# Moving Phobos to join Deimos for single moon.

1. Jul 14, 2011

### barycenter

With current technology, could humans move Phobos to join with Deimos to create a single Mars moon? Move moon as a whole/cut it up and move it in peices, etc.

2. Jul 14, 2011

### DaveC426913

1] Why?
2] Depends on what you mean by current technology. With current technology, we could build a superhighway around the equator, but it would break the budget of a passel of large countries.

3. Jul 14, 2011

### Drakkith

Staff Emeritus
It is within current scientific and technological understanding. We understand the math and have the technology to apply a force to the moon, arguably it is possible to apply enough to move it. However as Dave pointed out, the cost would be simply enormous.

4. Jul 14, 2011

### DaveC426913

The challenge would be delivering enough fuel there for the delta-v (.5km/s) of an asteroid-sized (10^15kg) object.

5. Jul 14, 2011

### Drakkith

Staff Emeritus
Yep. I wonder how much fuel that would take for something akin to a hundred plus Saturn V rockets....just to throw out something.

6. Jul 14, 2011

### DaveC426913

Deimos masses about as much as a million Pyramids of Cheops or a billion Saturn Vs.

7. Jul 14, 2011

### Drakkith

Staff Emeritus
Sorry, I meant how much fuel would be required if we use something akin to 100 saturn V's to provide the force to move the moon. IE bolt these massive engines to it and fire em up!

8. Jul 14, 2011

### DaveC426913

Yeah, I know. My point was that it doesn't really matter what you use to provide the thrust - you could use one Saturn or a hundred (it would just be faster). The thing that is immutable is the mass to be moved times the change in velocity.

And.

One must not forget that we'll have to carry all our fuel with us (no on-site mining - current technology, remember), which means we'll need fuel to move that fuel. And fuel to move the fuel to move the fuel.

What ends up happening is that you need, like 95% of your fuel just to get your fuel to the target, leaving only 5% left to do any work. So, since you have a fixed amount of work to do, you work backwards from that, meaning you need to bring 20 times more fuel than you thought you needed.

Someone more number-savvy than me could work this out on the back of a napkin.

9. Jul 14, 2011

### Drakkith

Staff Emeritus
Yep. Where is the star ship Enterprise when you need her...

10. Jul 15, 2011

### Ryan_m_b

Staff Emeritus
Even if we could move the moons do we have the technology to safely combine them together? It might be simpler to imagine mining one of them into powder and dumping this into the other moon.

11. Jul 15, 2011

### sophiecentaur

The same amount of energy would be needed, though.

12. Jul 15, 2011

### Ryan_m_b

Staff Emeritus
That's fine, I was just wondering if it was more practical.

13. Jul 15, 2011

### D H

Staff Emeritus
Just because we understand the math and physics does not mean we have the technological understanding. Example: We have a very good idea of the mechanism by which the Sun produces energy and we have very good measurements of how much energy the Sun is producing. That we do have that knowledge does not mean we have the technological understanding of how to build an artificial Sun that produces that amount of energy.

14. Jul 15, 2011

### DaveC426913

Perhaps true, but what about an example more relevant to the scenario? What's not doable?

Actually, I know what's not doable. Logistics. It would be the largest project ever undertaken by man, and it wold be a massive team of people, and they would be orders of magnitude farther from Earth than any human has ever been. And, as with fuel, so it is with people. 95% of people and survival resources might result in 5% of the people and the resources left over to actually do the work.

Where would they live? Not on the Moon... where would their air, food and water and building materials come from?

So, the project itself has just seen a 20-fold increase in size. And again, we need fuel to transport all that, which means we reapply the 20-fold factor to the fuel. Which means we now need 400 times more fuel than we originally anticipated.

Oh, did I mention we have to get all those people back home? Another 20-fold increase.

(There' s a reason why our current trips to Mars only send about a ton of payload, only send robots that don't need survival resources, and only send them on a one way trip.)

15. Jul 15, 2011

### Ryan_m_b

Staff Emeritus
Totally agree. Sticking with the stipulation that we can only use current technology there's no way this would be a manned mission. It would have to be robotic with delayed telepresence.

16. Jul 15, 2011

### D H

Staff Emeritus
That's not feasible, either. This simply isn't feasible, period, using current technology, or anything remotely resembling current technology.

17. Jul 15, 2011

### DaveC426913

The issue at-hand is the subtle distinction between technological capability and logistical capability.

Enough Saturn V's with enough fuel* attached to Deimos would indeed move it. But the OP probably didn't realize how incredibly difficult that would be to achieve.

* actually, even this is beyond us. We do not have the technology to store more than one or two SaturnVs worth of LOx and LHi at a time. You'd need something that would store thousands and thousands of SaturnVs-worth of fuel and a continual pump system to feed the rockets.

18. Jul 15, 2011

### D H

Staff Emeritus
Exactly. Just because we know how to do X does not mean we know how to do 10*x, let alone 106*X. Technology oftentimes does not scale.

19. Jul 15, 2011

### Drakkith

Staff Emeritus
What do you mean Dave? Would it not be possible to simply make a lot of storage tanks?

20. Jul 15, 2011

### DaveC426913

How long can LOx and LHi be stored? (Hours.)
How will we get it there? How will we store it for years in-transit?
How will we route it to the rockets?
Where will the power come from to refrigerate it?
etc.
etc.

21. Jul 15, 2011

### Drakkith

Staff Emeritus
I didn't realize you couldn't store Lox for more than a few hours.

22. Jul 15, 2011

### Lsos

Everybody seems to to have forgotten about the 5000 or so megatons of nuclear weapons we have lying around. That said, I'm sure we have means and the know-how to do this thing.

23. Jul 15, 2011

### sophiecentaur

I suspect that storing Lox in space may not be as difficult as storing it on Earth. A few layers of reflective screens between the tank and the Sun (andEarth) would put it in a 'deep space' situation as far as far as balancing absorbing and radiating energy are concerned.
I still think the project would be a wasted exercise. The resources would be better spent on food!

24. Jul 15, 2011

### DaveC426913

No we haven't. They're a drop in this bucket.

Did I not mention that Deimos masses as much as a million Pyramids of Cheops? Now accelerate that by .5km/s.

25. Jul 15, 2011

### DaveC426913

Again: current technology. We don't have that technology.