4 ms·

Yes, of course you wouldn't directly use an H bomb, the idea was that the quantities of fissile materials needed to propel a 100kg interstellar probe to 0.2c ar

by zeteo 15y ago

Yes, of course you wouldn't directly use an H bomb, the idea was that the quantities of fissile materials needed to propel a 100kg interstellar probe to 0.2c are easily within reach of several nations. Controlled fusion can be achieved in very confined spaces: http://en.wikipedia.org/wiki/Hohlraum http://en.wikipedia.org/wiki/Hohlraum I agree that communication equipment is a major problem. The best way to solve it is probably to oversize the local equipment: a dedicated space telescope and a powerful orbital laser. This may let you get away with a very lightweight emitter/receiver pair on the probe itself.

Joakal 15y ago
Assuming there's no microscopic debris in space and it's pretty empty, wouldn't it be possible to accelerate faster than c relative to Earth and get there sooner in terms of body age? I mean gradual increase of acceleration, of course. I understand that Earth will just see the ship time flow more slowly.
- johngalt 15y ago
  Lorentz factor only makes a large enough difference when you're very close to the speed of light. Edit: changed from 'c' to 'the speed of light'
  - Joakal 15y ago
    c, as in Earth's view of ship's speed?
- prewett 15y ago
  You can't go faster than c from anyone's reference frame (that's why space and time contract, to prevent that). "I understand that Earth will just see the ship time flow more slowly." You have that reversed: Earth will see time same as usual, but time for you will slow down.
Groxx 15y ago
I haven't seen the Hohlraum article before - interesting stuff. And for the earth-side receiver, I was generally assuming hugely-sensitive equipment. But I may be underestimating the sensitivity of what we can build - clearly we can detect individual photons, so the probe emitter would just need to ensure it sends enough that the receiver can capture enough to reconstruct the message... In any case, interesting stuff :) I'm sure there's a calculation that we could do to figure out the actual power requirements given background radiation and receiver sizes, but I don't know the associated math. -- A thought just occurred to me - given a big reflector, you could emulate a transmitter by varying its reflectiveness / target, beaming a massively-powerful, regular pulse from Earth, and watching what comes back. That could eliminate transmitters (and their power requirements) entirely from the probe, though you still have the solar wind problem if it's really big.
- shabble 15y ago
  Your second idea has already been done, to a certain degree. http://www.hindawi.com/journals/wcn/2005/930810/abs/ http://www.hindawi.com/journals/wcn/2005/930810/abs/ is one example of a (highly miniaturised) sensor network that communicates with a corner-cube retroreflector returning modulated laser light back to the base-station. It has no active comms emission.
jerf 15y ago
"Yes, of course you wouldn't directly use an H bomb" Well, hydrogen bombs, no. Nuclear bombs in general, sure! http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29 http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propul... If we had an emergency of some sort and Absolutely Had to lift several hundred thousand tons of material into orbit or beyond in the next couple of decades or face annihilation, and we have to work with real engineering and real physics as we know them, Project Orion is the only thing that stands a chance of really, truly working. However, the negative side effects are considered too much for people to bear. (Incorrectly, in my opinion. People badly overestimate the negative effects of a couple nuclear explosions in the atmosphere and really really really really really badly overestimate the negative effects of nuclear explosions in the solar system (hint: it's like it's being constantly nuked all the time by that big bright thing in the sky, the solar system isn't going to notice your wet squib of a firecracker), and against the value of what this would let us lift, I think it could be worth doing. But I concede the odds of this are basically identical to the aforementioned exisitential risk, since it would take nothing less to shift opinions that far within my lifetime.)

by zeteo 15y ago

Joakal 15y ago

Assuming there's no microscopic debris in space and it's pretty empty, wouldn't it be possible to accelerate faster than c relative to Earth and get there sooner in terms of body age? I mean gradual increase of acceleration, of course. I understand that Earth will just see the ship time flow more slowly.

johngalt 15y ago
Lorentz factor only makes a large enough difference when you're very close to the speed of light. Edit: changed from 'c' to 'the speed of light'
- Joakal 15y ago
  c, as in Earth's view of ship's speed?
prewett 15y ago
You can't go faster than c from anyone's reference frame (that's why space and time contract, to prevent that). "I understand that Earth will just see the ship time flow more slowly." You have that reversed: Earth will see time same as usual, but time for you will slow down.

Groxx 15y ago

I haven't seen the Hohlraum article before - interesting stuff. And for the earth-side receiver, I was generally assuming hugely-sensitive equipment. But I may be underestimating the sensitivity of what we can build - clearly we can detect individual photons, so the probe emitter would just need to ensure it sends enough that the receiver can capture enough to reconstruct the message... In any case, interesting stuff :) I'm sure there's a calculation that we could do to figure out the actual power requirements given background radiation and receiver sizes, but I don't know the associated math. -- A thought just occurred to me - given a big reflector, you could emulate a transmitter by varying its reflectiveness / target, beaming a massively-powerful, regular pulse from Earth, and watching what comes back. That could eliminate transmitters (and their power requirements) entirely from the probe, though you still have the solar wind problem if it's really big.

shabble 15y ago
Your second idea has already been done, to a certain degree. http://www.hindawi.com/journals/wcn/2005/930810/abs/ http://www.hindawi.com/journals/wcn/2005/930810/abs/ is one example of a (highly miniaturised) sensor network that communicates with a corner-cube retroreflector returning modulated laser light back to the base-station. It has no active comms emission.

jerf 15y ago

"Yes, of course you wouldn't directly use an H bomb" Well, hydrogen bombs, no. Nuclear bombs in general, sure! http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29 http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propul... If we had an emergency of some sort and Absolutely Had to lift several hundred thousand tons of material into orbit or beyond in the next couple of decades or face annihilation, and we have to work with real engineering and real physics as we know them, Project Orion is the only thing that stands a chance of really, truly working. However, the negative side effects are considered too much for people to bear. (Incorrectly, in my opinion. People badly overestimate the negative effects of a couple nuclear explosions in the atmosphere and really really really really really badly overestimate the negative effects of nuclear explosions in the solar system (hint: it's like it's being constantly nuked all the time by that big bright thing in the sky, the solar system isn't going to notice your wet squib of a firecracker), and against the value of what this would let us lift, I think it could be worth doing. But I concede the odds of this are basically identical to the aforementioned exisitential risk, since it would take nothing less to shift opinions that far within my lifetime.)