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UoSAT-3 & UoSAT-4 (1990)

First modular 50kg microsatellite design, now widely emulated, UoSAT-3 and UoSAT-4 (1990)

UoSAT-3 and UoSAT-4

UoSAT-3 was the first of the SSTL modular microsatellites, launched on the first ARIANE (40) ASAP flight V35 on the 22nd January 1990 into a 780km sun-synchronous, 98 degree inclined orbit.
The satellite carried a commercial Store and Forward communications payload with 13MByte of solid state storage and VHF and UHF 9600 bps CPFSK links. For the first 18 months it supported amateur service, but when this was taken over by UoSAT-5, it supported VITA, and later SatelLife as HealthSat-1, and Data Trax Inc. (USA).
The primary 80C186 on-board computer failed in May 1997, and it was decided that the Store and Forward transponder operations for VITA would be taken over by the more capable PoSAT-1 satellite, rather than develop operational software for UoSAT-3's secondary processor (based on the Zilog Z80). In 1999 the satellite was configured as an FM voice repeater (VHF to UHF) within the amateur service.
UoSAT-4 contained the scientific payloads to complement UoSAT-3, but the satellite failed due to an electrical fault after two days in orbit. The 47.5kg microsatellite was identical in shape to UoSAT-3.  Most of the experiments on UoSAT-4 were re-flown in 1991 on UoSAT-5.