  Structure formation in the early universe is expected to produce a
cosmological background of free-free emission. The Absolute Radiometer for
Cosmology, Astrophysics, and Diffuse Emission (ARCADE) will measure the
spectrum of the cosmic microwave background at centimeter wavelengths to detect
this signature of structure formation. I describe the ARCADE instrument and the
cryogenic engineering required to achieve mK accuracy at such long wavelengths.
