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Unmanned Spaceflight.com > Mars & Missions > MSL
Cugel
http://www.marsdaily.com/reports/Managing_...ssions_999.html

Michael Meyer, lead scientist for NASA's Mars Exploration Program, spoke at the recent Viking anniversary celebration. One remarkable quote:

"Considering how long the Spirit and Opportunity rovers have lasted beyond their design lifetimes, it almost boggles the mind to think how long MSL could last. It may be there to greet the astronauts when they arrive on Mars."

That's what I call optimism.
I always thought that the lifespan of an RTG was pretty predictable and that in case of MSL it lasted for about 2 earth years. Maybe he's talking about the solar array powered version?
djellison
Or the sort of failures we're seing on MER - actuators, motors etc.

Doug
climber
Do we know for sure whether MSL will be solar or RTG's?
OR
When will we know? Did they past the critical desgin yet?
Cugel
Apparently not.
According to Meyer the project is still in a 'conceptual' phase.
That sounds a bit scary, doesn't it?
Jim from NSF.com
MSL has its PDR in June. MSL DEIS briefings are this week.
climber
QUOTE (Jim from NSF.com @ Sep 25 2006, 06:47 PM) *
MSL has its PDR in June. MSL DEIS briefings are this week.

Those accronyms again! I've just got "june" and "week" biggrin.gif
Well, MSL too, but can you help with this Jim ?
BTW, I understand this week is important.
AlexBlackwell
QUOTE (climber @ Sep 25 2006, 07:38 AM) *
Those accronyms again! I've just got "june" and "week" biggrin.gif
Well, MSL too, but can you help with this Jim ?
BTW, I understand this week is important.

He's referring to the MSL preliminary design review and the draft environmental impact statement.
Analyst
QUOTE (Cugel @ Sep 25 2006, 10:01 AM) *
I always thought that the lifespan of an RTG was pretty predictable and that in case of MSL it lasted for about 2 earth years. Maybe he's talking about the solar array powered version?


The funny thing about RTGs is there predictable power reduction. They don't die instantly like an empty battery (after i.e. two years). The output decreases very gracefully. The Voyager RTGs are generating today more than half of their output at launch in 1977.

So if MSL uses a RTG (I can't imagine it using solar panels and I can't imagine this decision hasn't been taken already.) and if it behaves like the Voyager RTGs and if all the other rover subsystems keep working and if the rover can work with 50 percent power (like MER) it can still be arround after 30 years.

A lot of if's. But also a beancounters nightmare. Imagine the 15th mission extension. smile.gif

Analyst
helvick
QUOTE (Analyst @ Sep 25 2006, 07:55 PM) *
... if it behaves like the Voyager RTGs and if all the other rover subsystems keep working and if the rover can work with 50 percent power (like MER) it can still be arround after 30 years.

That might be the case for the RTG's itself but I'm certain that the RTG will be used to charge up a battery sub-system that will act as a buffer for power demands of the rover's main sub systems. It's less likely that the battery\power mangement sub system will be good for 30 years.

On the issue of solar vs RTG - I assume that this is being kept vague simply to avoid attracting the ire of the anti nuke crowd. I can't see how a solar panel solution would be sufficient given the power requirements and mission duration. The MER's survival for 2+ years through good luck does not change the fact that MSL's power requirements would require _huge_ panels (>8m^2) in order to ensure that it could survive the full blown Martian dust storms that it's mission duration absolutely requires that it needs to be able to survive.
Stephen
QUOTE (helvick @ Sep 25 2006, 08:25 PM) *
The MER's survival for 2+ years through good luck does not change the fact that MSL's power requirements would require _huge_ panels (>8m^2) in order to ensure that it could survive the full blown Martian dust storms that it's mission duration absolutely requires that it needs to be able to survive.

Using solar panels would also presumably limit the MSL to equatoral regions like the MERs (or else increase the panel acreage required even more).

======
Stephen
lyford
Maybe they are planning to use the ChemCam to zap the solar panels clean? I kid! tongue.gif
I can't see how this mission could be solar powered and still be the MSL we have come to expect in 2009.
I would also imagine that all things being equal electro-mechanically, a RTG mission lifetime would be very predictable, with none of the power budget uncertainty the MERs face.
edstrick
I do not know the possible engineering constraints on "supplementary" solar cells, but if the weight of a square meter or two on advantageously oriented surfaces on top of the rover wasn't a big problem, it seems that they might be useful as a supplementary power source. There's additional power handling hardware and cabling and the like, but it might be worth it.
Jeff7
QUOTE (helvick @ Sep 25 2006, 04:25 PM) *
That might be the case for the RTG's itself but I'm certain that the RTG will be used to charge up a battery sub-system that will act as a buffer for power demands of the rover's main sub systems. It's less likely that the battery\power mangement sub system will be good for 30 years.

They managed to squeeze more than 15 years out of Hubble's batteries, and they get recharged about every 90 minutes, if memory serves.
helvick
QUOTE (Jeff7 @ Sep 26 2006, 12:39 PM) *
They managed to squeeze more than 15 years out of Hubble's batteries, and they get recharged about every 90 minutes, if memory serves.

Those are very different beasties. Hubble uses pressurised Nickel Hydrogen batteries. Those have excellent life time and recharge cycle characteristics but are relatively inefficient from a power storage\density POV. The MER's use Lithium Ion\Lithium Polymer batteries and MSL almost certainly will too.



Spacecadet
MSL is an RTG powered rover.

Keep in mind there are two other benefits from RTG's.

1. Lots of waste heat which can be used to heat the rover. This is a significant power savings.

2. No batteries.. = mass savings ;)
djellison
MSL will still have a battery, as all other RTG powered spacecraft have - to allow for peak power useage over and above the RTG output.

Doug
Jim from NSF.com
QUOTE (djellison @ Dec 23 2006, 04:43 AM) *
MSL will still have a battery, as all other RTG powered spacecraft have - to allow for peak power useage over and above the RTG output.

Doug


Actually, MSL will be powered by the battery and the RTG will be used to charge it. Mission ops will be much like MER where there will be periods of "inactivity" to allow the battery to recharge.
Analyst
QUOTE (djellison @ Dec 23 2006, 10:43 AM) *
MSL will still have a battery, as all other RTG powered spacecraft have - to allow for peak power useage over and above the RTG output.


Voyager did not have a battery, I am pretty sure Pioneer 10/11 didn't have one too. Not sure about Galileo and Ulysses, but I guess both didn't have one eighter. Cassini has one to power the radar. New Horizons doesn't have one. I believe the ALSEPs did not have a battery too.

It's pretty uncommon for RTG spacecraft to have a battery.

Analyst
helvick
QUOTE (Analyst @ Dec 23 2006, 02:54 PM) *
It's pretty uncommon for RTG spacecraft to have a battery.

That is probably true but a power subsystem that enables power acumulation enables much higher peak power loads than the peak power output from your RTG and that is a very good thing for a rover even if it is not hugely important for orbiter\flyby space craft.

It wouldn't be a very effective use of the resources when you have 2400 whr of power per sol but you keep yourself limited by a 100watt peak load.
tedstryk
QUOTE (Analyst @ Dec 23 2006, 02:54 PM) *
Voyager did not have a battery, I am pretty sure Pioneer 10/11 didn't have one too. Not sure about Galileo and Ulysses, but I guess both didn't have one eighter. Cassini has one to power the radar. New Horizons doesn't have one. I believe the ALSEPs did not have a battery too.

It's pretty uncommon for RTG spacecraft to have a battery.

Analyst


Pioneers 10 and 11 did have a battery, though it was useless by the later part of the mission.
Analyst
QUOTE (helvick @ Dec 23 2006, 06:10 PM) *
That is probably true but a power subsystem that enables power acumulation enables much higher peak power loads [...]


I am well aware of the value of a battery, but to say "... as all other RTG powered spacecraft have" is clearly wrong.

Analyst
djellison
I thought they did....MSL certainly will, and I know others have, I assumed they all had - my bad.

DOug
Bob Shaw
Strangely, Sojourner's battery was a primary - ie non-rechargeable - battery - the solar panel didn't recharge it; and many allegedly 'non-nuclear' spacecraft have employed 'heaters' which use radioactive decay to heat the vehicle. Funny old world, eh?

Bob Shaw
DFinfrock
Off topic...

But when we get around to sending a lander/rover into Shackleton Crater at the lunar south pole, will there likely be only a battery to power it, for a short-term mission? I can't imagine sending an RTG there if there is a hope to use any possible ice resources that may exist. And a solar panel wouldn't be of much use in a perpetually shadowed crater.

David
Bob Shaw
QUOTE (DFinfrock @ Dec 27 2006, 12:57 AM) *
Off topic...

But when we get around to sending a lander/rover into Shackleton Crater at the lunar south pole, will there likely be only a battery to power it, for a short-term mission? I can't imagine sending an RTG there if there is a hope to use any possible ice resources that may exist. And a solar panel wouldn't be of much use in a perpetually shadowed crater.

David



David:

An RTG would be ideal - simple, light, happy in the cold and darkness! And although you might not want to hug one on a long-term basis, pretty safe. One problem with RTGs is their rarity - fuel and hardware production is erratic, to put it mildly.

Alternatives *might* include a long power cable leading to a sunlit lander, or even an internal combustion engine (the exhaust would be fun!). Still, there *have* been stranger propulsion systems suggested over the yeras, such as the mobile windmill on Venus (I kid you not)...

Bob Shaw
Geographer
Of all the things to protest in the world, tiny nuclear reactors on one-way trips into space for the pursuit of science is awfully trivial. I don't understand why procuring RTGs is a problem: shouldn't NASA with its government connections get top priority?
Jim from NSF.com
QUOTE (Geographer @ Jun 21 2007, 06:00 AM) *
Of all the things to protest in the world, tiny nuclear reactors on one-way trips into space for the pursuit of science is awfully trivial. I don't understand why procuring RTGs is a problem: shouldn't NASA with its government connections get top priority?

Government connections? NASA is the government and that why RTG procurement is hard. The "people" want a rigorous (maybe overly) process to make sure the environment and people are not endangered.

As for "top priority", there are other goverment users
edstrick
There's also the one minor detail.. Nukes are *** EVIL ***. Only practitioners of the dark side of the force dabble with nukes... (etc. etc. etc.. froth, rage, babble....)

I was VASTLY relieved that there has been a declining trend of anti-nuke hobbyists entertaining themselves at the Cape from Galileo to Cassini to New Horizons... may that trend continue!
mchan
QUOTE (Jim from NSF.com @ Jun 22 2007, 04:31 AM) *
Government connections? NASA is the government and that why RTG procurement is hard. The "people" want a rigorous (maybe overly) process to make sure the environment and people are not endangered.

As for "top priority", there are other goverment users

Interesting last comment. There were press stories that mentioned the use of RTG's by remote information collection equipment emplaced on the ocean floor and in the Himalayas. But that was during the Cold War.

QUOTE (edstrick @ Jun 22 2007, 09:47 PM) *
I was VASTLY relieved that there has been a declining trend of anti-nuke hobbyists entertaining themselves at the Cape from Galileo to Cassini to New Horizons... may that trend continue!

One can count on the hardcore anti-nuke folks to be at the MSL launch.
lyford
QUOTE (mchan @ Jun 23 2007, 01:16 AM) *
One can count on the hardcore anti-nuke folks to be at the MSL launch.

So they will then be standing in the "radioactive fallout zone" if there is a launch vehicle failure? biggrin.gif

Seriously, if one is going to spend one's time protesting nuclear material on top of a rocket, one would probably want to spend some time worrying about these ones, instead of a wee lil' RTG....

EDS - feel free to cull if too political for the board.
punkboi
QUOTE (djellison @ Dec 23 2006, 02:43 AM) *
MSL will still have a battery, as all other RTG powered spacecraft have - to allow for peak power useage over and above the RTG output.

Doug


New Horizons doesn't have a battery...which is why I think it actually has to dissipate the excess RTG power that it doesn't need to run its systems and instruments

QUOTE (mchan @ Jun 23 2007, 01:16 AM)
SOne can count on the hardcore anti-nuke folks to be at the MSL launch.


Which is pretty funny...considering that all the recent RTG flights have provided some kind of significant discovery during their missions. Not to state the obvious:

Galileo (A possible ocean on Europa)
Cassini (Possible water activity on Enceladus, and maybe Dione)
New Horizons (the first flight to Pluto and the Kuiper Belt)

Not to jinx anything, but if these anti-nuke folks want to stop looking like a bunch of schmucks with lots of free times on their hands, try waiting for something to go wrong on the next RTG launch...and then protest the RTG launch that comes after that one. They'll look less foolish. smile.gif
nprev
Well, the good thing, as Ed observed, is that UMSF RTGs are obviously drifting off the radar screens of these groups: the sky hasn't fallen, nor does such an event seem likely based on past performance. The entire issue is no longer a plausible casus bellum for them, and therefore also no longer a focus item except in token terms; good news.

Let's keep it that way...low visibilty has many advantages! wink.gif
David
QUOTE (nprev @ Jun 23 2007, 08:12 PM) *
The entire issue is no longer a plausible casus bellum for them


That seems very likely, but you've just hazarded the fury (ira) of the North American League of Latinists by incorrectly using the term casus belli, and their is not a power to be scorned (non contemnendum). biggrin.gif
dvandorn
QUOTE (nprev @ Jun 23 2007, 03:12 PM) *
Well, the good thing, as Ed observed, is that UMSF RTGs are obviously drifting off the radar screens of these groups: the sky hasn't fallen, nor does such an event seem likely based on past performance. The entire issue is no longer a plausible casus bellum for them, and therefore also no longer a focus item except in token terms; good news.

Let's keep it that way...low visibilty has many advantages! wink.gif

You really think UMSF use of RTGs, et al, has been successful and uneventful enough to push them off the anti-nuke crowd's radars? I will remind you that, in their last gasp at trying to look important to themselves, these same people INSISTED that Cassini be crashed in Saturn upon arrival instead of placed into orbit, since (they insisted) anything else meant that Cassini would eventually return to near-Earth space and pose a COMPLETELY UNACCEPTABLE RISK of a collision.

I'm not kidding.

-the other Doug
mchan
Something I had always wondered about regarding use of RTG on Earth flyby. If I recall correctly, the Europa Orbiter that was cancelled (c. 2001?) had to deal with tight launch mass contraints because it could not use an Earth flyby gravity assist. The EGE proposals in more recent OPAG studies have reverted to allowing an Earth flyby gravity assist.

Was there an edict from NASA HQ on no Earth flyby's for the earlier Europa Orbiter, and, if so, has this been rescinded so proposals like EGE are feasible from a launch mass constraint perspective? Furthermore, if there had been such an edict, how did it come into being, and how did it get rescinded?

(Mod: How about moving all RTG posts to a separate thread?)
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