Cosmic Ray Energetics and Mass (CREAM) is an experiment to determine the composition of cosmic rays up to the 1015 eV (also known as the "knee prospect") in the cosmic ray spectrum. It has been hypothesized that the knee prospect of the cosmic ray spectrum can be explained by the theoretical maximum energy that a supernova can accelerate particles to according to Fermi acceleration. The measurements are accomplished using a timing-based charge detector and transition radiation detector sent to an altitude of at least 34 km (21 mi) with aid of a high-altitude balloon.