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Nars Gloval Surveyor to Attemot Imaging of Features of Public Interest

Douglas Isbell
Headquarters, Washington, DC                  		 March 26, 1998
(Phone: 202/358-1547)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

RELEASE: 98-50

MARS GLOBAL SURVEYOR TO ATTEMPT IMAGING OF FEATURES OF PUBLIC INTEREST

     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 region. 

	     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 0.6 to 
1.2 miles (1 to 2 kilometers). 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 at: 

http://www.hq.nasa.gov/office/pao/facts/HTML/FS-016-HQ.html 

     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:  
http://photojournal.jpl.nasa.gov .

    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.
 
			-end-