MEASUREMENTS OF ISOTROPY OF COSMIC BLACKBODY RADIATION

The object of the flight was to measure the 3-cm (10 GHZ) cosmic radiation that is the remnant of the Big Bang fireball that existed several billion years ago and determine whether or not this radiation appears to be equally intense in all directions.

The instrument was an X-band Dicke radiometer carried by balloon to 24 km altitude to minimize noise due to atmospheric emissions. The receiver was a tunnel diode amplifier-detector chain with a noise figure of 5 dB and a pass band from 9.9 to 10.4 GHz. This frequency range was selected because it is a relatively unused portion of the X-band. Interference due to out-of-band emissions was eliminated by a bandpass filter, which provided 75 dB attenuation below 9.6 and above 10.7 GHz. The input to the receiver was switched at 2 kHz between two broad-beam (15° FWHM) horn antennas tipped in opposite directions at 45° from the zenith. The entire radiometer rotated about a vertical axis at 1 revolution per minute. Its orientation was monitored from the telemetered outputs of two flux-gate magnetometers afixed to the gondola. Thermal emission from the Earth was attenuated by aluminium shielding screens beneath the antennas. To avoid the large solar and lunar microwave power fluxes, the radiometer was flown on a moonless night. The twelve hours at altitude allowed observation of about half the northern celestial hemisphere, from ~3 h to ~15 h right ascension.

This flight resulted in the first measurement of the isotropy out of the equatorial plane. That is, previous work had been able to determine the isotropy only as a function of right ascension; this flight showed the declination dependence of this isotropy.

Balloon launched on: 1/8/1970 at 18:18 cst
Launch site: Hobbs, New Mexico, US  
Balloon launched by: National Center for Atmospheric Research (NCAR)
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen 322.000 cuft (1.0 mil. Stratofilm)
Balloon serial number: SF 92.5-100-NS-02 SN: 174
Flight identification number: 520H
End of flight (L for landing time, W for last contact, otherwise termination time): 1/9/1970
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 12 h 15 m
Landing site: In Hillsboro, Texas, US
Payload weight: 565 lbs.

• A measurement of the Isotropy of the Cosmic Microwave Background at a Wavelength of 3 Centimeters. Thesis (PH.D.) by Paul S. Henry, --PRINCETON UNIVERSITY, 1971
• Isotropy of the 3 K Background Nature, Volume 231, Issue 5304, pp. 516
• NCAR Scientific Balloon Facility Annual Report, 1970 National Center for Atmospheric Research, February 1971
• Paul S. Henry: Driven to drink - Pursuit of the cosmic microwave background radiation in Finding the Big Bang, pags. 401-425