[Beowulf] Max flops to watts hardware for a cluster

Jim Lux james.p.lux at jpl.nasa.gov
Mon Feb 16 20:22:51 EST 2004


> >
> If 5W of power goes to/from Mars - then the JPL are the ones to beat on
> this [makes QRP radio hams look positively profligate] :)

that 15W from Mars, on the omni antenna, only gets you 7-8 bits/second,
working into a 70 meter diameter dish and a cryogenically cooled receiver
front end.  A bit beyond the typical ham's rig or budget.

Going the other way, it's hundreds of kW into the dish.  Beyond QRO.

More realistically, they get a hundred kbps or so on the UHF link to the
orbiter from a basically omni antenna on the rover. I can't recall what the
max rate on the "direct to earth" X-band high gain antenna (which is about
20 cm in diameter) is, but it's probably in the same ballpark.

That's the actual signalling rate, also... there's some coding going on as
well, so the "data rate" is lower, after you take out framing, error
correction etc.

For those interested, all the deep space comm stuff is documented in CCSDS
specs at http://www.ccsds.org/

---
Actually, the low power per function (or more accurately, low energy per
function) champs are probably the cellphone folks.. Battery life is a real
selling point.  The little GPS receivers for cellphones are actually spec'd
in milliJoules/fix, for instance.

That said, I don't see anyone building a big crunching cluster out of
cellphones...  It's all those other issues you have to deal with..
interconnects, cluster management, memory, etc.  They all require energy.

Jim Lux
Spacecraft Telecommunications Equipment Section
Jet Propulsion Laboratory

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