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just a noob question: why transport all the fuel, and not start from a cannon/catapult, something that make you start with some speed? edit: it's not clear, I was talking about partially using a cannon, not about a complete ballistic launch.
Get the pieces up there as efficiently as possible, and then assemble a more efficient rocket that's not designed to leave the gravity well.
Earlier quoted context omitted.
Anything that pushes stuff out from a small hole in order to accelerate in the opposite direction is a rocket, by definition, and subject to the rocket equation. If a chemical reaction is used to create the energy to push the stuff out, it's a chemical rocket. If a nuclear reactor is used to heat the stuff so it's pushed out, it's a nuclear thermal rocket. If a nuclear reactor or solar panels are used to generate ele…
How about http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi... ?
Orion gets its momentum transfer from the plasma debris of the nuclear explosion, and the plasma speed comes from the explosion itself. Orion carries the source of the plasma, hence it is limited by the rocket equation.
"If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport." I thought this was quite though-provoking from a Drake Equation standpoint. From what I've gleaned, the earth-like planets we know of seem to be a big bigger than Earth. Perhaps if there's civilization out there, they are hampered by the misfortune of being on a planet that's practically impos…
Earlier quoted context omitted.
i'll spare everybody else the snark here
Zero feelings involved, just analysis before numerical computation. The concepts need to make sense first.
> ... accelerate upward then turn 90 degrees and accelerate horizontally
I am not for such a scenario at all. The point of the upward (upward only and not considering the atmosphere) acceleration to the desired location is to give the lower bound of the energy requirements. This is the baseline (baseline-1) and the rocket equation is as simple as possible.
In reality with an atmosphere and to put the object in orbit, the aerodynamics change and the energy requirement increases beyond the above baseline-1.
If you "accelerate upward then turn 90 degrees and accelerate horizontally", you can calculate an energy requirement for that and it is easy. Only two vectors involved. That should give some limit (call it baseline-2). We should expect to do better than baseline-2, how better? A calculation using the diagonal of the vectors involved in baseline-2 should give us baseline-3.
We shouldn't do better than baseline-3. Our launch designs and ingenuity should have an energy requirement between baseline-2 (this is bad, we are not thinking) and baseline-3 (this is maybe closer to ideal).
The rockets and shuttles do "pitch-over manoeuvres" to turn the straight upward acceleration into an elliptical acceleration.
* Note, I have not addressed the complications of the variations in atmospheric drag, but if it varies close to linearly along the vertical cross-sectional then how I think about it above does not change unless there is some other oversight.
"If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport." I thought this was quite though-provoking from a Drake Equation standpoint. From what I've gleaned, the earth-like planets we know of seem to be a big bigger than Earth. Perhaps if there's civilization out there, they are hampered by the misfortune of being on a planet that's practically impos…
At its core, a rocket isn't more complicated than a car. The challenges are just different. My dearest hope is that eventually rocket components will be as commoditized as car parts, so people can build and maintain their own spacecraft. I want to see rockets held together with duck tape and spit, because that's the point where spaceflight is available to everybody and gravity stops becoming a hurdle.
A quick disclaimer: I have the greatest respect for rocket engineers. They are taking the first steps, the most difficult ones, and I don't believe for a second that they their work is easy. I just believe that eventually, they'll become obsolete to the majority of spacetravel :)
Right. This has been known for a long time. It's why rockets aren't much better than they were 40 years ago. Chemical fuels are as good as they can get. Space travel with chemical fuels is just barely feasible. In the 1960s, it was assumed that nuclear power would be necessary for space flight. Everybody involved knew the rocket equation. The original plan for Apollo included a nuclear upper stage. The engine (NERVA)…
To certain extent, that only applies while assuming rocket launches are hard to iterate. Otherwise it would be a matter of launching enough of them.
just a noob question: why transport all the fuel, and not start from a cannon/catapult, something that make you start with some speed? edit: it's not clear, I was talking about partially using a cannon, not about a complete ballistic launch.
Earlier quoted context omitted.
Zero feelings involved, just analysis before numerical computation. The concepts need to make sense first.
@SamReidHughes > ... accelerate upward then turn 90 degrees and accelerate horizontally I am not for such a scenario at all. The point of the upward (upward only and not considering the atmosphere) acceleration to the desired location is to give the lower bound of the energy requirements. This is the baseline (baseline-1) and the rocket equation is as simple as possible. In reality with an atmosphere and to put the o…
Doing that with a track would be expensive because the track would have to be built hundreds of miles high over all of its length. It would be cheaper to build most of it lower, and maybe accept that we'll have to handle the air resistance somehow. If we build a track that doesn't go out of the atmosphere, we could still use it to build up a lot of speed and then turn the rocket upwards before the thing is self-powered. If we do build a track that goes out of the atmosphere, we'd still want to get as much ground-level acceleration as we can.
Maybe it's more practical to build the track on the Moon, where there's no atmosphere.
> In the 1970’s, an experimental nuclear thermal rocket engine gave an energy equivalent of 8.3 km/s. This engine used a nuclear reactor as the source of energy and hydrogen as the propellant. That was intriguing, but didn't go into detail on why a nuclear thermal rocket hasn't been tried since. The obvious explanation is that there could be serious consequences if such a rocket exploded, spreading radioactive materi…
Also, problems with space access are mostly market size-related problems. Cheap access to space is possible, only requires a vast market to pay back the investments, which is simply not there.