5 ms·

> Its beyond our current level of civilization. We have projected only milliwatts to any distance beyond the moon. We have a 2kW nuclear reactor rolling aroun

by keenerd 12y ago

> Its beyond our current level of civilization. We have projected only milliwatts to any distance beyond the moon. We have a 2kW nuclear reactor rolling around Mars at the moment. 400 watts in the interstellar neighborhood. 200W currently en route to Pluto. Maybe you think nuclear is cheating? Solar might make more sense for this mission anyway, since it is in the Earth-Venus neighborhood. The Rosetta probe would generate almost 10kW at that distance from the sun.

JoeAltmaier 12y ago
Curiosity has a 110 watt capacity. Ok, larger than milliwatts but nowhere near kW. What are those other sources you mention?
- keenerd 12y ago
  Voyager 1 and New Horizons. You are ignoring heat output. Curiosity's reactor produces 2kW of heat and 125W of electricity. The heat is more important - it is what keeps the rover from dying at night. Heat output is really useful for propulsion - more useful than electric if you need large amounts of thrust. Something like NERVA would help get astronauts to Mars before the radiation dose gets too high. Or if you wanted to give an asteroid the biggest push possible. http://en.wikipedia.org/wiki/NERVA http://en.wikipedia.org/wiki/NERVA
- Crito 12y ago
  http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Space http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen... Those are just RTGs. You can also put a proper fission reactor into space as well. This has been done in the past several times to power active radar surveillance satellites. They've been around since the early 70s, the TOPAZ-II from the early 90s could put out around 10kW. TOPAZ-I[aka TOPAZ] could do 5kW. As you would expect, they put out even more power as heat. Those 5kW-10kW numbers are just what you get in electrical power, through the thermionic converters, which are not particularly efficient. TOPAZ reactors are about half the mass of Voyager I. The upper bound on mass that we've already put into interplanetary space is probably the five S-IVB stages in heliocentric orbit right now, each with a dry mass of about 10,000kg. That's about 10 TOPAZ-II's or 30 TOPAZ's. There was a proposed manned Venus flyby mission using a wet-workshop S-IVB, which would have been much heavier.
arethuza 12y ago
We've also had fairly small devices (tens of tons) capable of yottawatt (10^24 W) levels of power output - admittedly not for very long....
- Crito 12y ago
  Do you have a source for that? Wikipedia has the largest lasers maxing out in the pettawats, with only Tzar Bomba crossing over into yottawatts: http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#yottawatt_.281024_watts.29 http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#yot...
  - arethuza 12y ago
    Yes, large H-bombs were what I meant - would be good to find a constructive use for them.
    - Crito 12y ago
      There are actually many peaceful uses of nuclear weapons, both the US and the Soviets experimented with using them to dig big holes, and the Soviets also used them for geographic surveys (like that "thumper" at the beginning of Jurassic Park, but much bigger ;)) and a few other things. Unfortunately all of these uses are politically untenable. It would be great to use them in space though; it would probably be much easier to convince the public to go for that.
      - JoeAltmaier 12y ago
        Getting them up there is the risk - a launch failure means raining radioactive death at random.
        Crito 12y ago
        It would be bad, but it wouldn't really be that bad. A launch failure would not cause a complete detonation (that is trivial to prevent, but difficult to orchestrate). A fizzle could be mitigated fairly easily as well, possibly even by putting the warhead on a launch escape system if you really wanted to go overboard. The most likely failure is just the device coming apart and being scattered, but in that situation Pu-239 is not particularly more concerning than Pu-238. More or less just an alpha emitter; not good to ingest, but otherwise pretty safe. We've launched plenty of things with Pu-238 in board.
JoeAltmaier 12y ago
Solar is definitely attractive - with the asteroid belt at triple the distance from the earth you'd expect n^2 reduction in efficiency ~10x, but without atmosphere you might end up about the efficiency of cells at sea level anyway. A solar sail kind of rig could be just the ticket.
- danielweber 12y ago
  In space, solar outperforms RTG on an energy-per-mass ratio until you get out past at least Saturn. I love nuclear but it's not always the best answer. (OTOH, it is the best answer for anything that's going to land some place and need to function for more than a few months.)

by keenerd 12y ago

JoeAltmaier 12y ago

Curiosity has a 110 watt capacity. Ok, larger than milliwatts but nowhere near kW. What are those other sources you mention?

keenerd 12y ago
Voyager 1 and New Horizons. You are ignoring heat output. Curiosity's reactor produces 2kW of heat and 125W of electricity. The heat is more important - it is what keeps the rover from dying at night. Heat output is really useful for propulsion - more useful than electric if you need large amounts of thrust. Something like NERVA would help get astronauts to Mars before the radiation dose gets too high. Or if you wanted to give an asteroid the biggest push possible. http://en.wikipedia.org/wiki/NERVA http://en.wikipedia.org/wiki/NERVA
Crito 12y ago
http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Space http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen... Those are just RTGs. You can also put a proper fission reactor into space as well. This has been done in the past several times to power active radar surveillance satellites. They've been around since the early 70s, the TOPAZ-II from the early 90s could put out around 10kW. TOPAZ-I[aka TOPAZ] could do 5kW. As you would expect, they put out even more power as heat. Those 5kW-10kW numbers are just what you get in electrical power, through the thermionic converters, which are not particularly efficient. TOPAZ reactors are about half the mass of Voyager I. The upper bound on mass that we've already put into interplanetary space is probably the five S-IVB stages in heliocentric orbit right now, each with a dry mass of about 10,000kg. That's about 10 TOPAZ-II's or 30 TOPAZ's. There was a proposed manned Venus flyby mission using a wet-workshop S-IVB, which would have been much heavier.

arethuza 12y ago

We've also had fairly small devices (tens of tons) capable of yottawatt (10^24 W) levels of power output - admittedly not for very long....

Crito 12y ago
Do you have a source for that? Wikipedia has the largest lasers maxing out in the pettawats, with only Tzar Bomba crossing over into yottawatts: http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#yottawatt_.281024_watts.29 http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#yot...
- arethuza 12y ago
  Yes, large H-bombs were what I meant - would be good to find a constructive use for them.
  - Crito 12y ago
    There are actually many peaceful uses of nuclear weapons, both the US and the Soviets experimented with using them to dig big holes, and the Soviets also used them for geographic surveys (like that "thumper" at the beginning of Jurassic Park, but much bigger ;)) and a few other things. Unfortunately all of these uses are politically untenable. It would be great to use them in space though; it would probably be much easier to convince the public to go for that.
    - JoeAltmaier 12y ago
      Getting them up there is the risk - a launch failure means raining radioactive death at random.
      - Crito 12y ago
        It would be bad, but it wouldn't really be that bad. A launch failure would not cause a complete detonation (that is trivial to prevent, but difficult to orchestrate). A fizzle could be mitigated fairly easily as well, possibly even by putting the warhead on a launch escape system if you really wanted to go overboard. The most likely failure is just the device coming apart and being scattered, but in that situation Pu-239 is not particularly more concerning than Pu-238. More or less just an alpha emitter; not good to ingest, but otherwise pretty safe. We've launched plenty of things with Pu-238 in board.

JoeAltmaier 12y ago

Solar is definitely attractive - with the asteroid belt at triple the distance from the earth you'd expect n^2 reduction in efficiency ~10x, but without atmosphere you might end up about the efficiency of cells at sea level anyway. A solar sail kind of rig could be just the ticket.

danielweber 12y ago
In space, solar outperforms RTG on an energy-per-mass ratio until you get out past at least Saturn. I love nuclear but it's not always the best answer. (OTOH, it is the best answer for anything that's going to land some place and need to function for more than a few months.)