Mars Lander Faces Slow Death

Riding with Robots writes "It's the beginning of the end for the Phoenix Mars Lander. As winter approaches in the Martian arctic, NASA says it's in a 'race against time and the elements' in its efforts to prolong the robotic spacecraft's life. Starting today, mission managers will begin to gradually shut the lander's systems down, hoping to conserve dwindling solar power and thereby extend the remaining systems' useful life. 'Originally scheduled to last 90 days, Phoenix has completed a fifth month of exploration in the Martian arctic. As expected, with the Martian northern hemisphere shifting from summer to fall, the lander is generating less power due to shorter days and fewer hours of sunlight reaching its solar panels. At the same time, the spacecraft requires more power to run several survival heaters that allow it to operate even as temperatures decline.'"

Re:Why heaters?

[MichaelSmith]

So honest question for all you rocket scientists out there: Why are heaters needed? Which parts of the spacecraft (electronics?) need to be above a certain temperature to operate? Is it possible to let the lander "freeze" and then revive it, or if not what components are sensitive to this?

Rich.

One issue is that solder joints between components can break if they are cooled down too much. Batteries and capacitors can fail if liquids inside them freeze and crystalise. While I think there is a chance that the lander will come back up next summer but the likelyhood of this is pretty slim IMHO.

Re:Why heaters?

[jm1234567890]

From the article

The heaters serve the purpose of keeping the electronics within tested survivable limits.

Re:what I do not understand.

[u38cg]

Metal parts can potentially crack, any components with liquids in them (batteries, capacitors, etc) can freeze and split. Certainly they will be keeping their fingers crossed that it might come back to life next year, but the odds are low.

Re:Pyrotechnic unit?

[Gordonjcp]

Lots of space hardware uses a small pyro charge to deploy antennas and things. On a lot of microsats, the antennas are rolled up like steel tape measures, and when the pyro blows they unroll and stick out.

Re:Why heaters?

[Anonymous Coward]

I don't think they use oil... in the past they used WS2 (tungstendissulfide), It is a powder that sticks to metal. but hey... IANARS

Re:what I do not understand.

[OriginalArlen]

You've got it. Firstly the batteries will be destroyed by the prolonged cold. The other thing is that the entire site will be cloaked in a couple of meters of CO2 ice over winter; as it accumulates on the solar panels, the weight is expected to physically snap them off.

Re:Why heaters?

[camperdave]

No, the electronics are kept warm during transit.

Re:Why heaters?

[Lumpy]

It's the mechanical moving parts as well as the batteries and other delicate systems. Problem is these parts are larger than the rovers that simply use hot radiation pellets of plutonium dioxide to do the heating for them.

They CAN shut it all down, park the moving parts and let it sit dormant for all winter, but when you shut a system down there is a good chance that when you fire it up in the spring that it will not fire up. Blown dust cakes into an armature hinge point and now it can no longer move.

Re:Nuclear batteries

[Carbon016]

They [space.com] might [theregister.co.uk] on the successor.

Re:Nuclear batteries

[Anonymous Coward]

The word nuclear scares the public. More specifically I live by the cape, when they launch nuclear powered missions like New Horizons Pluto mission local schools are required to keep children indoor and close their windows. This is a precaution. If the launch vehicle blows up nuclear fallout could be spread around by winds. So generally only missions where it is required because there isn't any sun light like a mission to Pluto do they use nuclear reactors.

Re:NASA

[Anonymous Coward]

Autumn.

Re:Why heaters?

[Tony Hoyle]

It's pretty cold in space....

Well that really depends on how near you are to a source of heat... in fact overheating is a problem in the solar system as it's difficult to get rid of the heat from the sun.

Re:Nuclear batteries

[Tweenk]

Those are not nuclear reactors, but radioisotope thermoelectric generators (RTGs). Rather than harnessing the energy from steam heated by the fission of heavy nuclei, they get the power directly from the heat of natural decay of radioactive isotopes using thermocouples. Link. [wikipedia.org]

Current nuclear reactor designs, even the compact ones used on ships and submarines, are too large and too heavy to be sent into space.

Re:Nuclear batteries

[Catmeat]

In this case, they aren't necessary as the lander has done all the science it was planned. What's the point of keeping it alive over the winter of all it's going to do in the spring is repeat the measurements it's already taken?

RTG's [wikipedia.org] and RHU's [wikipedia.org] are a massive, expensive, pain in the ass and are best avoided unless absolutely necessary.

Basically -

• They're heavy. They are must be designed to wishstand re-entry intact and not disperse Pu238 fuel everywhere if the rocket explodes during launch. Extra weight on the lander means there will be science instruments that have to be taken off.
• They're on 24/7 and they're only about 5% efficient so they produce about 20W of heat for every W of electricity. This is a huge problem when the spacecraft is buttoned up in it's Mars-entry aeroshell during the 9 month trip to Mars. Hundreds of W of waste heat must be dumped somehow or your lander will cook.

  This may well use some kind of fluid cooling loop that circulates through radiators on the crusie stage. This now gives you added problems of a pump (which must not fail or you'll lose the mission, so add a back-up pump) and how to disconnect the coolant pipes with absolute reliability when the time comes to ditch the cruise stage and enter the Martian atmosphere. More problems, cost and weight.

• Pu238 is on every terrorist's Christmas wish-list. You have the added problems and of turning the spacecraft assembly facilities into highly secure spacecraft assembly facilities. Assembling a Mars lander is already hard and expensive. You really don't want to add to this the cost and disruption of post-9/11 anti-terrorist, security paranoia. Donna Shirley discusses this in her book on the Mars Sojurner rover, and that was put together back in 96.

Re:what I do not understand.

[Sobrique]

Actually, that's practically impossible on a living person - you're effectively putting something 250+ degrees hotter into the liquid nitrogen, and you're circulating nice hot blood around it continuously - you'll thus be flash-boiling the nitrogen, which has quite a low specific heat capacity, and the bubbles as the nitrogen boils off forms quite an effective insulator. http://en.wikipedia.org/wiki/Leidenfrost_effect [wikipedia.org]

It's therefore possible to immerse parts of the anatomy in liquid nitrogen for a fairly substantial amount of time before it will freeze to 'shatter on a table' temperature. Of course, getting frostbite is somewhat faster, and not recommended, so don't try this at home :)

Re:Why heaters?

[LWATCDR]

Batteries are number one.
Capacitors would be number two.
Solder joints from uneven contraction.
We are talking about cold here. I mean a cold that makes Antarctica look warm.
Too bad they didn't use an RTG. The colder they get the more power they make.

Re:Nuclear batteries

[Spotticus]

Not entirely true, there have been several missions (not recently) where full blown nuclear reactors have flown. Between 1971 and 1988 the Soviets flew 31 RORSAT missions using the BES-5 nuclear reactor. The US launched one mission in 1965 carrying the SNAP-10A reactor. Both types used liquid sodium cooling and were extremely compact and lightweight. The advantage of not requiring shielding

Re:Why heaters?

[Radio_active_cgb]

The temperature extremes experienced in spacecraft (the Antarctic and Artic here on Earth) are such that considerable thermal expansion and contraction occurs. Because materials have different thermal expansion coefficients, everything is expanding and contracting at different rates, leading to mechanical stress. Such stresses cause hardening of materials - rather than flexing with the stress as when they were new, they break, and there-in lies the problem. (Remember bending wire coat hangers until they break? Even after a few bends, you would have problems straightening the now hardened wire.)

The break can take many forms - a solder joint fails, a bearing seizes or breaks, a screw snaps, or a structural weld breaks. Each of these can result in a failure that renders the device inoperative.

The heaters (often common power resisters) limit the cold extremes, and allows some predictability as to when failures can begin. In electrical systems, such heaters are used when the electronics can not keep themselves warm through continuous operation, or the electronics are shut down (you do want them to come back up, don't you?)

In any case, power consumption tends to be fairly constant whatever the operating mode is.

Re:Why is it less likely to survive than the rover

[MichaelSmith]

Spirit and Opportunity are both close enough to the equator to get solar power every day. Phoenix is north of the arctic circle and will go without any power at all for most of an Earth year.

Phoenix will freeze stone cold dead, but the rovers always have power for their heaters.