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Comment by dylan604 | Hacker News Reader

That would be a lot of power required to prevent refreezing. If we're just throwing nonsensical ideas out, why not drop your probe down one of the geysers? Let the planet make the holes for you. You just need to make it so it doesn't get blown out each time the planet/moon sneezes. Of course, because I used the hand wavy word just means you automatically get to triple the cost estimate.

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Would refreezing break the cable?

If you build the probe so that it has the spool of cable in it, then the probe has to be as large as the full load of cable. If you make the probe just big enough to do what it needs while pulling the cable from the lander then it can be much smaller. If using the smaller probe, then the cable will need to be fully movable as it melts deeper. The larger probe with the full length of cable will require much more energy as it needs to melt a much larger hole.

Where is all of this energy coming from?

I think our breakdown in understanding here is our concept of cables. When I say cable (and many others here) I mean fiber optic cable. Even with 25km of fiber optic cable it is rather small and light. Drones, missiles, and torpedoes are already doing this with many miles of cable in a tight space. The issue with this which I am not sure about is the dynamic of the ice on the fiber optic cable and how well it would hold up to refreezing of the ice.

Refreezing isn't the big issue; shifting of the ice (causing physical severing of the line) is. We don't have a great handle yet on how much it moves around.

Yes, I think we definitely have a gigantic misunderstanding of cable here. Mine is based in reality, while yours seems to be very unrealistic. How in the world is a fiber optic cable going to do what needs to be done? Where is the power coming from to heat the probe via a fiber optic cable? Even a fiber optic cable at a length of 25km is a very large spool. If you want the probe to hold the spool and unwind as it goes, it must be at least the size of the spool of cable. If you think this would work with an unsheathed piece of bare fiber cable, then your just not even trying to be serious.

I see another misunderstanding then. With this method the actual probe would use nuclear material to melt its way through the ice. In addition, the heat of the nuclear probe on one side and the ice on another (or melting ice) would make for the ideal conditions of a peltier (or just use a traditional RTG) device to power onboard sensors and electronics. The fiber optic cable is only for communication.

> use nuclear material to melt its way through the ice

All 300 watts of it? It's not going to even make an indentation, let alone through 10s of km of ice.

Simple reactors can be designed to be turned up and down according to need. A 300w RTG is more than enough to run all the necessary electronics. The ice-melting 30,000w+ heater can be a second rector that is spooled up only when ice needs melting.

we're attempting to search for life and the thing you want to do is use radioactive heaters? we deliberately crashed a satellite into the planet to avoid having it potentially contaminate the moons we are curious about, and yet you're thinking they'd just irradiate everything like this? it's really just not logical

In the outer solar system, under miles of ice, in total darkness and cold .. it is nuclear or nothing. Short of antimatter batteries, there is no other source of power that would be even theoretically suitable.

The concern is more spreading Earth life. NASA's Planetary Protection team (which is a delightful job title) is largely concerned with sterilizing stuff we send out so any discovery of microbes on Mars doesn't turn out to be hitchhikers.

Even a fully fleged nuclear reactor isn't gonna do much damage to Europa and potential life. Swimming in a nuclear reactor's fuel pool is quite safe; water's some of the best shielding we have. https://what-if.xkcd.com/29/

> Where is all of this energy coming from?

A nuclear reactor, probably.

https://en.wikipedia.org/wiki/Radioisotope_heater_unit

Really? To heat and melt sufficient ice around 25km of cabling? I don't know what temperature this ice is at, I think on the surface Europa averages around -300F, so it's probably at least that low. I guess a lot is going to depend on whether you're fine with the ice refreezing around the cable - if the ice shifts at all, the cable breaks. Keeping the whole thing heated continuously seems implausible

that would surely mess with any organics you might want to find

No, not really. Water is very effective shielding, and you could melt a base station through the ice and do exploration with subs it sends out if you want fairly pristine samples. In the Jupiter system, it's also hardly the biggest radiation source around.

The spool can be a long, thin "pipe" of wound cable that goes with one end of the "pipe" pointing to the rear (up). You can put an arbitrary amount of cable in a given hole diameter by making the spool taller.

(Google image search suggests that a similar approach has been taken by the TOW, it's not a spool that could be reversed by adding a motor to an axis, more like a tightly packed coil that gets straightened as wire is pulled out)

As for the energy, I assumed GP was thinking of solar panels on the surface. I also assume that we share scepticism based on the low sun intensity out in the orbit of Jupiter... (and that's before you even start wondering how much further away from the melting point that ice will be than all ice of conventional human experience)

>You can put an arbitrary amount of cable in a given hole diameter by making the spool taller.

Wouldn't this be limited to the tensile strength of the material and the weight of the cable? Granted, Europa has much less gravity, but 25km is a lot of cable weight.

Consider something as small as fishing line; one online estimate gives it .245g/m. At 25km, that's over 3 tons of line weight hanging down a hole on Earth or nearly 800 lbs on Europa.

The probe bears on the ice below it and the cable gets held by the ice that's re-frozen above the hole.

What you have to worry about is the ice shifting and severing the cable.

I think there are still mechanics at play that would have to be considered.

>The probe bears on the ice below it

This implies it is bearing the weight of the entire cable above it. So instead of the tensile stress being the limiting factor, it's not the compressive stress. If you're intent is to retract the spool, it would still be in tensile stress as it comes up. (And you'd need enough torque to do so. But maybe you the plan would be to abandon in place).

>What you have to worry about is the ice shifting and severing the cable.

I agree, that's a pretty big concern.

Could you embed a series of metallic needles as you melted your way down, then communicate via radio waves that travel needle to needle? They would not need to be connected. Just close by.

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