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## Main Question or Discussion Point

A spaceship with an arbitrarily large quantity of fuel cells departs Earth and accelerates away from it with a fixed trajectory until it reaches .9c. It continues to accelerate, but never reaches c because that is impossible for any object with mass.

From the frame of reference of the crew onboard the ship, their mass, rate of time, and length remains unchanged, so from their perspective, what is keeping the spaceship from continuing to accelerate to c?

From the frame of reference of mission control on Earth, what is keeping the spaceship from accelerating to c? I believe the answer to this is that it's relativistic mass increases as it's velocity approaches c, so that an infinite amount of energy would be required to fuel any further acceleration. However, I have a possibly erroneous understanding that time dilation and length contraction fit into this somewhere. Is the key that as the spacecraft approaches c, it's time becomes so dilated, and it's length so contracted, that it is getting no "bang for its buck" from the fuel it is using? If so, how does the spaceship's time dilating and it's length contracting affect it's velocity/acceleration as seen by mission control?

As always, thank you.

-coktail

From the frame of reference of the crew onboard the ship, their mass, rate of time, and length remains unchanged, so from their perspective, what is keeping the spaceship from continuing to accelerate to c?

From the frame of reference of mission control on Earth, what is keeping the spaceship from accelerating to c? I believe the answer to this is that it's relativistic mass increases as it's velocity approaches c, so that an infinite amount of energy would be required to fuel any further acceleration. However, I have a possibly erroneous understanding that time dilation and length contraction fit into this somewhere. Is the key that as the spacecraft approaches c, it's time becomes so dilated, and it's length so contracted, that it is getting no "bang for its buck" from the fuel it is using? If so, how does the spaceship's time dilating and it's length contracting affect it's velocity/acceleration as seen by mission control?

As always, thank you.

-coktail