To provide quick implementation of scientific opportunities for space science investigations, the National Aeronautics and Space Administration has begun a new part of its Explorer program. The Small-Class Explorer program is for missions that can be done on spacecraft carried by Scout-class launch vehicles and that will take less than 3 years from initiation to launch.
Explorer research areas include astrophysics, space physics, and upper atmospheric physics. Over the years, dozens of small- and medium-sized payloads have been launched in the Explorer program, for example, the Solar Mesospheric Explorer and the Active Magnetospheric Particle Tracer Experiment. The small-class program is for small free-flyers with focused investigations that complement major missions, prove new scientific concepts, or make other significant contributions to space science. The program includes special opportunities for bilateral international cooperation.