Newsgroups: sci.space.history,sci.space.policy,sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pop Sci article on Mars
Date: Sun, 7 Feb 1999 22:18:24 GMT

In article <79ku9c$s6k@crl3.crl.com>,
George Herbert <gherbert@crl3.crl.com> wrote:
>Some of these questions we don't have answers for yet; at some point
>we really need 10-20 cm resolution images of potential landing sites
>for manned landings (or a significant hover/translation budget to
>deal with uncertainties)...

The best proposal I've seen for dealing with this takes a slightly
different tack:  send a scout down first.

When a tentative landing site is chosen, an unmanned vehicle goes down
first.  It's a spin-stabilized aeroshell containing six penetrators.  The
first three split off at high altitude; the remaining three at low
altitude.  The spin gives them some outward velocity, so you get a small
triangle inside a big triangle.

The payload of each penetrator is a radio beacon and a descent imager.
The result is a series of image mosaics, at increasing resolution, of the
site.  The last few are from the inner penetrators only (because the
images from the outer penetrators no longer overlap) at very high
resolution -- quite a bit higher than you can easily get from orbit.
Those you use to pick the exact landing spot.

This gives you everything you need to select a good spot and fly a
precision landing there:  not only do you have pictures at steadily
increasing resolutions, but you also have six radio beacons at known
locations in the immediate vicinity.  With this level of information and
assistance, the landing could be entirely automatic, with a pilot merely
supervising.

Losing one or two of the penetrators on impact is not a big problem.  And
you can carry two or three sets, in case the first candidate site turns
out to have unsolvable problems.

(The same approach can be applied to other problems, incidentally.  Many
of the uncertainties of aerocapture are reduced if you send a few scouts
with similar ballistic coefficient ahead.)
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)