QUESTION:
In your answer to the question regarding MGS taking new photos of Cydonia,
you mentioned that only a limited amount of the surface will be imaged at
high resolution, and that even then it is uncertain whether every target
will actually be covered. What percentage of the Mars surface will the MGS
map at high resolution? What is the estimated probability of actually
hitting one of the sites in the target database?

ANSWER from Charles Whetsel on September 3, 1997:
Much less than 1% of the surface of Mars will be imaged by MGS at the full
1.5 meters per pixel resolution.  The original scientific objectives of the
mission called for collecting "samples" of all of the different types of
Martian terrain at high resolution, not the targetting of specific points of
interest (although this can supported on a case-by-case basis, to target
past or future potential landing sites, for example), or the return of a
large percentage of surface at this resolution.  The constraint on what
percentage of the surface can be imaged at high resolution is primarily
imposed by the strength of the radio signals.  The MGS telecommunications
system has a peak rate of about 85,000 bits per second (2-3 times faster
than typical computer modems).  In order to return images of the entire
surface of Mars at 1.5 meters/pixel, with 256 grey-scales (8 bits/pixel)
would require quite a long time at a data transfer rate of 80 kbps.  On the
other hand, the entire surface of Mars will be imaged at low resolution
(appr. 250 m/pixel) every day to support other scientific objectives
(weather, surface morphology, etc.).