3 ms·

The claimed power to thrust ratio of 165 MW / N does check out as less efficient than a photonic rocket at 150 MW / N assuming the beam is reflected off the c

The claimed power to thrust ratio of 165 MW / N does check out as less efficient than a photonic rocket at 150 MW / N assuming the beam is reflected off the craft.

iamgopal 7y ago
165 mega watt per Newton ? Is it theoretical or practical number ?
- trhway 7y ago
  Sun radiation is about 1.4KW/m2 at the Earth orbit and the pressure is 0.00001N/m2 - basically the same numbers as GP mentioned for the photonic drive - can be calculated as 1.5KJ (for roundness of numbers) of photons divided by c which gives 0.000005kg-m/s of momentum per second, double that for bounce and thus 0.00001N. As photons are usually the things being thrown for the thrust in the mass-less thrust schemas, then those photonic thrust numbers seems to be a theoretical limit .
gus_massa 7y ago
If you are bouncing the photos (like in a solar sail, aka a mirror attached to the back of the starship) then the minimal power is 150MW/N. If you are generating the photons (like in a photon rocket, aka laser attached to the back of the starship) then the minimal power is 300MW/N (and you need a generator). I didn't notice before the 165MW/N in the slides, but their device is not bouncing the photons, so the theoretical minimum is 300MW/N, so it is impossible to use only 165MW/N. So they must have an error (numerical or conceptual) in the calculation. In the slide, the energy is used to accelerate the particles, and then the energy is recovered when the particles return. So the article claim more efficiency, but let's ignore that part. I think the main problem is that the particles will emit a lot of energy in the sharp turn at the top, something like the https://en.wikipedia.org/wiki/Cyclotron_radiation https://en.wikipedia.org/wiki/Cyclotron_radiation This radiation is what really push the device. In the sharp turn at the bottom the particles are going more slowly, so the radiation and push is smaller. I don't understand why the calculation using a mix of classical and relativistic formulas give almost the correct result. The error is only in x2 (in the impossible direction), a x2 is not so off. I guess the main problem is assuming that the particles will have the same speed during all the turn???

The claimed power to thrust ratio of 165 MW / N does check out as less efficient than a photonic rocket at 150 MW / N assuming the beam is reflected off the craft.

iamgopal 7y ago

165 mega watt per Newton ? Is it theoretical or practical number ?

trhway 7y ago
Sun radiation is about 1.4KW/m2 at the Earth orbit and the pressure is 0.00001N/m2 - basically the same numbers as GP mentioned for the photonic drive - can be calculated as 1.5KJ (for roundness of numbers) of photons divided by c which gives 0.000005kg-m/s of momentum per second, double that for bounce and thus 0.00001N. As photons are usually the things being thrown for the thrust in the mass-less thrust schemas, then those photonic thrust numbers seems to be a theoretical limit .

gus_massa 7y ago

If you are bouncing the photos (like in a solar sail, aka a mirror attached to the back of the starship) then the minimal power is 150MW/N. If you are generating the photons (like in a photon rocket, aka laser attached to the back of the starship) then the minimal power is 300MW/N (and you need a generator). I didn't notice before the 165MW/N in the slides, but their device is not bouncing the photons, so the theoretical minimum is 300MW/N, so it is impossible to use only 165MW/N. So they must have an error (numerical or conceptual) in the calculation. In the slide, the energy is used to accelerate the particles, and then the energy is recovered when the particles return. So the article claim more efficiency, but let's ignore that part. I think the main problem is that the particles will emit a lot of energy in the sharp turn at the top, something like the https://en.wikipedia.org/wiki/Cyclotron_radiation https://en.wikipedia.org/wiki/Cyclotron_radiation This radiation is what really push the device. In the sharp turn at the bottom the particles are going more slowly, so the radiation and push is smaller. I don't understand why the calculation using a mix of classical and relativistic formulas give almost the correct result. The error is only in x2 (in the impossible direction), a x2 is not so off. I guess the main problem is assuming that the particles will have the same speed during all the turn???