It is the year 2150 and the United Nations Space Federation has ﬁnally perfected the storage of antiprotons for use as fuel in a spaceship. (Antiprotons are the antiparticles of protons. Preparations are under way for a manned spacecraft visit to possible planets orbiting one of the three stars in the star system Alpha Centauri, some 4.30 lightyears away. Provisions are placed on board to allow a trip of 16 years’ total duration. How fast must the spacecraft travel if the provisions are to last? Neglect the period of acceleration, turnaround, and visiting times, because they are negligible compared with the actual travel time.

It is the year 2150 and the United Nations Space Federation has ﬁnally perfected the storage of antiprotons for use as fuel in a spaceship. (Antiprotons are the antiparticles of protons. Preparations are under way for a manned spacecraft visit to possible planets orbiting one of the three stars in the star system Alpha Centauri, some 4.30 lightyears away. Provisions are placed on board to allow a trip of 16 years’ total duration. How fast must the spacecraft travel if the provisions are to last? Neglect the period of acceleration, turnaround, and visiting times, because they are negligible compared with the actual travel time.