From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.science
Subject: Re: Isn't it about time to send a crewed spacecraft to Jupiter's moon 
	Europa ? Do we have the technologie ?
Date: Fri, 10 Jul 1998 05:07:06 GMT

In article <35a442ed.23497966@newshost.cc.utexas.edu>,
Jeramie Hicks <Jeramie.Hicks@mail.utexas.edu> wrote:
>>to travel to Jupiter, THEN we MIGHT make a trip to
>>Europa if it would prove useful.
>
>And even after all the technology and techniques are capable of the
>trip, this will prove to be the ultimate deciding factor. What can a
>manned mission do that an unmanned one cannot, that can justify the
>danger/cost?

Almost anything more complicated than wandering around and snapping
pictures is much more easily done by humans on the spot, at present.  This
is particularly strongly the case for relatively distant locations like
Europa, where long speed-of-light delays make teleoperation painful
bordering on ridiculous.  (If you thought maneuvering Sojourner on Mars
was a slow and cumbersome process, try it with three or four times the
communications delay.)

Complex and unpredictable tasks like hunting for fossils in rough terrain,
or drilling through several kilometers of dirty ice and then operating
instruments at the bottom, are utterly impractical for unmanned systems
now.  Yes, I'm aware that folks are proposing unmanned missions to do
these things, but they tend to rely heavily on as-yet-undeveloped new
technology, and they also have a distressingly high probability of failure
when looked at carefully.  (Way too many of the people proposing Europa
drilling missions seem to know very little about real-life drilling.)

Unmanned missions look cheap mostly because they are so much simpler and
their results are so much more limited.

The one case where we have good comparative data is the Moon.  If we
disregard relatively minor missions which yielded little, the unmanned
surface missions were five soft landings, three sample returns, and two
long-duration rovers.  There were six manned Apollo landings.  The geology
of the Moon is the geology of the Apollo samples and the data from the
Apollo surface instruments; all the unmanned surface missions put together
do no more than add a few footnotes.  It's difficult to compare costs in
detail, but it's reasonable to say that the unmanned programs together
cost somewhere around a tenth as much as Apollo.  They did *not* yield a
tenth of the results.  A hundredth would be a better estimate.  Getting
Apollo-class results with unmanned missions would not have cost much less
than Apollo, and quite possibly would have cost much more (and taken much
longer).
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)