Planetary exploration: To boldly go - or what?

The direction of solar system exploration in the U.S. is examined. Planetary exploration missions from 1961-1976 are reviewed. The objectives of the Viking and Voyager missions are described. The effects of launch vehicles and access to space, the cost of exploration, the balance of planetary exploration with other space sciences, and international planet exploration missions on future planetary exploration programs are discussed. Inner and outer solar system exploration, comet exploration, extensive human visitations to Mars, joint U.S.-Soviet programs, and exploration beyond the solar system are proposed as future planetary missions.