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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 Martinís 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?
helvick
QUOTE (exobioquest @ Nov 27 2005, 05:46 PM)
God I hope solar is not a option is anyone pushing for it?
*

I seriously doubt that anyone is pushing for it. Even with significantly improved efficiencies Solar just has too many drawbacks for long term missions. The MER's have been lucky and no-one should fool themselves into thinking that the circumstances that have allowed them to survive can be relied upon.

With technology as it is right now any roving surface mission with a long term primary mission needs an RTG. To replace a ~100W RTG with a solar solution that could survive a major dust storm you would need approximately 16x the surface area of the panels on the MER's. Solar Cell technology has improved quite a bit since the MER's were put together but even so the best case I can see right now would be panels 10-12x the area of the MER's. And that is just for a near equatorial rover.
exobioquest
QUOTE (helvick @ Nov 27 2005, 12:30 PM)
The MER's have been lucky and no-one should fool themselves into thinking that the circumstances that have allowed them to survive can be relied upon.


Thatís what I'm worried about, I'm sure the anti-nuclear people (remember the ones that went apesh!t over cassini?) are going to be piss off about MSL and are going to use MER's two amazingly hard to survive years at the equator as proof that solar can be used for every mars mission no matter the latitude or conditions.

Iím also worried that MSL is going to use batteries, sure it could survive for a Martian year with Li-ion batteries but how about 5-10 years of over time, not likely, if its RTG only it could potentially run around for decades! Everything else should easily survive decades and hundreds of km of operation if maintain at a relatively constant temperature of course, as is MER has push a lot of components to and beyond there temp ranges and its still running! The power source should be the only significant limiter in life-time performance, and the use of chemical batteries will definitely shorten it.

By the way what advances in solar cells have happened since MERís launch that could improve solar cells performance so much.
helvick
QUOTE (exobioquest @ Nov 27 2005, 07:53 PM)
Thatís what I'm worried about, I'm sure the anti-nuclear people (remember the ones that went apesh!t over cassini?)
*

They are still there but the work done in pushing Cassini through seems to have led to a lot of folks realising that the threat was overhyped. NH seems to have avoided the drama so I don't think MSL is at risk from that sort of campaign.
QUOTE (exobioquest @ Nov 27 2005, 07:53 PM)
Iím also worried that MSL is going to use batteries, sure it could survive for a Martian year with Li-ion batteries but how about 5-10 years of over time, not likely.
*

I haven't seen any detailed outline of MSL's power subsystem but I'd be amazed if it was likely to be a problem. If batteries are required then there are battery systems that survive far longer than the type used on the MER's, think about the batteries in a host of satellites that survive for 5-10 years and multiple discharge\charge cycles per day. The MER batteries were chosen because they provided the best power density for a short mission, they are not the only option.
QUOTE (exobioquest @ Nov 27 2005, 07:53 PM)
By the way what advances in solar cells have happened since MERís launch that could improve solar cells performance so much.
*

Spectrolab (the manufacturers of the triple junction cells on the MER's) now have cells commercially available that are 28.3% efficient vs the 23.6% cells used on the MER's. They say they expect to have 35% eficiency cells on the market in 2006 according to their PR blurb here: Spectrolab. That may be PR but I'd say it's right - I can't find the link at the moment but I have seen some test results of sample cells of theirs that hit 33\34%.
35% conversion efficiency would (probably) increase the power output of the MER arrays by 50% so these are not trivial increases in efficiency.
exobioquest
Well maybe your right about anti-nuclear nuts, I haven't heard them complaining about New Horizon, but then again there is no other option for New Horizon, but if people think solar is all that is needed on mars their going to question MSL. The PR problem could get worse depending on how long the phoenix lander lasts, if it last all the way up until it's covered in dry ice its not going to look good for the high latitude argument.

35% efficiency?! Thatís got to be more then just 3 junctions! Talk about expensive but that should still be pennies for a space probe. What if solar panels are placed on a motorized stand and aimed at the sun, I'm sure that argument could be made, I donít know how much that would weigh in comparison to a RTG but it sure would be big and cumbersome in volume.

Nickel-Metal hydrides can survive several thousand recharge cycles and donít spontaneously decay, but could it last for a decade? Itís just after MER lasting for 2 years I would like to see MSL put MER in its place and outlast its optimum mission length by several times. By the way which one do you prefer the MMRTG or the SRG?
DEChengst
I'm quite sure MSL would survive after the batteries die. The main reason for adding batteries to a RTG powered probe is that RTGs supply the same amount of power 24/7. You don't design the RTG to give the peak power you need on the probe but you design it to deliver the average power you need. If you need peak power you run the probe from both the RTG and the batteries. If you're using less power than the RTG produces you recharge the batteries. Having dead batteries would limit the ammount of things you can do at once with the probe, but I don't think it would kill it.
exobioquest
Ya, but I don't think 100watts is enough to do much; MER supposedly needs 100 watts just to move around. Maybe if the RPS was at 200watts you could get most things done without the batteries, as is the laser chemcam thing is going to needs some big capacitors if its going to have enough power to burn through the layer of dust on rocks.
helvick
QUOTE (exobioquest @ Nov 27 2005, 09:38 PM)
35% efficiency?! Thatís got to be more then just 3 junctions! Talk about expensive but that should still be pennies for a space probe. What if solar panels are placed on a motorized stand and aimed at the sun, I'm sure that argument could be made, I donít know how much that would weigh in comparison to a RTG but it sure would be big and cumbersome in volume.
*

AFAIK that's still a triple junction design but I don't know for sure. The 28.3% units are triple junction.
Motorizing the panels doesn't have the payoffs that folks generally think they do. The complexity of a sun tracking mount for a ~1m^2 panel adds a lot of risk of mechanical failure. In most normal Martian SH summer conditions (tau~0.9) you gain 10-15% power but you won't need it then. In SH Winter at high latitudes when tau drops to 0.3 on average it might be worth as much as 50% at a time when it actually is useful as overall insolation will be down by almost that much. However for a long mission you have to design for when conditions are going to be at their worst, and that means you design for the high dust loading in the atmosphere with Tau >3. Under those conditions your aiming mount gains you nothing because >95% of insolation is diffuse and effective insolation is down to 20-25% so that is your limiting characteristic. For a long lived lander\rover you have to fly with a panel big enough to generate enough power when a major dust storm hits and the chances of that are ~20% per martian year. Since you have to have the panel area for that situation there is no need for an aiming mount and adding one is pointless.

Phoenix could well last quite a long time after it's primary mission but it will die as winter sets in because there are about 110 Sols of virtual total darkness at its latitude. I've been searching for data on the exact efficiency of the cells and the area of the panels but don't have anything at all yet. However assuming (for the moment) that it ships with panels like the MER's it would generate 850Watt hours on the day it lands (10 May 2008 I think), that will drop to 400 Watt hours by Sol 160, 185 by Sol 190, 200 by sol 210, 100 by sol 245 and zero around sol 300. That's assuming the dust deposition rates are the same as those experienced by MER. Anyway whatever the actual power output at the start is it will drop by >50% after 160 sols and fall rapidly after that. Those are my own calculations so I might be a bit off but they are based on Phoenix's landing site\date and the direct\diffuse Insolation model published by Applebaum and Landis that you can find online if you search for Mars Solar Power.

QUOTE (exobioquest @ Nov 27 2005, 09:38 PM)
By the way which one do you prefer the MMRTG or the SRG?
*

I didn't think the SRG had been proven in any significant way yet. The MMRTG is an evolution of the existing RTG's, proven and known to be reliable. Much as I like the SRG idea I'd hate to see MSL used as it's first flight test.
exobioquest
From what I have read SRG has survived several years of ground testing without any appreciable wear, of course thatís what they claim and is only from ground tests, but still the performance advantages of the SRG over the MMRTG seem good enough to warrant its first use on MSL, the fact it only needs 1/4 as much fuel is a big one, considering the price per gram of Pu238 and the production difficulties of lately. Also it weighs less and is smaller, and vibration should not be a problem for a rover.
mcaplinger
QUOTE (exobioquest @ Nov 27 2005, 08:46 AM)
Will it be 2 Boeing's MMRTG (at ~100 watts?) or Lockheed Martinís 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.
exobioquest
QUOTE (mcaplinger @ Nov 28 2005, 09:59 AM)
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
QUOTE (exobioquest @ Nov 28 2005, 08:57 AM)
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.)
BruceMoomaw
Apparently the Stirling version simply won't be ready by then.
exobioquest
QUOTE (BruceMoomaw @ Nov 28 2005, 07:18 PM)
Apparently the Stirling version simply won't be ready by then.
*


Is that inside info or can you reference it?
mcaplinger
QUOTE (mcaplinger @ Nov 28 2005, 09:30 AM)
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)."
mchan
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, ...
*


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.
mike
Gasoline production is a front so the military can fuel their killing machines.
exobioquest
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?
mcaplinger
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.
exobioquest
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.
mike
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
mcaplinger
QUOTE (exobioquest @ Nov 29 2005, 11:38 AM)
Maybe they mean 2 SRGs total, which would be 200w of power!
*


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.
helvick
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.
*

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.
exobioquest
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!
mcaplinger
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!
*


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
exobioquest
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
*


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
helvick
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.
*

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.
exobioquest
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
helvick
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.
mcaplinger
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
*


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.
Marslauncher
QUOTE (mcaplinger @ Nov 30 2005, 12:34 AM)
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.
*


Sir has there been any more development on the Skycrane issue? Just curious to find out when we would likely see initial work done on the system.

Thanks

Marslauncher

John Cooke
BruceMoomaw
It's about to be declared the officially, firmly selected landing system -- despite the fact that the actual desert tests won't start until 2007. They seem to have that much confidence in it.
mchan
QUOTE (exobioquest @ Nov 29 2005, 10:49 AM)
those nuts and their logic its scares me so, how likely you think they will make a effective stink?
*


They will be flatulent, you will hold your nose, the smell will pass, and NH will launch.
exobioquest
Well if the MMRTG is set I can only hope they can get enough fuel, really hope no problem that dooms the mission happens during cruise or EDL because of a thermal management issue. mad.gif
RNeuhaus
QUOTE (helvick @ Nov 29 2005, 06:10 PM)
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 think that the CPU capacity of MER along with the low bandwidth communication was the hidering factors to slow the advance of the Mars mission. The CPU capacity is a very important thing for analyzing the land obstacles before steping an advance for every around 40 seconds and then take some 15 seconds in analyzing the same task and over.

About the bandwidth of the communication of MER is no more than 128 kbits/sec that is enough to send at least 80 pictures per day (between 1kBytes to 350 kBytes each one). The MSL will take the advantage of greater bandwidth transmission capacity of MRO that might send from Mars to Earth between 1 to 3 GBytes depending upon to the distance between the Earth and Mars.

The others things that I expect the the new MSL incorporates three new instruments after taking the advantage of greater power supply capacity. These new instruments requires very few watts and they might be activated whenever they are needed.

1) Microphone to listen the environment sounds. It would be a very interesting thing and it might be a very valuable device after the camera. This is a good thing to improve the PR. Many people would get exited to listen the sounds from the other words. Very few words can be listen except to Venus, Mars, Titan, and what else more?

2) Two extra arms at both sides as an useful support to help any situation such as to shove, drill, lift MSL from emergency, scratch, hammer, or anything else on the surface. I feel deseperated that MER has no arms to touch, push (from Purgatory Sand) and neither grasp any thing from the surface. It is like a more complete geologist with eyes (ok), ears (not yet), legs (ok), smell (ok -miniTES, x-ray, spectrometer, etc.) and arms (not yet)

3) Anenometer to measure the wind speed and direction in order to help to understand better the geology (the wind also plays an important rol as an aeolian erosion).

Rodolfo
exobioquest
What is this:
"NASA is considering nuclear energy for powering the Mars Science Laboratory. The rover would carry a U.S. Department of Energy radioisotope power supply that would generate electricity from the heat of plutonium's radioactive decay. This type of power supply could give the mission an operating lifespan on Mars' surface of a full martian year (687 Earth days) or more and in extreme seasonal conditions such as those at high latitudes. NASA is also considering solar power alternatives that could meet the mission's science and mobility objectives." -- MSL Home Page

What, what, what! Solar is still a option can somebody clear this up? I thought things were a little more well defined on what the power supply was going to be.
mcaplinger
QUOTE (exobioquest @ Jan 14 2006, 08:57 PM)
Solar is still a option can somebody clear this up?
*


You'll also note that all the images of MSL on the website appear to have the power source "airbrushed out". As far as I can tell, this is NASA PIO's way of dealing with anti-nuke sentiment.

I haven't seen any indication that the MMRTG is not the power source. Solar would require a complete redesign of the system, if it was viable at all (certainly the MER experience is that you can go for a long time on solar, but I don't think one can count on random wind cleaning events for mission success.)
djellison
Yes - it's clearly just being 'polite' about it until they have to start with the 'it's actually quite safe and you have nothing to worry about' efforts in a few years. I've not seen any mention of anything other than an RTG, and no mention anywhere of Solar Arrays.

Doug
helvick
QUOTE (mcaplinger @ Jan 15 2006, 07:12 AM)
I haven't seen any indication that the MMRTG is not the power source.  Solar would require a complete redesign of the system, if it was viable at all (certainly the MER experience is that you can go for a long time on solar, but I don't think one can count on random wind cleaning events for mission success.)
*

The MER's have proven that Solar power for Mars surface operations isn't as marginal as had been thought but it would take one hell of an array to reliably equal the reliability of an MMRTG.
Even with a 50% improvement in solar cell and power management technology you would need a 10m^2 array in order to allow reasonable landing site selection.
The only rationale I can think of for going solar would be to limit the mission life time to something around the 90-120 Sols length which makes no sense for MSL. You could get away with an array of around 3m^2 for such a short mission starting in Summer that needed 2.4kwh per sol.
exobioquest
Well what is the max the MERs gets? what 900-1000w per day? And for MSl we want 2400w so assuming the same cell efficiency we would need 2.4 times more area of solar cells just to get 2400w on a really good day on the equator. How much square area does the MERs solar arrays take up? Give me that and maybe I can draw up what a fugly MSl with solar arrays would look like!
helvick
QUOTE (exobioquest @ Jan 15 2006, 07:06 PM)
Well what is the max the MERs gets? what 900-1000w per day? And for MSl we want 2400w so assuming the same cell efficiency we would need 2.4 times more area of solar cells just to get 2400w on a really good day on the equator.  How much square area does the MERs solar arrays take up? Give me that and maybe I can draw up what a fugly MSl with solar arrays would look like!
*

MER's have somewhere between 1.35 and 1.3m^2 of cell surface area (499 cells of ~4x6.5cm). The cells are 26.8% efficiency triple junction units from Spectrolab.
The maximum reported power out per sol was from Spirit on Sol 581 (956 watt hours).

Total daily Insolation in mid winter is ~46% of the Midsummer value when you exclude atmospheric effects, when you include them the variance is lower and idwinter insolation is ~56% of the summer maximum at Gusev, mostly because the midsummer numbers are reduced by increased Tau.

For a long term mission (like MSL) you'd need to have arrays that can generate 2.4 kilowatt hours in midwinter. So you need at least 7m^2 of array.
RNeuhaus
QUOTE (mcaplinger @ Jan 15 2006, 01:12 AM)
I haven't seen any indication that the MMRTG is not the power source.  Solar would require a complete redesign of the system, if it was viable at all (certainly the MER experience is that you can go for a long time on solar, but I don't think one can count on random wind cleaning events for mission success.)
*

MER's experience is that MSL must not depend upon to winds. It must incorporate own dust blowers which will be used whenever it is necessary.

Rodolfo
RNeuhaus
QUOTE (helvick @ Jan 15 2006, 01:57 PM)
For a long term mission (like MSL) you'd need to have arrays that can generate 2.4 kilowatt hours in midwinter. So you need at least 7m^2 of array.
*

Not so practical. 7 m≤ is like a small bathroom of the size 2.5 x 3.0 meters. The present technology solar power has improved by 50% so the present MER would reduce its solar panel from 1.3 m≤ to 0.75 m≤ now and the MSL would need at least 3.5 m≤ instead of 7 m≤, Not correct?

Rodolfo
helvick
QUOTE (RNeuhaus @ Jan 16 2006, 04:14 AM)
Not so practical. 7 m≤ is like a small bathroom of the size 2.5 x 3.0 meters. The present technology solar power has improved by 50% so the present MER would reduce its solar panel from 1.3 m≤ to 0.75 m≤ now and the MSL would need at least 3.5 m≤ instead of 7 m≤,  Not correct?
Rodolfo
*

Yes but only if MSL was intended for a short mission close to the equator.

Any long term mission will have to be built to handle a major dust storm. The MER's haven't had to deal with one yet but the frequency is about 1 major storm every 5 Martian years, any sensible long duration mission must be able to survive when insolation drops to around 20% of normal.

Even at 21deg S the minimum winter insolation is 30% lower than at Gusev (14deg South) so choosing Solar severely limits your ability to explore outside of equatorial regions.

The Northern hemisphere is even worse because the high tau season coincides with winter.
Analyst
Mike Griffin said at the NH press conference MSL will be the next RTG powered spacecraft. No solar arrays.

Analyst
pospa
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

monty python
Thanks pospa. I learned a lot from that.
jmknapp
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?
djellison
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.



jmknapp
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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