5 ms·
Whatever Happened to Photon Rockets? (2013)
- Animats 11y agoBecause, physics. Laser launch has some of the same problems. It takes about a megawatt to lift a kilogram.
- david-given 11y agoWay more than that. The numbers for photon rockets come out at about 300 MW/N. So to lift one kilogram against earth's gravity you need about three gigawatts. This is why people generally prefer to use the energy to accelerate reaction mass instead of just generating photons.
- randallsquared 11y agoUsually "laser launch" means using a ground-based laser to heat propellant on the rocket. These seem entirely different from photonic rockets to me, but the wiki article on laser propulsion lists them as two examples. Confusion has ensued. :)
- api 11y agoConventional rockets take many orders of magnitude more than that. Calculate e=mc^2 for the mass of propellant they expel. :)
- lukev 11y agoThis is laughably wrong. They aren't converting that matter to energy - they are just utilizing Newton's third law. Throwing the matter really fast exerts an opposite force in the other direction. As far as human energy production is concerned, e=mc^2 only comes into play in nuclear reactors. Edit: to elaborate a bit, rockets are still just using stored chemical energy and converting it to kinetic energy. They're not converting matter to energy (i.e, using e=mc^2). It just so happens that stored chemical energy is loads more efficient than anything output by a laser (at this point in time).
- api 11y agoMatter is energy. I was speaking to how much energy, in some form, is involved in propulsion. Rockets move more energy (as matter propellant) because they have lower isp, while a photon rocket has the theoretical maximum isp. Photon rockets are maximally efficient but require that all propellant be E, not m.
- InclinedPlane 11y agoPhoton rockets are only feasible if you have crap-tons of anti-matter. And even then, only in some uses.