Inventor preps robot to cut through ice on Europa

Apr 22, 2012 by Nancy Owano weblog
Inventor preps robot to cut through ice on Europa
Credit: Stone Aerospace

(Phys.org) -- Robots are being developed all the time to do what we wish and to go where we can’t. This week, inventor Bill Stone told attendees at NASA’s Astrobiology Science Conference in Atlanta that he intends to get an autonomous robot ready to visit the icebound sea of Jupiter’s moon Europa, cut through the icy crust, and explore the waters below. He told the participants that his goal is to send his robot Valkyrie to Europa, where it will use lasers to cut through the ice to explore the waters below, collecting samples, in search of life. His company, Stone Aerospace, has been working on the six-foot by ten inch robotic cylinder called Valkyrie.

The plan is for it to leave its power plant on the surface of the moon, with a high-powered laser travelling down miles of fibre-optic cable. “Our modest goal over the next three years is to use a 5,000-watt laser to send a cryobot through up to 250 meters of ice,” Stone said at the Atlanta assembly. If successful, Stone’s concept would resolve obstacles in the way of studying what may lie beneath Europa’s ice. A report in Wired says those obstacles include (1) solar power being unable to work below the surface (2) batteries not lasting long enough (3) too large a footprint of a device and (4) international treaty restrictions that would forbid testing of a nuclear robot.

Stone has a 2013-2014 dress rehearsal planned. He intends to test a working cryobot at Alaska’s Matanuska Glacier in June next year, where it will attempt to cut through ten to fifty meters of ice. Afterward the cryobot will try to get through 200 meters in Greenland, in fall 2014.

Last year, Stone announced that NASA awarded Stone Aerospace four-year, $4M funding to continue development of the Valkyrie project, to design and field-test an autonomous ice penetrating cryobot. Stone, who has a doctorate in structural engineering, is no stranger to such ambitious undertakings.

Generally, Stone is known for his inventions designed to enable humans to explore remote environments. He formed Texas-based Stone Aerospace to commercialize his systems for exploration. He and a team of researchers from several universities built DepthX, a deep-diving that went down Mexico's deepest watery sinkhole. He and his team also took on a mission to Antartica. He is often characterized, however, as looking toward his ultimate goal, a probe that can go through miles of ice on Europa and then explore through the sea. What intrigues scientists about Europa, one of ’s moons, is that under its icy surface its expanse of water might harbor life.

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User comments : 52

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Torbjorn_Larsson_OM
5 / 5 (6) Apr 22, 2012
This is an ingenious invention. I don't know if it is simpler and/or more efficient than an electric heated probe, but I assume the wire losses can be kept down and we are talking many km here. For Europe, maybe 100 km (!).

[What is up with the quaint and rare US measures anyway? I had to translate that to international standard measures to get a grip of the dimensions here.]
Raygunner
5 / 5 (3) Apr 22, 2012
I would assume that the fiber/power cable is pulled from the surface as the probe descends. I would also assume that the liquid melt from the probe laser would re-freeze within 30 seconds behind the descending probe, thereby encasing the cable in solid ice and locking it in place. The only solution would be to coil ALL of the cable in the top of the probe and spool this out as the probe descends - that's a lot of cable but doable. I assume this is what they have planned but I didn't see it mentioned in the article.
Lurker2358
1.6 / 5 (13) Apr 22, 2012
Ray:

They really don't know what they're getting into.

Europa is way, way colder than the coldest night in Antarctica. The maximum temperature on Europa is 61k colder than the record low temperature in Antarctica.

5000watts is NOTHING for a laser out there.

It will take 130 seconds to melt one LITER of ice at that temperature, even ignoring heat losses, and you have to figure the heat will want to travel into the surrounding ice after a certain point, before continuing to produce melt-water...

Additionally, they'll need to be able to pump enormous amounts of heat, probably through hot air or water, over the machinery at all times to prevent any parts being seized from the re-freezing of the water which will no-doubt splash around, and eventually cover the entire mechanism anyway.

Even if the reel is on the tunneler, it will be in serious trouble, because the water will try to very quickly re-freeze on contact with anything like that.
hopefulbl
not rated yet Apr 22, 2012
probably looking at kilometers of ice, anyway
Lurker2358
1 / 5 (9) Apr 22, 2012
What I would do, depending on power supply, is build a cylindrical shaped vacuum tube to serve as a casing for the bore hole. The bottom and top will be open, but the sides will be vacuum insulated to limit heat loss in the bore hole.

In the center would be a graphene heat exchanger which melts the ice through contact.

Water is pumped out of the bore hole through vacuum insulated tubing (with the inner pipe coated with a graphene heat exchanger to pump heat into the fluid in the tubes to prevent it from re-freezing before it is discharged. The water is then pumped into a container, or better, just sprayed onto the surface of the moon, where it will re-freeze.

This method would avoid any possible seizing, since it provides a way to remove the water from the bore hole, instead of just diving underneath it and hoping to keep going deeper.

The vacuum tube only needs to be a few feet long, since it only needs to confine the heat in a small area long enough for the liquid water's removal
antialias_physorg
5 / 5 (3) Apr 22, 2012
but I assume the wire losses can be kept down

We'll probably want some losses (or switchable losses, which is possible with fiber optics). As Raygunner points out the possibiity of getting stuck is a real probolem.

Alternatively the spool of wire is contained in the robot - but I don't know if we could cram that much into this contraption)


Europa is way, way colder than the coldest night in Antarctica. The maximum temperature on Europa is 61k colder than the record low temperature in Antarctica.

Which is good. The ice will be much dryer and better to get through.


It will take 130 seconds to melt one LITER of ice at that temperature,

There's no hurry once the probe lands. Slow and steady wins the day in space exploration. Always.
Lurker2358
1.4 / 5 (10) Apr 22, 2012
probably looking at kilometers of ice, anyway


Prevailing theory is tens, even scores of kilometers of ice.

Plus, we don't even really know how ice behaves in crystals at such low gravity levels and almost no atmosphere. We assume it's a crystalline form, but who knows? maybe it forms as nothing more than an unstable pile of powder held together only by gravity?

there's been countless experiments with aircraft and ISS and space shuttle, but that's not the same thing as a 0.1g moon with no atmosphere.

If it is an unstable pile of powder, then a bore hole might not work at all, because the walls may collapse like a pile of sand, in which case you'd need a permanently walled "well" type bore hole, which would be exponentially more expensive to do.
RealScience
4.2 / 5 (5) Apr 22, 2012
@L2358 - Valid points in your first post, it will be challenging.
But why do you assume that 'they really don't know what they are getting into'? The inventor has set world records before, so rather than concluding that you have seen more in a few seconds than he has seen in a few years, look for other possible explanations.

In this case the article is very short on details.
For example, they could use pulses of power to melt a few hundred nanometers of water all around the probe and a few tens of microns underneath it, and then have a piezoelectric actuator push the probe forward, humming at perhaps ten pulses per second.
That would greatly reduce the thermal conductivity losses.
Also, although the article says 5 kW for the tests here on earth, it doesn't say that that's what they'll use on Europa maybe 5 kW is scale down because the ice is warmer here, or because the distance is so much less.
RealScience
5 / 5 (3) Apr 22, 2012
@L2358 - there is decent pressure even a few meters down even under low gravity, and we know from the ridges that the ice near the top is mechanically stable.
A bigger question is near the bottom, where a mixture of dissolved salts may leave the ice too mushy to re-freeze. But then the probe can conserve energy and just sink through the mush (I hope that it has a 'swim bladder' so that it can control the stress on the optical fiber).

@AA - If they tried keeping the spool on the surface then the whole length would have to have a film of melt, in which case Lurker's thermal conductivity argument would be a show-stopper. Making the cylinder six feet tall gives it room to hold tens of kilometers of fiber.
RealScience
4.6 / 5 (13) Apr 22, 2012
@L2358 - yes, 5 kW is for a 'sub-scale variant', according to their web site.

http://www.stonea...nded.php

Here's some free advice for you:
If your quick calculation disagrees with years of work of experts in the field, it doesn't mean that you are wrong.
But it also doesn't mean that the experts are wrong.

First check your math (in this case correct), then check whether you have all the information (in this case, no), and then check their math.
If you still have a discrepancy, politely ASK others to help explain it, for the chances are still better than 50-50 that you are missing something.

Can you please try that for a year and see how it goes?
Thanks.
axemaster
2 / 5 (4) Apr 22, 2012
I have serious doubts that a 5kW laser is even close to enough...
Lurker2358
1.1 / 5 (8) Apr 22, 2012
Realscience:

The article you linked to doesn't give any specifications of what the target power for the final design might be.

Moveover, if you aren't using true "nuclear" power, you're better off just using direct thermal energy, like a heat exchanger.

In order to power a 5kw laser you'd need as many RTGs as every space probe ever launched combined, when you may as well skip the laser and use the heat to melt the ice directly.

Unless you plan on shipping a couple tons of chemical fuels.

Last I checked, the solar constant out there is like 1/25th that of Earth, so to make a 5kw laser from solar power you'd need a panel about the size of a football field, so that's out of the question...
plasticpower
5 / 5 (5) Apr 22, 2012
Nobody has mentioned the fact that melted water will evaporate into the "vacuum" that's Europa's atmosphere. It won't linger and freeze over. It will act a lot like "dry ice" up there. In fact, once they breach the ice to get to the liquid water underneath I suspect they're gonna have a geyser on their hands. That's where they'll need to plug the hole with something, which only then will lock the cable in place.
Lurker2358
1.4 / 5 (9) Apr 22, 2012
Nobody has mentioned the fact that melted water will evaporate into the "vacuum" that's Europa's atmosphere. It won't linger and freeze over.


Really, this would need to be tested in a vacuum chamber in free-fall.

Europa's water isn't going to be pristine, it's going to be dusty from comets and micro meteors and such.

When it contacts a solid surface, I suspect it will re-freeze on contact, given the absurdly low temperatures involved.

Obviously, it froze on contact the first time to make the moon...
Jeddy_Mctedder
1 / 5 (3) Apr 22, 2012
let's see this guy try a prototype on the edge of greenland. i doubt he'd get though the first 500 feet of hardened ice on top of a 2000 foot deep ice sheet.
nkalanaga
5 / 5 (2) Apr 22, 2012
Lurker2358: It was probably frozen before contact when the moon formed. Jupiter is well beyond the "snow line", so any water out there would be frozen to start with. Heat from impacts and contraction would melt enough of the moon for it to differentiate, but it likely never had liquid water at the surface, except maybe in cracks in the ice.
antialias_physorg
5 / 5 (5) Apr 22, 2012
Really, this would need to be tested in a vacuum chamber in free-fall.

Why? Europa pulls 0.134g. Free fall is way too stringent a test.


When it contacts a solid surface, I suspect it will re-freeze on contact

That really depends on the pressures involved. The atmosphere of Europa is barely above vacuum. So we might see some sublimation. But given that the thickness of the bore will be that of the cable (and the cable will be blocking that) I wouldn't expect a 'geyser' (or even a trickle).

hopefulbl
not rated yet Apr 22, 2012
the only thing that would happen is sublimation

From looking at the phase diagram for water it looks like for sublimation of ice to occur the pressure must be below .006atm
Sonhouse
not rated yet Apr 22, 2012
If enough energy is available to really melt the ice and the borehole freezes over, you might still have a small tube going the full length, 20 Km, whatever, that is in the borehole but still transmitting the optical power to keep it going down.

My guess is it would take a colony on Europa to do the job, you couldn't just send a couple of astronauts and a box of parts....

If the borehole refreezes and you reach the underside liquid and then have a sample ready for ascent, you can still run the thing in reverse, melt the ice ABOVE you just as you melted it below you on the way down. It still sounds doable if you have enough billions to spend and the political will to do it.
jamesrm
5 / 5 (4) Apr 22, 2012
http://www.wired....a-rover/ for anyone actually interested in what the cryobot is rather than what you imagine. And some one say Graphene a few more times, it makes you sound clever.
THENAMEIS_____
1 / 5 (1) Apr 22, 2012
SEXY :D
I love when new ways help out space exploration and life discovery other than on earth
RealScience
5 / 5 (3) Apr 22, 2012
Realscience:

The article you linked to doesn't give any specifications of what the target power for the final design might be.


I didn't see it anywhere in a few minutes of searching.
They may not have decided yet. Let us know if you find it.


Last I checked, the solar constant out there is like 1/25th that of Earth, so to make a 5kw laser from solar power you'd need a panel about the size of a football field, so that's out of the question...

With low gravity and no wind, a gossamer mirror could concentrate the sunlight as much as is needed - say 1000x, to 40 times stronger than on earth. And to cool the array, melt ice.

Not knowing what they plan to do does not mean that they don't have viable plans. It means that we we don't (yet) know.

El_Nose
5 / 5 (1) Apr 23, 2012
-- don;t know if it's been said -- but lets hope Greenland still has 200 meters of ice when the time comes to test
Llewellian
not rated yet Apr 23, 2012
There is only one problem: The lifting capactiy of the rope going down. It is even vital that the molten ice refreezes above the robot to support the rope with the fibreoptic.

I am not talking about the robots weight, it will sit on the ice. But which stuff can hold 10 km and more length of its own weight, loosely hanging. At -200 Celsius? Even if we count in the much lower gravity.
antialias_physorg
not rated yet Apr 23, 2012
But which stuff can hold 10 km and more length of its own weight, loosely hanging. At -200 Celsius?

That could be countered by minimally weaving to and fro.


With low gravity and no wind, a gossamer mirror could concentrate the sunlight as much as is needed - say 1000x

Don't know the numbers, but Europa has a big source of radiation hanging in the sky.
http://www.boston...ter.html
And since Europa is tidally locked it may be feasible to have 'solar' (or rather 'planetary') panels pointing at Jupiter?

javjav
not rated yet Apr 23, 2012
Better use a Plutonium head or other radioactive material. It would provide enough heat to liquefy ice and to produce electricity. Regarding communications, I am wondering if it would be possible for the probe to polish ice walls all the way to create a reflective tube made of ice, to route signals all the way to the surface.
RealScience
not rated yet Apr 23, 2012
@Llewellian - Not a problem. Ultra-pure silica glass optical fibers) can support ~4000 km of their own weight on Europa's surface. And the hole would refreeze anyway. (And as you point point out, the robot itself doesn't have to be supported. If the robot is close to the density of ice, it will float even after it breaks through).
RealScience
not rated yet Apr 23, 2012
@antialias - While the light would be constant, even if Jupiter were a perfect mirror, the light reflected from it would be less intense than the distant sun (spreading due to Jupiter's curvature). And with Jupiter's sizable optical diameter, the light couldn't be focused much for CPV.

But a gossamer blanket spread out on the surface would catch both, powering the electronics at 'night' by Jupitershine and powering the melting in the day by sunshine.

30% efficient epitaxial lift-off III/V cells would require 80,000 m2 for 100 kW to power 20 kW (guess) of laser. If made with 1 micron of semiconductor on 5 microns of plastic for ~15 g/m2 that's 1.2 tonnes. Add some wiring and it is probably 1.5 tonnes, which is doable. The radiation would kill it after a few months, but that's ok.

Still a good engineering challenge, though!
RealScience
not rated yet Apr 23, 2012
@javjav - yes, since heat is the main product needed, radioisotopes would make sense. Test it in Antarctica with something else, and then run it with a few-decade-half-life isotope on Europa.
nkalanaga
5 / 5 (1) Apr 23, 2012
For those wondering how it will get back up, are they even planning to return to the surface? If the robot can analyze what it finds, all that will be needed on the surface is the power supply and communications. They're certainly not returning anything to Earth, so putting the computers at the bottom would provide more radiation protection.
Cynical1
1 / 5 (2) Apr 23, 2012
@javjav - yes, since heat is the main product needed, radioisotopes would make sense. Test it in Antarctica with something else, and then run it with a few-decade-half-life isotope on Europa.

Not an astro engineer so this might be a dumb question, but... Wouldn't radioactive isotopes present a health hazard to any organisms that MIGHT be there? Plutonium was mentioned in an earlier post. Are there isotope species whose decay might be less injurious to cellular life forms?
TheGhostofOtto1923
1 / 5 (4) Apr 23, 2012
" (4) international treaty restrictions that would forbid testing of a nuclear robot."

A nuclear-powered probe would make much more sense and I cant see that some outdated treaty would prevent nuclear power from being used to explore the solar system, thereby rendering such unwieldy compromises as the above little more than an interesting exercise.

As the russians are working on nuclear propulsion I wonder if such a treaty even exists?
http://en.wikiped...elopment
antialias_physorg
not rated yet Apr 23, 2012
powering the electronics at 'night' by Jupitershine

Since Europa is tidally locked we'd have always 'Jupitershine'. And I'm under the impression that Jupiter is a source of radiation (not just a reflector of sunlight)

Better use a Plutonium head or other radioactive material.

This is expressly prohibited (by internatinal treaties and also by the mission profile which does not want to contaminate anything they find)

For those wondering how it will get back up, are they even planning to return to the surface?

No. That's not part of the plan. What would you want to bring it back up for? Better to have something sitting on the surface than to risk losing all the data on the way back up. Especially in light that engineers could update software or try other fixes if they have continuous communication with the probe head.
Cynical1
1 / 5 (2) Apr 23, 2012
Hmm.. Learned something new. I thought nuclear space treaties only applied to weaponization.

Your impression is right on, "Jupitershine" should be a fairly viable energy/radiation source inasmuch as Europa lies within the roughly 300k miles of "radiation belt" surrounding Jupiter, but at 270k miles distant, not so close as to pose immediate destruction risk to a collection device. Which prompts the question - are there radiation collection units similar to solar collection ones, available? Could be a whole new job market.
As to bringing a probe back up - would likely require leaving a bore hole, wouldn't it? And, if pressure is higher in the interior (likely) you would have a geyser shooting it back up before you got to make any observations. Lots of time, money and bottled-up curiousity lost.
As Real Science said - would require some interesting engineering.
javjav
not rated yet Apr 23, 2012
This is expressly prohibited (by internatinal treaties and also by the mission profile which does not want to contaminate anything they find)

International treaties do not apply to space missions. Cassini is powered by plutonioum, and also the ongoing New Horizons mission to Pluto. And more Plutonium production for space purposes has been already approved.
Regarding contamination, what has to be avoided is contamination with earth live, which is not the case (in fact plutonium may help to sterilize the probe..). In addition, the same plutonium could produce electricity for an ion engine during the travel, and then to produce heat on Europa and also electricity for electronics and communications. It can solve several problems. But the remaining problem is how to communicate with the surface, my question is if it would be possible to build a communication channel primarily made of ice, maybe polishing ice mirrors or building an ice metamaterial with the appropriated structure
RealScience
5 / 5 (1) Apr 23, 2012
Cynical, javjav, Ghost, etc. - the treaty banning nuclear applies to testing the device in Antarctica, not to using it on Europa.
So test with some other power source (24/7 solar in the antarctic summer, diesel, whatever), and then go nuclear for Europa.

Cynical1 - yeah, the Europans might be peeved about the radioactivity. But one 6' x 10" cylinder putting out a few tens of kW for a few decades in an ocean volume bigger than all Earth's oceans isn't much.

@javjav - the optical fiber will extend all the way to the surface, unspooled by the device as it descends.
TheGhostofOtto1923
1 / 5 (4) Apr 23, 2012
Cynical, javjav, Ghost, etc. - the treaty banning nuclear applies to testing the device in Antarctica, not to using it on Europa.
So test with some other power source (24/7 solar in the antarctic summer, diesel, whatever), and then go nuclear for Europa.

Cynical1 - yeah, the Europans might be peeved about the radioactivity. But one 6' x 10" cylinder putting out a few tens of kW for a few decades in an ocean volume bigger than all Earth's oceans isn't much.

@javjav - the optical fiber will extend all the way to the surface, unspooled by the device as it descends.
I figured but why not in some sovereign country? Test it in greenland or somewhere else above the arctic circle.
ziphead
1 / 5 (4) Apr 23, 2012
Nobody has mentioned the fact that melted water will evaporate into the "vacuum" that's Europa's atmosphere. It won't linger and freeze over.


Really, this would need to be tested in a vacuum chamber in free-fall.

Europa's water isn't going to be pristine, it's going to be dusty from comets and micro meteors and such.

When it contacts a solid surface, I suspect it will re-freeze on contact, given the absurdly low temperatures involved.

Obviously, it froze on contact the first time to make the moon...


serial pest know-it-all
nkalanaga
not rated yet Apr 23, 2012
Antlias: That was my thought also. Unless one plans a sample return mission it's better to let the hole freeze and do the analysis at the bottom.

As for nuclear power, it's fine in orbit, but there are treaties banning contamination of any body which may reasonably have life. Since we're going to Europa specifically to look for life, nuclear power would be forbidden on the surface.

That's one reason everything sent to Mars is sterilized to the best of our ability, and why Galileo was crashed into Jupiter. It hadn't been sterilized, and NASA wanted to avoid possible contamination of a moon. I'll admit, after years in Jupiter's radiation, it was probably cleaner than any clean room on Earth, but one never knows what might survive.
javjav
not rated yet Apr 23, 2012
As for nuclear power, it's fine in orbit, but there are treaties banning contamination of any body which may reasonably have life. Since we're going to Europa specifically to look for life, nuclear power would be forbidden on the surface.


No, this is not true at all. As an example, the next rover landing in Mars is nuclear. And indeed it is looking for traces of live. Again: what is forbidden is contamination with earth live, not the usage of radioactive isotopes.
nkalanaga
not rated yet Apr 24, 2012
Javjav: OK, my source was incorrect then. As you say, if we can send a nuclear rover to Mars, it would be legal on Europa.
antialias_physorg
5 / 5 (1) Apr 24, 2012
International treaties do not apply to space missions.

Why not? The Outer Space Treaty says:
"States shall avoid harmful contamination of space and celestial bodies."
Leaving a plutonium powered piece of metal floating around Europa's possibly life bearing oceans until it falls apart would qualify - in my book - as 'contamination'.

Mars isn't life bearing. So the what constitutes 'contamination' is debatable.

Cassini is powered by plutonioum, and also the ongoing New Horizons mission to Pluto.

Cassini doesn't land. Neither does Horizons. (The Huygens lander did not contain radioactive material).

javjav
5 / 5 (1) Apr 24, 2012

Mars isn't life bearing. So the what constitutes 'contamination' is debatable.

What? the unique purpose of the Curiosity rover is finding LIVE traces on mars!, either ancient live or present, and it is using plutonium as fuel. A Plutonium capsule is less contaminant than other fuels like Hydrogen Peroxide or Hydrazine. And a small Plutonium 238 capsule is not so bad, we are not talking about a fission reactor or a nuclear bomb. Plutonium 238 just radiates energy and stays warm, and it does not recombine chemically like the other fuels.
Solar is not a real option on Europe, and the other proposals are based on chemical fuel cells which seem much more contaminant to me.
TheGhostofOtto1923
1 / 5 (4) Apr 24, 2012
Leaving a plutonium powered piece of metal floating around Europa's possibly life bearing oceans until it falls apart would qualify - in my book - as 'contamination'.
There are plenty of radioactives on all the planets. There are plenty in our own oceans, including plutonium. "4.6 billion metric tons of uranium are estimated to be in sea water..."

Earth life on europa would be a problem, unless we are actually trying to seed the planets, and then it would be a good thing. Because you know, colonization and resource acquisition would be problematical unless these bodies were already 'accidentally' contaminated by previous generations, yes? And as we know, spreading ourselves around the system is absolutely Essential to long term survival. THE #1 Priority.
Mars isn't life bearing.
Mars is most likely life-bearing, and habitable. The fact that we continue to dump objects on it which crash and roam all over the place is somewhat suspicious.
antialias_physorg
5 / 5 (1) Apr 24, 2012
There are plenty of radioactives on all the planets. There are plenty in our own oceans, including plutonium. "4.6 billion metric tons of uranium are estimated to be in sea water..."

Though not in a concentration that will threaten any one eco system. Imagine the runoff from Fukushima: while certainly much less than the above number it did contaminate fish in a region around the powerplant.
Similarly with introducing a very concentrated source of plutonium (which - at least to Earth life - is chemically toxic in even the most minute quantities. Much worse than its radoactive effect, BTW)

Now for the crazy part: If Europa's oceans did harbor advanced life of some kind, then our first calling card probably shouldn't be some toxic bomb.

Mars is most likely life-bearing, and habitable. The fact that we continue to dump objects on it which crash and roam all over the place is somewhat suspicious.

Whut? Explain.
Cynical1
1 / 5 (2) Apr 24, 2012
Mars is most likely life-bearing, and habitable. The fact that we continue to dump objects on it which crash and roam all over the place is somewhat suspicious.


I tip a cynical hat to Vendicar.
Cynical1
1 / 5 (2) Apr 24, 2012
oops. I meant Otto.
antialias_physorg
not rated yet Apr 24, 2012
And I'm certain the fact that Mars is
- on of the closest planets to Earth
- has an atmosphere that allows some atmospheric braking
- a bit of gravity
- a bit of variety in the landscape
- and a surface AT ALL that we can roam on about
has absolutely nothing to do with it that we're sending most of our planetary explorers there.

Where else would you send them?
Mercury? Harsh radiation and temperature environment.
Venus? Killer atmosphere. No chance of roving, much less seeing anything when you're down there.
Saturn, Jupiter, Uranus, Neptune: dito (and also killer gravity/pressure and very far away by comparison)

Mars is easiest - by a VERY long shot - save for the Moon. The moons of Saturn and Jupiter are already an entirely different order of difficulty.

There is no conspiracy here - just commmon sense choices.
TheGhostofOtto1923
1 / 5 (4) Apr 24, 2012
Where else would you send them?
Mercury? Harsh radiation and temperature environment.
Venus? Killer atmosphere. No chance of roving, much less seeing anything when you're down there.
Saturn, Jupiter, Uranus, Neptune: dito (and also killer gravity/pressure and very far away by comparison)

Mars is easiest - by a VERY long shot - save for the Moon. The moons of Saturn and Jupiter are already an entirely different order of difficulty.
Sure. And this is why we are prepping it for habitation pragmatically.
just commmon sense...
mmm... the inverse of WWW... VIVIVI... 666...
Hmmm I think aunti knows more than he is letting on...
TheGhostofOtto1923
1.8 / 5 (5) Apr 24, 2012
Though not in a concentration that will threaten any one eco system. Imagine the runoff from Fukushima
OH COME ON. Snap out of it. A few pounds of plutonium in millions of cubic miles of ocean.
nkalanaga
not rated yet Apr 24, 2012
Antlias: Add to Mercury "Requires more energy (delta V) to reach than any other planet or moon in the Solar System." If travel time isn't an issue, it takes less energy to reach another star than to go into orbit around Mercury.
RealScience
5 / 5 (1) Apr 25, 2012
I'm all for treading gently, so I'm surprised that I agree with Otto's stance. But really, encase the Pu-238 in ceramic beads - Si3N4 is mighty durable and will last many times Pu-238's 88 year half life, even in a strong brine.