[Beowulf] blackbox on Mars?

Jim Lux James.P.Lux at jpl.nasa.gov
Wed Oct 18 16:12:54 PDT 2006

I was amused to see the scenario rendering of a Sun Blackbox on 
Mars.  leaving aside the not inconsiderable hassle of getting many 
thousands of kilos to Mars and those pesky issues like radiation tolerance.

It looks like they have 2 10x10 foot solar panels.. let's see.. 
that's about 20 square meters total.  Mars, being 50% farther from 
the sun, has about 45% the incident solar energy.. call it half. So 
that's roughly 500Watts/m^2 *20 m^2, or 10kW incident power (at 
noon?although the picture shows them tilted pretty close to 
vertical..).. figure 30% conversion efficiency, and they've got about 
3kW of electricity to work with.

We'll assume the Blackbox ME (Mars Edition) doesn't have external 
water cooling like the terrestrial one does.  There's probably no 
real need, after all, it's only dissipating 3kW, and that's when the 
sun shines.  However, the Martian atmosphere is pretty thin (a few 
torr.. comparable to Earth at 100k ft elevation), so getting the heat 
out of the racks might be tricky.  Maybe they've got the inside of 
the container pressurized?  It's pretty cold on Mars, especially at 
night, so they probably don't have a problem cooling it.   40x8x8 ft 
is about 100 square meters of radiating surface, so even with the 
feeble Mars wind blowing over it, at 30W/square meter, it shouldn't 
overheat. (The solar panels, after all, are dissipating well over 100 
W/square meter)

But someone on Slashdot did bring up the point that you might be 
better setting up a high speed data link back to earth.  Mars 
Reconnaissance Orbiter is sending back amazing high resolution photos 
these days at several Megabits/second, using a 100 Watt transmitter 
and a 3 meter dish antenna. If you could land a container on Mars, 
then putting a bigger antenna up there shouldn't be an issue. Data 
rate scales as the area of the antenna, so let's say you put a 12 
meter diameter antenna: 4x diameter, 16x datarate for 50-100 Mbps 
seems reasonable.

There IS a latency issue (Mars is 20 minutes away by radio) though.

James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875 

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