[X] My Assistant

[Guest_exobioquest_*]

Hi, new here.

I'm wondering if any news has come down about finalizing what MSL will run on?

Will it be 2 Boeing's MMRTG (at ~100 watts?) or Lockheed Martin’s SRG (again ~100watts?), have they decided yet? Willl MSL use the RPS to trickle charge a battery or will MSL run on the RPS only? God I hope solar is not a option is anyone pushing for it?

[mcaplinger]

Will it be 2 Boeing's MMRTG (at ~100 watts?) or Lockheed Martin’s SRG (again ~100watts?), have they decided yet?

According to
http://trs-new.jpl.nasa.gov/dspace/bitstre...6/1/05-0708.pdf
MSL will use an MMRTG. I would think that the use of batteries is inevitable, as there's no way the avionics can run directly from RTG output, much less the payload.

I'm sure they've done a detailed trade study of alternative RTGs, but I haven't seen those.

[Guest_exobioquest_*]

According to
http://trs-new.jpl.nasa.gov/dspace/bitstre...6/1/05-0708.pdf
MSL will use an MMRTG.  I would think that the use of batteries is inevitable, as there's no way the avionics can run directly from RTG output, much less the payload.

I'm sure they've done a detailed trade study of alternative RTGs, but I haven't seen those.

Well thats sad, hope they change their mind. By the way who put those notes on the pdf? I did not consider this but because the MMRTG puts out 2000w of heat they need a rather large radiator for the cruise stage, the SRG only puts out 500w.

[mcaplinger]

Well thats sad, hope they change their mind.

The report I referenced is probably just a baseline; I don't know if the final RTG configuration has been picked. However, I'm not sure that the Stirling RTG is a clear-cut winner. It's more efficient and lighter for a given power output, true, but it's far more mechanically complex and has its own set of problems (vibration, electrical noise, etc.)

[mcaplinger]

However, I'm not sure that the Stirling RTG is a clear-cut winner.  It's more efficient and lighter for a given power output, true...

Actually, doing a little more research, the SRTG is even less obviously a win. It saves Pu mass, but the additional mass of the more complex conversion hardware partially kills that advantage. Depending on exactly what mass the MMRTG finally comes in at, it can have a higher energy density than the SRTG. Getting rid of the additional waste heat, while an issue, is a fairly easy problem to solve.

Quoted from "Advances in Planetary Aerobots" by Erik Laan et al:

"The MMRTG will be designed to generate
110 Watts of electric energy over a minimum lifetime
of 14 years (3 years on the Martian Surface)
weighing 24-34 kg (218.8 - 309.1 kg/kW) including 4
kg Plutonium-238 (Boeing)
Another development is aimed at increasing the
efficiency of the conversion process. Current RTGs
are capable of converting heat into electricity with an
efficiency of ~8%. A number of new conversion
processes were proposed recently. The Stirling
Radioisotope Power Source is one of them. This
SRPS is using a Stirling heat engine, which produces
an acoustic pressure wave to drive a piston in a linear
alternator producing the electricity. The SRG
(Stirling RTG) delivers 93-114 Watt of electric
energy, weighing 27 kg (236.8 - 290.3 kg/kW) and
contains 1 kg of Plutonium-238 (LMM)."