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MSL's Power Source
mchan
post Nov 29 2005, 05:46 AM
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QUOTE (exobioquest @ Nov 27 2005, 12:38 PM)
Well maybe your right about anti-nuclear nuts, I haven't heard them complaining about New Horizon, ...
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They are doing the usual -- calling for cancellation of NH.

http://www.space4peace.org/

And the NH EIS has several inputs from these folks, containing the same old hysteria they spewed for Cassini. E.g., NH is a front for the military to put nuclear weapons / power systems in space.
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mike
post Nov 29 2005, 04:04 PM
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Gasoline production is a front so the military can fuel their killing machines.
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Guest_exobioquest_*
post Nov 29 2005, 06:49 PM
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mcaplinger,

Its unlikely the mass of the SRG will be more then the MMRTG, the mass estimates are ranged now so it is possible the MMRTG will weigh less, but so far SRG usually has a range average a few kg below the MMRTG.

Also your not considering all the extra weight of the radiators needed for the cruise staged to keep the MMRTG cool.

Pu238 last cost ~$1400 per gram, so for the purchasing of the fuel alone (not counting the making of the GPHS) the MMRTG's fuel will cost 5.6 million while the SRG's will cost 1.4 million. Can anyone find out how much a GPHS cost to make? So just fuel cost the SRG is 4.2 million cheaper, not much but when the mission goes over budget every dollar less overbudget it goes the less likely the mission will get bumped up.

mchan,

those nuts and their logic its scares me so, how likely you think they will make a effective stink?
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mcaplinger
post Nov 29 2005, 07:15 PM
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QUOTE (exobioquest @ Nov 29 2005, 10:49 AM)
Its unlikely the mass of the SRG will be more then the MMRTG, the mass estimates are ranged now so it is possible the MMRTG will weigh less, but so far SRG usually has a range average a few kg below the MMRTG.

Also your not considering all the extra weight of the radiators needed for the cruise staged to keep the MMRTG cool.

*


You make a fair point about the radiators, though even MPF and MER had radiator systems.

I can't assess the mass estimates of the RTG systems themselves without detailed technical descriptions.

However, from http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=705

"Initially, the MMRTG could have an advantage from a mass perspective, as current NASA/DOE guidelines recommend that early missions using SRGs carry at least one redundant SRG unit until its reliability has been verified [11]. This means that early missions using SRGs would need to carry a minimum of two SRG units. Thus, for early missions (where a redundant SRG would be required), the MMRTG (at <45 kg [10]) would be the lighter option for spacecraft requiring one or two RPS units."

And according to the NASA FY06 budget request ( http://www.nasa.gov/pdf/107489main_FY06_1_sae.pdf ), page 2-22 "MSL - Department of Energy for Multi Mission Radioisotope Thermoelectric Generators" and page 2-14 "Radioisotope Power System (RPS): Deleted Small RPS or second generation Sterling (SRG), and RPS Power Conversion Technology (RPCT)." I think it's clear from that that MSL is planning to use the MMRTG.


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Guest_exobioquest_*
post Nov 29 2005, 07:38 PM
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mcaplinger,

The SRG has 2 55w sterling engines so when they say an extra do that mean 3 55w engines? That could not allow for easy counter piston action and cause much vibration. Maybe they mean 2 SRGs total, which would be 200w of power! That would be Fing wonderful from a mission perspective, all that extra power! That would still be 1/2 the fuel and 1/2 the heat output of the MMRTG, but the weight on the rover its self would definitely be an extra 25-40kg.

I think they were talking about the second generation SRG: the ~350 watt version that was under development or something.
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mike
post Nov 29 2005, 08:09 PM
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Personally I don't think any anti-RTG-type protesters will be successful. The actual damage done by even the most horrific disaster is too low to be sufficiently scary, and the odds for that most horrific disaster are exceedingly low.

You don't even need an evil nukular power thingy, though. What if the rocket's navigation computers became confused and it slammed into the White House? What if it flew right into the house of your child? Or your workplace? What if the exhaust from the rocket landed in just the right place in your lung and you died? Nobody ever dies! BE AFRAID BE VERY AFRAID, SO VERY AFRAID
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mcaplinger
post Nov 29 2005, 08:24 PM
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QUOTE (exobioquest @ Nov 29 2005, 11:38 AM)
Maybe they mean 2 SRGs total, which would be 200w of power!
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The full document makes it pretty clear that yes, they mean two entire separate SRGs if you need the power from one.

If you were an advocate of the SRG you might say that was an unfair imposition, but them's the rules at the moment.


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helvick
post Nov 29 2005, 08:41 PM
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QUOTE (mcaplinger @ Nov 29 2005, 09:24 PM)
If you were an advocate of the SRG you might say that was an unfair imposition, but them's the rules at the moment.
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Well if I was paying hundreds of millions for a mission then I'd say that them would be reasonable rules, much as I like the SRG concept it needs to be flight proven before it's used for something as important as this.
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Guest_exobioquest_*
post Nov 29 2005, 08:57 PM
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I would be estactic if anything that can provide 200w (4800wh) of continues power was going on the MSL, be it a MMRTG or SRG. With 2 SRG weight is the only major problem, you still have less thermal and fuel needs then the MMRTG. weight over the whole spaceship could be negated with the reduction to the thermal control system and also is the cruise stage going to need solar panals?, maybe at 100w but most likely not with 200w, that some possible weight savings. At 200w (and considering the SRGs lasts a long as claimed) MSL would most likely last for a decade or more! At 200w (and not adding lighting for night time driving) MSL could do over a km a day of driving! It could do hundreds of km over its mission! Just the idea makes me drool!
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mcaplinger
post Nov 29 2005, 10:00 PM
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QUOTE (exobioquest @ Nov 29 2005, 12:57 PM)
At 200w (and considering the SRGs lasts a long as claimed) MSL would most likely last for a decade or more! At 200w (and not adding lighting for night time driving) MSL could do over a km a day of driving! It could do hundreds of km over its mission! Just the idea makes me drool!
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Even if any of these things were true (they're not, as far as I know -- there's nothing terribly enabling about going to twice the RTG power. You still need batteries, you still don't have enough power for active thermal control of all elements so you have thermal cycling wearout, you still have mechanical wearout problems, and there is no way that MSL is ever going to drive 1 km/day under any circumstances no matter how much power it has) MSL is using the MMRTG anyway. So your drool is wasted. smile.gif


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Guest_exobioquest_*
post Nov 29 2005, 10:26 PM
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QUOTE (mcaplinger @ Nov 29 2005, 04:00 PM)
Even if any of these things were true (they're not, as far as I know -- there's nothing terribly enabling about going to twice the RTG power.  You still need batteries, you still don't have enough power for active thermal control of all elements so you have thermal cycling wearout, you still have mechanical wearout problems, and there is no way that MSL is ever going to drive 1 km/day under any circumstances no matter how much power it has)  MSL is using the MMRTG anyway.  So your drool is wasted.  smile.gif
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Now just wait a minute, you have heat from the RPS keeping the body of the rover warm, and all your going to need to heat is the arms, pancams and wheels. As long as the wheels (any motor in fact) is not running cold they can survive a huge number of thermal cycles so that leaves all the extremities long lasting as well. Motors wear (for the wheels that is) can be fix mostly with the ability to disengage the defective motor from the wheel (a clutch spring) or simply drag defective wheels. Iím sure a wheel can be made to survive several hundred km of travel easily. What would need batteries? Is there any item that would suck up more then 200w at a time and canít run by pulsing from a capacitor (Iím thinking of the laser here). Many batteries exist that can last a decade or more considering the recharge cycles. Viking 2 lasted for 5 years on archaic nickel cadmium batteries, Viking 1 lasted 7yr and did not even die from battery failure. Do you know what the max crawl speed is for MSL? And unless you got inside information you don't know the MMRTG is a go. tongue.gif
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helvick
post Nov 29 2005, 10:30 PM
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QUOTE (mcaplinger @ Nov 29 2005, 11:00 PM)
and there is no way that MSL is ever going to drive 1 km/day under any circumstances no matter how much power it has)  MSL is using the MMRTG anyway.
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That's an important point. Raw speed isn't of much use, the objective is to try to find things and that requires that MSL looks very closely at the stuff around it, not just race along for the sake of it. There might be the odd dash or two that are marginally faster than the flat out rates we've seen from Opportunity and Spirit but I suspect it will spend a lot of time making about the same rate of progress that the MER's do. And there's nothing wrong with that.
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Guest_exobioquest_*
post Nov 29 2005, 10:49 PM
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helvick,

Sure there is nothing wrong wit MER speeds, but MSL will have:

-10X the upload speed with MRO in orbit, Even without MTO, MRO is going to provide major communication bandwidth improvements.

-A much faster processor (RAD750?) so autonav would be faster and/or more advance, might be able to command MSL to go up to a rock sample it and then go up to another sample it and so forth by sending only one set of commands and the rover does all the rest autonomously.

-Onboard sample loader: if all the instruments (except the microcam) run of samples provided by the arm to a sample loader in the rovers body, then MSL could get a sample from one rock and move on to another while its analyzing the sample it drilled up: so MSL could sample several rocks in the time it takes MER to do one!

edit: spelling/grammer
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helvick
post Nov 29 2005, 11:10 PM
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QUOTE (exobioquest @ Nov 29 2005, 11:49 PM)
Sure there is nothing wrong wit MER speeds, but MSL will have..
*

All true and those will allow it to progress faster but it will also have good reason to carefully examine what it comes across more carefully than the MER's because it can.

I'm of the opinion that the biggest speed boost will actually come from the RAD 750. It has 10x the integer performance and about 20x the fp performance of the RAD6000's on the MER's. Combined with the increased on board storage that alone should allow MSL to do safely drive much faster.

I don't think it will though, the whole point is to gather data and study it. While I love the idea of whizzing around on the surface of Mars I really think they will be taking things very easy. At least until such time as they have hit all primary mission objectives.

Then again they might land it on Meridiani and find themselves a kilometer or two from somewhere really interesting. That might warrant a quick dash across the plains at the start but otherwise I'd say she'll be taking things slow and easy.
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mcaplinger
post Nov 30 2005, 12:34 AM
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QUOTE (exobioquest @ Nov 29 2005, 02:26 PM)
And unless you got inside information you don't know the MMRTG is a go.  tongue.gif
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Seems to me that the 2006 NASA budget I cited is clear proof that they have selected the MMRTG. And I'll just leave it at that.


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