# Energy requirement for melting through five klicks of ice?

1. Oct 9, 2017

### Noisy Rhysling

Related to exploration of Europa: If we elect to send a probe to bore through (guessimate) five kilometers of ice to reach the Covered Seas, and have a diameter of 100 mm and length of one meter, how much energy will the probe require to reach unfrozen areas? AND given that figure, is it currently feasible to build a probe that will have an energy supply to do the boring without supply from the surface? (I assume a line connected to the surface so the probe can report results, but not a power line. Note that the comm line will have to be heated so as to prevent freeze lock and allow the probe to proceed.)

I'm quite willing to expand on the information provided so far, as best I can.

2. Oct 9, 2017

### JRMichler

Diameter 4" times 16,400 feet time 57 lbs/ft^3 = 81,600 lbs of ice to melt. That's a theoretical minimum, the actual would be somewhat higher.

Assume surface temperature -300 deg F, temperature at liquid boundary 32 deg F, and linear variation in between. Then the average ice temperature is -134 deg F. Average specific heat of ice is about half that of water, so (32 - (-134)) X 0.5 BTU / lb-deg F + 144 BTU / lb = 227 BTU/lb to heat the ice to 32 degrees and melt it.

227 BTU/lb X 81,600 lbs / 3412 BTU/kwh = 5400 kwh. That's a theoretical minimum that assumes zero heat loss into surrounding ice. The actual requirement would be at least twice that much. Battery power is not possible. Even 5 km long power cables may not be possible, given that the ice will refreeze behind the probe. It might be possible to melt the ice and pump it up to the surface. That would require an insulated heated tube 5 km long and a pump capable of 950 PSI.

3. Oct 9, 2017

### Noisy Rhysling

Thanks. I'm betting ESA/NASA have done the same math.

4. Oct 9, 2017

### Staff: Mentor

Darn. I learned the neatest word in the 1960s. I've been waiting for more than 50 years for the chance to use that word in a sentence. This is my chance but now I can't remember the word.

Anyhow, the word described a machine that (a) melts the surrounding material, and (b) is self propelled via moving feet that pull on the surrounding solid walls. The material re-freezes behind the device as it passes. A nuclear powered machine like that could burrow its way through Eruopa's ice, grab a sample, then burrow its way back to the surface. No 5 km hole or tunnel is needed.

The article in the 1960s, was the same basic idea, but the application was to burrow a nuclear warhead through the Earth's crust from USA to Russia. It was a silly idea, but they had a very cool word for that type of device. I would be very grateful to any PF reader who can tell me the word that I'm grasping for.

5. Oct 9, 2017

### Noisy Rhysling

I read a story about underground battleships that basically did the same thing.

But as JRM points out, the power supply would be impractical at this time.

6. Oct 11, 2017

### CWatters

Perhaps you could use a heat pump to re-freeze the water behind the probe and move the heat to the front?

7. Oct 11, 2017

### Vitro

There's no new tech needed for such a probe. An RTG (https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator) powered submersible robot could easily melt through the ice sheet and explore around. RTGs run for decades and are old technology that space agencies have long experience with. Not sure how difficult it would be to communicate with the probe from the surface or orbit though.

8. Oct 11, 2017

### x_engineer

The calculation above assumes that the refreezing happens because the heat of melting is lost.
If you use a heat pump that pumps heat from the back end to the front, you just have to compute how much free energy you need to work through that much ice.

If you had 5km of communication line on a spool inside the probe, there would be no need to worry about freeze locking of the comm cable.
Even better, ice is a pretty lossless dielectric, maybe you dont NEED a cable for comm.

9. Oct 11, 2017

### CWatters

Is there a contamination issue? I'm asking not saying.

10. Oct 12, 2017

### Vitro

While one can never say never, from what I've read about them they sound pretty much indestructible, designed to survive a rocket explosion during launch or crashing back to earth from space. A space scientist or engineer can make that call.

Another interesting advantage is that the probe could also melt its way back to the surface at the end of the mission so we don't leave a dead rotting probe polluting the ocean.

11. Oct 12, 2017

### Staff: Mentor

I think you misunderstood. The concern is that a probe will carry with it Earth microorganisms that contaminate the alien climate. We had the same concern about borring through the ice in Antarctica to the ancient lakes below. Sterilization can never be perfect.

If we ever send people to Mars, one consequence would be inevitable massive biological contamination of the planet.

12. Oct 13, 2017

### Staff: Mentor

13. Oct 13, 2017

### Staff: Mentor

Mole sounds apropos, even though the version I read about melted its way rather than burrowing.

Thanks.

14. Oct 13, 2017

### Staff: Mentor

15. Oct 13, 2017

### Staff: Mentor

Wow. Good research. That's very close to a device that could be used on Europa. I wouldn't be surprised if NASA isn't researching things like that.