Next up, on October 24 at 01:27 UTC, a Chinese Long March 3B put the Shijian 21 satellite into geostationary transfer orbit from the Xichang Satellite Launch Center in south-central China.

The first satellite in the Shijian series was launched in 1971. Over the years, this series of satellites have varied widely to test new technologies for China. Shijian 21’s stated purpose is to “test and verify space debris mitigation technologies”, though the Chinese government did not elaborate on exactly how the satellite will perform this mission.

Space debris is generally a big problem for the future utilization of the space around Earth, particularly around the geostationary orbit. There is a narrow strip of altitude that satellites can be in the GEO belt and still get the advantages of rotating with the Earth. If you are more than a few tens of kilometers above or below that sweet spot, angular momentum will carry the satellite out of its assigned slot. This means a satellite can only maintain its orbit outside of the sweet spot for a few orbits unless it uses a lot of fuel for staying in place, which reduces the amount of time it can do its mission.

Humanity has been sending satellites into geostationary orbit for nearly sixty years, and a lot of the early satellites had no propulsion upon reaching final orbit. Back in those days, there were fewer satellites, and the year or two it took for the pull of the Sun and Moon to take them out to the graveyard was plenty fast enough. Fast forward to today, and the belt is packed with satellites every 200 or so kilometers. A satellite slowly being pulled out to the graveyard orbit by the Sun and Moon’s gravity will cause chaos in this environment, so any attempt to clean up geostationary orbit is worthwhile.

Companies and governments have been concerned about space debris since the 1980s, but only now has the technology advanced enough to do something about it. Previous methods were limited to mandates about deorbiting satellites at the end of life, if possible, or at least lowering their orbit enough so the atmosphere would cause them to reenter in a shorter period of time. Another policy was ensuring that rocket stages had no propellant or battery chemistry in them after they were done with the mission if they couldn’t be deorbited so that they wouldn’t explode in orbit and make more space debris.

More Information

China launches Shijian-21 satellite (Xinhua)

SJ 1 info page (Gunter’s Space Page)

Launch video