>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-