# Relativistic mass for an interstellar craft

1. Mar 10, 2013

### Hercuflea

So there have been some theoretical designs for ships in the past that would be used for interstellar missions, i.e. Daedalus, Ramjet, Orion, etc. that may send ships to near relativistic speeds. I think daedalus had a max. speed goal of around .1c. My question is do you think that relativistic mass could be the downfall of these designs? I don't think around .1c would be fast enough to warrant relativistic treatment of the flight, but I have read that some antimatter powered designs could potentially reach .4-.5c which would certainly be relativistic.

So by special relativity, say an antimatter powered ship is going ~.5c

m = m0 / sqrt(1 - v^2 / c^2)

m = m0 / sqrt(1-.5^2)

m = m0 / .866 = 1.155 m0

So a ship at this speed would have gained 15% more mass than when it left earth. Woudln't all of this extra mass cause enough stress on the structure of the ship to practically rip it apart? I don't really know where the extra mass comes from, but I assume that the ship would be basically growing as it speeds up towards c? Or is the "relativistic mass" basically just the mass change as measured from an observer on earth, whereas the astronauts on the ship would not notice any difference in the mass, or length for that matter, of the ship?

Does relativity basically preclude us from building super fast craft, because the mass growth of the ship would basically destroy the design of the ship?

2. Mar 11, 2013

### Filip Larsen

That is correct. Relativistic mass is the apparent Newtonian mass of a moving object and is purely an observational effect.

Special relativity do not impose any special limit to where you (as an astronaut in a suitably build spaceship) can go in the visible universe. You are even allowed to go to Andromeda, our next door galaxy neighbor, if you really want to. See [1] for some details.

[1] http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html [Broken]

Last edited by a moderator: May 6, 2017