NASA's Phoenix Mars Lander Killed By Ice 113
coondoggie writes "NASA officially ended its Phoenix Mars Lander operation today after a new image of the machine showed severe ice damage to its solar panels, and repeated attempts to contact the spacecraft had failed. 'Apparent changes in the shadows cast by the lander are consistent with predictions of how Phoenix could be damaged by harsh winter conditions. It was anticipated that the weight of a carbon-dioxide ice buildup could bend or break the lander's solar panels. [Michael Mellon of the University of Colorado] calculated hundreds of pounds of ice probably coated the lander in mid-winter.'"
Re:What? (Score:3, Informative)
In the science of cold, solid CO2 has had the colloquial name of dry ice for as long as I can remember. Saying "CO2 ice" gets the meaning across perfectly that you mean solid CO2.
In this context, it forms in the same way as water ice does here in winter conditions, it's just a different molecule.
This mission was not a failure. (Score:5, Informative)
Re:What? (Score:3, Informative)
On a substantially drier and colder planet, it seems even more appropriate...
Re:Too bad they didn't use RTGs. (Score:2, Informative)
NASA built the lander from a previously canceled project, hence Phoenix, no way to redesign the whole power system.
Re:What? (Score:3, Informative)
Probably not, unless it's in very small quantities. Atmospheric concentration is pretty low, and either way, at 1 bar it doesn't freeze until about -78C. I don't think there are any natural places on Earth that cold.
http://en.wikipedia.org/wiki/File:Carbon_dioxide_pressure-temperature_phase_diagram.svg [wikipedia.org]
That suggests you are going to need some serious pressure before you can solidify it at Earth-natural temperature ranges.
Re:What? (Score:3, Informative)
Umm... Even on our rather aqueous planet, where the only CO2 ice is either synthetic or located in seriously inhospitable places [...]
Just out of curiosity, is there a place on earth where there is naturally-ocurring dry ice? A Google search comes up empty.
Apparently it freezes at -78.5 degrees C [answers.com] which is uncommon but not impossible on Earth.
Re:Are we adding "ice" to the no-fly list? (Score:4, Informative)
Destroying one of our rovers is a hostile act!
I feel your pain. It destroyed a Boeing 777 [wikipedia.org] a couple of years ago.
Re:Ironic (Score:5, Informative)
It was a re-do of the Mars Polar Lander. (Failed due to an un-debounced landing sensor switch).
Phoenix rose from the ashes of MPL.
Re:Too bad they didn't use RTGs. (Score:5, Informative)
Of course, an RTG would mass much more than solar power so every part of the system would have to be beefed up. Launcher, cruise stage, aerobraking. Before you know it you are paying for two missions when one at that location was all you needed.
Re:What? (Score:4, Informative)
Astronomers refer to lots of things in their solid state as "ice", and almost always refer to what you would call "ice" as "water ice". And it makes plenty of sense.
Re:De-icing? (Score:3, Informative)
The solar panels provide power. You cannot provide more heating power than the sun does. The sun is putting energy into everything. Everything is still frozen. I hope you can work out the rest of the logic yourself.
Re:De-icing? (Score:5, Informative)
The sun was down too far on the horizon to generate any useful power (or absorb heat directly) during winter.
Mars has axial tilt of 25 degrees; Earth's is 23.5 degrees or so. So there's an equivalent Arctic Circle zone where the sun's below the horizon during the worst of winter. Earth's Arctic Circle is at 66 degrees north; with slightly greater tilt, Mars' Arctic Circle will be even lower. The landing site was around 67 degrees north on Mars.
The sun would have been down long enough that no reasonable amount of batteries could have kept it warm overwinter. A RTG could - as discussed - or little RHU units (Radioactive Heater Unit - it's like a mini-RTG heat source module, with the protection but no power generation units, just designed to keep parts warm). But there was a decision made that the lander was unlikely to survive with all the overwinter issues, so they didn't bother.
Re:What? (Score:4, Informative)
Yes there is. Those temperatures have been observed on the south pole. (Read a report about a team that did stay “overnight” [= over winter]) And that doesn’t even include the windchill effect. Which can make it feel like a horrible -140C. A temperature that literally smacks you in the face so hard you fall over backwards. A temperature that lets your breath crackle and freeze before it lands on the floor. A temperature where pissing in the snow may make you impotent trough freezing the inside of your penis all the way. ;)
Yes, there you might find some dry ice... (e.g. the one that you just did breath out.)
But good luck finding it in nothing but endless planes of real actual ice.
Re:What? (Score:4, Informative)
and either way, at 1 bar it doesn't freeze until about -78C. I don't think there are any natural places on Earth that cold.
Actually it's been down to -89C in Antarctica, so -78C is well within the extreme. But you go find it first, I'll stay inside by the fire long before that...
Re:What? (Score:3, Informative)
The windchill effect is basically a made up term that is _supposed_ to tell you how likely the surrounding atmosphere is to give you frostbite, though no one can agree on a decent standard that works well. It is pointless trying to apply it to freezing rates of any substance (notice how ice (basically) always freezes at 0, whatever the windchill?).
Re:What? (Score:4, Informative)
Ok, I just found a page with waaaaaaaaay too much information [wattsupwiththat.com], but I'll give you the short brief. First by the lower pressure at the poles and higher elevation of the coldest measurement stations, you might not pass the freezing point at all, it seems right on the border. Secondly, because there's so little CO2 in our athmosphere the sublimation effect is much stronger than the freezing effect, dry ice won't last even if held below the freezing point.
Re:Too bad they didn't use RTGs. (Score:3, Informative)
But, if the mass of the RTG's meant removing sensors in order to hit mass and volume budgets, there wouldn't have been any reason to care if it survived the winter. The MER's were done with basically the same launcher as Sojourner, so the fact that they accomplished as much as they did compared to Sojourner is truly amazing, IMO. Unfortunately, it's all about tradeoffs. Hopefully, Mars gets some serious attention and we can deploy some serious long duration hardware on the surface. Without major budget consideration, that just can't happen by itself.
Re:De-icing? (Score:3, Informative)
Sigh, honestly. I give people the benefit of the doubt in terms of logical thinking and this is the replies I get.
Mars!=Earth. If we had a magical energy storage device we could have the lander run at full power 24/7 without any problems. Clearly we don't in this one, I figured it went without saying. Batteries are very much short term. A RTG would work but the rover doesn't have one and the question was limited to the current situation.
It's all practical questions in these sorts of cases. Saying "in a magical world where X is true" is a foolish attempt to escape ones own stupidity.
Defrosting wires use external energy stored beforehand by other means or generated by other means. The Mars lander does not have this sort of energy.
The Mars lander has one long term energy source from the sun at roughly 5% efficiency I'm guessing. The same energy source that heats the environment. The environment absorbs more than 5% of the energy and is nonetheless below freezing. The panels cannot get above freezing for long durations with solar power alone. There is no other source of power.
If you used solar energy to heat a proportionally small insulated object such as electronics it'd work perfectly fine. It does work perfectly fine on most of Mars. The problem here is that the area you heat is the same as the energy you gather energy on. And it's not insulated in any way. Energy that on it's own is not enough to keep that area over freezing. 5% of that won't keep it above freezing.
Once you get frost on the panels you're screwed. Energy absorption, converted to electricity and plain heat, drops due to reflection. Ergo you need to keep the panels above freezing 24/7. Short term and one off solutions won't work. And as I pointed out in my reply to the other guy once you get any decent amount of ice it won't come off unless you sublime a sizable chunk of it. Even if you could you can't afford to wait for it to build up because you need that constant solar power to just keep the rest of the systems warm.
The full power of the sun cannot accomplish this. A smaller percentage of that won't accomplish it. There is no other long term energy source. You use your batteries and how will you magically recharge them? There isn't enough solar energy to just keep the panels defrosted so where the heck would you get the energy to recharge the batteries?
Re:What? (Score:4, Informative)
The vapor pressure of 'dry' CO2 ice is larger than the partial fraction of gaseous CO2 in our atmosphere. That means that it will sublimate, even if it's below the freezing point. You have to go far below the freezing point, until you find the temperature where the vapor pressure is lower than the partial fraction.
This is why water ice will sublimate in very cold, very dry air. If the humidity is low enough, a blanket of snow will slowly disappear, even at -20 C. You can see that in the Midwest every winter.