The Chinese Tsinghua-1 microsatellite orbiting above the limb of the Earth imaged by SNAP-1 just seconds after its deployment when the spacecraft were approximately 8m (30 feet) apart. Photo: SSTL

A tiny British experimental satellite prepares for a rare rendezvous with a Chinese spacecraft, which accompanied it on its way to orbit three months ago.

The 6.5-kilogram SNAP-1 satellite built by the Surrey Satellite Technology Ltd., or SSTL, started its maneuvers several weeks ago, slowly closing in on the 50-kilogram Tsinghua-1 spacecraft built by the same company in collaboration with China's Tsinghua University.

Both spacecraft were launched onboard Russian Cosmos-3M rocket as a piggy-back payloads to Russia's Nadezhda-M navigation satellite on June 29.

By the time SNAP-1 started firing its miniature butane-gas thrusters, it was around two kilometers below Tsinghua-1. After "working" with its engines four times a day over the last month, SNAP-1 climbed about one kilometer higher then the Chinese spacecraft. Now, flight engineers controlling the satellite from the ground control station in Guilford, England, have to wait when Tsinghua-1 catches up with SNAP-1. Then, SNAP-1 will perform the final maneuver "to intercept" Tsinghua. The rendezvous is expected in November, officials say.

The engineers hope to use a unique "vision system" consisting of four single-chip video cameras size of the 50-cent coin onboard SNAP-1 to inspect Tsinghua and relay images to Earth.

The Russian Nadezhda COSPAS-SARSAT satellite imaged by SNAP-1 just two seconds after deployment when the spacecraft were approximately 2.2m (8 feet) apart. Photo: SSTL

The super-miniature system has already been successfully tested, when SNAP-1 shot its "mother" spacecraft just two seconds after separation. The photos show Nadezhda-M satellite from the distance of about eight feet (2.2 meters). Pictures were released by SSTL on October 1.

Several seconds later SNAP-1 also photographed Tsinghua-1 as it was drifting about 30 feet (eight meters) away.

SNAP-1 was designed and built as a research mission by a joint academic-commercial team at the Surrey Space Centre and SSTL. The project was funded entirely by SSTL.

The spacecraft was intended to demonstrate in orbit the capabilities of advanced, highly integrated small satellites and their use as autonomous robots for observing orbiting space vehicles.

"One of the principal objectives of the SNAP-1 mission is to demonstrate the ability of nanosatellites to act as robotic 'eyes-in-the-sky' to allow astronauts and ground controllers to examine the outside of their space vehicles," said Dr. Craig Underwood, chief architect of the SNAP project at the Surrey Space Center.

Along with the cameras and the engines, SNAP-1 features momentum wheel and magnetometers for 3-axis attitude control, a Global Positioning System receiver for autonomous orbit determination, a 220 MHz StrongARM 1100 on-board computer for housekeeping and high level vision functions and an S-band communications system.