Suppose we want to send an astronaut on a round trip to visit a star that is 200 light-years distant and at rest with respect to Earth. The life support systems on the spacecraft enable the astronaut to survive at most 20 years. At what speed must the astronaut travel to make the round trip in 20 years of spacecraft time?

Suppose we want to send an astronaut on a round trip to visit a star that is 200 light-years distant and at rest with respect to Earth. The life support systems on the spacecraft enable the astronaut to survive at most 20 years. At what speed must the astronaut travel to make the round trip in 20 years of spacecraft time?