The big problem I see with the "cryobot" is that it would probably immediately get swallowed by a Europan fish.

Well, it should send back some really good data then, shouldn't it? [img]/phpBB/images/smiles/icon_wink.gif[/img]

I've heard or read somewhere that melting your way through the ice is actually a very bad idea.

1) Obviously melted (and possibly very hot) water can corrode metals, though this is likely not to interfere with something as robust as a landing spacecraft. Any idea on what the salt content is in Europa's crust?

2) Liquid water can short electronics, should a breech ever occur. Not likely though.

3) Melting burns away any signs of life: live organisms or fossils. Wouldn't that be embaressing?

4) If you melt your way through you must combat boancy effects created by the surrounding water. As the ice melts it expands up into the shaft, and tries to push the cryobot back up. In order to negate this the bot may need an engine to force its way down, and that means more power, which means heavier and costlier.

5) Melted ice is very likely to refreeze. This could create an underground pocket of high pressure which could cause cracking along the shaft, which may disrupt the drilling process.

Sure the cryobot as it is sounds fast and "cool", but maybe one with a slow drill is safer and more science-worthy.

Once you melted the ice into water, you wouldn't continue to heat it. So, the water temperature would be rather predictable at around 0 degrees Celsius.

Water is denser than ice (which is why ice cubes float). Melting the ice into water would cause it to contract.

I would assume the biggest problem with melting your way through the ice would be the ENORMOUS amount of energy it would take.

Imagine you had a block about 1 foot on a side. Now, take your hair dryer and melt it.
How long and how much energy would that take?

The probe would possible have to melt through hundreds or thousands of feet of ice. You can't put that much energy in a battery.

- Mike Allen

[quote]
On 2001-12-21 18:23, mallen wrote:
A fair point. I'll give you that one.


The bot would certainly be denser and sink, water would be forced to move up to the shaft, in other words, the bot will be at the bottom of a pool. Expands was probably not the best of words there. I wonder what would happen if the water that floats up refreezes too quickly and traps the rear/top of the bot?

It's supposedly nuclear powered, but your point remains. You can't melt the ice to just over 0 C AND do it quickly. It's either going to be very slow or some of that water is going to be very hot. At least with a drill the only ice you affect is directly ahead; heat transmits through the ice and can melt a rather uneven shaft.

You could just give it a warm butt. [img]/phpBB/images/smiles/icon_smile.gif[/img] That would take care of the problem.

Just for fun, I ran some numbers:

Suppose we wanted to melt a hole 1 m^2 to a depth of 3 km. That would involve melting 3000 m^3 of ice or 3x10^9 g.

The surface temperature of Europa is -160 C, and if we assume that the temperature rises linearly with depth up to the melting point, we get an average temperature of -80 C which the probe will have to raise to 0 C and then melt.

Ice has a specific heat of 2 J/gC, so it would take (80 C)(3x10^9 g)(2 J/gC) = 4.8x10^11 J to raise the temperature of the ice to 0 C.

That amount of energy is small, however, compared to the latent heat of fusion (the energy it takes to melt the ice into water). The value for ice/water is 333 J/g, so the process would take (3x10^9 g)(333 J/g) = 1x10^12 J to melt the ice.

For reference, the Space Shuttle expends about 10^13 J on takeoff, so you would need 1/10 the energy used by the Shuttle. And that is if we assume that we are not going to lose any energy into the surrounding ice that we are not interested in melting.

On the other hand, if you simply took the ice and threw it into orbit around Europa, even that would take less energy than melting it. [img]/phpBB/images/smiles/icon_smile.gif[/img]

- Mike Allen

<font size=-1>[ This Message was edited by: mallen on 2001-12-27 21:19 ]</font>

<font size=-1>[ This Message was edited by: mallen on 2001-12-28 07:21 ]</font>

Does anyone know whatever happened to this Europa craft, supposedly it was supposed to be getting to Europa next year - I have a feeling it must have been much delayed or called off all together, anyone know what happened to it?

To me, this sounded like one of the most exciting missions since the Voyagers, seems a pity it has apparently dropped off the radio.

Might have a look for it.

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"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident." Arthur Schopenhauer - renowned 19th Century German philosopher.

The wonders of Wikipedia,

Europa Orbiter

Europa Orbiter cancelled in 2002/03

JIMO

Its replacement, the JIMO (Jupiter Icy Moons Orbiter) cancelled in 2005 - even though it wasn't planned to be launched until 2017 at time of cancellation! So, even 12 years ahead of time they're cutting back and cancelling projects - disgraceful really.

These are exactly the type of missions that really create a lot of public interest, much more so than something like Chandra for instance. Anyway.

Only Jovian mission coming up we have to look forward to is now Juno. Well, at least there's something on the drawing board, although it doesn't seem as exciting as those that fell before it.

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"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident." Arthur Schopenhauer - renowned 19th Century German philosopher.

Any mission named after a good synthesizer is a good mission .

I'd love to see a proper landing mission on/in Europa.

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I realize this is a moot point since the mission has been cancelled, but my guess is that if we ever did send a probe to bore through Eurpa's ice, it would bore a much smaller hole. With progress in miniturization, I would think you could do the job with a hole on the order of a few (maybe 5) centimeters diameter.

This would reduce your energy requirements by 5 orders of magnitude. Still a hefty energy bill, but nothing like the numbers for a meter diameter hole.

Apart from ecological concerns what would be wrong with dropping a bomb on europa to make a fissure in the ice (I know there's no oxygen...but a nuke would do) and then dropping a probe in and going swimming?

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The nuke would contaminate the environment we intend to measure, *and* would probably not come close to getting all the way through the ice layer, which is thought to be several ten of kilometers thick, based on some craters on the surface.

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"The cryobot would melt its way through the super-cold surface using nuclear power, he said."

Uh-oh...

The anti-nuke folks are going have a field day with this one. This time about intentionally contaminating another world.

I can see the headlines now:

NASA intentionally crash-lands a nuclear reactor on Europa.

The entire under-ice life permanently contamined, possibly killed, by E3.

Etc.

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Yeah but but ...they can't just funnel the money into Cowboys in Space at the expense of good science. Right? These projects will take a significant lead time. We'll be old. Or werse. Shouldn't we become a lobby or something? For the same investment you can either have a Phoenix on Europa or a 4 slice toaster on Moonlab 2021, know what I mean? How many of you don't believe in robots?

That ionizing radiation at the surface of Europa, Helium nuclei juiced up to MeV's. The flux is intense. 10 million RADs. Isn't there a way to harness that energy to melt ice? A flux capacitor is out of the question, but there must be a way, eh?

My solution is, why melt through? Simply have an impact penetrator create a hole and just drop through the resulting slush. Any small meteor would do, and they're like a dime a dozen in our solar system.

Ok, ok - go ahead and sit there warming your buns on the ice if you must... But I can see it now - one burp and you'd be frozen in ice for a long time.

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I am Mugs, of the Alien clan of Usa, Nordamerica, a Terran, of Sol.

"A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort." - Herm Albright

An impactor does sound better and the deep impact experiment worked a charm. Plus it would be fairly easy to collect samples lofted into space. Also, I keep wondering how frequently a melting event occurs. Has that been determined? If a significant surface area melted, then you would have liquid water exposed to very low pressure. What would happen? Would Europa suddenly develop a temporary water atmosphere until everything refroze? If that happened today I guess we wouldn't know, unless Hubble got onto it, right?

i saw something a while back on tv or on the internet or somewhere where they were showing off some protoype Europa landers melting thru the ice in antarctica to get into the lakes under the glaciers.
it was kind of neat. the thing just kind of sank into the ice.
one thing i'm wondering, tho, is what happens to the water above the probe after it melts? does the probe just sink deeper into the ice, with the water freezing above it?
or does the water instantly boil off into space due to the lack of an atmosphere? this would leave a nice emtpy shaft until the probe got thru and the water below rushed in to fill it- probably spitting the probe right back out..

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No need to boil off the water, or even keep it all melted.

The distance in melted water beneath the probe will be measured in milimeters. But the distance above it could be several meters, until it refreezes, while the distance to the sides will be milimeters to less than a meter.

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"A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort." - Herm Albright