Some new methods for planetary exploration

For many centuries the planets of our solar system have been objects of study by astronomers. Before the invention of the telescope, these studies were restricted to an attempt to understand and predict their motion. Telescopes and accurate clocks allowed more precise observations to be made. By the 19th century, minor perturbations of the motions of the planets were being analyzed. By the end of this century, however, astronomers were becoming more interested in stellar and galactic problems, and the group interested in celestial mechanics and planetary observations appeared to be decreasing to a vanishing point in the mid-20th century. Then came the space program, and the possibility of performing experiments on, or at least near, other planets encouraged interest in the solar system to a remarkable degree