Suppose you are planning a trip in which a spacecraft is to travel at a constant velocity for exactly eleven months, as measured by a clock on board the spacecraft, and then return home at the same speed. Upon return, the people on earth will have aged exactly one hundred fifty years. According to special relativity, how fast must you travel?

(Express your answer to at least 5 significant figures as a multiple of c -- for example, 0.95585c.)