Such close encounters could allow China topractice rendezvous procedures between its future space station andother spacecraft, as well as learn about satellite formation flying,said Brian Weeden, a former U.S. Air Force orbital analyst and nowtechnical adviser for the Secure World Foundation.
The satellite rendezvous tests could also permit close-up inspection ofanother satellite, not unlike demonstrations performed by the UnitedStates and other countries in the past.
According to Weeden, China's SJ-12 satellite made at least six setsof maneuvers between June 20 and Aug. 16. During those maneuvers, thesatellite made passes near SJ-06F, an older Chinese satellite thatlaunched in October 2008.
The satellite's behavior does not fit the profile for an anti-satellitetest, Weeden wrote in an analysis for Space Review. But he added thatthe mysterious nature of the test could have an effect on perceptionsof trust and safety in space activities.
"There's no evidence there was any damage to the satellite or debris,so I wouldn't characterize it as a collision," Weeden told SPACE.com."More like a bump."
How it happened
SJ-12 launched on June 15 from Jiuquan Satellite Launch Center inChina. That launch center has also served as the starting point forChina's manned spaceflights on Shenzhou spacecraft in 2005 and 2008.
Weeden said the SJ-12 satellite's first moves allowed its orbital planeto eventually match that of SJ-06F over the course of 50 days. Thelatter mission consists of a pair of satellites, including a smallermaneuvering satellite and a larger satellite.
One of the closest passes between SJ-12 and SJ-06F created a change inSJ-06F's orbit on the night of Aug. 18, according to public data fromthe U.S. Air Force. SJ-12 also made many close approaches with lessthan 984 feet (300 meters) between the satellites.
"As far as we can tell, SJ-12 is still doing a bunch of little maneuvers close to SJ-06F," Weeden explained.
NASA previously experienced its own satellite bump when it launched theDemonstration for Autonomous Rendezvous Technology mission on April 15,2005. That DART mission was supposed to demonstrate automatedrendezvous with a defunct U.S. Navy MUBLCOM communications satellite.
A navigation error led to DART and MUBLCOM bumping at a speed of 4.9feet per second (1.5 meters per second) — fast enough to cause a majorchange in the MUBLCOM satellite's orbit.
The orbital change for the MUBLCOM satellite was about 100 timesgreater than the change in SJ-06F's orbit, Weeden points out. Thatsuggests the Chinese satellites most likely did not suffer any damageduring their presumed bump, if that happened.
Concerns about the unknown
The SJ (Shi Jian, or "practice" in Mandarin Chinese) satellitestypically conduct what the Chinese government has termed "scientificmissions."
But some outside observers believe the satellites actually receiveelectronic signals for the Chinese military. They point out that noscientific research based on the work of the satellites has everappeared.
China has good reason to want to experiment with close space maneuvers,given its plans to build a space station that would require continuosresupply. Still, the lack of official Chinese information about themaneuvers has certainly allowed room for speculation.
First notice of the satellite bump came from Igor Lissov, a well-respected Russian space observer.
Russia's Interfax-AVN news service quoted him in a story on Aug. 19,and China's state-run Xinhua news agency later picked up the story.
The Russian story suggested that the Chinese space maneuvers may pointto the possibility of inspecting both their own satellites and perhapsforeign spacecraft.