Flight Status Report

After conducting a "go/no-go" poll of Surveyor's flight controllers at 5:45 p.m PDT today, lead controller Kyle Martin reported to flight operations manager Joe Beerer that "all systems are go for the Mars orbit insertion burn." Beerer's concurrence with the status check enabled project manager Glenn Cunningham to give the official "go ahead" for the engine firing to put Surveyor in orbit around Mars.

Almost 46 minutes later, at 6:31 p.m. PDT, the onboard computer command Surveyor's tiny attitude-control thrusters to fire for 20 seconds. These tiny thruster rockets are normally used to stabilize the spacecraft during main-engine firings. The initial, 20-second thruster firing settled the liquid in the spacecraft's tanks to ensure a smooth flow of propellant to the more powerful main rocket engine that was used for the orbit insertion maneuver.

Immediately after the small, settling burn, the computer commanded Surveyor's main engine to fire. Ignition occurred at an altitude of about 930 miles (1,500 km) with the spacecraft moving at a velocity of 11,390 m.p.h. (5,090 meters per second). Twelve minutes into the burn, Surveyor passed behind Mars. Although contact was lost when the spacecraft passed behind Mars, the computer continued to carry out the orbit insertion burn without incident.

When Surveyor reemerged from behind Mars at 6:57 p.m PDT, the burn had already completed. Over the course of the 22-minute burn, the engine expelled over 617 pounds (280 kilograms) of nitrogen tetroxide and hydrazine propellant to slow Surveyor by a total of 2,176 m.p.h. (973 meters per second).

Chief navigator Dr. Pat Esposito has announced that tracking data gathered by stations in California and Australia confirm that the burn was executed successfully and flawlessly. Although the navigation team is currently performing a detailed analysis to determine the exact nature of Surveyor's orbit around Mars, preliminary indications show that the orbit's low point is about 155 miles (250 km) above the Martian surface, and the high point is at an altitude of just over 31,000 (50,000 km). In this orbit, Surveyor will take roughly 45 hours to circle the red planet.

The flight team at the Jet Propulsion Laboratory in Pasadena and the Lockheed Martin Astronautics facility in Denver is currently busy monitoring the health and status of the spacecraft. However, initial data shows that all systems are functioning normally. One of the next tasks will the preparation of command sequence T2 for transmission to Surveyor. This sequence will be sent Saturday morning, just prior to the start of the second orbit around Mars. The primary purpose of T2 will be to configure the spacecraft and science instruments for orbital and aerobraking operations.

After a mission elapsed time of 308 days from launch, Surveyor is 158.06 million miles (254.38 million kilometers) from the Earth and in an orbit around Mars with a period of 45 hours. The spacecraft is currently executing the T1 command sequence, and all systems continue to be in excellent condition.

                        Mars Global Surveyor
                     Orbit Insertion Timeline
                   Thursday, September 11, 1997
        All times are Earth-received, Pacific Daylight Time (PDT)
                        PDT = UTC - 7 hours

12:40 p.m. Deep Space Station 14 at Goldstone, CA, begins tracking
12:40 p.m. Deep Space Station 15 at Goldstone, CA, begins tracking
 4:31 p.m. Gyro #2 turned on
 4:35 p.m. Deep Space Station 43 in Australia begins tracking
 4:35 p.m. Deep Space Station 45 in Australia begins tracking
 5:01 p.m. Spacecraft begins loading maneuver control parameters
 5:17 p.m. Deep Space Station 15 transmitter off
 5:31 p.m. Spacecraft begins maneuver command block
 5:55 p.m. Spacecraft transmitter switches from high-gain antenna to low-gain 
           antenna #1
 5:55 p.m. Spacecraft's telemetry turned off; transmits only carrier signal
~5:59 p.m. Deep Space Stations re-acquire signal
 6:01 p.m. Thrusters enabled for steering and attitude control during orbit 
           insertion
 6:14 p.m. Spacecraft starts turn to align rocket engine in burn direction
 6:15 p.m. Solar arrays begin turning to orbit insertion orientation
 6:29 p.m. Inertia measurement unit set to supply accelerometer data
 6:30 p.m. Fuel and oxidizer valves enabled and armed
 6:31 p.m. Main engine burn begins
 6:40 p.m. Deep Space Station 45 transmitter on
 6:43 p.m. Spacecraft passes behind Mars; radio signal lost
 6:44 p.m. Closest approach to Mars (periapsis #1)
 6:53 p.m. Main engine burn ends
 6:55 p.m. Attitude control returned to reaction wheels
 6:55 p.m. Spacecraft turns to Earth point and resumes array-normal-spin attitude
 6:56 p.m. Solar arrays moved to array-normal-spin position
 6:57 p.m. Spacecraft emerges from behind Mars
~6:57 - 7:03 p.m. Deep Space Stations acquire spacecraft carrier signal
 7:10 p.m. Spacecraft transmitter switches from low-gain antenna to high-gain 
           antenna
 7:10 p.m. Spacecraft resumes transmitting telemetry (data)

NASA's Mars Global Surveyor, the first in a series of orbiters and landers to explore Mars in the next decade, performed a critical engine burn this evening and successfully entered orbit around the red planet.

The spacecraft executed a 22-minute engine burn at 01:17 Universal Time (6:17 p.m. Pacific Daylight Time) and slowed its speed by more than 3,200 kilometers per hour (2,000 miles per hour) to be captured in Martian orbit. (Because radio signals traveling at the speed of light take 14 minutes, 6 seconds to reach Earth from Mars, the start of the engine burn was detected by ground controllers at 6:31 p.m. PDT.) Doppler data after the burn indicated that the spacecraft is now in a highly elliptical orbit which takes it within about 250 kilometers (155 miles) of Mars at its closest point and about 56,000 kilometers (34,800 miles) at the most distant.

Global Surveyor is the first U.S. spacecraft to orbit Mars in more than 20 years and the first to use aerobraking rather than propulsive maneuvers to adjust its orbit upon arrival. The technique was demonstrated during the final months of the Magellan mission to Venus in the summer of 1993, and found to be a plausible design for circularizing a spacecraft's orbit while saving fuel.

Preparations for this evening's orbit insertion burn began two days ago, on September 9, when Global Surveyor pressurized its propellant tanks. Pressurization occurred at 9:15 a.m. PDT and was nearly instantaneous. The propellant tanks reached the required value of 18.6 bars (270 pounds per square inch), which was necessary to perform the capture burn tonight.

Today's activities began about 17 minutes before the orbit insertion burn, when Mars Global Surveyor powered up its small 2.3-kilogram (5-pound) thrusters and prepared to turn its main engine in the direction of the spacecraft's motion, or toward Mars. After this reorientation, and at an altitude of 1,490 kilometers (926 miles) above Mars, the spacecraft fired its 660-newton main engine for approximately 22 minutes, 39 seconds.

Twelves minutes after the start of the engine burn, the spacecraft passed behind Mars as seen from Earth and was temporarily blocked from communications with Earth. This occultation lasted 12 minutes. The spacecraft emerged from behind Mars nearly four minutes after the engine burn had been completed. Two of NASA's Deep Space Network tracking facilities at Goldstone, CA and Canberra, Australia, were monitoring the spacecraft's orbit insertion burn and reacquired Mars Global Surveyor's signal within seconds of its reappearance from the back side of Mars at 6:57 p.m. PDT.

Global Surveyor has arrived at Mars during fall in the northern hemisphere and spring in the southern hemisphere, which usually coincides with the start of the dust storm season. Although dust storms are a concern for the navigation team, the spacecraft will be able to raise its orbit and fly over these storms if it becomes necessary. Data from the surface of Mars, furnished by the highly successful Mars Pathfinder lander and rover mission, in addition to data from the orbiting Hubble Space Telescope and the National Radio Astronomy Observatory microwave antenna in Boulder, CO, will assist the Mars Global Surveyor team as they begin to dive into the upper atmosphere and understand the dynamics of the Martian environment.

Mars Global Surveyor will complete three revolutions around Mars in its initial, highly elliptical orbit, and gather some science data. On September 17, the spacecraft will perform its first aerobraking maneuver. Each time the spacecraft reaches the farthest point in its orbit around Mars –- known as the apoapsis –- it will perform an engine burn to trim the orbit. After four engine burns at apoapsis -- on September 17, 20, 22 and 24 –- Global Surveyor's orbit will be reduced to about three hours, meaning the spacecraft will be completing one revolution around Mars about every three hours.

During the next three months, the navigation team will continue to fine-tune the spacecraft's apoapsis and periapsis, or farthest and closest points over Mars, respectively. In January 1998, the navigation team will begin three weeks of final orbital adjustments. Then the science instruments will be turned on around March 10 and the mapping mission will begin on March 15, 1998.

Office of the Flight Operations Manager Mars Surveyor Operations Project
NASA Jet Propulsion Laboratory California Institute of Technology Pasadena, CA 91109