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Uh oh... "PM: You've suggested an asteroid could be brought closer to the Earth to make it easier to mine. Is that really feasible? EA: It is. One of the ways

Uh oh... "PM: You've suggested an asteroid could be brought closer to the Earth to make it easier to mine. Is that really feasible? EA: It is. One of the ways that we could do that is simply to turn the water on an asteroid into rocket fuel and burn it in a thruster that nudges its trajectory. Split water into hydrogen and oxygen, and you get the same fuels that launch space shuttles. Some asteroids are 20 percent water, and that amount would let you move the thing anywhere in the solar system." Wtf? EA just suggested a perpetual motion machine. He suggests using energy to hydrolyze water, but then de-hydrolyzing the water to get energy. He's making it sound like more energy will come out than went in (allowing propulsion), when really it would be == at best, and really < because of inefficiency. The only way his concept of storing the energy is even slightly useful is if you were to spend years and years collecting solar energy and storing it as H2 + O2 to burn later in one quick burst. But that's you storing the energy over a long long time, and getting back less than you put in.

typpo 14y ago
It doesn't seem unreasonable to split water using a solar or nuclear energy source, and then use the hydrogen and oxygen as rocket fuel to actually move the asteroid. Anderson's goal is not a net energy gain, it's to move the asteroid.
kolinko 14y ago
I think he's not de-hydrolyzing water to get energy per se, but to generate thrust. Say, you've got a nuclear reactor (or whatever else is more practical) on an asteroid. You cannot use the energy from the reactor to propel the rock, you need to generate thrust. So you take water, you split hydrogen & oxygen, you burn it, you get thrust.
- pjscott 14y ago
  If you're already bringing a nuclear reactor into space, you could use it to heat up the hydrogen and use it as propellant directly, for more efficient travel. (In situations where you need bursts of high thrust and are willing to sacrifice efficiency, you can also go with a hybrid system that uses both nuclear heat and combustion.) Oh, and fun safety fact: a nuclear reactor isn't actually particularly radioactive until it's turned on. If you launch it out of Earth's orbit before turning it on, you're sitting pretty.
  - Tuna-Fish 14y ago
    Also, assuming a lot of electricity, some form of ion engines would likely be (much) more efficient than heating. Also, nuclear reactors aren't the ideal way to make electricity in space. Proper nuclear reactors work as heaters for a heat engine, and heat sinks are proportionally much more expensive in space than on earth. However, solar power is much more efficient. You get 100% efficiency all the time, and it's 30% better in space (near Earth) than it is down here at best. Also, since no structure has to carry any significant weight, you can build things like a flexible paper-thin sheet of solar cells printed on plastic that is spun about it's axis to keep it deployed and spread out.
- ChuckMcM 14y ago
  Yeah, or just heat the water into steam and shoot it that way, saves a lot of work. There was an interesting paper done on turning a comet off course by basically throwing a supercritical mass of uranium at it. If you can set it up with a 'cool' side (perhaps leading non-metal penetrator cover) and a 'hot' side (the fissioning core) then the thing tries to dig into the comet by vaporizing ice at the back and shoving it out the hole that it made when it went in. Poof, instant rocket engine changing the orbit of the comet (hopefully in a good way)
- jonmrodriguez 14y ago
  Makes sense. Thanks.
ricree 14y ago
I didn't see anything about using the H2 O2 as an energy source. Presumably, he meant that they would use some other energy source (presumably solar) to hydrolyze the water, then use that to generate thrust. I have no idea if that's the best way to convert solar energy to thrust, or if it's even feasible, but bringing perpetual motion into it seems a little harsh.
zem 14y ago
do the man the basic favour of assuming he isn't an idiot. the problem here isn't energy, it's momentum; storing energy over a long time and then releasing it in precisely timed bursts to eject reaction mass when you need a course correction is perfectly feasible way to do things. you could probably even supplement the energy collection with some sort of moon-based laser if you threw enough up-front resources at the problem.
ovi256 14y ago
I think you're pretty much putting words in his mouth. He didn't say a single word about energy balance. He just said "burning water", which is badly formulated and unclear, but does not exclude using an external energy source for the hydrolysis. That energy could come from solar panels as you mentioned, with the drawbacks you mentioned. But it looks to be a good enough method.
mikeash 14y ago
You'll probably collect energy with solar panels or similar. You'll expend energy with rocket thrust, and all else being equal, rocket thrust is most efficiently used for orbital maneuvering when done over a short time. So you have energy collected over a long period of time, then released in a short period of time. That means you need to store that energy. It's not feasible to ship batteries up from the surface with current battery technology, since the energy/mass ratio is awful, so you'll need some other way to store the energy. Chemical storage would be one way. Use local materials and transform them into new materials with more chemical potential energy. Chemical storage tanks can be reasonably light. When the time comes, you can reverse the process and transform your stored chemicals back into electricity. But wait, we don't actually want electricity, we want thrust. A traditional rocket engine is a great way of transforming chemical potential energy into thrust. So let's skip the electrical middleman, and burn our chemical energy storage reagents in a rocket engine. All that's left to do is choose the chemicals. If there's water, then it's easy to make oxygen and hydrogen from it using electricity, and hydrogen is a great rocket fuel.
- danielweber 14y ago
  Hydrogen is a pretty good rocket fuel in terms of Isp, but it has a tendency to boil off in space. I still think it's very practical to consider moving asteroids around from a technical perspective. The political ramifications are huge. If the people in charge are malicious they could completely devastate the planet. I think this is generally solvable by using lots of small thrusters that are independently controlled to make sure that no one can smash the thing into the planet, but getting sign-off from everyone who might have veto power is huge.
InclinedPlane 14y ago
Most asteroids in our Solar System are bathed in about 1 KiloWatt/m^2 of readily available power 24/7 in the form of ordinary sunshine.

typpo 14y ago

It doesn't seem unreasonable to split water using a solar or nuclear energy source, and then use the hydrogen and oxygen as rocket fuel to actually move the asteroid. Anderson's goal is not a net energy gain, it's to move the asteroid.

kolinko 14y ago

I think he's not de-hydrolyzing water to get energy per se, but to generate thrust. Say, you've got a nuclear reactor (or whatever else is more practical) on an asteroid. You cannot use the energy from the reactor to propel the rock, you need to generate thrust. So you take water, you split hydrogen & oxygen, you burn it, you get thrust.

pjscott 14y ago
If you're already bringing a nuclear reactor into space, you could use it to heat up the hydrogen and use it as propellant directly, for more efficient travel. (In situations where you need bursts of high thrust and are willing to sacrifice efficiency, you can also go with a hybrid system that uses both nuclear heat and combustion.) Oh, and fun safety fact: a nuclear reactor isn't actually particularly radioactive until it's turned on. If you launch it out of Earth's orbit before turning it on, you're sitting pretty.
- Tuna-Fish 14y ago
  Also, assuming a lot of electricity, some form of ion engines would likely be (much) more efficient than heating. Also, nuclear reactors aren't the ideal way to make electricity in space. Proper nuclear reactors work as heaters for a heat engine, and heat sinks are proportionally much more expensive in space than on earth. However, solar power is much more efficient. You get 100% efficiency all the time, and it's 30% better in space (near Earth) than it is down here at best. Also, since no structure has to carry any significant weight, you can build things like a flexible paper-thin sheet of solar cells printed on plastic that is spun about it's axis to keep it deployed and spread out.
ChuckMcM 14y ago
Yeah, or just heat the water into steam and shoot it that way, saves a lot of work. There was an interesting paper done on turning a comet off course by basically throwing a supercritical mass of uranium at it. If you can set it up with a 'cool' side (perhaps leading non-metal penetrator cover) and a 'hot' side (the fissioning core) then the thing tries to dig into the comet by vaporizing ice at the back and shoving it out the hole that it made when it went in. Poof, instant rocket engine changing the orbit of the comet (hopefully in a good way)
jonmrodriguez 14y ago
Makes sense. Thanks.

ricree 14y ago

I didn't see anything about using the H2 O2 as an energy source. Presumably, he meant that they would use some other energy source (presumably solar) to hydrolyze the water, then use that to generate thrust. I have no idea if that's the best way to convert solar energy to thrust, or if it's even feasible, but bringing perpetual motion into it seems a little harsh.

zem 14y ago

do the man the basic favour of assuming he isn't an idiot. the problem here isn't energy, it's momentum; storing energy over a long time and then releasing it in precisely timed bursts to eject reaction mass when you need a course correction is perfectly feasible way to do things. you could probably even supplement the energy collection with some sort of moon-based laser if you threw enough up-front resources at the problem.

ovi256 14y ago

I think you're pretty much putting words in his mouth. He didn't say a single word about energy balance. He just said "burning water", which is badly formulated and unclear, but does not exclude using an external energy source for the hydrolysis. That energy could come from solar panels as you mentioned, with the drawbacks you mentioned. But it looks to be a good enough method.

mikeash 14y ago

You'll probably collect energy with solar panels or similar. You'll expend energy with rocket thrust, and all else being equal, rocket thrust is most efficiently used for orbital maneuvering when done over a short time. So you have energy collected over a long period of time, then released in a short period of time. That means you need to store that energy. It's not feasible to ship batteries up from the surface with current battery technology, since the energy/mass ratio is awful, so you'll need some other way to store the energy. Chemical storage would be one way. Use local materials and transform them into new materials with more chemical potential energy. Chemical storage tanks can be reasonably light. When the time comes, you can reverse the process and transform your stored chemicals back into electricity. But wait, we don't actually want electricity, we want thrust. A traditional rocket engine is a great way of transforming chemical potential energy into thrust. So let's skip the electrical middleman, and burn our chemical energy storage reagents in a rocket engine. All that's left to do is choose the chemicals. If there's water, then it's easy to make oxygen and hydrogen from it using electricity, and hydrogen is a great rocket fuel.

danielweber 14y ago
Hydrogen is a pretty good rocket fuel in terms of Isp, but it has a tendency to boil off in space. I still think it's very practical to consider moving asteroids around from a technical perspective. The political ramifications are huge. If the people in charge are malicious they could completely devastate the planet. I think this is generally solvable by using lots of small thrusters that are independently controlled to make sure that no one can smash the thing into the planet, but getting sign-off from everyone who might have veto power is huge.

InclinedPlane 14y ago

Most asteroids in our Solar System are bathed in about 1 KiloWatt/m^2 of readily available power 24/7 in the form of ordinary sunshine.