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Mars Global Surveyor is On Its Way to Mars

Mars Global Surveyor Launch
on a McDonnell Douglas Delta II
November 7, 1996

The Mars Global Surveyor (MGS) spacecraft was launched on November 7, 1996, and is cruising to Mars in excellent condition.

The spacecraft was launched on the second day of its launch period because the weather at Cape Canaveral was bad at the time of the scheduled liftoff on the first day. However, the next day, November 7, was beautiful, and the McDonnell Douglas Delta II rocket gave the spacecraft a perfect launch into a perfect midday sky. NASA's Deep Space Network first acquired the radio signal from the spacecraft at its Canberra, Australia, tracking station. The telemetry data indicated that all spacecraft systems were performing as expected with the exception that one solar panel was not fully deployed.

mgs2.jpegThe solar array along the spacecraft's Y axis did not fully deploy at launch. Telemetry data and the results of several tests performed in-flight since launch indicate that the panel is about 20 degrees from its fully latched position. This is not a problem for cruise and mapping because the solar panel can be positioned with its electrical actuators to point the panel at the Sun. Thus there is no loss of electrical power generation.

The project team, consisting of Lockheed Martin Astronautics personnel in Denver, Colorado, and JPL personnel in Pasadena, California, is, however, evaluating this situation in relation to the use of the panel as a drag surface for aerobraking after the spacecraft arrives at Mars. Because the panel is not latched, the atmospheric drag forces, caused by dipping into the top of the Martian atmosphere during aerobraking, would tend to close up the panel and reduce its capability to be a good drag surface. The plan is to turn the panel around and use the side with the solar cells on it to face into the atmospheric flow. The final assessment of this plan is expected about April 1.

The project team feels that the solar panel is not fully latched because a small lever arm broke off during the deployment and is lodged in the hinge joint, preventing the full rotation to the latched position. The lever arm connects a damper that was to limit the speed at which the solar panel moved while being deployed.

Several in-flight tests "wiggled" the solar panel in December and again in January to characterize the performance of the panel in its unlatched state. The tests all succeeded in showing that the panel is free to move in the unlatching direction, but that it is difficult to move against the debris restricting its latching in the other direction. The debris did not move out of the way in these tests.

The first of four trajectory correction maneuvers was perfectly executed on November 21. This very small change (27 m/s or about 60 mph) in the spacecraft's velocity was made to better aim the spacecraft at Mars. Other small course corrections were made in late March, late April, and will be made again just before arrival at Mars in late August.

All the instruments of the science payload were turned on for in-flight checkout and calibrations. All of them were found to be working very well. Much of this activity took place during the last week of November. The Earth was used as a calibration source for the Mars Orbiter Camera and the Thermal Emissions Spectrometer. The Mars Orbiter Laser Altimeter was turned on, and its proper operation was verified. A test to send and receive a laser beam from the spacecraft to a station on the Earth was foiled by very stormy weather. More than 100 amateur radio enthusiasts listened for the signal from the Mars Relay system (a number of them actual heard it), and a ground station at Stanford University transmitted a test signal to the relay that was properly received and relayed back to Earth. Focus checks and bakeout of moisture acquired on Earth from the optics assembly of the Mars Orbiter Camera have been accomplished.

The spacecraft transitioned into what we call "Outer Cruise" early in January when we started to use the spacecraft high-gain antenna for communications. We can do this because the direction to the Earth from the spacecraft is now within the beam width of the antenna. This significantly increases the rate that data can be sent from the spacecraft. Earlier in the mission, a more broad-beamed antenna was used. This use of the high-gain antenna also allows us to operate the experimental Ka-band communications system every day when the spacecraft is in view of a special tracking station at Goldstone, California.

A number of engineering tests have been accomplished to better characterize the spacecraft performance in space as opposed to how it operated in Earth's environment. We are very pleased with how well the spacecraft and its science payload are operating.

On March 20, 1997, MGS performed the second trajectory correction maneuver at 10 a.m. PST. The 26-second burn, designed to refine Surveyor's flight path to Mars, achieved a change in spacecraft velocity of about 3.87 m/s (about 8.6 mph). The burn was performed in two stages, in which flight controllers first commanded the spacecraft to fire its small thrusters for 20 seconds, then to fire its main engine for another 6 seconds.

During the rest of the time before MGS arrives at Mars on September 12, we will be completing preparation for Mars Orbit Insertion and the critical aerobraking activities during the first 5 months after arrival. This involves preparing operational procedures, installing some new ground software, and testing our capabilities for controlling the aerobraking events from Earth.

All of this flight operations work is being accomplished by the Mars Surveyor Operations Project (MSOP). MSOP was formed almost a year ago with the purpose of providing the facilities and personnel to operate all of the Surveyor spacecraft. (MGS is the first of this decade-long program of Mars exploration spacecraft.) MSOP, besides doing all the work described above to fly the MGS spacecraft, is also preparing the processes and the system of software and hardware that will handle the data to and from the next Surveyor spacecraftthe Mars 98 orbiter and lander. MSOP personnel will also fly these spacecraft, just as they are operating the Mars Global Surveyor.

Glenn E. Cunningham, Manager
Mars Surveyor Operations Project