ACCESS (Advanced Cosmic-ray Composition Experiment on the Space Station)
ACCESS (Advanced Cosmic-ray Composition Experiment on the International Space Station was to have been an experiment to study the origin and makeup of cosmic rays over a three-year period. It was to have been attached to the International Space Station (ISS) and was due to replace AMS (Alpha Magnetic Spectrometer) in 2007. Its two instruments, the Hadron Calorimeter and the Transition Radiation Detector, would have measured the elemental makeup of cosmic rays from lightest nuclei to heaviest, and determine if the flux of high-energy electrons in cosmic rays varies with direction, as would be the case if some come from local sources.
In the event, ACCESS was not launched but its science objectives were addressed by the Cosmic-Ray Energetics and Mass (CREAM) investigation, which places a successful balloon-borne instrument aboard the ISS where it gathers an order of magnitude more data, which has lower background interference because Earth's atmosphere is no longer interfering. CREAM's instruments measure the charges of cosmic rays ranging from hydrogen up through iron nuclei, over a broad energy range. The modified balloon instrument is carried aloft on a Space X Dragon Lab cargo supply mission and placed on the Japanese Exposed Module for a period of at least three years.