[Beowulf] Re: blackbox on Mars?

Robert G. Brown rgb at phy.duke.edu
Fri Oct 20 09:52:27 EDT 2006


On Thu, 19 Oct 2006, Jim Lux wrote:

> At 03:56 PM 10/19/2006, steve_heaton at iinet.net.au wrote:
>> G'day Jim and all
>> 
>> Pushing further from the topic (given your day job Jim ;) Also freely 
>> accepting
>> this is pure speculation...
>> 
>> 30% efficiency on the solar cells?! A generous round up I suspect? I 
>> thought
>> Deep Space 1 only got ~23%? And that was the soopa doopa focus layer, no 
>> dust
>> out there to speak of flavour?
>
> You betcha.. by the time you can put 4-5000 kg of container on the surface of 
> Mars, I suspect that 30% solar cells will be a reality.  Actually, Mars 
> Science Lander (MSL) for launch in 2009 is probably pretty close to 1000kg 
> (I'd have to go check, but it's widely described as being roughly the size 
> and mass of a Mini).

Has anyone remarked on the absurdity of sending a cluster to the surface
of Mars under any cirmcumstances?  What in the world would it do that
couldn't be done far cheaper back on earth, or in orbit?  There are damn
few things that I can think of that might even NEED a cluster's worth of
compute power on that end of things -- maybe, just maybe, running AI
robots or helping to preprocess images -- but the former SEEMS like it
could be managed with a very small cluster -- 4-8 CPUS tops, mostly for
failsafe -- and the latter could be done anywhere.

Moving data is cheap.  In fact, it is "free" -- available at opportunity
cost on a communication channel that has to exist no matter what, and
bandwidth in that channel is similarly cheap, all the way to Earth.  The
only thing that is obviously limited in the channel is latency -- order
of an hour to Earth, order of 0.001 sec to various possible orbits
around Marse.

One MIGHT consider sending a cluster to sit in a geosync orbit AROUND
Mars with a high bandwidth uplink (literally) from the surface and order
ten millisecond latencies.  That's fast enough to permit the cluster to
drive a rover or do other AI stuff and still beat human reaction times
of 100 msec.  It also permits it to get power from LARGE solar panels or
a LARGE reactor (relatively speaking, with the usual, fairly easily
solvable, engineering problems associated with dumping heat in a
vacuum).  It is so much cheaper a solution than dropping something so
extraneous and useless to the actual surface that nobody sane would EVER
consider the latter.  That's if they don't decide to skip the not
inconsiderable expense of shipping a cluster to Mars orbit and ship the
DATA all the way back to Earth, where clusters are cheap and easy to
maintain and don't have to be failproof to five nines for a decade in a
hostile environment.

Just a thought... so regardless of the "corporate hype" about sending
ANY sort of cluster "to Mars" only a complete idiot would seriously
contemplate sending one to the surface, and only a RICH idiot (something
oxymoronic in that, no?) could afford it.

    rgb

-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu


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