintain prime shift builds, only four may be allowed to execute at times. Orbit timing predictions continue to be very good.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 13.8 % maximum battery discharge depths each orbit. There is now 3.2 minutes of primary charger margin. The minimum MOLA laser temperature observed this period was 12.1°C using a 35 minute warming maneuver each orbit. The largest temperature increase due to aero-heating was 69°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

The weekly reset meeting was held today to discuss aerobraking progress and to review sequence parameter changes. The dynamic pressure running mean was changed to include 7 orbits, up from 6. The MOLA laser warming maneuver was shortened in duration by 10 minutes to 25 minutes per orbit. The playback from corridor control maneuvers was delayed an additional 50 minutes following the maneuver to assure data is received following Earth occultation. The number of backup orbits was increased from 2 to 3 each sequence to allow margin in case ground processing problems do not allow timely sequence uploads.

UPCOMING EVENTS:

Periapsis for Orbit 766 DOY329/22:10:10 UTC Through
Periapsis for Orbit 788 DOY334/17:04:08 UTC

(Note: MST = UTC-7 hours DOY329=11/25)

SPACECRAFT COMMANDING:

There were 11 command files radiated to the S/C during this period. The total files radiated since launch is now 3000. These commands were sent in support of the following activities:

Nominal drag pass sequences (P753, P758, P762)

Nominal corridor control maneuver sequences (A764)

Command loss timer resets

Nominal star catalog and ephemeris file updates

Last Orbit Covered by this Report = 752

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 179

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 8128 km
Apoapsis altitude decrease since start of aerobraking = 45898 km

Periapsis altitude = 114.7 km

Current Orbit Period = 05:29:17
Orbit Period decrease since start of aerobraking = 39:30:16

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues successful phase 2 aerobraking operations with no concerns. The past 13 drag passes have provided about 13.5 minutes of orbit period reduction. About 1 minute reduction per drag pass is desired to maintain the baseline plan. The current period maintains about a 9 minute lead on the baseline. The 6-orbit running mean is 0.155 N/m2 which is below the 0.23 N/m2 corridor control trigger limit. There was 1 corridor control maneuver executed on the apoapsis portion of orbit 747 to raise periapsis and lower the drag force.

Currently, sequence P749 is controlling the S/C activities. It will be replaced early this evening with P753 which will control activities starting with orbit 753 through orbit 756. Each sequence continues to be built with 5 primary orbits even though, in order to maintain prime shift builds, only four may be allowed to execute at times. Orbit timing predictions continue to be very good.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 11.5 % maximum battery discharge depths each orbit. There is now 9.3 minutes of primary charger margin. The minimum MOLA laser temperature observed this period was 12.1°C using a 35 minute warming maneuver each orbit. The largest temperature increase due to aero-heating was 61°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

UPCOMING EVENTS:

Periapsis for Orbit 753 DOY327/00:09:49 UTC Through
Periapsis for Orbit 760 DOY328/14:07:22 UTC

(Note: MST = UTC-7 hours DOY327=11/23)

SPACECRAFT COMMANDING:

There were 7 command files radiated to the S/C during this period. The total files radiated since launch is now 2982. These commands were sent in support of the following activities:

Nominal drag pass sequences (P740, P744, P749)

Nominal corridor control maneuver sequences (A747)

Command loss timer resets

Last Orbit Covered by this Report = 739

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 166

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 8536 km
Apoapsis altitude decrease since start of aerobraking = 45490 km

Periapsis altitude = 113.5 km

Current Orbit Period = 05:42:44
Orbit Period decrease since start of aerobraking = 39:16:49

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues successful phase 2 aerobraking operations with no concerns. The past 13 drag passes have provided about 14 minutes of orbit period reduction. The period reduction rate has been reduced to conform with the original baseline rate rather than accumulate more margin. The current period is about 9 minutes ahead of the original baseline. The 6-orbit running mean is 0.199 N/m2 which is below the 0.23 N/m2 corridor control trigger limit. There were no corridor control maneuvers required during this period.

Currently, sequence P736 is controlling the S/C activities. It will be replaced early this evening with P740 which will control activities starting with orbit 740 through orbit 743. The decision to increase the number of primary orbits to 5 and thus the predicted orbits to 6 was made at this week’s reset meeting on Wednesday. All sequences are now being build with 5 primary orbits, although the 5th orbit may be superseded by a new sequence if required to keep builds on prime shift. Orbit timing predictions continue to be very good. The Navigation team is incorporating an updated wave model to improve timing predictions.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 11.0 % maximum battery discharge depths each orbit. There is now 11 minutes of primary charger margin. The minimum MOLA laser temperature observed this period was 12.1°C and is expected to drop a little lower as the shorter, 35 minute, warming maneuver takes effect. The largest temperature increase due to aero-heating was 67°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

Preparations for the upcoming mapping mission continue. Weekly planning meetings are being held to discuss progress, changes and product review and testing. The STL has successfully created a 2 PM mapping baseline and has been validating changes to the 2 AM mapping profile.

UPCOMING EVENTS:

Periapsis for Orbit 740 DOY323/23:36:25 UTC Through
Periapsis for Orbit 752 DOY326/18:27:25 UTC

(Note: MST = UTC-7 hours DOY323=11/19)

SPACECRAFT COMMANDING:

There were 10 command files radiated to the S/C during this period. The total files radiated since launch is now 2982.

These commands were sent in support of the following activities:

Nominal drag pass sequences (P728, P732, P736)

Nominal corridor control maneuver sequences (none)

Command loss timer resets

Nominal star catalog and ephemeris file updates

Last Orbit Covered by this Report = 726

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 153

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 8950 km
Apoapsis altitude decrease since start of aerobraking = 45075 km

Periapsis altitude = 113.5 km

Current Orbit Period = 05:56:37
Orbit Period decrease since start of aerobraking = 39:02:56

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

Aerobraking operations continue to be uneventful as planned. The past 15 drag passes have provided 21.5 minutes of orbit period reduction. The rate of period reduction continues to out perform the baseline plan by 8.8 minutes. The margin is a valuable asset as long as orbit phasing does not become adversely affected. The project is now trying to decrease the average dynamic pressure to a value closer to 0.20 N/m2 which should maintain the 8.8 minute margin. The 6-orbit running mean is currently 0.270 N/m2 which is above the 0.23 corridor control trigger limit. Periapsis raise maneuvers have been executed on orbits 714 and 726. The results of the latter maneuver has not yet been seen, therefore the running mean continues to climb due to the lag.

Currently, sequence P724 is controlling the S/C activities. It will be replaced early this evening with P728 which will control activities starting with orbit 728 through orbit 731. Since the orbit period is below 6 hours, a new sequence is being built in slightly less than 24 hours. Currently, the Navigation team predicts the period for 5 future orbits. The 1st is not used and the next 4 provide timing for the primary orbits in a sequence. Two additional orbits are included using the 6th and 7th predicted orbit periods as backup, but are not intended to be used. The decision to increase the number of primary orbits to 5 and thus the predicted orbits to 6 may be made at this week’s reset meeting on Wednesday. Orbit timing predictions continue to be very good, although a slight delta V under prediction has been observed over the past 4 days.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. The panel stiffness calculation has only been valid 3 times during the period but shows no degradation when the data is available. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 11.7 % maximum battery discharge depths each orbit. There is now 10.1 minutes of primary charger margin. The minimum MOLA laser temperature observed this period was 11.2°C during the corridor control maneuver on orbit 714. The largest temperature increase due to aero-heating was 67°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance. A short two hour S/C communications outage was experienced on DOY 317 (11/13) due to Lunar occultation.

UPCOMING EVENTS:

Periapsis for Orbit 727 DOY320/20:01:42 UTC Through
Periapsis for Orbit 735 DOY322/18:53:53 UTC

(Note: MST = UTC-7 hours DOY320=11/16)

SPACECRAFT COMMANDING:

There were 9 command files radiated to the S/C during this period. The total files radiated since launch is now 2972. These commands were sent in support of the following activities:

Nominal drag pass sequences (P712, P716, P720, P724)

Nominal corridor control maneuver sequences (A714, A726)

Command loss timer resets

Last Orbit Covered by this Report = 711

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 138

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 9583 km
Apoapsis altitude decrease since start of aerobraking = 44443 km

Periapsis altitude = 112.7 km

Current Orbit Period = 06:18:07
Orbit Period decrease since start of aerobraking = 38:41:26

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues Phase 2 aerobraking operations in excellent health. Progress continues per plan as 17 minutes of orbit period have been removed over the past 11 drag passes. The 6-orbit running mean is currently 0.268 N/m2 which is above the 0.23 corridor control trigger limit. The project has elected to gain a little orbit period margin and allow the overshoot to occur for a short period. The 2 minute deficit from the baseline plan has now been erased. One corridor control maneuver was executed on the apoapsis of orbit 710 which raised the periapsis altitude about 1/2 corridor.

Currently, sequence P708 is controlling the S/C activities. It will be replaced early this evening with P712 which will control activities starting with orbit 712 through orbit 715. The sequence contains command for orbits 716 and 717 as backup in case ground sequence generation problems occur. All timing estimations continue to be well within the 232s, excessive fuel use limit.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Stiffness values have not been valid this period due to lack of sun light on the -Y panel sun sensor during the drag pass. The system structural frequency has been maintained at about 0.153 Hz. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 11.0 % maximum battery discharge depths each orbit. There is now 13 minutes of primary charger margin. The minimum MOLA laser temperature observed this period was 11.2°C during the corridor control maneuver on orbit 710. The largest temperature increase due to aero-heating seen was 68°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

In the STL, re-validation of the Pop-Up maneuver contingency sequence has been completed. Initial testing of the 2 am mapping flight software changes is underway.

UPCOMING EVENTS:

Periapsis for Orbit 712 DOY317/00:21:07 UTC Through
Periapsis for Orbit 726 DOY320/13:45:32 UTC

(Note: MST = UTC-7 hours DOY317=11/13)

SPACECRAFT COMMANDING:

There were 9 command files radiated to the S/C during this period. The total files radiated since launch is now 2963. These commands were sent in support of the following activities:

Nominal drag pass sequences (P701, P705, P708)

Nominal corridor control maneuver sequences (A710)

Nominal star catalog and ephemeris file updates

Last Orbit Covered by this Report = 700

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 127

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 10073 km
Apoapsis altitude decrease since start of aerobraking = 43952 km

Periapsis altitude = 113.8 km

Current Orbit Period = 06:35:07
Orbit Period decrease since start of aerobraking = 38:24:26

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

Phase 2 aerobraking operations continue with the S/C maintaining excellent health. Progress continues per plan as 21 minutes of orbit period have been removed over the past 15 drag passes. The 6-orbit running mean is currently down to 0.208 N/m2 due to last period’s periapsis raise maneuvers. This value remains within the upper corridor limit of 0.23 N/m2. Only 2 minutes separate the baseline planned orbit period and the current. There were no corridor control maneuvers ordered during this period.

Currently, sequence P698 is controlling the S/C activities. It will be replaced early this evening with P701 which will control activities starting with orbit 701 through orbit 704. These sequences are built with 4 primary orbit and 2 backup orbit command sets. This allows for only 1 sequence build per day with 12 hours of contingency orbits in case ground sequence generation problems occur. All timing estimations continue to be well within the 232s, excessive fuel use limit.

Subsystems continue to report excellent S/C health and performance. The -Y solar array yoke has shown no change in structural performance. Stiffness values, when valid, show no change in the panel structural degradation. The system structural frequency has been maintained at about 0.153 Hz. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 12.6 % maximum battery discharge depths each orbit. There is now 9.5 minutes of primary charger re-charge margin. The minimum MOLA laser temperature observed this period was 11.2°C. The largest temperature increase due to aero-heating seen was 60°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

In the STL, re-validation of the Pop-Up maneuver contingency sequence is underway.

UPCOMING EVENTS:

Periapsis for Orbit 701 DOY314/01:29:40 UTC Through
Periapsis for Orbit 707 DOY315/19:38:05 UTC

(Note: MST = UTC-7 hours DOY314=11/10)

SPACECRAFT COMMANDING:

There were 9 command files radiated to the S/C during this period. The total files radiated since launch is now 2954. These commands were sent in support of the following activities:

Nominal drag pass sequences (P687, P691, P694, P698)

Nominal corridor control maneuver sequences (None)

Command loss timer reset

Last Orbit Covered by this Report = 685

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 112

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 10669 km
Apoapsis altitude decrease since start of aerobraking = 43357 km

Periapsis altitude = 112.6 km

Current Orbit Period = 06:56:04
Orbit Period decrease since start of aerobraking = 38:03:29

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft maintains excellent health and performance as aerobraking operations have reduced the orbit period to less than 7 hours. The last 16 drag passes have removed 32 minutes from the orbit period. The 6-orbit running mean is currently 0.295 N/m2 but should start to decrease dramatically since the desired drag corridor has been reduced in force. Results presented at this week’s reset meeting shows the period deficit (suffered due to the late start of Phase 2) has been nearly eliminated. Two periapsis raise maneuvers were executed during this period to reduce the drag force and to average about 0.20 N/m2. A new target corridor, 0.17 - 0.23 N/m2, has been established to slow aerobraking. It is desired to keep the period reduction rate close to the baseline plan to maintain the orbit phasing and inclination desired for the mapping orbit.

Sequence P684 is currently controlling S/C activities through the remainder of orbit 686. The reset 10 parameter selections further reduce the MOLA warming maneuver to 45 minutes and calls for all drag sequences to be built using 4 primary orbits and 2 backup orbits. This is an increase of 1 primary orbit and will allow the flight team to continue building only 1 drag sequence per day. The primary charger connect time has been increased to maintain margin. P687 will take control of spacecraft activities later tonight and will continue control through orbit 690. All timing estimations have been well within the 232s, excessive fuel use limit. Due to a sequence generation problem, P679 was not built in time to uplink to the S/C. Orbit 679 activities were commanded as a backup orbit from sequence P676. A P680 sequence was built to execute orbits 680, 681 and 682.

All subsystems report excellent S/C health with no performance concerns. The -Y solar array yoke has shown no changes in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 11.0 % battery discharge depths each orbit. There is now 15 minutes of primary charger re-charge margin. The minimum MOLA laser temperature observed this period was 12.1°C. The largest temperature increase due to aero-heating seen was 66°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

The System Test Lab (STL) has been repaired. Testing will return to the lab tomorrow. Tests to be completed are, aerobraking pop-up re-verification, 2 am mapping flight software update validation, and nominal 2 am mapping sequence testing. About 3.5 weeks has been lost in the schedule. The revised test schedule will likely require 7 days per week operations.

The Thermal Emissions Spectrometer (TES) was powered off this week for the duration of aerobraking.

UPCOMING EVENTS:

Periapsis for Orbit 686 DOY309/20:14:20 UTC Through
Periapsis for Orbit 700 DOY313/18:44:53 UTC

(Note: MST = UTC-7 hours DOY309=11/5)

SPACECRAFT COMMANDING:

There were 18 command files radiated to the S/C during this period. The total files radiated since launch is now 2945. These commands were sent in support of the following activities:

TES power off

Nominal drag pass sequences (P670, P673, P676, P680, P683, P684)

Nominal corridor control maneuver sequences (A682, A685)

Command loss timer reset

Nominal star catalog and ephemeris file updates

Last Orbit Covered by this Report = 669

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 96

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 11560 km
Apoapsis altitude decrease since start of aerobraking = 42466 km

Periapsis altitude = 113.6 km

Current Orbit Period = 07:28:03
Orbit Period decrease since start of aerobraking = 37:31:30

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues Phase 2 aerobraking operations in excellent health. Ten drag passes have occurred during the past 3 days, reducing the orbit period by 23.5 minutes. Since the beginning of Phase 2 operations on 9/23, over 4 hours have been removed from the orbit period. The 5-orbit running mean drag force is currently 0.294 N/m2 with the peak dynamic pressure of 0.35 N/m2 recorded on orbit 668. One maneuver was ordered to raise periapsis 1 half corridor prior to the orbit 669 drag pass. Excellent progress towards reaching the baseline trajectory continues, helped by excellent periapsis timing predictions.

Sequence P667 is currently controlling S/C activities through the remainder of orbit 669. P670 will take over early this evening and control activities through orbit 672. No non-standard builds have been required due to periapsis timing errors. All timing estimations have been well within the 232s, excessive fuel use limit.

All subsystems report excellent S/C health with no performance concerns. The -Y solar array yoke has shown no changes in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 11.9 % battery discharge depths each orbit. There is now 2 minutes of primary charger re-charge margin. If the margin falls below zero, then the remaining deficit will be supplied by the trickle chargers which remain connected at all times. The minimum MOLA laser temperature observed this period was 12.2°C. The largest temperature increase due to aero-heating seen was 68°C on the -Y solar array, cell side. The telecommunications subsystem continues solid performance.

The System Test Lab (STL) was still inoperable this period. Efforts are continuing through proper channels to hire outside help to solve the problems. Tests to complete aerobraking pop-up verification, 2 am mapping flight software update validation, and nominal 2 am mapping sequence testing are all on hold.

UPCOMING EVENTS:

Periapsis for Orbit 670 DOY305/01:11:54 UTC Through
Periapsis for Orbit 679 DOY307/18:47:13 UTC

(Note: MST = UTC-7 hours DOY305=10/31)

SPACECRAFT COMMANDING:

There were 7 command files radiated to the S/C during this period. The total files radiated since launch is now 2927. These commands were sent in support of the following activities:

TES NIPCs

Nominal drag pass sequences (P661, P664, P667)

Nominal corridor control maneuver sequences (A668)

Command loss timer reset

Last Orbit Covered by this Report = 659

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 86

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 12200 km
Apoapsis altitude decrease since start of aerobraking = 41826 km

Periapsis altitude = 113.1 km

Current Orbit Period = 07:51:31
Orbit Period decrease since start of aerobraking = 37:08:02

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

Spacecraft operations continue successful aerobraking activities. About 15 minutes have been removed from the orbit period over the last 6 passes. The drag force each pass has been maintained at the upper corridor limit and above averaging 0.295 N/m2 over the last 6 orbits. The variations in atmospheric densities have been very modest and the project has taken advantage by keeping the drag forces high. This has allowed further reduction in the gap between the planned period reduction and the actual. At the current rate of period reduction, the baseline period trajectory should be intercepted in 2 weeks. There were no maneuvers required during the period.

Sequence generation, review and execution has remained uneventful this period. The P658 sequence will be replaced later today by P661 and will control S/C activities through orbit 663. The weekly reset meeting was held for week 8 today to discuss aerobraking progress and sequence parameters for the coming week. P661 is the first sequence built from the reset 8 set of parameters.

All subsystems report excellent S/C health with no performance concerns. The -Y solar array yoke has shown no changes in structural performance. Attitude knowledge has been maintained throughout the period with excellent star processing. The power subsystem reports strong performance with 11.3 % battery discharge depths each orbit. Starting with P661, the primary chargers will be connected for 2 minutes longer each pass to maintain at least 5 minutes of charger margin. Solar panel heating has peaked at 60°C again during this period. The minimum MOLA laser temperature observed this period was 11.8°C. The telecommunications subsystem continues solid performance.

The System Test Lab (STL) was still inoperable this period. Efforts are continuing through proper channels to hire outside help to solve the problems.

UPCOMING EVENTS:
Periapsis for Orbit 660 DOY301/20:48:49 UTC Through
Periapsis for Orbit 668 DOY304/17:39:02 UTC

Operations Readiness Review Part 2 - October 30, 1998

(Note: MST = UTC-7 hours DOY301=10/28)

SPACECRAFT COMMANDING:

There were 10 command files radiated to the S/C during this period. The total files radiated since launch is now 2920. These commands were sent in support of the following activities:

TES NIPCs

Nominal drag pass sequences (P655, P658)

Nominal star catalogs and ephemeris files

Command loss timer reset

Last Orbit Covered by this Report = 653

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 80

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 12600 km
Apoapsis altitude decrease since start of aerobraking = 41426 km

Periapsis altitude = 112.7 km

Current Orbit Period = 08:06:23
Orbit Period decrease since start of aerobraking = 36:53:10

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor Spacecraft maintains excellent health and performance during aerobraking operations. There has been over 20 minutes removed from the orbit period this weekend and excellent progress has been made closing the gap between the baseline plan period and actual. Over the last 8 orbits the peak dynamic pressure was 0.31 N/m2 and the highest integrated drag force was 0.33 N/m2. The integrated value is computed based on the integrated delta V as reconstructed from accelerometer data. The peak value is based on the peak acceleration value recorded during the pass and is used in determining the load applied to the -Y solar array yoke. There was one maneuver executed during orbit 647 that lowered periapsis about 3/4 km to increase the drag force. The atmospheric density has been less variable with the period near the 8 hour value. The project has been taking advantage of the reduced variability by allowing the average drag force to creep above the high corridor trigger limit of 0.28 N/m2. The current 5-orbit running mean is now 0.285 N/m2.

Currently, the P652 sequence is controlling the S/C through orbit 654. The replacement sequence (P655) has been built, is in review and will be loaded for execution later this evening. It will wait until about 1 hour before the periapsis time for orbit 655, cancel P652 and execute orbits 655 through 657. If, for some reason, the P655 sequence could not be loaded, the existing P652 script would continue controlling the S/C for up to 2 additional orbits. Predictions for periapsis times have been very good, therefore no emergency builds have been required.

There continues to be no change in the -Y solar array yoke structural performance. The monitor data has remained stable with no false indications. Attitude control continues excellent performance with no concerns with momentum management or star processing. The power subsystem reports strong performance with 11.0 % battery discharge depths each orbit. The deficit is restored each orbit by connecting the primary chargers for 1 hour and 22 minutes. Only 4 minutes of overcharge occurs each pass, preserving battery health. Solar panel heating has been as high as 60°C during the drag pass, well within limitations. The minimum MOLA laser temperature observed this period was 11.2°C during orbit 647. The telecommunications subsystem continues solid performance. Flight software and C&DH report no anomalous activity.

The System Test Lab (STL) developed a failure on 10/16/98 in the Non-Flight Spacecraft (NFSC) section. The externally generated 10 Hz interrupt is apparently not propagating through the NFSC hardware as expected. Outside expertise is being called in to investigate and repair the failure. In the mean time, scheduled tests of the aerobraking pop-up sequence update and 2 am mapping verification is being delayed.

UPCOMING EVENTS:
Periapsis for Orbit 654 DOY299/21:04:07 UTC
Periapsis for Orbit 655 DOY300/05:07:56 UTC
Periapsis for Orbit 656 DOY300/13:09:05 UTC
Periapsis for Orbit 657 DOY300/21:08:17 UTC
Periapsis for Orbit 658 DOY301/05:04:55 UTC
Periapsis for Orbit 659 DOY301/12:59:05 UTC
Operations Readiness Review Part 2 - October 30, 1998

(Note: MDT = UTC-6 hours DOY299=10/26)

SPACECRAFT COMMANDING:

There were 7 command files radiated to the S/C during this period. The total files radiated since launch is now 2910. These commands were sent in support of the following activities:

TES NIPCs

Nominal drag pass sequences (P646, P649, P652)

Nominal aerobraking maneuver sequences (A647)

Last Orbit Covered by this Report = 645

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 72

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 13132 km
Apoapsis altitude decrease since start of aerobraking = 40894 km

Periapsis altitude = 113.6 km

Current Orbit Period = 08:26:30
Orbit Period decrease since start of aerobraking = 36:33:03

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

Spacecraft performance during Phase 2 aerobraking operations continues to be excellent. About 14.5 minutes have been subtracted from the orbit period over the last 5 drag passes. The peak dynamic pressure was encountered during the orbit 642 drag pass and registered 0.33 N/m2 . A maneuver to lower periapsis was performed on orbit 641 to increase the drag force for future passes. The orbit period is nearing 1/3 the planet’s daily rotation period (SOL) and thus visits the same planet longitude every third orbit. During this resonance period, the atmospheric density will be less variable and easier to predict. Also, since there is an observed 3-wave density profile, the density encountered from one pass to the next will be nearly equal. Predictions show the resonant densities will be relatively low and that more periapsis lowering maneuvers will be necessary to maintain efficient aerobraking. The current 5-orbit running mean is now 0.271 N/m2. Since the atmospheric variability will be reduced over the next week, the project has elected to allow the running mean to rise above the 0.28 upper limit in an effort to regain more lost period reduction due to the late start of aerobraking.

The current executing sequence is P643. Uplinked yesterday, it required two rebuilds to correct timing parameters for the ER high voltage off and for the start of the -Y panel powered hold state. This was the first sequence following the change in parameter set from the reset meeting on Wednesday. Because of the changes, re-builds are more likely. The next sequence, P646 has been built, verified and ready for uplink. It will take over execution later this evening

The -Y solar array yoke structural performance remains solid and consistent. No monitoring data has shown any degradation so far during Phase 2. Attitude control continues excellent performance with no concerns with momentum management or star processing. The power subsystem reports strong performance with 11.5 % battery discharge depths each orbit. This DoD is slightly larger than last report due to the longer drag attitude now being utilized. The MOLA warming maneuver has been reduce to 60 minutes for this period and has maintained temperatures above 11.5°C. The telecommunications subsystem continues solid performance.

An express SSR playback was required to retrieve the engineering data for orbit 644. Problems at the DSN station prevented the nominal playback.

UPCOMING EVENTS:
Periapsis for Orbit 646 DOY297/03:02:13 UTC
Periapsis for Orbit 647 DOY297/11:26:29 UTC
Periapsis for Orbit 648 DOY297/19:49:05 UTC
Periapsis for Orbit 649 DOY298/04:09:38 UTC
Periapsis for Orbit 650 DOY298/12:27:58 UTC
Periapsis for Orbit 651 DOY298/20:44:36 UTC
Operations Readiness Review Part 2 - October 30, 1998

(Note: MDT = UTC-6 hours DOY297=10/24)

SPACECRAFT COMMANDING:

There were 7 command files radiated to the S/C during this period. The total files radiated since launch is now 2903. These commands were sent in support of the following activities:

MAG/ER & TES NIPCs

Nominal drag pass sequences (P640, P643)

Nominal aerobraking maneuver sequences (A641)

Express SSR engineering data playback

Last Orbit Covered by this Report = 639

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 66

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 13514 km
Apoapsis altitude decrease since start of aerobraking = 40512 km

Periapsis altitude = 113.5 km

Current Orbit Period = 08:41:01
Orbit Period decrease since start of aerobraking = 36:18:32

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft maintains excellent health during Phase 2 aerobrkaing operations. The last 8 drag passes have provided over 21.5 minutes of orbit period reduction, averaging 0.27 N/m2 in dynamic pressure. The peak drag force was encountered during the orbit 639 drag pass and registered 0.33 N/m2 . Small periapsis raising maneuvers were executed on orbits 632 and 635 to reduce the drag pressure on later orbits that were projected to eclipse the immediate action limit for dynamic pressure. A series of lower density drag passes are expected for the remainder of this week so periapsis lowering maneuvers may be required to maintain the excellent rate of period reduction. The current 5-orbit running mean is now 0.305 N/m2. This value is higher than the current upper corridor limit of 0.28, but because predictions indicate lower densities coming up, the flight operations manager elected to waive the corridor control maneuver. The current orbit period is now about 43 minutes behind the original Phase 2 schedule. As the period nears 8 hours, the periapsis longitudes will repeat and atmospheric densities will be less variable. The project will use this opportunity to further reduce the 43 minute deficit by taking advantage of better orbit to orbit density predictions.

The current executing sequence, P637, will be replaced by P640 later today. Today at the reset meeting, it was decided that P640 will be the last sequence built that uses the first predicted orbit from the OPTG Navigation Team product. Because of the reducing orbit period, there is not enough time to receive the orbit solution from the Nav Team and build / upload a sequence that will take effect on the following orbit. Therefore, the subsequent orbit will be targeted as the first of the sequence which will continue to contain commands for 3 primary and 2 backup orbits. An increase in the Pre-Drag Delay parameter was incorporated to accommodate a larger periapsis timing error without tripping rate faults due to encountering atmosphere while still under reaction wheel control. This was desired because of the increased probability of encountering larger periapsis timing errors when using the fourth predicted orbit from the OPTG. The MOLA warming maneuver duration will also be reduced to 1 hour since the Sun geometry is becoming more favorable and the orbit period is shrinking.

The -Y solar array yoke continues solid structural performance. The algorithm for determining the structural frequency has been modified to work more consistently and lessen the chance of false alarms. The results of the new routine places the nominal frequency close to 0.155 Hz rather than the previous nominal result of 0.167 Hz. Attitude control continues excellent performance with no concerns with momentum management or star processing. The power subsystem reports strong performance with 11.1 % battery discharge depths each orbit. This deficit is being easily replaced by the primary charger with 4.5 minutes of margin. The minimum MOLA temperature has been maintained above 12.0°C using the 70 minute warming maneuver. The telecommunications subsystem continues solid performance.

An express SSR playback was required to retrieve the engineering data for orbit 637. Problems at the DSN station prevented the nominal playback reception due to lower that expected signal level.

UPCOMING EVENTS:
Periapsis for Orbit 640 DOY294/23:47:38 UTC
Periapsis for Orbit 641 DOY295/08:25:56 UTC
Periapsis for Orbit 642 DOY295/17:02:39 UTC
Periapsis for Orbit 643 DOY296/01:37:07 UTC
Periapsis for Orbit 644 DOY296/10:09:25 UTC
Periapsis for Orbit 645 DOY296/18:40:23 UTC

(Note: MDT = UTC-6 hours DOY294=10/21)

SPACECRAFT COMMANDING:

There were 15 command files radiated to the S/C during this period. The total files radiated since launch is now 2896. These commands were sent in support of the following activities:

MAG/ER & TES NIPCs

Nominal drag pass sequences (P632, P634, P637)

Nominal aerobraking maneuver sequences (A632, A635)

Express SSR engineering data playback

Nominal star catalogs and ephemeris file update

Last Orbit Covered by this Report = 631

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 58

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 14074 km
Apoapsis altitude decrease since start of aerobraking = 39952 km

Periapsis altitude = 113.9 km

Current Orbit Period = 09:02:37
Orbit Period decrease since start of aerobraking = 35:56:56

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The spacecraft health continues to be excellent as the 9 hour orbit period is reached in Phase 2 aerobraking. The orbit period has been reduced by 36 minutes over the past 13 drag passes during this reporting period. A periapsis lowering maneuver was executed on the apoapsis portion of orbit 622 to increase the drag pressure by about 10 percent. The 4-orbit running mean has been modified to use the last 5 orbits in the calculation. The current 5-orbit running mean is now 0.276 N/m2. The mean ran slightly over the 0.28 N/m2 upper corridor limit following orbit 628 registering 0.292 N/m2. The peak dynamic pressure on this orbit was recorded as 0.34 N/m2, just under the first alarm limit of 0.35 N/m2. Per Wednesday’s reset meeting decision, the flight operations manager exercised discretion and did not order a periapsis raise maneuver based on reliable predictions that the following drag passes would provide less drag force. Navigation predictions are now based on the Wave-3 model which indicates relatively higher atmospheric densities at drag altitudes occurring over 110°, 230° and 350° East longitudes.

Sequence P632 will be built today to replace the current P630 sequence that was loaded yesterday. On Friday it was noticed that orbit 625 was executed by the P622 sequence and not the P624 sequence as planned. The planned uplink of the P626 sequence was rejected by flight software due to the target memory area being in use. An unplanned build of sequence P627 was required to take over before the last command of the P622 sequence forced contingency mode entry. An investigation found that the P624 sequence, following successful uplink and initiation, encountered an error and aborted its execution at the same time the P622 sequence should have been canceled. The error was caused by a Send’Two’ Word command that was being executed during the same second as another flight software command. A FSW idiosyncrasy does not process commands successfully when Send’XX’Word commands are issued concurrently with other commands. A flight rule will be implemented to prevent this from recurring and checks are being executed to prevent this command configuration. The MAG/ER calibration executed on Wednesday was cut short when an error in the Load and Go sequence caused it’s execution to cease. Analysis shows a back-to-back timing constraint violation using PDS (Payload Data Subsystem) commands. This restriction, implemented as a flight rule, was not checked by ground processes and was left undetected. The remainder of the MAG/ER calibration will be performed using NIPCs. A command sequence was generated and loaded to correct the telemetry state left by the aborted calibration successfully. The two incidents have been recorded in ISAs.

The -Y solar array yoke continues solid structural performance. Attitude control continues excellent performance with no concerns with momentum management or star processing. The power subsystem reports strong performance with 10.7 % battery discharge depths each orbit. This deficit is being easily replaced by the primary charger with 7 minutes of margin. The minimum MOLA temperature continues to stay above 11.2°C using the shorter 70 minute warming maneuver. The telecommunications subsystem continues solid performance.

UPCOMING EVENTS:
Periapsis for Orbit 632 DOY292/00:57:45 UTC
Periapsis for Orbit 633 DOY292/09:57:32 UTC
Periapsis for Orbit 634 DOY292/18:54:35 UTC
Periapsis for Orbit 635 DOY293/03:38:39 UTC
Periapsis for Orbit 636 DOY293/12:39:13 UTC
Periapsis for Orbit 637 DOY293/21:25:28 UTC

(Note: MDT = UTC-6 hours DOY292=10/19)

SPACECRAFT COMMANDING:

There were 32 command files radiated to the S/C during this period. The total files radiated since launch is now 2881. These commands were sent in support of the following activities:

MAG/ER & TES NIPCs

Nominal drag pass sequences (P619, P622, P624, P626, P627, P630)

Nominal aerobraking maneuver sequences (A622)

Command Loss Timer resets

Express SSR 1A playback

Full SCP memory read-out

Contingency Mode script update

MAG/ER calibration

Recovery from aborted calibration test

Last Orbit Covered by this Report = 618

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 45

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 14991 km
Apoapsis altitude decrease since start of aerobraking = 39035 km

Periapsis altitude = 115.9 km

Current Orbit Period = 09:38:38
Orbit Period decrease since start of aerobraking = 35:20:55

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues excellent health and performance during Phase 2 aerobraking. The past 14 orbits have provided over 36.5 minutes of period reduction, 2 minutes and 37 seconds average each pass. One Immediate Action maneuver was required on the apoapsis portion of orbit 615 due to an alarm of the -Y solar array yoke structural frequency. The red alarm is tripped when the computed system frequency due to panel motion is 0.02 Hz lower than the previous pass or of the 5 orbit average. Usually a pop-up maneuver would be called for indicating a serious response to a major change in structural performance. In this case, evidence of corrupted data being processed by the automated routines was discovered and the response was down graded to a 0.15 m/s corridor control maneuver. The 4-orbit running average of the integrated dynamic pressure ran as high as 0.247 N/m2 on orbit 616 and is currently at 0.205 N/m2. The peak drag force encountered during this period was 0.33 N/m2 on orbit 615 which is still below the immediate action limit of 0.35 N/m2. The highest integrated dynamic pressure observed so far during Phase 2 operations occurred on the same orbit. The atmospheric density seems to be declining slightly at periapsis altitudes as evidenced by lower drag forces seen on the last 3 orbits. The gravity trend causes the periapsis altitude to drift lower but the expected increase in density is not occurring. More customization of the dynamic pressure corridor may be discussed at tomorrow’s reset meeting to allow for better period reduction.

Sequence P619 will be built today to replace the current P617 sequence that was loaded yesterday. Periapsis timing predictions have been good, so no un-planned sequences have been ordered. The P619 sequence will be used through 3 primary orbits, 619, 620 and 621 provided the predicted timing continues to be accurate.

The -Y solar array yoke structural performance remains solid despite the perceived red alarm on structural frequency. Analysis is being performed to determine methods to prevent the false alarm indication in the future. For now, the data will be manually inspected to verify quality before allowing a possible invalid alarm to propagate. Attitude control continues excellent performance with no concerns with momentum management or star processing. The power subsystem reports strong performance with 10.2 % battery discharge depths each orbit. This deficit is being easily replaced by the primary charger with 7.5 minutes of margin. The minimum MOLA temperature is now staying above 11.5°C with the shorter warming maneuver. The telecommunications subsystem continues solid performance.

UPCOMING EVENTS:
Periapsis for Orbit 619 DOY286/23:46:37 UTC
Periapsis for Orbit 620 DOY287/09:22:30 UTC
Periapsis for Orbit 621 DOY287/18:55:36 UTC
Periapsis for Orbit 622 DOY288/04:26:10 UTC
Periapsis for Orbit 623 DOY288/13:54:26 UTC
Periapsis for Orbit 624 DOY288/23:20:16 UTC

(Note: MDT = UTC-6 hours DOY286=10/13)

SPACECRAFT COMMANDING:

There were 22 command files radiated to the S/C during this period. The total files radiated since launch is now 2849. These commands were sent in support of the following activities:

TES NIPCs

Nominal drag pass sequences (P605, P607, P609, P612, P614, P617)

Nominal aerobraking maneuver sequences (None)

Immediate Action ABM (A615)

Nominal star catalogs and ephemeris files

Command Loss Timer resets

Last Orbit Covered by this Report = 604

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 31

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 15903 km
Apoapsis altitude decrease since start of aerobraking = 38122 km

Periapsis altitude = 115.4 km

Current Orbit Period = 10:15:11
Orbit Period decrease since start of aerobraking = 34:44:22

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft maintains excellent health and performance 31 orbits into Phase 2 aerobraking operations. The drag force 4-orbit running mean has fallen to 0.208 N/m2 due to lower than expected dynamic pressures recorded for orbits 602 and 603. The past 5 drag passes have produced about 13 minutes of period reduction. The peak drag force encountered during this period was 0.27 N/m2 on orbit 601 which is well below the immediate action limit of 0.35 N/m2. At today’s reset meeting the decision was made to allow the running average drag force to reach 0.265 N/m2 before requiring a corridor control maneuver to place the S/C into the middle of the corridor. This strategy should allow the project to recover period reduction (lost due to the late start of aerobraking) by early December.

The current executing sequence, P602, was allowed to perform 3 primary orbits to maintain the prime shift build schedule. Due to the unexpected low atmospheric densities at periapsis altitudes for orbits 602 and 603, the projected periapsis times provided to the P602 build process were in error by about 300 seconds for the drag pass of orbit 604. This resulted in an increase of fuel use to about 20 grams for the 604 orbit. Sequence periapsis timing must be controlled to prevent excessive fuel use or undesired fault protection activity that can result from reaction wheel control during drag. The current limit of 231 seconds of periapsis timing error is used to determine if a replacement sequence should be generated. Current sequence parameters transition from wheel control to thrusters 5 minutes before periapsis and transitions back 10 minutes following periapsis. Five minutes following the drag pass, the thruster mode is commanded to control the S/C attitude to reduce body rates. In the case of orbit 604, the accumulated timing error resulted in the thruster control law being commanded to reduce body rates while the S/C was at periapsis. Therefore thrusters were controlling the attitude during the last half of the drag pass rather than allowing the attitude to drift, costing more fuel.

The -Y solar array yoke structural performance remains solid. Due to the current Sun / Mars geometry, the -Y array mounted Sun sensor is not illuminated during the entire drag pass in every case. The automated determination of orbit by orbit change in structural stiffness has been disabled due to inaccurate results caused by the missing data. The level stiffness checks are still employed. Attitude control continues excellent performance. The minimum MOLA temperature is now staying above 12.1°C. The MOLA warming maneuver duration will be reduced by 10 minutes. The telecommunications subsystem continues solid performance. Battery depth of discharge levels continue to be about 12% each orbit. The charger connect time is being reduced to by 10 minutes to lessen the battery overcharge period.

UPCOMING EVENTS:

Periapsis for Orbit 605 DOY281/05:02:02 UTC
Periapsis for Orbit 606 DOY281/15:14:07 UTC
Periapsis for Orbit 607 DOY282/01:23:21 UTC
Periapsis for Orbit 608 DOY282/11:29:52 UTC
Periapsis for Orbit 609 DOY282/21:33:38 UTC
Periapsis for Orbit 610 DOY283/07:34:11 UTC

(Note: MDT = UTC-6 hours DOY281=10/8)

SPACECRAFT COMMANDING:

There were 11 command files radiated to the S/C during this period. The total files radiated since launch is now 2827. These commands were sent in support of the following activities:

TES NIPCs

Nominal drag pass sequences (P600, P602)

Nominal aerobraking maneuver sequences (None)

Nominal star catalogs and ephemeris files

Express playback of MOLA warming maneuver data

Last Orbit Covered by this Report = 594

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 21

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 16612 km
Apoapsis altitude decrease since start of aerobraking = 37414 km

Periapsis altitude = 116.6 km

Current Orbit Period = 10:44:05
Orbit Period decrease since start of aerobraking = 34:15:28

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft continues excellent performance during Phase 2 aerobraking. No corridor control maneuvers have been required to maintain the average ( 4-orbit running mean) dynamic pressure within the desired corridor of 0.14 to 0.24 N/m2. Over the past 6 orbits 17 minutes and 34 seconds have been trimmed from the orbit period. Periapsis altitudes have been mostly stable, varying only about 1 km every 3-4 orbits. The dynamic pressures have ranged from 0.13 - 0.26 N/m2 over the past six orbits, exhibiting over 100% orbit to orbit variability in some cases. Even though the dynamic pressure 4-orbit running mean has remained in the denser half of the corridor during this period, the deficit in period reduction has not been compensated at the desired rate. A decision to again raise the upper corridor limit may occur on Wednesday. The first dynamic pressure alarm is set at 0.35 N/m2 (which requires Flight Operations Manager notification) and has been avoided thus far by about 0.10 N/m2 margin in peak drag force. The drag force allowed can be increased so long as the S/C remains healthy and the peak drag forces encountered stay below the 0.35 N/m2 limit.

The current sequence is P593 and it has performed the S/C activities for orbits 593 and 594. The next sequence, P595, has been loaded and it will take control early this afternoon. All sequences built this period have contained 3 primary and 2 backup orbits. In all cases this period, only 2 of the primary orbit commands have been allowed to execute before a new sequence was prepared and loaded. For P595, all 3 primary orbit commands will execute before being replaced by P598 on Sunday. Operations will continue to use either 2 or 3 of the 3 loaded primary orbits in order to keep drag sequence builds during the prime shift.

There continues to be no indication of -Y solar array structural degradation. Attitude control performance has been excellent with no problems in star processing. Peak heating rates have ranged from 0.065 to 0.102 W/cm2 with panel temperatures rising from 24 to 42° C during the drag pass. The minimum MOLA laser temperature has reached about 11°C. The telecommunications subsystem continues solid performance. Battery discharge depths have ranged from 12.5% to 13% each orbit with 14 minutes of battery charger margin.

There were 5 Command Change Requests (CCRs) reviewed and approved during this period. Four were attitude control related and called for increasing the Drag’Duration parameter for contingency mode, return the SAP position error threshold to 12 counts from 36, set the SAP azimuth soft stops closer to the surveyed hard stop location, and add rate mode commands to the contingency mode script to aid in recovery efforts in case the gimbals are in powered hold on contingency mode entry. The latter requires STL testing and will be loaded later. The 5th CCR approved raises the PSE telemetry verification time-out threshold from 5 to 15 counts.

UPCOMING EVENTS:
Periapsis for Orbit 595 DOY276/20:24:33 UTC
Periapsis for Orbit 596 DOY277/07:05:38 UTC
Periapsis for Orbit 597 DOY277/17:43:32 UTC
Periapsis for Orbit 598 DOY278/04:17:51 UTC
Periapsis for Orbit 599 DOY278/14:48:42 UTC
Periapsis for Orbit 600 DOY279/01:16:17 UTC

(Note: MDT = UTC-6 hours DOY276=10/3)

SPACECRAFT COMMANDING:

There were 18 command files radiated to the S/C during this period. The total files radiated since launch is now 2811. These commands were sent in support of the following activities:

TES NIPCs

Nominal drag pass sequences (P589, P591, P593, P595)

Nominal aerobraking maneuver sequences (None)

Lower the SAP position error threshold

Contingency mode drag duration update

PSE verification fault persistence threshold update

Update the SAP soft stop

KaBLE clock source to VCO 2

Last Orbit Covered by this Report = 588

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 15

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 17038 km
Apoapsis altitude decrease since start of aerobraking = 36988 km

Periapsis altitude = 115.9 km

Current Orbit Period = 11:01:39
Orbit Period decrease since start of aerobraking = 33:57:54

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft remains healthy as Phase 2 aerobraking operations continue. There have been no corridor control maneuvers ordered during the past 5 orbits as the four orbit average drag force remains within the corridor limits. The peak dynamic pressure experienced ranged from 0.10 N/m2 to 0.24 N/m2 over the past 5 orbits. About 3 minutes and 20 seconds are being removed from the orbit period each pass. At today’s weekly reset meeting, a decision was made to increase the upper limit of the corridor from 0.23 N/m2 to 0.24 N/m2 and to use half corridor up maneuvers to reduce the drag force once the upper limit is reached. This strategy is being introduced in an effort to make up the 20 minutes of period reduction lost due to the 9 day late start to Phase 2. The upper corridor limit may be increased again at a later date if experience shows the orbit to orbit density variations to be within expectations.

The P587 sequence is now on board but will be replaced by the P589 sequence later this evening. Starting with P589, drag sequences will contain 3 primary orbits and 2 backup orbits which is an increase from 2 prime and 2 backup. The sequence will be allowed to execute either 2 or 3 of the prime orbits, controlled by the desire to build sequences during daylight hours. Periapsis timing is checked by subsystem analysis. If the timing error exceeds 232 seconds, a new replacement sequence can be ordered and loaded before the 3 primary orbits complete. The backup orbits are used only for contingencies that prevent a new sequence from being loaded due to ground processing problems. These orbits allow for much greater periapsis timing errors, but cost more fuel due to the relaxed margins.

The -Y solar array yoke structural integrity is still sound. Lack of Sun sensor data following the drag pass continues to trigger alarms that are invalid. A change, installed today, to use the pre-drag steady state angle will be used for determining the return angle. The modification requires a lag in verification of 1 orbit since the data is not available until the following drag pass. The minimum MOLA laser temperature has reached about 11°C and only drops lower when a corridor control maneuver is selected. The expected minimum after a maneuver is 9°C. The telecommunications subsystem continues solid performance. The power subsystem group has reported a maximum battery discharge depth of 12%, as expected.

The Phase 2 weekly reset meeting #4 was held today to discuss period reduction progress and new sequence parameters for the coming week. The only parameter change made was to move the second of three engineering drag pass data playbacks earlier by 20 minutes. This allows for faster post drag pass data analysis for -Y solar array structural health.

More uplink attempts have been made to fire the TES instrument primary calibration lamp. So far no joy. Use of the backup lamp is being preserved for the mapping phase.

UPCOMING EVENTS:
Periapsis for Orbit 589 DOY274/03:01:49 UTC
Periapsis for Orbit 590 DOY274/14:14:47 UTC
Periapsis for Orbit 591 DOY275/01:09:02 UTC
Periapsis for Orbit 592 DOY275/11:59:45 UTC
Periapsis for Orbit 593 DOY275/22:47:09 UTC
Periapsis for Orbit 594 DOY276/09:31:30 UTC

(Note: MDT = UTC-6 hours DOY274=10/1)

SPACECRAFT COMMANDING:

There were 13 command files radiated to the S/C during this period. The total files radiated since launch is now 2793. These commands were sent in support of the following activities:

TES NIPCs

Star catalogs and ephemeris file updates

Nominal drag pass sequences (P586, P587)

Nominal aerobraking maneuver sequences (None)

Monday, September 28 (DOY 268/19:00:00 to DOY 271/19:00:00 UTC)

Last Orbit Covered by this Report = 583

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 10

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 17375 km
Apoapsis altitude decrease since start of aerobraking = 36651 km

Periapsis altitude = 117.7 km

Current Orbit Period = 11:15:44
Orbit Period decrease since start of aerobraking = 33:43:49

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The S/C continues excellent performance of Phase 2 aerobraking operations. The past 6 orbits have reduced the orbit period by about 15 minutes, slightly less than predicted last Wednesday. The last four orbits have averaged 0.173 N/m2 drag force with the peak dynamic pressure arriving on orbit 583 at 0.21 N/m2. A periapsis lowering maneuver has been ordered for every other orbit this period to increase the drag force to this level. A burn maneuver ordered for the apoapsis portion of orbit 578 was not accomplished due to DSN station problems supporting the MGS uplink. Minimum magnitude ABMs (0.18 m/s) were used for orbits 580 and 582. The average dynamic pressure represents about the middle of the desired corridor for this phase of aerobraking. Discussions have been held to determine if a higher density corridor should be selected for use until the orbit period reduction lost during the 9 days start delay can be replaced. It is easier to make up lost time during the longer orbits than when the orbit period becomes shorter. Projections show the current drag force to slowly increase and the periapsis altitude to gradually decrease over the next two weeks.

The structural performance of the -Y solar array yoke continues unchanged from last week. Part of the monitoring process requires Sun light to illuminate the -Y solar array mounted Sun sensor head during and following the drag pass. Because of the current geometry, the desired illumination does not occur during the latter portions of the drag period causing a loss of -Y panel return angle data. This verification is now being made post drag pass through real-time data return, but the geometry is expected to improve to allow automated methods to take over in the future. The minimum MOLA laser temperature has reached 9°C and is not expected to drift any lower. Currently a 75 minute warming maneuver is being utilized. All attitude control functions continue to be excellent with no concerns. The telecommunications group reports solid performance. The power subsystem group has reported a maximum battery discharge depth of 12%. A command to allow software autonomous charging control was successfully loaded which, once the batteries are fully charged, commands the primary chargers to the lowest rate setting.

The P584 sequence has been prepared and loaded on-board, ready to take control later this afternoon. The next sequence build (P586) will commence tomorrow morning at 6:30 am MDT. Although this sequence will contain two primary orbits, only 1 orbit will be allowed to execute. The sequence will be replaced by P587 to be built tomorrow early evening. This allows builds to continue to be generated during the prime shift hours.

Command files were uplinked on Saturday to power the TES and MAG/ER. The special load and go sequence successfully executed the instrument power on, but the TES primary calibration lamp did not fire. A second attempt to power the lamp was also unsuccessful. Plans will be put into action to try again.

UPCOMING EVENTS:
Periapsis for Orbit 584 DOY271/19:38:18 UTC
Periapsis for Orbit 585 DOY272/06:50:25 UTC
Periapsis for Orbit 586 DOY272/17:58:54 UTC
Periapsis for Orbit 587 DOY273/05:03:45 UTC
Periapsis for Orbit 588 DOY273/16:04:51 UTC
Periapsis for Orbit 589 DOY274/03:01:49 UTC

(Note: MDT = UTC-6 hours DOY271=9/28)

SPACECRAFT COMMANDING:

There were 22 command files radiated to the S/C during this period. The total files radiated since launch is now 2780. These commands were sent in support of the following activities:

TES NIPCs

Sequence to power the TES and MAG/ER

Nominal drag pass sequences (P578, P580, P582, P584)

Nominal aerobraking maneuver sequences (A580, A582)

Update the reaction wheel tach hold speeds

Express SSR playback

Enable FSW control of battery charging

Friday, September 25 (DOY 266/19:00:00 to DOY 268/19:00:00 UTC)

Last Orbit Covered by this Report = 577

Total Phase I Aerobraking orbits accomplished = 180

Total Phase II Aerobraking orbits accomplished = 4

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 17720 km
Apoapsis altitude decrease since start of aerobraking = 36306 km

Periapsis altitude = 120.6 km

Current Orbit Period = 11:30:20
Orbit Period decrease since start of aerobraking = 33:29:13

Starting Phase II orbit period = 11:38:02

RECENT EVENTS:

The Mars Global Surveyor spacecraft maintains excellent health. The walk in portion of the Phase II aerobraking operation has been accomplished. Orbit 577 was the first to provide a drag force between 0.13 and 0.23 N/m2 with a value of 0.14 N/m2. The AB-2 and AB-3 walk in maneuvers were executed successfully with no concerns. AB-2 was a 0.36 m/s down maneuver executed on the apoapsis portion of orbit 574 which provided a drag force of about 0.1 N/m2 on the following periapsis. The last walk in maneuver provided 0.18 m/s delta V and was executed on the apoapsis portion of orbit 576.

Daily drag sequence builds and APG (Aerobraking Planning Group) meetings will continue. The opportunity exists for 1 corridor control ABM (Aerobraking Maneuver) per day. Immediate action maneuvers can be ordered for any orbit.

The -Y solar array structural performance shows no change from the end of the Phase I operations. The MOLA warming maneuvers continue to be performed for 75 minutes each orbit. The lowest MOLA laser temperature observed since the re-start of aerobraking has been 9°C. This value may trend a little lower before stabilizing but is not expected to reach the lower limit of 7.5°. Attitude control performance has been excellent. No star processing troubles have been reported. The telecommunications group reports solid performance. The power subsystem group has reported a maximum battery discharge depth of 10.6%. This deficit is easily replaced by the primary chargers. A command has been prepared to reset a flight software flag that will permit the autonomous charger management to execute. This enable flag was set when the S/C entered contingency mode due to power alert.

The P578 sequence has been prepared and is in the review process. This sequence will be loaded later this afternoon and will control S/C activities through orbits 578 and 579 with backup commands for orbits 580 and 581. Commands are prepared for powering the TES and MAG/ER instruments tomorrow morning. These instruments were powered off when the S/C entered contingency mode.

UPCOMING EVENTS:
Periapsis for Orbit 578 DOY268/23:23:52 UTC
Periapsis for Orbit 579 DOY269/10:51:43 UTC
Periapsis for Orbit 580 DOY269/22:17:03 UTC
Periapsis for Orbit 581 DOY270/09:39:58 UTC
Periapsis for Orbit 582 DOY270/21:00:35 UTC
Periapsis for Orbit 583 DOY271/08:18:54 UTC

(Note: MDT = UTC-6 hours DOY268=9/25)

SPACECRAFT COMMANDING:

There were 5 command files radiated to the S/C during this period. The total files radiated since launch is now 2758. These commands were sent in support of the following activities:

Nominal drag pass sequences (P574, P576)

Nominal aerobraking maneuver sequences (A574, A576)

Update GDE maximum acceleration parameter

Last Orbit Covered by this Report = 573

Total Aerobraking orbits accomplished = 180

Total Science Phasing orbits accomplished = 290

Apoapsis altitude = 17866 km
Apoapsis altitude decrease since start of aerobraking = 36160 km

Periapsis altitude = 171.1 km

Current Orbit Period = 11:38:02
Orbit Period decrease since start of aerobraking = 33:21:31

RECENT EVENTS:

The Mars Global Surveyor spacecraft is in excellent health following today’s main engine maneuver that started Phase 2 aerobraking operations. The 4.8 second burn provided 11.62 m/s change in velocity and hit the target of 127 km periapsis altitude perfectly. The P573 drag sequence is on board and will be controlling all on-orbit S/C activities until this evening when the new P574 sequence takes over.

The burn maneuver was originally planned for last Thursday but was delayed due to an unexpected entry into contingency mode by the spacecraft. A sequence block error, that passed through STL testing undetected, placed the +Y solar array gimbal drive in the powered hold mode and left the panel pointed away from the Sun. The lack of power production caused energy to be drawn from the S/C batteries until fault monitoring on board reacted to their low state of charge. At 10:43 UTC (04:43 MDT) the S/C entered contingency mode, corrected the panel position and mode, pointed panels at the Sun and canceled the on-board sequence execution, including the already initiated main engine burn sequence.

The low power entry path into contingency mode called for swapping the power subsystem mode controller to the backup unit. This transition introduced a temporary power drop on the power bus causing the IMU DC power supply, PSE (Power Subsystem Electronics) and the I/O bus to swap to their respective backup units. After analysis, commands were generated and uplinked that restored the IMU, PSE and bus to their nominal configurations by Friday evening. On Saturday, the mode controller was swapped back to primary which, as expected, caused the swap of the PSE and bus but not the IMU.

The remainder of the recovery required a short mini-sequence to enable and disable the star processing algorithm to prevent Mars albedo interference with the CSA (Celestial Sensor Assembly). With this sequence (Z568) in place, inertial reference was re-established while the S/C was Sun pointed and the uplink and downlink was at low rate via the LGA. Because of the low uplink rate via the LGA path, a normal drag sequence would have required over 75 minutes of continuos uplink time. This was deemed unacceptable due to the low link margins available using the LGA uplink path. An intermediate sequence, P570 was built, tested and executed that transitioned the S/C from LGA / Sun pointing to HGA / Earth pointing and continued to manage the star processing as well as maneuver to warm the MOLA instrument. This provided a safe HGA uplink path from which the return to aerobraking could be accomplished.

The P573 sequence was loaded late Tuesday then took control early Wednesday morning and performed the drag pass activities while the S/C was still above the atmosphere as a rehearsal. This pass resulted in the +Y solar array drive electronics being swapped to side 2 due to fault protection. The fault was discovered to be caused by a gimbal drive acceleration parameter that caused the panel to slightly overshoot the commanded target before converging on the desired position. This overshoot did not present a problem during the SPO operations but in aerobraking, the panel is moving toward the hard stops where, from a low rate, the gimbal came to a halt while the drive control was still trying to converge on the target. Commands to reset the GDE to side 1 and to increase the persistence threshold for the fault response were developed, tested and uplinked. STL testing re-created the problem and confirmed the need to change the acceleration parameter back to the Phase 1 aerobraking value. That update will be radiated later tonight.

The main engine maneuver, A573, was loaded at the same time as the P573 sequence and executed the fully successful burn at 17:49 UTC (11:49 MDT). The first drag pass will occur tonight at 19:30 MDT.

All spacecraft subsystems report excellent health. The power subsystem reports strong performance, however the battery charge profile did not occur as expected following the rehearsal drag pass on orbit 573. Normally when the flight software detects full battery state of charge it will command the primary chargers to it’s lowest setting of 0.85 amps. This command did not occur on the first orbit and analysis is under way to determine the cause. The sequence disconnects the primary chargers and attaches the trickle chargers 20 minutes following full battery state of charge, preventing any concern of battery overcharging.

Temperatures remain well within limitations with the minimum MOLA instrument value riding above 10°C. Telecommunications performance remains strong. The TES and MAG/ER were powered down by the contingency mode response and remain un-powered now. These instruments will be re-powered by the end of the week.

The 3rd aerobraking Phase 2 reset meeting was held this week to discuss period reduction goals, schedules and parameters for the first sequence and AB-1.

The STL performed various tests on the products to recover from the contingency mode entry and the repaired drag pass sequence.

UPCOMING EVENTS:
Periapsis for Orbit 574 DOY267/01:09:54 UTC 1st Drag Pass
AB-2 Maneuver Apoapsis for Orbit 574 DOY267/06:58:40 UTC
AB-3 Maneuver Apoapsis for Orbit 576 DOY268/06:11:17 UTC

SPACECRAFT COMMANDING:

There were 57 command files radiated to the S/C during this period. The total files radiated since launch is now 2753. These commands were sent in support of the following activities:

TES NIPCs.

Nominal star catalogs and ephemeris file updates.

Errant drag pass sequence (P560)

AB-1 maneuver sequence that was canceled by C’Mode (A560)

Recovery from C’Mode command (44 files)

AB-1 sequence (A573)

Nominal drag pass sequence (P573)

Swap the GDE back to side 1

Reset of battery charge counters

Command Loss timer resets

Memory readout of on-board computer memory

Status as of 00:00 UTC 19 September (DOY 262, Friday Evening):

Command Status:

The Mars Global Surveyor spacecraft remains in "contingency mode" in a safe and stable state at the end of the day. Downlink remains at 10 bps and the uplink is at 7.8 bps.

With the exception of the power subsystem Mode Controller, all other spacecraft hardware which had switched to the redundant sides has been returned to the primary side, with the hardware and software redundancy restored. The Mode Controller will be commanded back to Primary on Saturday morning during the DSS15/14 support period, when the 70M ground station will increase the visibility into the spacecraft for this event. There is some slight possibility that the power bus transient which will occur with the Mode Controller swap will cause a repeat of the other component side swaps which will necessitate re-commanding units back to their primary sides. If necessary, this will be pursued over the weekend.

Return to Normal Operations:

The balance of the weekend will be spent building and testing command sequences which will recover the spacecraft from Contingency Mode and return the spacecraft to normal operations. These uplinks will commence Sunday evening. The spacecraft is current projected to return to high-gain antenna operations shortly after Periapsis 570 (Appr. 98-265T02:40, Monday Evening)

Resumption of Aerobraking:

During the day on Monday, the Navigation and Spacecraft Teams will complete the redesign of the first aerobraking maneuver (AB-1) which is currently scheduled to execute near Apoapsis 573 (appr 98-266T18:00, Mid-day Wednesday) during the DSS15 support. Another drag rehearsal sequence will be executed at Periapsis 573 outside of the atmosphere, prior to the maneuver execution near Apoapsis 573. On Tuesday morning, an Aerobraking Reset Meeting will be held at 15:00 UTC (8:00 Pacific, 9:00 Mountain). The first drag pass is expected to be at Periapsis 574 on Wednesday evening.