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MSL's Power Source
pospa
post Nov 23 2011, 12:20 PM
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DoE's Idaho National Laboratory (MMRTG supplier) has released some virtual tour from their manufacturing and testing activities on the MSL unit.
Similarly as James in other thread I was surprised how is the finished unit treated without any strict requirements for super-clean environment...

... at one moment I'd swear I saw shoulders of Homer Simpson holding one plutonium pellet with pincers. biggrin.gif

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monty python
post Nov 24 2011, 10:52 AM
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Thanks pospa. I learned a lot from that.
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jmknapp
post Jul 12 2012, 08:05 PM
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I saw a presentation on YouTube where it was stated that the RTG produces 2000 thermal watts and 110 electrical watts. So only 110 watts is sufficient to move a one-ton rover around? Also it was mentioned that the X-ray instrument consumes 4 kw, so I guess there's some kind of storage to handle the peak demands?


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djellison
post Jul 12 2012, 09:19 PM
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MSL has a battery, just like MER. Don't think of the MMRTG as MSL's power source. Think of it as solar arrays that always see the sunshine. It charges the batteries and then the batteries drive all the stuff on the rover. The battery can be recharged overnight.

Peak consumption is > 110 watts - especially when heating things before driving or using the arm.

Where did you see the 4kw value for the 'X-Ray instrument' ? Only thing I can find suggests that CheMin's XRay source uses about 42 watts.



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jmknapp
post Jul 13 2012, 12:09 AM
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QUOTE (djellison @ Jul 12 2012, 04:19 PM) *
MSL has a battery, just like MER. Don't think of the MMRTG as MSL's power source. Think of it as solar arrays that always see the sunshine. It charges the batteries and then the batteries drive all the stuff on the rover. The battery can be recharged overnight.

Peak consumption is > 110 watts - especially when heating things before driving or using the arm.


I wonder how expensive (in watts) driving works out to be.

QUOTE
Where did you see the 4kw value for the 'X-Ray instrument' ? Only thing I can find suggests that CheMin's XRay source uses about 42 watts.


Check out this video:

http://www.youtube.com/watch?v=F3nJSqc2Uck

At the 25:51 mark he refers to a "40-thousand watt X-ray beam." I did some searching around & I think he just misspoke and meant to say a 40 KeV x-ray beam.


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djellison
post Jul 13 2012, 07:22 AM
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QUOTE (jmknapp @ Jul 12 2012, 05:09 PM) *
I wonder how expensive (in watts) driving works out to be.


Not too bad. The killer is the heating requirement to get the rover ready to drive. That's something on the order of 600 Whrs.


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jmknapp
post Jul 13 2012, 02:43 PM
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QUOTE (djellison @ Jul 13 2012, 03:22 AM) *
Not too bad. The killer is the heating requirement to get the rover ready to drive. That's something on the order of 600 Whrs.


Is that needed to heat up the joints/bearings? So I guess the ~2000 thermal watts from the RTG are not available for that?


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mcaplinger
post Jul 13 2012, 04:12 PM
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QUOTE (jmknapp @ Jul 13 2012, 07:43 AM) *
Is that needed to heat up the joints/bearings? So I guess the ~2000 thermal watts from the RTG are not available for that?

The fluid loop that's warmed by the RTG only goes inside the rover body; the actuators and other extremities have to be heated electrically.


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nprev
post Jul 13 2012, 09:26 PM
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What fluid is used in the loop, Mike? An ammonia solution?

EDIT: Found a reference to freon, but not sure if that's for the mechanically-pumped system used during transit to Mars or the MSL surface ops system (if they indeed do use different fluids.)


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RoverDriver
post Jul 13 2012, 09:34 PM
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QUOTE (djellison @ Jul 13 2012, 12:22 AM) *
Not too bad. The killer is the heating requirement to get the rover ready to drive. That's something on the order of 600 Whrs.


And that is why the available drive time unfortunately will still depend on the season. mad.gif

Paolo


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mcaplinger
post Jul 13 2012, 10:02 PM
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QUOTE (nprev @ Jul 13 2012, 02:26 PM) *
What fluid is used in the loop, Mike?

According to http://ntrs.larc.nasa.gov/search.jsp?R=201...ICAL%2BSCIENCES both the cruise and surface systems use CFC-11 (freon).


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nprev
post Jul 13 2012, 10:44 PM
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Ah. Thanks!


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MarsEngineer
post Jul 14 2012, 06:06 PM
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The cooling loop (heat rejection subsystem or HRS) on the rover is very similar to the one on the cruise stage that runs around the cruise stage and down into the rover. This is based on the same design we first used on Mars Pathfinder then MER for the cruise HRS. Same dual redundant pumps on all of these loops.

I really love them. Essentially they maintain the rover body near room temperature most of the time taken from heat from the hot MMRTG that would otherwise radiate out to the Mars environment. As Paolo points out though, the rover freon only controls the temperature inside the rover but not its appendages. We need old fashioned electric heaters for that.


-Rob

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