China remains silent on satellite rendezvous
BY STEPHEN CLARK
Posted: September 8, 2010
The U.S. Air Force last week acknowledged tracking Chinese satellites secretly testing orbital rendezvous technologies, nearly two weeks after the spacecraft may have bumped into each other more than 350 miles above Earth.
A Department of Defense spokesperson confirmed numerous reports of two satellites deliberately flying in close formation.
"Our analysts determined there are two Chinese satellites in close proximity of each other," the military spokesperson said in an e-mail to Spaceflight Now.
Experienced amateur satellite observers have been watching the satellites passing close to each other since mid-August, when they noticed a slight disturbance in their orbits indicating the craft may have briefly touched.
Brian Weeden, a former Air Force space officer, published a lengthy analysis of the Chinese rendezvous in The Space Review last week, concluding the satellites may have contacted each other.
The first public reports of the rendezvous came from Russian space observers.
One of the amateur Russian analysts, Igor Lissov, began closely tracking the orbits of two Chinese satellites after receiving an online tip Aug. 14.
Lissov found a satellite named SJ-12 was on a trajectory approaching an older spacecraft called SJ-6F.
Both are members of the Shijian series of technology demonstration satellites. SJ-6F launched in October 2008 and SJ-12 blasted off June 15 into an orbit shadowing the older target vehicle.
The newly-launched satellite chased down SJ-6F through early August before executing a series of up-and-down maneuvers designed to bring the spacecraft closer together, according to Lissov.
Shijian means "practice" in Chinese.
Lissov says U.S. Air Force tracking data show the satellites passed within 200 meters, or 656 feet, of each other Aug. 19. But public orbital elements are just single points of data and may have missed other maneuvers that could have brought the spacecraft much closer together.
"We do not know if they have made physical contact," the U.S. military spokesperson said. "The Chinese have not contacted us regarding these satellites."
Weeden, Lissov and other observers base their bump hypothesis on circumstantial evidence since Aug. 19 showing unexplained changes to the satellites' orbits. The available orbital elements are not detailed enough to know for sure if they spacecraft touched, according to Lissov.
If the satellites did bump, Lissov and Weeden say the force was quite small. They say an accidental collision between NASA's DART automated rendezvous demo satellite and the U.S. military's MUBLCOM communications spacecraft in 2005 occurred with about 100 times more energy.
The contact between DART and MUBLCOM was at a relative velocity of about 3.3 mph, according to a NASA investigation of the mishap.
Ted Molczan, a seasoned Canadian skywatcher, said the evidence presented by Lissov and Weeden is "intriguing" but he doesn't know whether the spacecraft actually bumped.
Observers have since tracked a second rendezvous attempt Aug. 28, but details of this close approach are even more murky. The Air Force's orbital elements show erratic behavior, making it difficult to judge the miss distance of the second rendezvous.
Lissov and other amateur satellite-watchers say orbital data indicate the two craft may now be about one mile apart.
Other than a Xinhua news story quoting Lissov, China has been silent on the matter.
"As reflected in the United States' new National Space Policy, the DoD believes it is in the shared interest of all nations to act responsibly in space to help prevent mishaps, misperceptions and mistrust," a military spokesperson said.
A top U.S. Air Force space commander also tacitly acknowledged reports of a secret Chinese mission testing orbital rendezvous technologies, saying the trials are "one more step forward" for the nation's space program.
"What the Chinese are doing is working hard to develop their space capability, in my mind," said Lt. Gen. Tom Sheridan, commander of the Air Force's Space and Missile Systems Center. "This is probably one more step forward."
China had not tried a known rendezvous attempt to date, but the country's human space program is on the verge of an ambitious series of docking tests between a research module and Shenzhou space capsules.
The Tiangong 1 laboratory module has finished construction, according to a report last month by the state-run Xinhua news agency. The centerpiece of a modest space station, Tiangong 1 will launch in 2011 and receive the unmanned Shenzhou 8 spacecraft for an automated docking late next year.
Piloted Shenzhou spaceships will be launched in 2012 to dock with the Tiangong 1 module, giving Chinese astronauts more spacious living quarters for unspecified research missions.
It isn't clear whether the Shijian rendezvous tests are demonstrating capabilities for next year's Shenzhou docking or are part of a larger military technology program with broader applications.
"Let's face it, we proved rendezvous capabilites with the Gemini program (more than) 40 years ago, and it was exciting to see all that happen," Sheridan said in a Sept. 1 media roundtable. "I think our Chinese partners, who are a spacefaring nation as we know, these folks are working hard to come up with good capabilities in space, and that's what I think they're working toward."