After the trajectory correction maneuver yesterday, a latch valve was closed to shut off the flow of high-pressure helium to Surveyor's propellant tanks. This activity was performed as a safety precaution against leakage from the pressure regulator that moderates the flow of high-pressure helium into the propellant tanks. Undesired leakage would cause an over-pressure condition in the propellant tanks.
Early this afternoon, the onboard computer commanded the firing of a pyrotechnic device to close valve number 10 in the propulsion system. The firing physically sealed the line between the nitrogen tetroxide propellant tank and a check valve located between the nitrogen tetroxide and the helium tank. This closure will prevent nitrogen tetroxide vapors from damaging the check valve during the 10 months between now and Mars orbit insertion.
Because Surveyor's propellant is now isolated from its pressure source, the remaining three maneuvers prior to Mars orbit insertion will be performed in 'blow-down' mode using the residual pressure remaining in the propellant tanks. The propellant tanks will be repressurized in mid-September 1997 during the week prior to the Mars orbit insertion burn.
This weekend, the flight team will power up the science instruments for the first time during the mission. After the operational status of the instruments has been verified, the Mars Orbiter Camera and the Thermal Emission Spectrometer will image the Earth for calibration purposes. Instrument calibration activities will continue until Tuesday, November 26th.
Surveyor is now 4.3 million kilometers from the Earth and moving away with a velocity of 3.11 kilometers per second.