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Wednesday, Dec. 12, 2012
NPO, JAXA join hands in guarding satellites
By YUZO SUWA
Every day, observers at the Japan Spaceguard Association stare steadfastly at the skies 36,000 km above the equator. And they are deadly serious about their job — to guard Japanese satellites from colliding with space junk and debris.
"Due to gravity, the sky above the Indian Ocean is the 'grave' where satellites that have completed their missions gather," explained Noritsugu Takahashi, board chairman of the nonprofit organization. "In the case of an approaching old satellite possibly headed for collision with a Japanese satellite along the path, we will reposition the Japanese satellite."
But Takahashi's group was founded in 1996 on a different premise — surveilling the skies to discover threats to Earth, such as an asteroid or comet.
While such events are believed to occur only once every 100 million years, should an asteroid or comet hit Earth it would have a grave impact on all living beings — including the possible extinction of the human race.
The Bisei Spaceguard Center is located on a hill in Ibara, Okayama Prefecture. The area — known for having one of the most pitch-black night skies and a large number of clear days — offers excellent conditions for stargazers.
During a recent event for giving children hands-on experience at the center, Takahashi, 54, explained how observations are made using the optical telescope.
"Using the computer, we control the CCD camera attached to the telescope and take pictures of the same location at certain time intervals," he said. "Then, by overlapping the images and analyzing them, we can find things that are moving."
Trying out the computer software, the children were able to locate objects with relative ease.
The association has so far discovered about 1,000 asteroids and keeps in contact with similar organizations in Europe and the U.S. to exchange information.
Having won the trust of the Japan Aerospace Exploration Agency with its outstanding observation record and technology, it has been commissioned to keep watch over the safety of Japanese communications, broadcast and weather observation satellites in geostationary orbit.
When they find satellites or space debris approaching Japanese satellites, group members notify JAXA, which takes the appropriate measures to avoid collisions.
"We can also immediately figure out the size and shape (of the satellite or debris concerned) from the moving patterns and changes in brightness. Our detection knowhow is among the best in the world," Takahashi said.
Space debris includes objects such as satellites in Earth orbit that are no longer in use as well as fragments from launched rockets.
"(Debris) flies around at a speed of 7 to 8 km per second," astronaut Soichi Noguchi said. "It is possible for (debris) to penetrate the body if hit during a spacewalk, and one may lose consciousness if hit in the head. (Astronaut) training is conducted based on that premise."
The International Space Station, located about 400 km above Earth, uses bumpers to protect it from possible collisions with space debris. It can be repositioned to avoid larger debris and has emergency plans for astronauts to escape using the Soyuz spacecraft in the event of a catastrophic collision.
However, the area being watched by the Spaceguard Association is less congested as it is located higher up and thus more costly to place satellites there.
Right now, the spotlight is on the area that lies in between — an orbit altitude of 700 km to 1,000 km that is often used for Earth observation satellites. It is the most congested zone, partly because its lower altitude means less costly operations.
Debris is increasing rapidly in this zone, which is also where China experimented in 2007 with destroying a weather satellite with a ballistic missile, and where a Russian and U.S. satellite collided in 2009.
"It is predicted that collisions of old satellites and other objects will continue to occur once every four to seven years," said Satomi Kawamoto of JAXA's Aerospace Research and Development Directorate. "This is, so to speak, the self-replication territory for debris."
At this altitude, there are an estimated 20,000 large pieces of debris measuring at least 10 cm, the size believed capable of triggering catastrophic collisions.
In addition, there are hundreds of thousands of pieces around 1 cm in size and more than 100 million measuring around 1 mm, making it extremely difficult for the Spaceguard Association team to detect them.
Kawamoto said JAXA hopes to extract some of the debris.
"If about five to 10 pieces of large-scale debris can be removed each year for 10 years, it will make do," said Kawamoto, who leads research on recovering debris. "We aim to begin around 2020."
The plan he has in mind is to launch a satellite into the same orbit as the targeted debris. It would then gradually approach an object and attach an aluminum wire of about 10 km in length to it. Making use of the relationship between the Earth's magnetic fields and the flow of electricity, this will induce the debris to fall to Earth.
There have also been other proposed methods for removal, such as Russia's use of spacecraft to round up the junk, and Europe's use of robot satellites to attach engines to the debris.
"Japan's space technology is good at autonomous control in which satellites power their own movements, as symbolized by the Hayabusa," Kawamoto said, referring to JAXA's most well-known unmanned spacecraft. "The method of attaching a wire is low cost and thus a promising one."