As already noted, we don’t need to drill through “6 miles” of ice in order to evaluate the ocean environment or potential for conditions which could support life. Even setting aside that particular goal, Europa is interesting for other reasons, and despite the radiation could potentially be a place to house a future crewed outpost underneath its oceans where it could be protected from radiation and provide ready access to water for coolant and various human life supporting activities. Science goals are always somewhat arbitrary–astronomers want more telescopes, planetologists want probes, geologists want rocky moons, exobiologists want water and organic molecules–but Europa is relatively easy to reach and holds a lot of readily accessible information and conditions.
Personally, I’d like to see missions to Uranus and Neptune because of the sparse amount of information that we have about them, but planning and executing a long duration probe to go into orbit of those planets is a rough orer of magnitude more complicated than a Jovian or Saturnian mission, and is unlikely to happen in the foreseeable future.
Rather than use a drill, could they use a heater to melt the ice beneath? Then as the probe descends it spools out fibre-optic cable behind it to the base station. Finally, once the probe breaks through the bottom of the ice, a ROV goes exploring.
It takes way more energy to melt a volume of ice than to remove it via drilling, just as it takes more energy to melt a hole in a thick metal plate than to cut or punch through it.
I wasn’t asking if studying other planets and moons is worthwhile, just if this congressman asked NASA first, or if it’s just cool sounding, like George Bush giving the US a vision of putting men on Mars.
True, but a probe designed to melt its way through thick ice could be a lot simpler than one designed to drill - it could even include a radioisotope heat source and have no moving parts at all.
But sampling one of these squirty jets is a much better idea, IMO - or even just sampling the ice at a site where the ice crust appears to have cycled a bit.
Radioisotope thermal generators provide very low levels of power which would be completely insufficient to melt a significant sized hole through solid ice. As anyone who has worked on equipment or facilities which have to be cleared of ice in arctic conditions is aware, ice is a major problem to both remove and keep clear. The initial concept is always “Oh, we’ll just melt it away with heaters,” and the initial concept almost always end up in the idea ashcan because it will end up taking enormous amounts of power.
Drilling through ice, on the other hand, is a technology we have well in hand. Doing so on another planet increases the complexity to be certain but it is far from the biggest challenge to face. However, I doubt a near term Europa mission is going to have the capability to drill through hundreds or thousands of meters of ice, nor is it really necessary to do good research and get a reasonable idea of what lies beneath Europa’s frozen exterior.
Do we have any idea how ‘dirty’ Europa’s ice is below the surface? Does our drill/heater have to deal with anything from grit to boulders along the way?
Europa’s surface is fairly ‘dirty’. Do we need to assume that we’ll see a similar mix of ice and dirt all the way through? If it’s unevenly distributed, do we have the ability to find relatively clear paths through the ice? Ground penetrating radar or a magnetometer or something like that?
One thing I’d hope an early Europa would achieve is to really characterize the surface and provide the data needed to find the best way through that ice layer - or if we even need to. If the moon is spitting its ocean into space, we might discover life by collecting that water.
Really? Even when the depth is a matter of kilometres, not centimetres? The advantage of melting is that the water freezes above you holding the cable in place.
Why couldn’t you drill and just move the slurry behind you as you descend? Pressure will cause it to turn into solid ice again anyway. You wouldn’t have to have it removed from the shaft.
But even if a drill is more energy efficient, there are significant mechanical issues that would have to be dealt with. Designing a drill that can keep functioning through many kilometers of ice under tremendous pressure seems like a tall order - especially if it has to handle large rocks and things that might be embedded in the ice in its path. A melter is theoretically simpler, I’d think.
We already have drills which can keep functioning after cutting through kilometers of ice, or in fact, hard rock. Deep core drilling is an established technology. Doing so with an automated probe in a vacuum rather than a crew of roughnecks in a shirt sleeve environment is challenging, to be sure, but is probably the most feasible means.
People just don’t realize how much energy is required to melt ice until you look at the latent heat of fusion of water and realize that it is the most difficult of all commonly encountered substances to turn from solid to liquid; its extreme stability is one of the reasons that we look for water as a precursor for life. You would essentially need to have a nuclear fission reactor in the tens of megawatt power output per square meter of forward aspect to make headway through solid ice. Even if you leave the reactor up top and convey power to electric elements via cable, you are still going to end up with a massive, complex system compared to screw or vibratory “plow” type probe.
Maybe I don’t understand the question, but…what? Are you proposing dropping nuclear weapons on Europa in order to attempt to crack open hundreds or thousands of meters thick of ice, with all of the attendant destruction and contamination that would bring?
I wasn’t thinking of melting a hole and keeping it open, but rather, allowing a heated probe to sink through the ice by melting the ice it rests on, then allowing it to refreeze above.
It still requires vastly more energy to completely melt a hole than it does to remove a slush of material by drilling or vibratory methods. This just isn’t a practical proposal, and if you haven’t dealt with ice removal (which I have) then you can’t appreciate the difficulties and effort to remove it via melting by direct heating versus mechanical displacement.
I think the OP’s ambivalence on this point is over whether the level of specificity in Congress’s direction to the agency is stepping too far into the agency’s scientific expertise. By analogy, Congress might mandate that NIH conduct AIDS research, but we would not typically expect Congress itself to pick and choose among specific grant proposals;* after all, the whole point of creating the agency was to delegate authority in such a way as to make use of its technical knowledge.
Personally, I think that the level of direction from Congress regarding the Europa program was at an appropriate level of generality, but I don’t think it’s absurd to raise the question.
I’m not saying that Congress does not have the authority to legislate at that level of specificity; of course it does. I’m just saying it’s not common practice.
Yes. I am thinking a two part probe, with an orbiter and a lander. A small nuke (like those ultralight Pershing and Gryphon warheads) will create a crater. Where the lander can then go and investigate the lower layers thrown up.
I read that in NASA’s final analysis of the lunar missions, they felt that most of the science had come from the orbiting CSM observations and except for the returned rocks, the landing did not return as much data since they needed to dig, which they could not do.
Can you show the math for this please? One being more costly than the other doesnt necessarily mean that the more costly one is prohibitively expensive, especially if other factors are at play in the choice.
The radioisotope method doesn’t seem too bad IMHO.
A 10 cm sphere of Pu-238 weighs about 10.5 kg and generates 5240 W of heat. Supposing Europa is around 100 K, raising the temperature to 273 K and melting it requires 356+334=690 J/g of energy. So, the sphere can melt 7.6 g of ice per second, or equivalently 7.6 cm^3. The cross-section of a 10 cm sphere is 78.5 cm^2, so the sphere can melt through 0.096 cm of ice/s. If the ice is 10 km thick, then it takes 1.04*10^7 s to melt through, or 121 days.
The ice will refreeze above the probe, but it should be able to unreel a data line from below.
