Space is getting crowded. An increasing number of space science missions aimed at improving basic understanding of planetary science have been launched or proposed in the past few years. These missions have been part of spaceflight since its advent but long were launched only by traditional space powers: the United States, Europe and Russia. Today, a new set of players has entered the arena, launching missions to the moon, the asteroids and other planetary bodies. China, Japan and India have all performed, attempted or announced missions to Mars in the past three years. The proliferating global use of space will be a defining feature of the 21st century, and science missions are only one part of this trend. Access to space will be essential in order for nations to pursue both military and economic objectives.