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Experiment Title: Passive Exposure of Earth Radiation Budget Experiment Components

Original Principal Investigator(s): Griffin, Francis - Invest. Role: Original, Mooney, Thomas A. - Invest. Role: Present, Smajkiewicz, Ali - Invest. Role: Present, Hickey, Mr. John R. - Invest. Role: Present, Hickey, Mr. John R. - Invest. Role: Present,

The PEERBEC experiment of the LDEF mission was composed of sensors and components associated with the measurement of the Earth Radiation Budget (ERB) from satellites. These components include the flight spare sensors from the ERB experiment which operated on Nimbus 6 and Nimbus 7 satellites.

Earth Radiation Budget (ERB) experiments require accuracies on the order of fractional percentages in the measurement of solar and Earth flux radiation. In order to assure that these high-accuracy devices are indeed measuring real variations and are not responding to changes induced by the space environment, it is desirable to test such devices radiometrically after exposure to the best approximation of the orbital environment.

The reason for proposing this experiment was to help explain the results which were obtained by the ERB of Nimbus 6. The Nimbus ERB experiments contained 10 solar radiation measurement sensors (channels) and 4 earth-flux measurement sensors. The solar sensors were mounted on the leading edge of Nimbus and the earth-flux sensors were looking down. Channel 10S of Nimbus 6 (a UV sensing channel) was replaced by a cavity radiometer for total solar radiation measure- ments for the Nimbus 7 Mission. Nimbus 6 was launched June, 1975, during the decline of solar cycle 20. After initial measurements, the solar channels having filters showed a slow degradation. Nimbus 7 was launched in October 1978, as the peak of solar cycle 21 was approaching. After allowing for a period of protection from outgassing contamination, the ERB solar channels were opened and started measurements on November 16, 1978. After initial measurements, the solar sensing channels having filters or windows, exhibited a major degradation. With the increase in solar activity of solar cycle 21 there was a major recovery of the signal for these channels. When the recovery was experienced for Nimbus 7, it was found that the Nimbus 6 sensors (then more than 4 years in orbit) had also recovered. After the initial events the response of the various channels differed. Channel 6S and 9S measured levels higher than their initial readings, while the other 2 interference filter channels (7S and 8S) showed steep declines. The channels with fused silica windows acted differently. While channel 2S showed a decline with only partial recovery, the normally shuttered channel 1S showed very little change until later in the mission when its shutter was left open. As solar cycle 22 approached maximum most of the channels exhibited some measure of recovery.

Much information on the contamination of the ERB filtered channels could be gained from the Nimbus data. Nimbus 6 apparently suffered degradation due to its own outgassing and then was cleaned once by AO. The Nimbus 7 record, shows a much greater initial degradation due to contamination and a remarkable recovery due to AO cleaning. But the degradation of some channels, with only partial recovery due to AO cleaning at the next solar maximum, requires further explanation.

Photograph Classification: Postflight

Associated Photograph(s):
LaRC - L90-13421
KSC - KSC-390C-1031.11
JSC - None
LaRC - L84-07116
KSC - KSC-384C-294.07
JSC - None
LaRC - L90-10388
KSC - None
JSC - S32-76-054
LaRC - L90-10380
KSC - None
JSC - S32-76-026
LaRC - L91-11718
KSC - KSC-390C-1997.02
JSC - None
LaRC - L84-07165
KSC - KSC-384C-317.08
JSC - None

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