Because the author is also deputy technical director of the Gemini Project for the Martin-Marietta Corporation (which manufactures spacecrafts and booster rockets) Appointment in the Sky is completely authoritative while presented in non-technical language. A great deal of the material here, though, is an unexciting rehash of information most casual newspaper readers already know and which history may not find worth remembering. Project Gemini is the midway stage between the old Project Mercury (sub-orbital flight) and Project Apollo (moon flight). Object of Project Gemini is to rendezvous in space with an unmanned vehicle, remain in space for two weeks, and then land on a predesignated strip of land back in the States. (The name Gemini is from the ""twin"" constellation containing Castor and Pollux sitting side by side--there will be two astronauts in the Gemini spacecraft). Mr. Levine also covers Russian activities in space and reveals the interesting facts behind three Russian losses in space before the announced success of Yuri Gagarin: one manned ship exploded during launching and two went up that have never come down. Training of astronauts, problems encountered in space, and landing the spacecraft by paraglider and a description of a moon trip occupy most of this recap.