Author Topic: Current NASA studies of the Europa mission  (Read 19524 times)

Offline Robotbeat

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Re: Current NASA studies of the Europa mission
« Reply #20 on: 01/10/2012 04:40 am »
I've got a question:

Is it possible to do an orbiter and a lander mission at the same time with no high-resolution mapping done beforehand?

What I mean is that the orbiter and lander arrive together (ala Cassini), the orbiter enters a mapping orbit around Europa until a suitable landing spot is discovered, and only then is the lander deployed? I understand that might be a little risky, but it also means you don't need two separate launches. Perhaps if the lander does direct-to-Earth communication, the lander could take the power source and computers (and possibly some of the ACS/RCS thrusters) with it to the surface. Or, the two could be almost entirely separate with the lander merely piggy-back on the orbiter, with the orbiter acting as a relay.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline GClark

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Re: Current NASA studies of the Europa mission
« Reply #21 on: 01/10/2012 05:48 am »
You could - $$$$$.

IIRC, the major problem w/Europa is that it is so deep in Jupiters' trapped radiation belts that you basically have around 30 days (+/- YMMV) from the time you enter orbit until your electronics are fried.

Enter orbit, do a survey, pick a landing spot, de-orbit/land, surface ops - all in 30 days or less.  Sounds just a bit dicey to me.

Again IIRC, the cost of the rad-hardened electronics and radiation vault was killing JEO.  Jupiter is a tough place.

(Blackstar, pls feel free to correct me/kick me in the head if I'm wrong anywhere in there).

Offline Zed_Noir

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Re: Current NASA studies of the Europa mission
« Reply #22 on: 01/10/2012 07:44 am »
You could - $$$$$.

IIRC, the major problem w/Europa is that it is so deep in Jupiters' trapped radiation belts that you basically have around 30 days (+/- YMMV) from the time you enter orbit until your electronics are fried.

Enter orbit, do a survey, pick a landing spot, de-orbit/land, surface ops - all in 30 days or less.  Sounds just a bit dicey to me.

Again IIRC, the cost of the rad-hardened electronics and radiation vault was killing JEO.  Jupiter is a tough place.

(Blackstar, pls feel free to correct me/kick me in the head if I'm wrong anywhere in there).


Just out of curiosity how does the vintage vacuum tube electronics fare in the radiation environment around Jupiter in comparison to modern IC electronics?

 

Offline ugordan

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Re: Current NASA studies of the Europa mission
« Reply #23 on: 01/10/2012 07:53 am »
Just out of curiosity how does the vintage vacuum tube electronics fare in the radiation environment around Jupiter in comparison to modern IC electronics?

Probably much better, but then again, their mass makes it a wash. Bottom line is you need mass to survive near Io/Europa.

Offline Warren Platts

Re: Current NASA studies of the Europa mission
« Reply #24 on: 01/10/2012 08:08 am »
Here's an idea for a cheaper Europa mission: land on Callisto instead. It also has a liquid water interior.
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Offline ugordan

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Re: Current NASA studies of the Europa mission
« Reply #25 on: 01/10/2012 08:15 am »
Well, yes, other than the fact Callisto's ice shell is modeled to be roughly an order of magnitude thicker and the existence of geothermal energy sources at the rock/liquid interface is questionable. People want to land on Europa not because it's super hard, but because of its astrobiological potential. In that light your suggestion reminds me of looking for your car keys where the light is good, not where you dropped them.
« Last Edit: 01/10/2012 08:21 am by ugordan »

Offline Warren Platts

Re: Current NASA studies of the Europa mission
« Reply #26 on: 01/10/2012 08:31 am »
Well, yes, other than the fact Callisto's ice shell is modeled to be roughly an order of magnitude thicker and the existence of geothermal energy sources at the rock/liquid interface is questionable. People want to land on Europa not because it's super hard, but because of its astrobiological potential. In that light your suggestion reminds me of looking for your car keys where the light is good, not where you dropped them.

Yeah, well the fact is, if you knew where you dropped your keys, you wouldn't have to look for them. Thus the logical place to start is where the light is good.

 There are places on Callisto where eruptions/geysers/fumaroles take place. Since there is liquid water, there is by definition "geothermal energy sources"; that's just another way of saying the interior is hotter than the exterior.
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Offline ugordan

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Re: Current NASA studies of the Europa mission
« Reply #27 on: 01/10/2012 10:51 am »
There are places on Callisto where eruptions/geysers/fumaroles take place.

There are? I'm woefully out of the loop then, could you point me out to these current findings? My understanding of Callisto was that its surface is as dead as a door nail.

Offline Warren Platts

Re: Current NASA studies of the Europa mission
« Reply #28 on: 01/10/2012 03:49 pm »
Moore et al. describe "pits" that appear superficially, at least, to be similar to pits found on the Moon and Mercury that are now thought to have resulted from gas explosions:

Quote
A 375 km x 225 km region at 1°S, 6°W (Figure 17.18)
shows a landscape with numerous pits, which often occur
in clusters (Moore et al. 1999). They are sharply outlined,
closed depressions with steep walls but no raised rims.

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Offline ugordan

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Re: Current NASA studies of the Europa mission
« Reply #29 on: 01/10/2012 04:51 pm »
Having skimmed the paper you linked to, I don't see any evidence to support the claim that there are "eruptions/geysers/fumaroles" seen on the surface. As for the pits you mention, your conclusion about them is at adds with the authors':
Quote
Callisto’s pits may have formed from initially unremarkable local depressions by differential sublimation of a volumetrically substantial volatile.

Furthermore, the Conclusions section opens with this:

Quote
Along with the discovery of Callisto’s conducting layer, major Galileo discoveries about Callisto include the complete absence of cryovolcanic resurfacing, the relatively undifferentiated interior, and the presence of massive landform erosion likely from sublimation processes.

I don't know how you managed to conclude that Callisto is cryovolcanically active in the current epoch from that paper. There is no current evidence for that just like there is no evidence for anything of the sort ongoing at Europa either. Maybe we haven't looked hard enough, but the evidence is not there and claims like that are unsubstantiated.

Offline Warren Platts

Re: Current NASA studies of the Europa mission
« Reply #30 on: 01/10/2012 05:28 pm »
I didn't say there was major cryovolcanic activity on Callisto. I was thinking of the apparent morphological similarity between the pits described by Moore et al. and the pits in the Spudis article. Similarly, a more or less steady stream of warm gas from the interior would also cause such pits to form as it would erode the icy surrounding matrix. Sure, these hypotheses are not what Moore et al. invoke to explain the pits, but so what? They're as good an explanation as what Moore et al. offered, which was written a few years before the Mercury results came out. We simply do not know enough about Callisto to infer that there is absolutely no communication between the salty see that underlies the icy crust and surface itself.

Since you skimmed the book chapter from the most important book on Jupiter, you may have missed the conclusion:

Quote
Callisto, once unknown and then disregarded
after Voyager, has emerged in the post-Galileo era worthy
of the same intense scientific scrutiny that is lavished upon
her siblings

"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Robotbeat

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Re: Current NASA studies of the Europa mission
« Reply #31 on: 01/10/2012 05:45 pm »
I agree that Callisto is treated a little like the ugly sister, unfairly to a certain extent.

I think it more points to the wealth of interesting worlds around Jupiter than necessarily the lack of interesting science to do at Callisto.

If only we had an enormous planetary science budget, we could have landers on all these worlds.

And I don't think the radiation problem is as dire as is sometimes presented here, where there's somehow a strict 30 day limit or something like that. It's just an engineering trade that needs to be done. What level of reliability is required, what level of risk, how long do we want it to last, what level of redundancy can we use to mitigate, what is our mass budget for shielding, what level of radiation hardening do we use, what science targets do we pick if the trade becomes too difficult (i.e. is there enough science to do at Callisto for a mission to be worth it? can it serve as a cheaper substitute for the other icy moons?) etc. It's easy to get a single concept, like "lots of radiation, impossible to do more than 30 days" and then stop thinking about it because the trade is too complex. The dismissal of solar power is one example (though I agree it's a poor surface power source for a lander), where there are several choices of ways to mitigate the radiation threat, of which Juno picked only one (i.e. just more shielding on a conventional array).

For selecting between proposals for certain classes of missions, it's certainly acceptable to dismiss slightly lower TRL approaches, but it seems like a huge waste to leave promising solutions to these complex trades in the "TRL Valley of Death" forever. There will never be a time when there's not a strong motivation to pick the less risky approach, but then the more promising solutions will never be advanced and our state-of-the-art will be at a stand-still.
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Offline ugordan

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Re: Current NASA studies of the Europa mission
« Reply #32 on: 01/10/2012 05:47 pm »
I didn't say there was major cryovolcanic activity on Callisto.

I never said you claimed major activity. You obviously did claim activity, for which there simply is no evidence.

Quote
I was thinking of the apparent morphological similarity between the pits described by Moore et al. and the pits in the Spudis article.

Morphological similarity is not a very convincing argument, especially when observations from rocky bodies are applied to mostly icy bodies.

Quote
Sure, these hypotheses are not what Moore et al. invoke to explain the pits, but so what? They're as good an explanation as what Moore et al. offered, which was written a few years before the Mercury results came out.

Not every explanation is as good as any other. There are those which are better supported by evidence and those which aren't.

Quote
We simply do not know enough about Callisto to infer that there is absolutely no communication between the salty see that underlies the icy crust and surface itself.

We don't. Since everyone seems to agree that in terms of astrobiological potential Europa rates significantly higher than Callisto, what do you hope to figure out about Europa by exploring Callisto? Their composition and evolution histories are significantly different. At the end of the day you will have learned about Callisto, not Europa.

Quote
Since you skimmed the book chapter from the most important book on Jupiter, you may have missed the conclusion:

I haven't missed that. I never said Callisto isn't worth exploring. I'm saying it's not a substitute for Europa. It's certainly off topic for this particular thread.

Offline Robotbeat

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Re: Current NASA studies of the Europa mission
« Reply #33 on: 01/10/2012 05:52 pm »
Not an exact substitute (nothing ever is), but we've never landed on any icy moons at all (unless you count Titan, but that seems like a stretch).
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Offline baldusi

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Re: Current NASA studies of the Europa mission
« Reply #34 on: 01/10/2012 05:56 pm »
I agree that Callisto is treated a little like the ugly sister, unfairly to a certain extent.
If I'm not mistaken, it's very close to landing on the Moon. I would put off the study until more moon landers are developed. A lot of development from there can be used for a Callisto lander.

Quote
It's easy to get a single concept, like "lots of radiation, impossible to do more than 30 days" and then stop thinking about it because the trade is too complex.
From what I understand, the problem is not making the vehicle last more than 30 days, it's the sensors. You can't shield the sensors and get data. The more you shield, the less data you get. And it might directly block certain information. So, while you could do a longer mission, the science output would be low due to the degradation of the sensors.

Offline ugordan

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Re: Current NASA studies of the Europa mission
« Reply #35 on: 01/10/2012 06:15 pm »
Not an exact substitute (nothing ever is), but we've never landed on any icy moons at all (unless you count Titan, but that seems like a stretch).

Why is Titan a stretch?

Yes, we've never landed on anything else in the outer solar system and the present and likely future funding constraints ensure we will land on very few additional places. Thus we can't really afford to visit the "less interesting" places, but need to prioritize. You can't just build a Discovery class mission and try it out on Callisto. It would be nice if you could.

I'm all for landing on every single rock out there. If you look close enough each is unique and interesting in some way, but dreaming is one thing. Being realistic and practical is another.

Offline Robotbeat

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Re: Current NASA studies of the Europa mission
« Reply #36 on: 01/10/2012 06:29 pm »
Not an exact substitute (nothing ever is), but we've never landed on any icy moons at all (unless you count Titan, but that seems like a stretch).

Why is Titan a stretch?

Yes, we've never landed on anything else in the outer solar system and the present and likely future funding constraints ensure we will land on very few additional places. Thus we can't really afford to visit the "less interesting" places, but need to prioritize. You can't just build a Discovery class mission and try it out on Callisto. It would be nice if you could.

I'm all for landing on every single rock out there. If you look close enough each is unique and interesting in some way, but dreaming is one thing. Being realistic and practical is another.
Maybe not a lander, but you could perhaps do a Callisto orbiter with a Discovery budget, since the radiation hardening needed for Juno wouldn't be required but solar power could still be used. And... it's not entirely inconceivable that a very small battery-powered lander (perhaps patterned after whoever wins the Google Lunar X-Prize) could piggy-back, though that likely would blow the Discovery budget.
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Offline Warren Platts

Re: Current NASA studies of the Europa mission
« Reply #37 on: 01/10/2012 07:11 pm »
I didn't say there was major cryovolcanic activity on Callisto.

I never said you claimed major activity. You obviously did claim activity, for which there simply is no evidence.

I call volcanoes "major" activity. I never said there were volcanoes. I was thinking of the "gas eruptions" described in the Spudis article, which leave behind pits similar to some of those described on Callisto.


Quote
Quote
I was thinking of the apparent morphological similarity between the pits described by Moore et al. and the pits in the Spudis article.

Morphological similarity is not a very convincing argument, especially when observations from rocky bodies are applied to mostly icy bodies.

Do you know what the Moh's hardness factor for water ice at Callisto temperatures is? It's in the 5-7 range. Hard as rock in other words.

Quote
Quote
Sure, these hypotheses are not what Moore et al. invoke to explain the pits, but so what? They're as good an explanation as what Moore et al. offered, which was written a few years before the Mercury results came out.

Not every explanation is as good as any other. There are those which are better supported by evidence and those which aren't.
Uh huh. And there are those that can't be decided by the evidence. That's where we're at with Callisto. It's totally premature to say just what the cause of those pits are.

Quote
Quote
We simply do not know enough about Callisto to infer that there is absolutely no communication between the salty see that underlies the icy crust and surface itself.

We don't. Since everyone seems to agree that in terms of astrobiological potential Europa rates significantly higher than Callisto, what do you hope to figure out about Europa by exploring Callisto? Their composition and evolution histories are significantly different. At the end of the day you will have learned about Callisto, not Europa.

So? The goal is astrobiology, not planetary geology, right? My point is, Callisto has liquid water: follow the water, if there's life there, there's probably evidence for it somewhere on the surface. If Callisto really is a lot easier to operate on than Europa, then why not try Callisto first? To use your lost keys analogy, odds are you won't find what you're looking for in the light, but you might as well start there.

Moreover, Callisto has the best ISRU potential of the Jovian Moons. The surface has more water ice and volatiles than Europa or Ganymede, and certainly has a lot less radiation than Europa (Ganymede is partially protected by its own, self-generated magnetic field, so it may not be much worse than Callisto on the surface).

So by landing on Callisto, you could kill two birds with one stone: you could look for biomarkers, and you would be doing some useful scouting that would pave the way for a future human landing.

In any case, I don't have much faith that the kinds of rovers we've been sending to Mars, for example, are capable of detecting life definitively, whether they were sent to Europa or Callisto. All they'll do is deliver tantalizing results that raise more questions than they answer. If you really want to find life on the Jupiter Moons, it would be best to send in a human team of operators, and A LOT of heavy equipment. Which again, argues for Callisto as a first target.

Quote
Quote
Since you skimmed the book chapter from the most important book on Jupiter, you may have missed the conclusion:

I haven't missed that. I never said Callisto isn't worth exploring. I'm saying it's not a substitute for Europa. It's certainly off topic for this particular thread.

The whole topic of landers on Europa versus Callisto versus Ganymede is moot anyways. We won't be able to do real prioritizing until we get high-rez maps of all the Moons. Too bad JIMO got cancelled. (Now why did that happen??)
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Offline spectre9

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Re: Current NASA studies of the Europa mission
« Reply #38 on: 01/10/2012 11:38 pm »
I think Ganymede has a liquid ocean beneath the surface too.

Magnetosphere, Smooth surface features?

I found this report.

Oceans in Europa and Callisto:
Independent Evidence from
Magnetic Perturbations

Quote
Of the
two icy Galilean satellites, it would be more plausible for Ganymede to have a subsurface
liquid water ocean. Ganymede is completely differentiated and extensive endogenic
modification of its surface and the existence of an intrinsic magnetic field’ imply a
dynamic interior in the past and even to the present28, Perhaps Ganymede also has an
internal liquid water ocean if Callisto has one, but Ganymede’s intrinsic magnetic field
obscures any induction signal.

Offline alexw

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Re: Current NASA studies of the Europa mission
« Reply #39 on: 01/11/2012 04:53 am »
Not an exact substitute (nothing ever is), but we've never landed on any icy moons at all (unless you count Titan, but that seems like a stretch).
Why is Titan a stretch?
  Titan's got that lovely thick atmosphere, which permits energy-shedding techniques like heat shields and parachutes and (one day perhaps) balloons.  The true icy moons require propulsive, or, uhh, lithobraking.
     -Alex

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