Monday, 25 August 1997
Contact: Diane Ainsworth
Mars Global Surveyor fired its thrusters and performed the last of its flight path correction maneuvers at 9:30 a.m. Pacific time today.
"The 11-second burn achieved a change in spacecraft velocity of about 0.3 meters per second (about 0.67 miles per hour) and puts the spacecraft on target for its arrival at Mars on September 11," said Dr. Pasquale Esposito, Mars Global Surveyor navigation team chief at NASA's Jet Propulsion Laboratory.
Flight controllers positioned the spacecraft's solar arrays in such a way that forces exerted by the thruster firings would not have damaging effects on the spacecraft's tilted solar panel. Currently one of the spacecraft's two solar panels is tilted about 19 degrees from its fully deployed position.
Spacecraft operations and instrument calibrations have gone very well as Global Surveyor now nears the red planet. Last week, at a distance of 5.3 million kilometers (3.3 million miles), the spacecraft's camera shot a series of eight images of Mars that will be processed to create a rotational movie of the planet. Three of the new black-and-white images taken on August 19 and 20 are available on JPL's website, or on the Mars Global Surveyor Orbiter Camera home page (click on August 20 pictures).
Today the spacecraft is approximately 237 million kilometers (about 147 million miles) from Earth, and 4 million kilometers (2.5 million miles) from Mars, traveling at a speed of about 10,800 kilometers per hour (6,375 miles per hour) with respect to Mars.
Mars Global Surveyor will arrive at Mars at 6:31 p.m. Pacific Daylight Time on September 11. At that time the spacecraft will perform a 22-minute engine burn using its 600- newton main engine to slow its speed enough to be captured in orbit around Mars. "The Mars orbit insertion burn is critical to the start of the Mars Global Surveyor aerobraking operations and mapping," said Glenn Cunningham, Global Surveyor project manager at JPL.
After entering orbit around Mars, Global Surveyor will spend about four months aerobraking in the Martian atmosphere to lower and circularize its orbit. Aerobraking was first tested in the fall of 1993, using the Magellan spacecraft orbiting Venus. The technique allows a spacecraft to use the drag of a planet's atmosphere to lower its orbit without having to rely on propellant.
During each of its orbits, Global Surveyor will pass through the upper fringes of the Martian atmosphere each time it reaches periapsis, the point in its orbit closest to the planet's surface. Friction from the atmosphere will slow spacecraft slightly and lose some of its momentum during each orbit. This will cause the spacecraft's apopasis, or highest point of the orbit, to be slightly reduced as well. The gradual orbit trim will continue through mid-January 1998, until the spacecraft reaches the final, 350-kilometer by 410-kilometer (217-mile by 254-mile) mapping orbit. Mapping operations will begin on March 15, 1998.
Mars Global Surveyor is the first spacecraft in a new NASA program of Mars exploration, called the Mars Surveyor Program. The program will send pairs of orbiters and landers to Mars every 26 months well into the next century. These robotic explorers will answer a variety of scientific questions about Mars' history, surface, atmosphere, interior and current condition, and pave the way for eventual human expeditions to Mars.
Office of the Flight Operations Manager Mars Surveyor
Operations Project
NASA Jet Propulsion Laboratory California Institute of Technology Pasadena,
CA 91109