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The First Europa Lander, What can be done first, cheapest & best?
nprev
post Sep 6 2006, 01:43 AM
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I still think a hard-lander, a penetrometer, or some variation of the Pathfinder/MER EDL system is the way to go for the first landing. There are WAY too many unknown unknowns at the 10 cm-10m scale on Europa's surface, and the close flybys of Enceladus by Cassini make me suspect that Europa might be rough indeed... unsure.gif...better to send out something with max survival potential rather than a traditional soft-lander given that the host orbiter will also be the primary means of determining surface topography at this scale.

It would be both a tragedy and a first-class fiasco to send a lander out there only to find out that its probability of surviving the landing is vanishingly small.


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algorimancer
post Sep 6 2006, 12:55 PM
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Something like the MER's autonomous navigation system could solve the landing-in-rough-terrain problem. Just need a fast computer to do a quick 3D model/analysis of the surface prior to landing, and be prepared to adjust the position as needed to avoid particularly troublesome areas. The low gravity ought to be helpful as well.
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ugordan
post Sep 6 2006, 01:27 PM
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Still, the biggest problem is soft landing via powered descent. The fuel allocation would be huge, you still need to kill some 1.5 km/sec orbital velocity + lower the altitude + propellant margins. IF you had plenty of fuel, you could easily hover above the final descent area searching for a nice spot. By the time we get a Europa lander flown, autonomous navigation will surely mature, but propellant will still be the limiting factor on what you can do.


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algorimancer
post Sep 9 2006, 09:24 PM
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I just had one of those Aha! moments and came up with an interesting means of aerocapture. We launch a combination lander/impactor. Sometime prior to arrival at Europa (or any other ice world) the lander/impactor separate, and the lander portion decelerates slightly to allow the impactor to arrive in advance. The impactor (could be a big ball of ice) impacts the surface, vaporizes itself + a substantial volume of surface ice/volatiles. The lander portion arrives just in time to aerobrake on the explanding impact plume, possibly landing within the crater or somewhere beyond.

Variations on this theme might involve diverting a small near-earth asteroid or Jupiter Trojan asteroid (using some of that creative low-delta-v chaotic orbital mechanics that's come into vogue lately) to act as the impactor - get a big enough impactor and penetrate Europa's ice shell, so that the lander can drop directly into the ocean below.

Details of plume size as a function of impactor mass, as well as how to ensure that the plume is predominantly gaseous or fine particles (rocks would be bad), are left as an exercise for the mission planners smile.gif

Odds are someone will drop a link to some paper somewhere that pre-invented this notion decades ago.
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Guest_Myran_*
post Sep 10 2006, 07:42 AM
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Thats a wild idea algorimancer.

But regardless how I scrutinize it from front and the rear I cant get it to work.
If we think of the gas released by one such impact, it would be in such one limited area that the breaking you get from that are extremely limited. When aerobreaking you need to break around a halfcircle of a world at least and sometimes dipping into the atmosphere many times.

Then about the dust plume. Without an atmosphere you cant count on the fact that bigger boulders fall back faster so you can get your lander down on finer dust since it wont be supported by any air molecules.
They will in fact fall with almost exactly the same speed. Since the 'atmosphere' or Europa are thinner than the diluted remants of one homeophatic ghost.
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algorimancer
post Sep 10 2006, 01:05 PM
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QUOTE (Myran @ Sep 10 2006, 02:42 AM) *
Thats a wild idea algorimancer.

But regardless how I scrutinize it from front and the rear I cant get it to work.
If we think of the gas released by one such impact, it would be in such one limited area that the breaking you get from that are extremely limited. When aerobreaking you need to break around a halfcircle of a world at least and sometimes dipping into the atmosphere many times.

Then about the dust plume. Without an atmosphere you cant count on the fact that bigger boulders fall back faster so you can get your lander down on finer dust since it wont be supported by any air molecules.
They will in fact fall with almost exactly the same speed. Since the 'atmosphere' or Europa are thinner than the diluted remants of one homeophatic ghost.


Yeah, it is pretty wild. Timing would be critical, and it would demand a lot of the hardware. On the other hand, it could be the difference between a 500 million dollar mission and a 2 billion dollar mission.

The intent here is not a traditional aerobraking approach, but somewhere between a hard impact and traditional aerobraking. The idea is to aerobrake into the expanding plume from above, orthogonal to the surface, rather than from the side as in a traditional aerobraking maneuver (though that may work as well or even better). The deceleration would be heavy (orbital speed to near zero in no more than tens of kilometers, if not less than a kilometer), but still something which robust hardware can be designed to accomodate. A tough ablative heat shield would be helpful. Consider that natural impacts can toss intact rocks from Mars or the Moon to Earth.

Most of the deceleration would occur within a fraction of a second, but it's a dramatically more survivable proposition than simply impacting the surface. You wouldn't want to ride along though smile.gif I think the biggest challenge here would be to generate a sufficiently large plume.
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nprev
post Sep 10 2006, 09:00 PM
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Hmm. Given that the Galileo data was a bit limited due to the comm restrictions implicit in the antenna deployment failure, what do you suppose the odds are that there are some natural plumes that a lander could use for aerobraking?

I know that there have to be some severe constraints on Europan vulcanism already from the Galileo data set, but still...I would be very surprised if there aren't a few geysers somewhere on the surface.


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Drkskywxlt
post Sep 11 2006, 01:32 PM
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I think any such impact with the surface of Europa would create so many large fragments (even very small fragments would be damaging at the speed the lander would be going) that a some very heavy protection would be required. That would add further weight and complexity to an already complex mission. I imagine that the fuel required to slow the lander or orbiter to reasonable speeds would be much lighter than any ablative shield to protect the lander from ice and debris thrown up by the impactor.
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AndyG
post Sep 11 2006, 03:34 PM
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The (admittedly ill-fated) penetrators of Deep Space 2, the Mars' impactors carried with MPL in '99, had electronics designed to survive up to 60000g of deceleration.

Assuming a Europa lander hits the surface of Europa at around the local escape velocity (2.02 km/s), then it would need "only" 7m of decelerant in order to bring it to a halt and not exceed that deceleration.

Compressible "somethings" like LEM legs? An airbag? A controlled explosive device fired under the lander when <4 milliseconds from touchdown?

I saw the original animations for the MER entry and landing sequences, and had to laugh at the unlikelihood of everything working just so. These days I wouldn't rule anything out.

Andy
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remcook
post Sep 11 2006, 04:12 PM
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Most importantly IMO is the whole uncertainty of the plan: noone knows exactly what happens when you impact Europa. Designing a mission with these enormous uncertainies will give you a mission that is overly robust and thus too heavy and too costly. And that without a good idea if it even works! I'd spend my money on something else...
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algorimancer
post Sep 11 2006, 05:47 PM
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QUOTE (remcook @ Sep 11 2006, 11:12 AM) *
...
noone knows exactly what happens when you impact Europa
....


The nice thing about Europa is that, of all the icy satellites out there, it is the one with the least uncertainty about material composition. Essentially we're looking at a surface which, to considerable depth, and beyond reasonable doubt, is predominantly water ice with contamination from salts and sulfur compounds. Rocky material should be virtually non-existent. This is the sort of material which can be (relatively) neatly modeled in a laboratory or a computer, and engineering feasibility determined with confidence. (yes, I'm simplifying a great deal here)

The implicit tradeoff in this notion is that between the mass of the fuel and hardware needed for traditional deceleration, versus the mass of an impactor and shielding for impact-assisted aerobraking [IAA]. This leaves open a lot of unanswered engineering questions, such as whether it is possible to design an impactor which will do a good job of vaporizing a volume of Europan ice rather than simply fragmenting it (I like the notion of an impactor which splits into many small pieces prior to impact, perhaps a bag of water with a small explosive charge which detonates shortly before impact). If the mass balance tradeoff is in favor of IAA then it might be worth testing a prototype.

Certainly you'd want to test a notion like this prior to sending a full-scale rover. If you're sending several penetrators anyway, why not replace one or two of them with IAA technology demonstrators.

One more thing, any Europa orbiter/lander might benefit from aerobraking at Jupiter prior to arrival at Europa, which could substantially reduce the approach velocity to something like AndyG's figure. The impactor component of an IAA package could do the opposite and use Jupiter for a gravity assist so as to impact Europa with maximum velocity.

Lot's of unanswered questions. I too initially thought the Pathfinder/MER airbag approach was pretty outrageous, but it worked rather well. Heck, they designed a manned vehicle (Orion) designed to be powered by H bombs, and demonstrated a prototype. Just at the moment I think IAA is outrageous but might still work, and I'll leave it at that.
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Julius
post Sep 12 2006, 07:37 PM
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Main objective should be to get a Europa lander safely with a technique that has been proved to work (in the case of Mars).I believe the airbag system should be the solution if so many uncertainties exist on the characteristics of the Europan surface.One should opt for simpler ways rather than be complicated.
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rasun
post Nov 29 2007, 05:35 PM
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Hi!

Apparently, NASA's Astrobiology, Science and Technology for Exploring Planets program funded the DEPTHX, an autonomous underwater robot.
(See Depthx home here:
http://www.frc.ri.cmu.edu/depthx/
many images here:
http://www.jsg.utexas.edu/news/rels/030807b.html
and here:
http://geology.com/zacaton/
or many links at NASA:
http://astrobiology.arc.nasa.gov/news/expa...ws.cfm?id=10644

DEPTHX and it's follow-up, ENDURANCE are "advertised" as robots that are largely developed so that their next version would be operating in the oceans of Europa, at least that's what I get from the articles. But the Europa Explorer, if approved, will at best fly around 2015, and then a first Europa lander, if approved, probably not before 10 years later; and THEN probably a submarine (but this still sounds very optimistic)

So isn't it too early to start to develop a submarine 20-30 years before it can be launched? Of course it's never too early, and i'm no way against it, but it still sounds strange...? Is this project really seriously meant to have anything to do with Europa?
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JRehling
post Nov 29 2007, 08:36 PM
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QUOTE (rasun @ Nov 29 2007, 09:35 AM) *
So isn't it too early to start to develop a submarine 20-30 years before it can be launched? Of course it's never too early, and i'm no way against it, but it still sounds strange...? Is this project really seriously meant to have anything to do with Europa?


NASA does a lot of low-levels-of-funding exploration of new technologies. I used to work one building over from the robotics building at NASA Ames, and I saw stuff in development over there that doesn't remotely resemble anything that's ever flown, or is scheduled to soon.

Whether or not it actually speeds exploration, it also has public outreach value, encouraging interest in exciting ideas that may one day be put into effect.

I think a real key is that most of this stuff costs almost nothing compared to an actual mission.

One of the interesting things (in a sense, a very uninteresting thing) about a submarine is that remote sensing would be very limited. It would be mainly about analyzing the water immediately in/around the submarine. And maybe the floor, but visual/IR imaging would be limited to meters. There probably wouldn't be much point in wandering horizontally anywhere above the floor.
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DDAVIS
post Dec 3 2007, 11:17 AM
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This discussion is of particular interest to me as I am doing an animation sequence soon of a Europa lander. I have visualized such a thing in the past for the PBS show 'Life Beyond Earth' as a surveyor type lander carrying a probe underneath which would be weighed at the bottom with a plutonium 'lens', with the instruments above this. This probe resembes a blunt version of the Galileo probe entry shell. When released the heat from the lower probe lining melts a hole below it and the probe merrily tunnels its way to the liquid far below.
Any thoughts about this general means to get to the deep ocean with a probe as opposed to other spacecraft schemes being contemplated?

Don
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