Purpose of the flight and payload description

XPER was a balloon-borne experiment that measured the absolute temperature of the cosmic microwave background radiation (CMBR) at 10.7 GHz.

The payload (which can be see at left) was composed by a cold (25 K) corrugated horn antenna with a 158 FWHM beam coupled through a cold waveguide switch to a total power radiometer. The switch alternately connects the radiometer to the antenna signal and to an internal temperature-regulated reference load, which consists of an iron-loaded epoxy absorber thermally sunk inside a 2.8 kg copper waveguide block. The switch period is 85 seconds.

The horn antenna views the sky through a thin polypropylene window that separates the Dewar vacuum from the ambient pressure at ?oat. The input of the radiometer incorporates a cryogenic circulator and a second temperature-regulated load to mitigate errors associated with small differences in the reflection coefficients of the horn and reference load.

The signal is ampli?ed in a cryogenic 9-12 GHz HEMT amplifier. The gondola was located ~355 m below the balloon, and rotated about once a minute for much of the ?ight, so that the instrument observed a broad swath of the sky. Most of the data was taken with the beam center at a zenith angle of 40º. The antenna beam is shielded from ambient temperature emission from Earth and the balloon by an inner ground screen attached to the Dewar, while a ?xed outer ground screen provided additional rejection of ground radiation.

Details of the balloon flight

Balloon launched on: 12/9/1995 at 23:35 utc
Launch site: Scientific Flight Balloon Facility, Fort Sumner, (NM), US  
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon SF3-190.76-080-NSC-ST
Balloon serial number: R2.830-1-01
Flight identification number: 411N
End of flight (L for landing time, W for last contact, otherwise termination time): 12/10/1995 at 6:56 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 8 h
Landing site: 20 miles SSO of Lawton, Oklahoma, US
Payload weight: 2130 lbs

External references

Images of the mission

XPER mounting

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