3 ms·

There's the EM drive, maybe. Some recent discussion: https://news.ycombinator.com/item?id=12995125 https://news.ycombinator.com/item?id=12995125 If you can cre

by ant6n 10y ago

There's the EM drive, maybe. Some recent discussion: https://news.ycombinator.com/item?id=12995125 https://news.ycombinator.com/item?id=12995125 If you can create trust out of electricty (ion drives also come to mind), then if you have nuclear power or fusion, things get interesting again in terms of propulsion. To reach orbit, there are a bunch of interesting proposals: skyhooks (i.e. space elevator light), launch loops, railguns.

jcranmer 10y ago
The EM drive is reported as producing maybe 1 mN per kW. The largest power plant in the world produces about 22 GW of energy--at that ratio, an EM drive could produce maybe 22 kN. The first stage of the Saturn V rockets produced 35,000 kN of thrust. As a practical engine, EM drives are worse than chemical rockets or even ion thrusters (which produce about 25-250 mN/kW, according to Wikipedia).
- bitJericho 10y ago
  Once we understand the physics, if it's a real phenomenon, we might be able to make it much more efficient. Compare a modern li-on battery to a lemon, coin and nail, for example.
- ant6n 10y ago
  This was a response to 'Problem is we don't really know where to go next'. Saying that there's basically nothing beyond chemical rockets. My point is that there are plenty of possibilities to continue to develop propulsion technology.
- VLM 10y ago
  If your numbers are correct, and I did the math correctly in my head, that's about five thousand pounds of thrust. A nuclear submarine might weigh ten thousand times that. Obviously a nuclear sub operates at much lower power level and obviously the hull doesn't have to be as thick for a spacecraft so I think it not a ridiculous comparison. Also you're spacecraft need not carry dozens of ICBMs, torpedoes, hundreds of sailors, etc. Obviously the first engine ever exhaustively tested is usually not the highest performance achievable. A factor of a thousand seems possible although a hundred is more likely. So for a very large nuclear plant, if the EM drive were weightless (LOL) then maybe 1/10th G applied to that nuclear sub is some kind of theoretical limit not entirely ridiculous but possible. Now consider that to one sig fig a G of acceleration for a year is the speed of light. And if you're careful maybe you could run the plant for three decades. So a round trip to the speed of light and back again is more or less back of the envelope possible to visit some distant star. Relativity rears its ugly head and ten years of ship time around the speed of light is a lot further than 10 lightyears and time passing on earth is a lot longer than ten years. Of course at the speed of light you're going to need a rather substantial hull, an active radar that can avoid interstellar crud, etc. If you can detect "stuff" at a day out, at a tenth of a G accelerating for an entire day you can be quite far away indeed by the time you pass it. I can't run the numbers in my head like above, but even 1/100th G slices a very substantial amount of time off a Mars mission. Some unverified google results imply 1/100th G means Mars in a month not a year and a half. At least as a back of the envelope calculation its quite a useful vehicle.
marcosdumay 10y ago
If you have a fusion power plant, you also have plenty of spent fuel to use as reaction mass.

by ant6n 10y ago

jcranmer 10y ago

The EM drive is reported as producing maybe 1 mN per kW. The largest power plant in the world produces about 22 GW of energy--at that ratio, an EM drive could produce maybe 22 kN. The first stage of the Saturn V rockets produced 35,000 kN of thrust. As a practical engine, EM drives are worse than chemical rockets or even ion thrusters (which produce about 25-250 mN/kW, according to Wikipedia).

bitJericho 10y ago
Once we understand the physics, if it's a real phenomenon, we might be able to make it much more efficient. Compare a modern li-on battery to a lemon, coin and nail, for example.
ant6n 10y ago
This was a response to 'Problem is we don't really know where to go next'. Saying that there's basically nothing beyond chemical rockets. My point is that there are plenty of possibilities to continue to develop propulsion technology.
VLM 10y ago
If your numbers are correct, and I did the math correctly in my head, that's about five thousand pounds of thrust. A nuclear submarine might weigh ten thousand times that. Obviously a nuclear sub operates at much lower power level and obviously the hull doesn't have to be as thick for a spacecraft so I think it not a ridiculous comparison. Also you're spacecraft need not carry dozens of ICBMs, torpedoes, hundreds of sailors, etc. Obviously the first engine ever exhaustively tested is usually not the highest performance achievable. A factor of a thousand seems possible although a hundred is more likely. So for a very large nuclear plant, if the EM drive were weightless (LOL) then maybe 1/10th G applied to that nuclear sub is some kind of theoretical limit not entirely ridiculous but possible. Now consider that to one sig fig a G of acceleration for a year is the speed of light. And if you're careful maybe you could run the plant for three decades. So a round trip to the speed of light and back again is more or less back of the envelope possible to visit some distant star. Relativity rears its ugly head and ten years of ship time around the speed of light is a lot further than 10 lightyears and time passing on earth is a lot longer than ten years. Of course at the speed of light you're going to need a rather substantial hull, an active radar that can avoid interstellar crud, etc. If you can detect "stuff" at a day out, at a tenth of a G accelerating for an entire day you can be quite far away indeed by the time you pass it. I can't run the numbers in my head like above, but even 1/100th G slices a very substantial amount of time off a Mars mission. Some unverified google results imply 1/100th G means Mars in a month not a year and a half. At least as a back of the envelope calculation its quite a useful vehicle.

marcosdumay 10y ago

If you have a fusion power plant, you also have plenty of spent fuel to use as reaction mass.