NSSDCA ID: 1970-025A-01
Mission Name: Nimbus 4The Nimbus 4 Monitor of Ultraviolet Solar Energy (MUSE) experiment was designed (1) to look for temporal variations in the solar UV flux in five bands from 1150 to 3300 A, (2) to measure the solar flux in these regions, and (3) to measure the atmospheric attenuation at these wavelengths as the sensors on board viewed the setting sun after the spacecraft had crossed the terminator in the Northern Hemisphere. The sensors had their maximum responses at 1216 A (plus a 1350- to 1600-A continuum), 1800 A, 2100 A, 2800 A, and 2600 A (including a 2600- to 3300-A interval). The 1216-A, 1800-A, and 2600-A sensors were identical to those carried on Nimbus 3, while the 2100-A and 2800-A sensors, utilizing interference filters, were new and replaced the two that malfunctioned on Nimbus 3. The MUSE instrument, which consisted of five vacuum photodiodes housed in an electronics package and a sensor package, was mounted in the rear of the Nimbus spacecraft. All sensors except the 1216-A photodiode had semitransparent photocathodes that were deposited on an aluminum oxide window. The 1216-A sensor had a solid tungsten cathode. The spectral regions of the sun to which three of the sensors responded (1216 A, 1800 A, and 2600 A) were determined by filter transmittance on the short wavelength side, while the long wavelength cutoffs were produced by the varying degrees of opacity of the photocathode materials. The shortwave cutoffs for the 2100-A and 2800-A sensors, however, were obtained by the interference filters, while the cesium telluride photocathode provided the longwave cutoff. The appropriate bands of UV flux entered the photodiodes and produced a current that was measured by an electrometer and digitized by the Nimbus versatile information processor (VIP) system. The VIP data were stored on magnetic tape and transmitted on playback to the data acquisition facility. The instrument could operate in either the automatic or manual mode. In the automatic mode, the instrument had a basic 48-s cycle and an analog-to-digital conversion rate of two samples per second. In the manual mode, the instrument locked on a selected sensor and remained there (two samples per second) until the instrument was commanded back into the automatic mode. The field of view of the sensors was about 90 deg in the satellite nadir direction. Solar acquisition, therefore, began at 45 deg prior to the earth day/night terminator and completely ceased at the satellite day/night transition. The instrument had only an inflight electrical calibration sequence, since there were no known suitable UV sources that could provide an inflight optical calibration. No archival data have been produced due to lack of funding.
Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office
Name | Role | Original Affiliation | |
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Dr. Donald F. Heath | Principal Investigator | NASA Goddard Space Flight Center |