Part task trainers are an integral and important group of training devices now being used in the manned space programs. These devices are used to train the astronauts in discrete portions of a flight profile. It may operate one day as a rendezvous trainer and the next as a lunar landing trainer. The device consists of a computer complex, simulated cabin interior, external out-the-window display, and an instructor's complex. Arriving at a design philosophy requires a good working knowledge of the purpose of this type of trainer and the state of the art of various electronic, optical, and mechanical devices required by the trainer. Selecting the computer and optical systems is a difficult task requiring many compromises and trade-offs to arrive at the best and most economical system possible.