MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASEMarch 26, 1998
MARS GLOBAL SURVEYOR TO ATTEMPT IMAGING OF FEATURES OF PUBLIC
NASA's Mars Global Surveyor spacecraft is about to begin a
summer-long set of scientific observations of the red planet from
an interim elliptical orbit, including several attempts to take
images of features of public interest ranging from the Mars
Pathfinder and Viking mission landing sites to the Cydonia
The spacecraft will turn on its payload of science
instruments on March 27, about 12 hours after it suspends
"aerobraking," a technique that lowers the spacecraft's orbit by
using atmospheric drag each time it passes close to the planet on
each looping orbit. Aerobraking will resume in September and
continue until March 1999, when the spacecraft will be in a
final, circular orbit for its prime mapping mission.
It will not be possible to predict on which orbit the
spacecraft will pass closest to specific features on Mars until
Global Surveyor has established a stable orbit and flight
controllers are able to project its ground track. This process
should be completed in the next few days. The exact time of
observations and the schedule for the subsequent availability of
photographs on the World Wide Web are expected to be announced
early next week.
"Global Surveyor will have three opportunities in the next
month to see each of the sites, including the Cydonia region,
location of the so-called 'Face on Mars,' " said Glenn E.
Cunningham, Mars Global Surveyor project manager at NASA's Jet
Propulsion Laboratory, Pasadena, CA. "The sites will be visible
about once every eight days, and we'll have a 30- to- 50-percent
chance of capturing images of the sites each time."
Several factors limit the chances of obtaining images of
specific features with the high-resolution mode of the camera on
any one pass. These factors are related primarily to
uncertainties both in the spacecraft's pointing and the knowledge
of the spacecraft's ground track from its navigation data. In
addition, current maps of Mars are derived from Viking data taken
more than 20 years ago. Data obtained by Global Surveyor's laser
altimeter and camera during the last few months have indicated
that our knowledge of specific locations on the surface is
uncertain by 1 to 2 kilometers (0.6 to 1.2 miles). As a result,
the locations of the landing sites and specific features in the
Cydonia region are not precisely known.
In addition, the Mars Pathfinder and Viking landers are very
small targets to image, even at the closest distance possible,
because they are the smallest objects that the camera can see.
The Cydonia features, on the other hand, are hundreds to
thousands of times larger and the camera should be able to
capture some of the features in that area.
Global Surveyor's observations of the Viking and Pathfinder
landing sites will provide scientists with important information
from which to tie together surface observations and orbital
measurements of the planet. Data from landing sites provide
"ground truth" for observations of the planet made from space.
As for the "Face on Mars" feature, "Most scientists believe
that everything we've seen on Mars is of natural origin," said
Dr. Carl Pilcher, acting science director for solar system
exploration in NASA's Office of Space Science, Washington, DC.
"However, we also believe it is appropriate to seek to resolve
speculation about features in the Cydonia region by obtaining
images when it is possible to do so."
Information about Viking observations of the Cydonia region
and a listing of those images are available on the World Wide Web
New images of the landing sites and Cydonia region taken by
Mars Global Surveyor will be available on JPL's Mars news site
at: http://www.jpl.nasa.gov/marsnews and on the Global Surveyor
home page at http://mars.jpl.nasa.gov . These sites will also
carry detailed schedules of the imaging attempts once they have
been determined. Images will also be available on NASA's
Planetary Photojournal web site at
So far in the aerobraking process, Global Surveyor's orbit
has been reduced from an initial 45-hour duration to less than 12
hours. During the aerobraking hiatus, the spacecraft will be
orbiting Mars about once every 11.6 hours, passing about 106
miles (170 kilometers) above the surface at closest approach and
about 11,100 miles (17,864 kilometers) at its farthest distance
from the planet. The pause in aerobraking allows the spacecraft
to achieve a final orbit with lighting conditions that are
optimal for science observations.
Mars Global Surveyor is part of a sustained program of Mars
exploration, managed by JPL for NASA's Office of Space Science,
Washington, DC. Lockheed Martin Astronautics, Denver, CO, which
built and operates the spacecraft, is JPL's industrial partner in
the mission. Malin Space Science Systems, Inc., San Diego, CA,
built and operates the spacecraft camera. JPL is a division of
the California Institute of Technology, Pasadena, CA.