Radiometer, Microwave, U2

Display Status:

This object is on display in the Explore the Universe exhibition at the National Air and Space Museum in Washington, DC.

Collection Item Summary:

This dial channel microwave radiometer contains two pairs of collecting apertures, or horns, one for 33 (the large pair of horns) and the other for 53 (the small pair of horns) ghz radiometers. The assembly was designed and built by George Smoot and his colleagues at the University of California, Berkeley, to study the cosmic microwave background first detected by Penzias and Wilson at Bell Laboratories. This instrument flew on the NASA Ames U-2 aircraft in California (1975-1976) and in Chile and Peru (1979) at altitudes in excess of 60,000 feet, where the air is thin enough to permit observations in the region of 0.9 cm wavelength (or 33 GHz), a region where interfering radiation from the Milky Way itself is minimized. Another set of smaller radiometer horns, operating at the higher frequency of 53 GHz, monitored the atmosphere. Data from those flights showed that the background is extremely uniform and consistent, but that there is a hemispherical bias caused by the movement of the Earth with respect to the background radiation. This movement is the sum of all known motions of the Earth: on its axis, around the sun, with the solar system around the galaxy, and the galaxy itself. In sum, the movement is 300 km/sec or 1 million miles per hour with respect to the background radiation. This instrument flew in an open hatch behind the U-2 pilot cockpit and was rotated during the flight.

This flight instrument was a prototype for the Differential Microwave Radiometer (DMR) that flew on the Cosmic Background Explorer Satellite (COBE) in 1989 and provided confirming data for the hot thermal Big Bang theory of the origin of our Universe. The radiometer was transferred to NASM by DOE and the University of California at Berkeley's Lawrence National Laboratory in 1997. It is now on display in the Explore the Universe gallery.