Date: 15 Jul 91 19:03:42 GMT
From: ssc-vax!bcsaic!hsvaic!eder@beaver.cs.washington.edu  (Dani Eder)
Subject: Re: Aerobraking

In article <586@hub.ucsb.edu> 3001crad@ucsbuxa.ucsb.edu (Charles Frank Radley) writes:
>
>
>Aerobraking is extremely risky, and was rejected by the Stafford report.
>The main problem is variations in Mars' atmosphere which could easily
>result in an error by a facotr of two in the braking drag.
>  Much too risky.

There are several ways to attack this problem (note that the organization
I work for is working on aerobraking for Mars missions, so I have access
to a real expert).  One approach is to send a precursor probe ahead of
the main spacecraft and measure the drag force on the probe with an
accelerometer.  A dispersed pattern of probes can be used if they are
light enough.  All they have to do is survive the heating and transmit
acceleration measurements.

The second approach is to brake by succesive approximation.  On the
initial arrival at Mars, brake enough to capture into a Mars orbit,
but keep the maneuver small enough that in a worst case high density
atmosphere, you will still be above the final desired orbit.  On following
orbits do slight aerobrake passes (at higher altitudes) and converge
on the desired parking orbit.  This method only works if your Mars
arrival velocity is not too high.  If your velocity is too high
then a factor of two in braking takes you past where you want to be.

Note that the Stafford report rejected on-orbit assembly as risky also,
despite the fact that by then the Space Station, if it does nothing
else, will have taught us how to assembl large complex things in     t.


-- 
Dani Eder/Boeing/Advanced Civil Space/(205)464-2697(w)/461-7801(h)/#905, 1075
Dockside Dr.,Huntsville,AL35824/Member: Space Studies Institute
Physical Location: 34deg 37' N 86deg 43' W +100m alt.
***THE ABOVE IS NOT THE OPINION OF THE BOEING COMPANY OR ITS MANAGEMENT.***