If such a hypothetical power source existed, we could literally replace the propulsion systems of nuclear submarines and have an instant space fleet... Complete with torpedoes ;-)
If you are talking about single-stage-to-orbit (SSTO) submarines, I should tell you that the Sea Dragon is kind of like that. It is 75 feet in diameter, and produced in an ordinary maritime shipyard out of steel. This is larger in diameter than any submarine ever made. The Russian Typhoon submarine class is 75 feet wide, but it is not round (it is shorter high than it is wide; flat top). http://en.wikipedia.org/wiki/Typhoon_class_submarine
A major difference between the Sea Dragon and an SSTO submarine would be the fact that a Sea Dragon is a staged vehicle. Only part of it would make it to orbit. It does launch from the sea, by the way. It could potentially be scaled up to whatever your preferable size is. Is there a particular reason why you would want a big metal submarine in orbit?
I guess I'm not following you. What problem is this hypothetical power source attempting to solve? Before, it sounded like you were talking about a need to launch cargo into orbit. Why are you using the term power source?
By the way, high-thrust, and high Isp (rocket fuel efficiency = propellant speed), goals generally conflict with each other. To launch from Earth requires high thrust. To travel through space requires high Isp.
Because to do anything useful in space we've got to get stuff there, i.e. heavy industrial machinery for mining, and people to operate it, and a way to sustain them, and a way to get what they produce back to Earth. Getting in an out of a gravity well has to be routine. It's only expensive and difficult now because we don't have anything with enough energy density to do it. If you can make a powered re-entry you don't even need to bother with the Shuttle's elaborate heat shielding, you just take your time, match orbit with the Earth and come "straight down" in an hour or two.
Power source, energy source, fuel, these terms are interchangeable.
to do anything useful in space we've got to get stuff there, i.e. heavy industrial machinery for mining
That is what the Sea Dragon is for. The payload capacity is 1.2 million pounds, and can be expanded with minor modifications.
-
It's only expensive and difficult now because we don't have anything with enough energy density to do it.
We have kerosene and liquid oxygen. Chilled propane works, too. Are you thinking that these fuels and oxidizers are somehow not adequate? If so, in what way?
-
If you can make a powered re-entry you don't even need to bother with the Shuttle's elaborate heat shielding
The Shuttle requires elaborate heat shielding for reasons that have nothing to do with the fact that it does not make powered re-entries. The Russian Soyuz capsule re-enters with a basic heatshield and lands on the Kazakh steppes. It's cheap. It's reliable.
Powered re-entries to Earth are not feasible and not desirable. They would be outrageously expensive and probably unreliable (read: dangerous).
