The Tsinghua-1 satellite was a 50 kg microsatellite that was carrying an experimental imaging system. SNAP, on the other hand, was a technology demonstrator satellite that could show a small 6.5 kg satellite capable of three axis pointing, having its own GPS navigation system and a small butane based propulsion system.
The opportunity afforded by the dual launch of these two satellites allowed the Astrodynamics group to consider a rendezvous experiment where the SNAP satellite could use its propulsive capability to catch up with the Chinese microsatellite and image it from close proximity using its novel CMOS based vision system.
The two satellites were launched in June 2000 on a Russian launcher. Shortly after separation the SNAP vision system automatically imaged the launcher and Tsinghua-1 microsatellite, which was still attached. This launch date was around the time of Solar maximum, and so we anticipated a significant atmospheric drag on the satellites. Since SNAP was so much lighter, there was a differential loss in altitude of the nanosatellite which also needed to be compensated for by the propulsion system.
This would be a world first demonstrating formation flying and proximity manoeuvres between two satellites in orbit. While there had been much interest in the possibility of satellites orbiting together, a demonstration of the technology was yet to be made.
Determination of Separation Parameters
Using the NORAD TLEs immediately after the separation of the satellites, the Astrodynamics group was able to determine the separation parameters of the two satellites. From this we determined the heading direction of the upper stage at the time of separation was not orthogonal to the direction of its orbital motion but at 95 degrees.
This had the effect of altering the relative orbits of the two satellites as part of their ejection velocity was in the radial direction rather than the along track direction. The parameters found are shown below along with the full geometry of the separation.