# Thread: Hitting the light speed breaks.

1. Let's say, over the course of a year, a space ship accelerates to light speed and consumes 100 gallons of space fuel (it's very good space fuel). It then decides to make a full stop by shooting the thrusters in reverse. Would it take the same amount of time and the same amount of gas to decelerate to zero?

2.

3. Originally Posted by hencook
Let's say, over the course of a year, a space ship accelerates to light speed and consumes 100 gallons of space fuel (it's very good space fuel). It then decides to make a full stop by shooting the thrusters in reverse. Would it take the same amount of time and the same amount of gas to decelerate to zero?
It must be good, as it take an infinite amount of energy to accelerate any mass to c. Presumably it also takes as infinite amount of energy to decelerate from c to zero.

4. As exchemist says it would be an infinite amount in both cases.
But you would still be saving the infinite amount of fuel it took to accelerate that hundred gallons of space fuel you burned getting to lightspeed as you slowed down.

5. If you throw out that light speed detail, then the answer is no in both cases. The spaceship will be missing 100 gallons of fuel mass when slowing down. So you'll get more acceleration for the same force and you'll need less fuel to stop.

6. If light speed was achievable, then yes - it would require the same amount of energy to decelerate as to accelerate.
But, as MagiMaster said, the weight of the fuel would complicate things.
If the ship refuelled before slowing down, it would take the same amount of fuel to decelerate.

7. Have a read of this webpage:

The Relativistic Rocket

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