Editing Relativistic rocket (section)

{{Short description|Type of spacecraft}}
'''Relativistic rocket''' means any [[spacecraft]] that travels close enough to [[light speed]] for [[special relativity|relativistic]] effects to become significant. The meaning of "significant" is a matter of context, but often a threshold velocity of 30% to 50% of the speed of light (0.3''c'' to 0.5''c'') is used. At 30% c, the difference between relativistic mass and rest mass is only about 5%, while at 50% it is 15%, (at 0.75''c'' the difference is over 50%); so above such speeds special relativity is needed to accurately describe motion, while below this range Newtonian physics and the [[Tsiolkovsky rocket equation]] usually give sufficient accuracy.

In this context, a rocket is defined as an object carrying all of its reaction mass, energy, and engines with it.

No known technology can bring a rocket to relativistic speed. Relativistic rockets require huge advances in spacecraft propulsion, energy storage, and engine efficiency which may or may not ever be possible. [[Nuclear pulse propulsion]] could theoretically reach 0.1''c'' using current known technology, but would still require many engineering advances to achieve this. The relativistic [[gamma factor]] <math>\gamma</math> at 10% of light velocity is 1.005. A 0.1''c'' speed rocket is thus considered non-relativistic since its motion is still quite accurately described by Newtonian physics alone.

Relativistic rockets are usually seen discussed in the context of [[interstellar travel]], since most would need a lot of space to reach such speed. They are also found in some [[thought experiment]]s such as the [[twin paradox]].