PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASE
August 25, 1997
MARS GLOBAL SURVEYOR FINE-TUNES ITS FLIGHT PATH TO MARS
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 at http://www.jpl.nasa.gov, or on
the Mars Global Surveyor Orbiter Camera home page at
http://www.msss.com/ (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.
The mission is managed by the Jet Propulsion Laboratory for
NASA's Office of Space Science, Washington, DC. The spacecraft
was built by NASA's partner, Lockheed Martin Astronautics, in
Denver, CO.
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