Once you go mobile (ships, rockets) space and weight considerations become more important.
That brings up a question. How much energy does it take to accelerate a 1 Kg mass at 1 g? Assume perfect conversion to kinetic energy, for the moment.
The question is rooted in the fact that it takes 143 years to accelerate a 100 metric ton spacecraft to 1% c, if it only has a 100 Mw power plant, and perfect conversion. I want to launch from Earth's surface, what size BFR do I need?
Actually, the funky thing is that accelerating something that isn't moving relative to you doesn't take any power no matter how fast you do it. Once a relative velocity develops, THEN it takes power. This is why high-Isp (high exhaust velocity) drives take more power for the same amount of thrust as low-Isp ones.
It's also why criticizing SpaceShipOne for having a peak kinetic energy of some tiny % of orbital energy is a red herring - sure, going ten times as fast requires that you have 100 times the kinetic energy at the end of it, but it only requires that you burn 10 times as much fuel, or even less if you take mass fraction into account...
It's also why there's no known theoretical limit to the thrust efficiency (N/W) of a Mach-effect thruster (assuming it works at all; it's a significantly longer shot than Polywell)... proponents talk about 1 N/W as an "achievable" goal; just for comparison, this would result in a 1 MW reactor being able to get a 100 ton spacecraft to 0.01c in three and a half days - yes, that's at a constant acceleration of 1 gee... it also assumes that enough of the universe is moving about that fast in roughly that direction that the drive will still work...
What I'm trying to say is that the energy expended by a reaction drive system doesn't go into the spacecraft in the starting reference frame. It goes into the exhaust in the spacecraft's reference frame. Your calculation is invalid.
For a reaction drive, the higher the propellant efficiency gets, the worse the thrust efficiency becomes.
Also, the Mach effect is supposed to arise within General Relativity, given a certain interpretation of Mach's principle. I'm not holding my breath, but it is illustrative of the point.
93143 wrote:What I'm trying to say is that the energy expended by a reaction drive system doesn't go into the spacecraft in the starting reference frame. It goes into the exhaust in the spacecraft's reference frame. Your calculation is invalid.
For a reaction drive, the higher the propellant efficiency gets, the worse the thrust efficiency becomes.
Also, the Mach effect is supposed to arise within General Relativity, given a certain interpretation of Mach's principle. I'm not holding my breath, but it is illustrative of the point.
Do you think there's anything to the Mach effect thruster ? I assume you are referring to the "Woodward Effect" ? It has been a subject that i've been very interested in for several years, but it seems to have been dropped as a research project. At one time, it was being investigated by John G. Cramer of the University of Washington with a Nasa grant, but they never resolved whether there was anything to it or not.
Looking at their design for testing the theory, my first thought was "how could you ever expect THAT to work? " It looked like a recipe for feedback, which indeed is exactly what happened.
Is anybody out there looking at validating or disproving the "Mach Effect?"
I haven't checked in a while, but last I saw, it was reported as still being worked on at the nasaspaceflight forum. Probably in the Advanced Concepts subforum.
Roger wrote:I thought it was either 6 coils or 12 coils?
Truncube or truncdodec.
Cube or dodec.
Limiting ourselves to the Platonic solids, it can be 4, 6, 8, 12, or 20 depending on which faces you wish to make real and which virtual, if any.
Please stop thinking truncated and think rectified (fully truncated). It helps.
With more detail.
4 using the alternating faces of the pure octahedron. (Real/Virtual (R/V))
6 using the "square" faces of the cuboctahedron. (R/V)
8 using EITHER all the faces of the pure octahedron (R/R) or the "trianglular" faces of the cuboctahedron. (R/V)
12 using the "pentagonal" faces of the icosadodecahedron. (R/V)
20 using the triangular" faces of the icosadodecahedron. (R/V)
ravingdave wrote:Is anybody out there looking at validating or disproving the "Mach Effect?"
Betruger wrote:I haven't checked in a while, but last I saw, it was reported as still being worked on at the nasaspaceflight forum. Probably in the Advanced Concepts subforum.
Yep. Latest news was that Woodward had set up a device that was designed to clearly show the Mach effect rather than generate thrust, and it supposedly showed an effect in antiphase to electrostriction, with S/N of about 10 dB. The claim is that no predicted effect, besides the Mach effect, can explain this result.
Unfortunately I haven't looked into the matter closely, being somewhat busy with more conventional rocket science...
4 using the alternating faces of the pure octahedron. (Real/Virtual (R/V))
That will get you an S pole at the "missing" faces (assuming N in). Not good.
You want to shrink the S poles as much as possible.
Please show me ANY reference to this. I think you are mistaken.
From DrB's Valencia paper he says he wanted to make the toroidal magnet into a square plan-form. This would have made the S in (N out) BIGGER relative to the N in, NOT smaller.
4 using the alternating faces of the pure octahedron. (Real/Virtual (R/V))
That will get you an S pole at the "missing" faces (assuming N in). Not good.
You want to shrink the S poles as much as possible.
Please show me ANY reference to this. I think you are mistaken.
From DrB's Valencia paper he says he wanted to make the toroidal magnet into a square plan-form. This would have made the S in (N out) BIGGER relative to the N in, NOT smaller.
It would amount to a greatly expanded funny cusp with a lower and more diffuse field over most of the cusp. Not good.
Look at some of Indrek's field simulations and then imagine what they would look like with one face missing.
Engineering is the art of making what you want from what you can get at a profit.