abstract
| - A relativistic rocket is any spacecraft that is travelling at a velocity close enough to light speed for relativistic effects to become significant. What "significant" means is a matter of context, but generally speaking a velocity of at least 50% of the speed of light (0.5c) is required. The time dilation factor, mass factor, and Lorentz contraction factor are 1.15 at 0.5c. Above this speed Einstein's physics are required to accurately describe motion. Below this speed, motion is reasonably well described approximately by Newtonian physics. We define a rocket as carrying all of its reaction mass, energy, and engines with it. Thus Bussard ramjets, RAIRs[1], light sails, and maser or laser-electric vehicles are not pure rockets, though they do use reaction-drives like rockets. Achieving relativistic velocities is difficult, requiring advanced forms of spacecraft propulsion that have not yet been adequately developed. Nuclear pulse propulsion could theoretically achieve 0.1c using current known technologies, but would still require many engineering advances to achieve this. The relativistic gamma factor () at 10% of light velocity is 1.005. Generally a rocket that achieves at least 50% of light velocity is a relativistic rocket. The time dilation factor of 1.005 which occurs at 10% of light velocity is too small to be of major significance. A 0.10c velocity interstellar rocket is thus considered to be a non-relativistic rocket because its motion is very accurately described by Newtonian physics alone. Relativistic rockets are usually seen discussed in the context of interstellar travel, since most would require a great deal of space to accelerate up to those velocities. They are also found in some thought experiments such as the twin paradox.
|