Shubedobedubopbopbedo wrote:Anyway, I'm assuming that the shock absorbers are actually shock absorbers. If they were what you describe, they would be called springs, not shock absorbers.
They're gasdynamic springs, as far as I can tell.
Hmm... Actually, from Figure 2.4 in the report, it looks like the dissipation in the secondary system is about 7% per half cycle. I can't see any dissipation in the primary system (Figure 2.3), so I'll assume 10% in total.
So double my estimate for heating. Or redesign the system - this is a conceptual study, after all...
Where does this leave us? Steady-state would be 1380 K, which looks a bit dubious, but we don't need to worry about steady-state. After firing 800 pulses, assuming no cooling, we're at 634 K, or 361ºC, or 681ºF.
Apparently it's still not a problem.
Larger vehicles would have to deal with longer burn times and more energy in the pusher system, but could hopefully be designed with more sophisticated and efficient shock absorbers, and perhaps some nominal cooling/radiator systems (nothing that sticks out past the pusher plate's shadow cone, of course)... For instance, I heard about a droplet radiator system that ejects the droplets forward from an accelerating starship, then collects them once the starship catches up...
Also, without actually running the numbers, I'm wondering if your estimate of vibration frequency is correct ~1 second? Don't you think this would shake the spacecraft to pieces?
Why? It's not the speed that matters; it's the induced loads (unless the vibration gets so fast that fatigue is a concern...) Ares I TO was significantly faster, at a higher gee loading, with structural resonance thrown in into the bargain, and the only hazard was to the astronauts.
Besides, do you really think they didn't take this into account? There's a vibroacoustic analysis in the report.
Judging from Figure 2.3, it's 1.10 seconds for half a cycle of the secondary system (the primary system is 9 times as fast). So 2.2 seconds for a full oscillation. (This also means my equilibrium power dissipation calculation is about 9% too high, all else being equal...)
The low-yield fission bombs are radation bombs, giving off up to 80% of their energy as neutrons and x-rays.
Hence the massive chunk of tungsten and beryllium oxide in between the physics package and the spacecraft.
But I'm not convinced that a low-yield bomb is the best choice.
It's not. It's just easier to build a spacecraft that can make use of it. Projections indicate that the effectiveness of the Orion design increases continuously with the yield of the pulse units, all the way up to megaton-range deuterium bombs.
I think the pusher plate design is inherently massive due to the compression members needed in the structure. There is a way to make the whole thing less massive, and hence faster.
Medusa?
It has its advantages and disadvantages with respect to a conventional Orion...