Key to Real Time Telemetry Status

General Info on Page Headers: (Applies to Most Pages) Working from Right to Left (Reverse Order)
Most pages have two timestamps to describe the data that you are receiving. The Earth-Received Time ("ERT") tells you when the data was received at the tracking station on the surface of the earth. The SpaceCraft Event Time ("SCET") shows what time the events being seen actually happened onboard the spacecraft. There are two reasons why the SCET is always different from the ERT: first, even data that are sent immediately from the spacecraft require several light-minutes to travel from Mars to the earth (during aerobraking, this takes about 14-15 light-minutes), and secondly, it is also possible to record data onboard the spacecraft for replay at a later date (Like taping programs on your VCR). The Station ID number of the antenna within the Deep-Space Network which is currently tracking the spacecraft is also shown. The antennae used most frequently by Mars Global Surveyor are DSS 15 & 25 (at Goldstone, California), DSS 45 & 34 (at Canberra, Australia), and DSS 65 & 54 (outside Madrid, Spain).

Ground System Status Page: On the top row of the page is shown the status of the ground system receiving antenna. First, the Station ID number of the antenna within the Deep-Space Network which is currently tracking the spacecraft is shown. The antennae used most frequently by Mars Global Surveyor are DSS 15 & 25 (at Goldstone, California), DSS 45 & 34 (at Canberra, Australia), and DSS 65 & 54 (outside Madrid, Spain). Next the status on CONical SCAN search mode is displayed (This mode is used when you are not quite sure where you should be pointing - MGS seldom needs to use this mode). The type of receiver ("RCVR", Block "5") and whether or not it is in lock on the spacecraft radio signal ("IN/LOCK" or "OUT/LOC") is shown. The Automatic Gain Control ("AGC") Level is shown, to report how much the incoming signal needed to be amplified by before passing it on to the downstream components. This is an indirect way of reporting how strong the signal received from the spacecraft is, in decibels (referenced to 1 milliwatt). At the far right of the top row is shown the elevation above the local horizon where the antenna is pointing.

The second row begins by reporting the status of the older "Block 3" receivers. These are usually shown as "OUT/LOC" since MGS usually uses the "Block 5" receivers whose status is reported on the first row. The next subsystem is the Base-Band Assembly ("BBA") which is used to demodulate the digital bits from the radio signal. The input to the BBA is the output of the RCVR, so it cannot start to do its job until the RCVR reports "IN/LOCK". It reports both its status (OPERational, or OUT/LOC) and the Signal-to-Noise Ratio ("SNR"). The next assembly is the Maximum-Likelihood Convolutional Decoder ("MCD") which is used to decode the outer layer of error-correcting coding in which the spacecraft wraps its data (Vitterbi Coding). Again, the input to the MCD is the output of the BBA, so it cannot begin its job until the BBA is "IN/LOCK". As with the BBA, lock status and SNR are reported. Finally, the lock status of the Frame Synchronization Subsystem (FSS). Once the MCD begins sending its stream of error-corrected bit on to the FSS, the FSS start looking for repeatable synchronization codes which the spacecraft places in the data stream which allows the rest of the telemetry to be decoded from this bit stream.

The third section from the top reports on the signal being transmitted from the ground to the spacecraft including transmitter status, transmit frequency (in hertz, or cycles per second), and the transmitted power in kilowatts. The data bit rate at which commands can be sent to the spacecraft (in bits per second, or bps). Most of the rest of the page contains detailed information which is seldom used by the flight team, or is repeated and described on other pages.

Signal strength plot: This page shows a plot of the signal strength of the radio signal transmitted by the spacecraft as received at the ground station. The Automatic Gain Control ("AGC") Level is shown, which reports how much the incoming signal needed to be amplified by before passing it on to the downstream components. This is an indirect way of reporting how strong the signal received from the spacecraft is, in decibels (referenced to 1 milliwatt).

Telemetry Segment Plot: Once the Frame Synchronization Subsystem is "IN/LOCK" on the spacecraft telemetry, it decodes the telemetry from the spacecraft in a set of "chapters" know as "frames." The spacecraft assigns each successive frame a sequential number between 0 and 63 (6-bits worth of data or 2^6). After the number 63 is assigned, then the number 0 is recycled and the numbering scheme starts over. When telemetry data is flowing, this plot looks like a sawtooth, or a zebra. When there is data missing, it shows up on this plot (Unfortunately, this happens frequently when the workstation is busy doing other things, like converting these pages to GIF's and transferring them to the our web server!).

Avionics Systems Page: (See previous discussion regarding the 3-line page "header" banner) The page shows an overview of the spacecraft's aviation electronics ("avionics") systems. It provides a quick overview of the spacecraft data systems, along with summaries of some telemetry channels that appear on other pages.

In the first column the left-hand side of the page, the major data systems are shown. At the top of the column is the Engineering Data Formatter (EDF), which monitors the major engineering subsystems of the spacecraft and collects most of the measurements shown on these pages. As with many subsystems, there is a primary unit (side 1) and a spare (side 2). Below EDF, is the Payload Data Subsystem, which provides a similar function as the EDF for the Payload Instruments. Again, there is a prime (side A) and a spare (side B). Below the PDS are the 4 Solid-State data recorders (SSR 1A, 1B, 2A, and 2B). The SSR's provide a function similar to the hard disk on your computer and take the place of digital tape recorders used on older spacecraft. Unlike hard disks or tape recorders, the SSR's have no moving parts, and instead store all of the data in banks of RAM memory chips. The power state (on/off), mode (record/playback), and Data ENAble (DENA) state (enabled/disabled) are shown for each unit.

To the right of the data sources is shown the Cross-Strap Unit ("XSU") which is used to choose which data source is routed to the radio system for downlink to the earth. During aerobraking, this is usually the EDF. During mapping it will usually be the SSR's which will replay data recorded from PDS. Again, there is a prime and a spare (Side 1 or Side 2). The Process Gain Control ("PGC", also known as the Modulation Index) determines how much of the radio signal is dedicated to the "carrier tone" and how much to the actual data bits. Under the PGC setting, the currently selected data source is shown.

To the right of the XSU, the telecommunications system is show. The Ka-Band Link Experiment (KABLE) power status (On/Off) is shown at the top. Next, the status of the Mars Orbiter Transponder is shown. This is the heart of the telecommunications system and consists of an Low Power Exciter (XCTR) and a Receiver (RCV). One of the frequency sources that the transponder can use is the Ultra-Stable Oscillator (or USO) which is primarily intended for science use to observe the Martian atmosphere. The Command Detector Unit (CDU) status is shown below the MOT's. This unit detects and decodes commands sent by radio from the ground to the spacecraft. To the far right of the screen is shown both the Traveling Wave Tube Amplifiers (TWTA's) which amplify the low power signal from the MOT XCTR, and then routes it through the various Radio-Frequency Switches (RF_S1, S2, S3) to either of the wide-beam Low Gain Transmit (LGT1, LGT2) antennae or narrow beam High Gain Antenna (HGA).

Across the bottom of the bottom of the page are four boxes that show status for:

1) Command and Data Handing Subsystem (Command Interface Unit - CIU, and Command Interface Extender - CIX, which form the central nervous system of the data signals which control the spacecraft.

2) Mission Phase Relays (M_PHASE_R) which help the spacecraft remember how far through the mission it has progressed (AEROBRK, MAPPING) in case the computer ever reboots.

3) Attitude Control Subsystem (Comprised of the Celestial Sensor Assembly- CSA, Sun Sensors-SS1,SS2, Gyro Scopes, Inertial Measurement Unit power supplies (Primary, Backup, AC, DC), Mars Horizon Sensors, and Reaction Wheel Assemblies (RWA's, which spin around either the spacecraft X, Y, Z, or Skew axis to control the spacecraft pointing.

4) Power Supply Electronics (which shows the voltage level of the power supply bus, and the amount of current required to supply the spacecraft loads). The voltage levels as well as the charge or discharge current going into or out of the batteries is also shown.

Solar Array Current Plots: This page shows plots of the number of Amperes generated by each of the spacecraft's four solar panels (two on each of two "wings" on either side of the spacecraft). In the cruise/aerobraking configuration, the spacecraft slowly rolls about the line between the spacecraft and the earth (mainly for communications reasons). As it does so, the different panels produce different amounts of energy.

Bus Current Plots: This page shows a plot of how many Amps are being consumed by the payload (blue plot, blue scale), and the engineering subsystems (red line, red scale). If the panels are producing more Amperes than required, then the surplus can either be used to recharge the batteries, or it can be radiated into space using what is called a partial-shunt radiator. If the bus loads are temporarily higher than the array can supply, then the deficit can be made up by the batteries.

Power Subsystem Schematic: This page begins with the status of the two solar array wings (on the +y and -y sides of the spacecraft). The current being generated and the panel temperatures of each are reported. To the lower right of the solar array status, the Partial Shunt Assembly is monitored. This is the assembly responsible for dissipating any excess power generated by the solar array beyond what is required to power the spacecraft and keep the batteries charged. To the upper right of the shunts is shown the Power Supply Electronics. This is the box which is the brains of the power subsystem. It monitors all of the power sources (arrays, batteries) and the consumption rates (engineering systems, science instruments, dissipation shunts) to keep the system regulated and in balance. Finally, across the top row, estimates for the power consumption of each engineering subsystem (S/C_BUS) and science instrument (PAYLOAD) are provided. Back on the left side of the page, in the lower half, the status of the batteries is reported. The inputs to the batteries are through the Battery Charge Regulators (BCR) which allows the array to recharge the batteries when excess power is available. The output of the batteries flows through the Boost-Voltage Regulator (BVR) which assures that the battery output will be at the same voltage as the output of the solar arrays, so that the devices being powered on either the engineering or payload buses will not be able to tell the difference between energy provided by the array or the batteries.

Telecom Page: First, the status of the two Mars Orbiter Transponders (MOT1, MOT2) is shown. These are the heart of the telecommunications system and each unit consists of a Low Power EXCITER (XCTR) and a Receiver (RCV). The optional switches for the exciter configuration are shown at the top of each box. Below that, the receiver lock status is shown, as well as the Automatic Gain Control level (a measure of signal strength) for the uplink from the ground to the spacecraft is shown, along with other status parameters and the temperatures of two key components.

Below the MOTs is shown the status of both Traveling Wave Tube Amplifiers (TWTA's) which amplify the low power signal from the MOT XCTR to a signal level that can be detected on the ground. To generate a signal, both the filament (FILMNT) and the High Voltage (HV) switches must be on. The unit's power draw in Amperes and volts is shown, as well the temperatures at key locations.

The Command Detector Unit (CDU) status is shown below the TWTAs. These units detect and decode commands sent by radio from the ground to the spacecraft. Their "lock" status indicates whether or not they are currently detecting commands being sent from the ground and the bit rate at which the command data is expected. Other parameters are reported below.

At the top of the right-hand column on this page is shown the Ultra-Stable Oscillator (or USO), one of the frequency sources that the transponder can use to generate its signal. It is primarily intended for science use to observe the Martian atmosphere. Next is the Redundant Crystal Oscillator (RXO), which is used to provide a clock signal for the computers onboard the spacecraft. Below the RXO, is shown the status for the Ka-Band Link Experiment (KABLE). The main radio system for MGS operates in the X-Band frequency range, but the experimental KABLE system is being flown to demonstrate how similar performance levels can be achieved using less power, if a much higher frequency band is used (four times higher than X-Band).

The Cross-Strap Unit (XSU) status is shown below the KABLE status. This unit controls the interface between the digital data system and the radio system. For a more detailed description of the XSU, refer to the Avionics Systems page.

Finally, the Radio Frequency (RF) Switch Status and "Pick-Bits" Status are shown. These switches are used to control the routing of the various radio signals throughout the spacecraft between the different antennae and the different receivers and transmitters onboard the spacecraft.

Mars Orbiter Transponder Receiver Strength Plot: This plot shows the Automatic Gain Control level for the receivers for each of the Mars Orbiter Transponders. This is a measurement of the strength of the signal sent from the ground as received by the spacecraft.

Propulsion Page: The first item displayed on this page is the Main Engine. This rocket engine is the largest onboard the spacecraft and is located on the center-line of the spacecraft. It is used for the largest maneuvers that the spacecraft is required to perform. To prevent accidental firings, it must be both armed and enabled before it can be fired. It also must be pre-heated by flange heaters for 30 minutes before use (ME_FLNG). The temperatures of the valve and the flange are reported to assure that it is adequately preheated before use. "Flight" software, running in the computers onboard the spacecraft, keeps track of how many seconds the engine has been used recently (since the last clock reset).

In addition to the main engine, the spacecraft also has 12 smaller thrusters located on the corners of the spacecraft. They can be used both for changing the spacecraft's velocity through space, or in coupled-pairs to spin or de-spin the spacecraft (or control its pointing). Again, to prevent accidental firings, the engines must be both armed and enabled before use. The temperatures and total on-time is reported.

Along the left side of the page is reported the positions of the various commandable latch-valves which control the flow of fluids and gases through the systems.

At the bottom of the left column, the pressures of the Gaseous Helium (GHe), the propulsion lines (LINE), the Nitrogen Tetroxide Oxidizer (NTO) and the Hydrazine (N2H4) tanks are reported.

In the lower right corner of the page, the temperatures of the various propulsion components is reported, along with the enable/on status of the heaters used to keep these temperatures under control.

Science Payload Status Page: This page shows the status of the various payload science instruments, their heaters, and their temperatures. The first instrument shown is the Electron Reflectometer (ER) which is part of the Magnetometer (MAG) experiment, which is shown just below it. The Mars Orbiter Camera (MOC) status is shown below the MAG. The temperatures of the different parts of the MOC are shown, which vary considerably from those parts kept constantly warm by being close to the spacecraft, to those on the upper tube structure of the telescope which vary considerably when the spacecraft spins while in the cruise and aerobraking configuration. The Mars Orbiter Laser Altimeter (MOLA) status is shown below the MOC. Below MOLA is shown the status of the Mars Relay (MR) antenna, which will be used to relay data through MGS from future landers and rovers being sent to the surface of Mars. Next is the Thermal Emission Spectrometer (TES), the infrared mapping instrument which is also capable of determining the chemical composition of the surface below. The Ultra-stable Oscillator status is shown below the TES. This is a radio oscillator which will be used in conjunction with the main spacecraft radio system in order to make observations of the Martian atmosphere as the spacecraft radio beam passes through the atmosphere twice each orbit during the mapping mission. The last three lines of the page show first, how many Amperes of power the payload is drawing, and also two temperature sensors mounted to nadir panel where most of the instruments are mounted.

Mars Orbiter Camera Temperature Plot: This page show a time-history plot of four temperature sensors which are mounted to the Mars Orbiter Camera. The temperatures of the different parts vary considerably between those parts kept constantly warm by being close to the spacecraft, to those on the upper tube structure of the telescope which vary considerably when the spacecraft spins while in the cruise and aerobraking configuration.

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