Space Science and Microsatellites - A Case Study Observations of the Near-Earth Radiation Environment using the Cosmic-Ray Effects and Dosimetry (CREDO) Payload On-Board UoSAT-3

The University of Surrey's technology demonstration microsatellite: UoSAT-3 launched in January 1990. carries on-board a Cosmic-Ray Effects and Dosimetry (CREDO) payload for characterizing the low-Earth orbit (LEO) radiation environment. Measurements made with this payload are correlated with radiation effects observed in the spacecraft's microelectronics, in particular, the occurrence of single event upsets (SEUs) in solid-state memory devices. The CREDO payload consists of two Sub-systems, the Cosmic Particle Experiment (CPE) and the Total-Dose Experiment (TDE). The CPE houses an array of large-area PIN diode detectors, connected to a pulse-height analysis network. Particles incident on the detector are counted and logged according to their linear-energy transfer (LET). Results are integrated over five minute intervals and the data are stored in the PACSAT Communications Experiment (PCE) memory. The TDE consists of specially manufactured p-channel MOSFETs which are monitored for changes in threshold voltage due to accumulated radiation dose. During the first year's operation, CREDO has provided measurements of the cosmic-ray background, the trapped particle population of the South Atlantic Anomaly (SAA), and has observed a number of large solar proton events - most recently, the major events of June 1991. This paper reviews the results obtained so far and comments on the suitability of microsatellites for this kind of small-scale space science mission.