ARCADE

ARCADE (for Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission) was an instrument package (virtually, a telescope) flown in a balloon to about 120,000 feet. It was flown four times, in 2001, 2003, 2005, and 2006, then decommissioned. The latter two flights had an improved instrument package named ARCADE 2. They sensed microwave from the sky in the range of centimeter-wavelengths. They used radiometers cooled to 3 K, attempting to measure temperature differences of 0.001 K. Effectively, they viewed the cosmic microwave background (CMB), but looking for variations (secondary CMB anisotropies) in its long-wavelength tail due to the heat of ancient stars and galaxies, and also EMR from early universe particle interactions.