QUESTION:
What are biggest dangers of MGS aerobraking? In what way will bad
weather on mars found by HST affect aerobraking? What problems and
dangers you think it will cause to MGS?
 
ANSWER from Charles Whetsel on June 2, 1997:
Weather IS the biggest risk to MGS aerobraking.  We are so concerned about
it, that we have designed our aerobraking trajectory to basically allow the
atmosphere to "swell-up" to 190% of it's normal value without damaging the
spacecraft.  We will be using not only HST (Hubble Space Telescope)
observations of Mars, but also some of our own instruments to make
measurements of the Martian atmosphere to give us any hints about what the
weather is doing.  If we detect any increases in the height or density of
the atmosphere, we will plan to continue aerobraking, but at a higher
altitude than the current plan.  Our planning doesn't require us to
aerobrake at a specific altitude, just a specific density. If the weather
does something different, we will just hunt for the right altitude to get
the right density.  Ironically, the HST pictures that show a perfectly
clear atmosphere could be good for the Mars Pathfinder Lander, but
troublesome for us:  Some the atmospheric scientists studying the Martian
atmsohpere say that if the sky starts perfectly clear, it doesn't take very
long for a dust storm to cause a large percentage increase in the average
densities, whereas if there is a little bit of dust already in the air, it
takes longer for the storm to build up and increase the global atmospheric
height.