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Huygens' Titan Descent



 
 
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  #21  
Old January 19th 05, 11:24 PM
Volker Hetzer
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Marc 182 wrote:

So long as I'm dreaming here, and discarding everything else I've said,
it would have been nice if they had just programmed the gas
chromatograph to make one more run starting at the end of the nominal
mission, 180 seconds after landing. That hot spacecraft ("hot" being a
very relative term here) was probably boiling all kinds of interesting
stuff off of the surface and a GC is great at unambiguous identification
of organics.

Yes, that'd be great.
Do you think you could tell EAS about this?
http://www.esa.int/export/esaCP/SEMK...ndex_0.html#O9 would be a
start.


But, of course, they never expected it to live for any length of time on
the surface... or did they? I wonder what the thinking was when they
slipped in the big batteries.

There's lots of things you can do with spare power. Maybe boost
something, do more software upgrades, show pictures from the stars if
the mission would have been impossible and huygend had to be jettisoned
into another direction, whatever.
Maybe they would have been able to reprogram the probe and send half
an hour later if they had to change cassinis orbit for some reason.
Remember the approach actually taken wasn't the plan either.

Lots of Greetings!
Volker
  #22  
Old January 20th 05, 02:36 AM
Henry Spencer
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In article ,
Marc 182 wrote:
you've just got to keep your radio, computer, electronics, and batteries
warm, which I suspect the RHUs were positioned to do anyway.


The trick is keeping them adequately warm in a dense atmosphere at LOX
temperatures, while not frying them in space beforehand. Just good
insulation almost certainly is not enough; the atmosphere is likely to
increase heat transfer enough that you'll need to either add electric
heat, or have some sort of variable heat leak which switches off during
descent. It's feasible but it adds mass and complexity.

(While there are insulation types whose effectiveness is different in
atmosphere than in vacuum, unfortunately, the change goes the wrong way:
good in vacuum and bad in atmosphere rather than vice-versa.)

But, of course, they never expected it to live for any length of time on
the surface... or did they?


They weren't even sure it would survive impact (and on a really hard
surface, it probably wouldn't have). The primary mission lasted three
minutes after impact -- just long enough for a few pictures and some
readings from the simple little set of surface-material sensors.

I wonder what the thinking was when they slipped in the big batteries.


If memory serves, the requirement was to reliably complete the primary
mission with one battery cell failed. That meant having some safety
margin against worst-case conditions *after* taking one cell out of the
picture. The result, unsurprisingly, was that with all cells working and
conditions generally not too bad, there was a large reserve of energy.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |
  #23  
Old January 20th 05, 11:31 AM
Michael Smith
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On Fri, 14 Jan 2005 23:45:48 -0500
"furtig" wrote:

I have another question. The one photo I have seen from the surface
(unprocessed?) seems to have plenty of light. I found this surprising
and am assuming this was considered in the planning stage and the
photo system is extra sensitive.


Basically, yes. You can take a long exposure in a dark room with fast film and get good results. You just have to wait for the right number of photons.

(?) Any comments on the data size of
the images.


I think it was about 35k per image. Very heavily compressed. Considering the environment it was collected in I think the images are fastastic.

It's a shame that the Galileo/Jupiter entry probe didn't have a simlar scaled down imaging capability.
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Michael Smith
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