UoSat 2 and 12

We managed to synchronise our UoSat-2 and UoSat-12 satellites with a pre-existing formation.

Outcomes

Due to the non-spherical nature of the Earth, the orbital planes drift around the Earth's equator at differing rates, so active control is required to maintain the orbit crossings at the same passage time. In order to determine whether the control system had been successful, we switched on an RF receiver on UoSat-12 to listen for the broadcast telemetry from UoSat-2.

The signal would provide a large spike that would enable us to determine precisely the time of closest approach. The units are dBm. The predicted time of closest approach was 11:59:23 which corresponds extremely well with the peak. The closest approach distance was estimated at 16.43 km.

We had the discriminator output (in kHz), which reflected the Doppler shift in the signal. This provides information about the relative motion between the two satellites at closest approach. A more accurate estimate of the encounter time comes from the zero crossing of this curve. The discriminator data can be tested by an orbit model fit which had an RMS fitting residual of 0.06 kHz.

Successive encounters were maintained over several orbits, each encounter lasting approximately 20 seconds. A table of encounter times and separations is given below.

Time Separation
09:32:58 25.86 km
10:21:44 14.01 km
11:10:38 13.33 km
11:59:23 16.43 km

Further information can be found in our Astrodynamics Research Group.

History of UoSAT-2

Built in just 6 months from scratch and launched from Vandenberg AFB on a Delta with Landsat-D on 1 March 1984, UoSAT-2 (UO-11) was still transmitting on 145.825 MHz AFSK-FM at 1200 bps after 26 years in orbit! The on-board batteries are exhausted, so the satellite now only operates in sunlight and has inactive beacons at 435.025 MHz and 2401 MHz.

UoSAT-2 carried a Digitalker speech synthesiser and experiments including magnetometers, a CCD camera, a Geiger-Muller tube and a microphone to detect micrometeoroid impacts. The satellite was instrumental in providing a communications link from the Canadian-Soviet Ski-Trek support teams to the expedition party in 1986. The position of the skiers' emergency beacon was calculated daily by Cospas-Sarsat ground stations and relayed to them, and thousands of amateur radio listeners, as a spoken message from the Digitalker on board UO-11. The message could also serve as an emergency channel to the skiers in the event that all other radio links failed.

UoSAT-2 also carried the Digital Communications Experiment that was the first digital packet store-and-forward payload on a microsatellite. Find out more about UoSAT-2's thirty years in space.