Probe to the Ocean of Enceladus

[majortom]

Summary:: Speculative question on the feasibility of using a nuclear powered probe to reach the subsurface ocean of Saturn's moon Enceladus.

I was thinking about the problem of how to put a probe in the ocean of Enceladus.
Enceladus is a moon of Saturn which has some interesting properties.
It is thought to have a large subsurface ocean, under 15km+ of surface ice.
And, I thought it would be handy to put a probe there.

The idea I came up with was to use energy from nuclear fission to melt through the ice.
Any thoughts on feasibility? How much fuel would be needed to melt through 15km of ice?
I can't think of any other way to get there. Mechanical boring seems far fetched to me.

 

[berkeman]

Google and Wikipedia are your friends:

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

If melting (and suctioning the liquid waste water) were a better alternative, they likely would have been used here in terrestrial applications.

Probably a better alternative on that moon would be nuclear detonation excavation. But then there is the pesky Prime Directive...

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

 

[majortom]

No, it's a totally different problem. I'm not talking about drilling a shaft. Getting the equipment to do that to Enceladus would be outrageously expensive and impractical.

Also, there's no 15km thick ice sheet on Earth. The scale of the problem is way larger, and the equipment used must be much smaller.

Imagine a device that's simply a big, hot ball bearing. It would melt the ice and gravity would pull it down, no suction needed.
Then, the water would refreeze behind the ball bearing. This could possibly even be advantageous, as it would avoid explosions due to pressure differentials with the shaft.
Such a device would likely need to be nuclear powered. I don't see another way to put a lot of heat in a small device.

I think the temperature would need to be moderated, so it didn't melt too fast or too slow. And, so it keeps melting evenly when the pressure builds under all that ice.
Also, I think testing such a device on Earth would not be preferable if there was any other way to get the job done. Dropping unrecoverable nuclear devices into pristine Antarctic subglacial lakes, for example, would not be an option.

 

[berkeman]

Imagine a device that's simply a big, hot ball bearing. It would melt the ice and gravity would pull it down, no suction needed.
Then, the water would refreeze behind the ball bearing.

And the communication cable, freezing the descent...

 

[majortom]

And the communication cable, freezing the descent...

That or wireless relays, or a combination of the two.
Cable would have to reeled up on the device itself, so there's a maximum length.

 

[Astronuc]

How much fuel would be needed to melt through 15km of ice?

How large a diameter hole does one need? Take the 15000 m * πr² * 1000 kg/m3 * (heat of fusion + heat required to raise the temperature the required difference), which would give the energy required. Depending on how fast (1 km/hr), one can determine the power required. An RTG might work, or a micro-reactor.

Given that the gravity on Enceladus is very low, 0.113 m/s² (0.0113 g). One might be able to pump the water up to the surface and way from the borehole.
https://en.wikipedia.org/wiki/Enceladus

Surface temp.    min      mean     max
Kelvin         32.9 K     75 K    145 K
Celsius        −240°C   −198°C   −128°C

 

[berkeman]

That or wireless relays, or a combination of the two.
Cable would have to reeled up on the device itself, so there's a maximum length.

Wireless relay through ice? What is the ice made of? What is the attenuation of EM in that ice?

 

[majortom]

Wireless relay through ice? What is the ice made of? What is the attenuation of EM in that ice?

The attenuation length was found to be 300-500m for frequencies from 75MHz to 1.25GHz.
(Found on some other forum thread.)
Going straight through 15km seems unreasonable, but maybe 15 relays at what 10x amplification? That's not too bad.

 

[majortom]

How large a diameter hole does one need? Take the 15000 m * π^r * 1000 kg/m3 * (heat of fusion + heat required to raise the temperature the required difference), which would give the energy required. Depending on how fast (1 km/hr), one can determine the power required. An RTG might work, or a micro-reactor.

Given that the gravity on Enceladus is very low, 0.113 m/s² (0.0113 g). One might be able to pump the water up to the surface and way from the borehole.
https://en.wikipedia.org/wiki/Enceladus

Surface temp.    min      mean     max
Kelvin         32.9 K     75 K    145 K
Celsius        −240°C   −198°C   −128°C

I think you could get away with pumping the water from the bottom of the device to the top of the device, if any pumping was needed at all.
Thanks for the equation, that helps!

 

[BillTre]

Here is a link to a really great podcast of Sean Carroll interviewing Kevin Hand (Deputy Chief Scientist for Solar System Exploration at NASA’s Jet Propulsion Laboratory).
Among many other things, they discuss exactly the problem of getting through the ice layer.

Here is an earlier thread, on a rover for under the ice layer, for exploring such worlds.

In the podcast he talks about something like this rover, being inside something that melt/sinks through the ice (presumably unspooling a cable or deploying relays as it goes), until it reaches the liquid underneath.
The melter would be inside something else (rocket ship), which transports it to its celestial destination.

 

[majortom]

I was thinking about the cable, and if the cable was heated, I think you could leave a big spool at the surface and it would work. If it wasn't heated, then it would get frozen in the ice and stop unspooling.

I also thought of another problem. What if the probe gets to 10km and there's a big boulder in the way?
I was thinking about that water pumping idea, and I think using maybe hot water jets and some way to push the probe horizontally through the ice instead of just vertically would do the trick.

OTOH, maybe a boulder free vertical path could be discovered by some method. I think really high powered radar can only get a third of the way there, so I'm not sure if there's a better technique. Who knows, though, maybe by then we'll be using neutrino based radar or some other exotic tech.

 

[anorlunda]

I also thought of another problem.

Its good that you're thinking about possible problems. Any space thing needs lots and lots of thinking. But a real mission needs lots of problem solvers, whereas problem discoverers are a dime a dozen.

Problem solving takes lots of hard work, and the hard work begins with your studies. Are you a student? What are your academic plans?

 

[majortom]

Its good that you're thinking about possible problems. Any space thing needs lots and lots of thinking. But a real mission needs lots of problem solvers, whereas problem discoverers are a dime a dozen.

Problem solving takes lots of hard work, and the hard work begins with your studies. Are you a student? What are your academic plans?

Well, the thing is that thinking of possible problems is a creative, synthetic exercise, whereas problem solving is really more about brute force and bloody mindedness. It takes a certain type. Which isn't actually my forte. Call it a personality quirk.

I was a student at one point. I went to school at a time when tuition was still quite affordable in my country, so I used that freedom to experiment, and I completed courses in physics, various required math, programming, computability and complexity, literature, philosophy, sociology, psychology, and astronomy. Since then I've studied casually along the same lines, but more filling in the gaps in economics, linguistics, political science and history. I've definitely migrated towards the social sciences. As you can see, I'm not the kind of student that takes kindly to the registrar telling me what good education looks like. Honestly, it looks to me like they're offering career advice more than anything else.

In my professional capacity, I'm entirely people and relationship oriented, so my interpersonal skills and ability to sell, charm and manipulate are also quite well honed.

So, I actually don't appreciate being called a dime a dozen. Because I'm not. And, it comes across as quite condescending. I'm exceptionally well educated, I just have a broad education.

Which allows me to parachute into various forums and have a perspective that's usually quite valuable.
For people open minded enough to notice.

I think my plans are probably to pursue creative writing, if I can situate myself financially.

 

[anorlunda]

Which allows me to parachute into various forums and have a perspective that's usually quite valuable.

Physics Forums is not like many other forums. The following is from our mission statement.

• We wish to discuss mainstream science. That means only topics that can be found in textbooks or that have been published in reputable journals.

Normally, a thread like this one would start with a link to a published paper, or a textbook, discussing exploration of Europa. That's different than brainstorming. If you do have such a link, it would be welcome.

 

[Vanadium 50]

You have made the discovery that if we ignore practicality, virtually anything is possible. However, you are not the first to have discovered this.

• Ice boring in the Antarctic is far from trivial, and that's only down to a depth of a kilometer or so. To set the scale, the Wikipedia article on ice drilling is 3x as long as the one on lightsabers.
• Space travel is far from trivial. Deep space even more so.
• Compact nuclear reactors are far from trivial.

The total mass humans have ever sent to Saturn is only about 4 tons. Not much for a completely roibotic 15 km ice drill.

 

[jrmichler]

Speaking as a person who has worked as a college professor, engineer, inventor, and research scientist, I can say that you are, indeed, condescending. I once had to deal with a manager exactly like you. Fortunately he did not last long. But while he was there he did a lot of damage. It took a full year after he left for us to kill off his stupid ideas.

Your ideas could possibly pay very well. You need only to write that book. Others have done so, and I can point to two who explained how they did it:

Spider Robinson, in the Forward of Callahan's Crosstime Saloon, explains how writing got him out of the sewer. Literally.

John Scalzi, in the Author's Note and Acknowledgements of Agent to The Stars, explains how he fell into the author game.

My sister wrote some books, and retired off what she earned.

ALL of the above wrote while they had other employment, and used their book earnings to change to writing as their source of income. It's easy. You need only to write that book, get it published, sell a lot of copies, and have the royalties deposited to your account. Writers write, windbags talk about writing.

 

[Vanadium 50]

So, this engineer interviews for a job. The interviewer says "We have this great product we're developing. You order a food item, and out it comes! Say 'apple pie', and out pops a slice of apple pie! Just like Mom used to make. Say 'steak and potatoes' and out pops steak and potatoes - the best you've ever tasted! Say 'spaghetti and meatballs' and out pops spaghetti and meatballs. What do you think?"

"That's amazing, the engineer says. How does it work?"

"You're the engineer - that's what we are hiring you to figure out!"

 

[Vanadium 50]

You have a reading comprehension problem, along with an ego problem.

In my professional capacity, I'm entirely people and relationship oriented, so my interpersonal skills and ability to sell, charm and manipulate are also quite well honed.

I can see that.

 

[berkeman]

Thread closed for Moderation and cleanup...

 

[Mark44]

Several posts that are borderline insulting have been excised from the thread.

The thread will remain closed.