Article Posted on : - Mar 24, 2009

ESA image

STANFORD, California: In a band 1,000 kilometers above Earth, a growing collection of mechanical debris is accumulating. Old rocket boosters, retired satellites, and even pieces of an intentionally exploded Chinese satellite threaten to destroy millions of dollars worth of orbiting surveillance, weather, and telecom satellites that we increasingly rely on in our daily lives.

A month ago, a first-ever collision occurred between two large satellites: A defunct Russian military orbiter and a live American commercial satellite. And recently the crew of the International Space Station was forced to take refuge in their escape ship as junk whizzed by, missing the facility.

Reported in this month’s Stanford Knowledgebase, mathematical analysis by two Stanford researchers suggests that if space programs around the world could be forced to take out their own “garbage,” the problem of colliding space debris could be reduced to less than one chance in a thousand that a live satellite would be damaged by a passing object.

NASA’s own mathematical simulations calculate that the odds of space collisions are on the rise. In 2007, when China sent up a missile to demolish one of its own satellites, the resulting explosion brought home the fact that any such accident could exacerbate the space debris problem exponentially.

Even tiny objects pose a risk to satellites and spacecraft orbiting Earth. Because objects in orbit are moving on different paths, at different inclinations, and at speeds of 17,500 miles per hour and faster, NASA estimates something as small as a grain of sand can impact with the power of a bowling ball moving at 100 mph, reported Reuters on March 13.

To address the problem, NASA researchers have suggested creating 1,000-kilometer-long (roughly 600-mile) tethers to literally lasso some of the fragments and drag them closer to the atmosphere, where friction eventually would burn them up. Removing the current accumulation from orbit would reduce future collisions. “The problem is there’s no cost-effective technology for doing it,” says Lawrence Wein, the Paul E. Holden Professor of Management Science at the Stanford Graduate School of Business and the author of a study recently published in Advances in Space Research.

A better approach than building new technologies to guard against space junk, argue Wein and coauthor Andrew Bradley, a doctoral student at Stanford’s Institute for Computational and Mathematical Engineering, is to emphasize compliance with rules already on NASA’s books requiring objects be removed from orbit within 25 years of their launch.

“Spacecraft are supposed to have enough ‘gas’ in their tanks to propel them downward toward the atmosphere when their life cycle is concluded,” says Wein. “But international compliance, while perhaps greater than 50 percent, is not extremely high.”

“It appears that if full compliance of the 25-year spacecraft deorbiting guidelines can be achieved within the next few decades and no ASATs [anti-satellite weapons] are used or tested in the future, then the lifetime risk from space debris ... may be sustainable at a tolerable level,” write the authors. They call for focusing future policy on achieving full compliance with rules to get equipment out of orbit, and making it taboo to intentionally blow up equipment already in orbit.

Wein and Bradley also suggest setting fees for every launch and penalizing those who ignore their floating trash, although they warn that this will require heavy political as well as economic negotiations. “The political and economic issues associated with the establishment of such fees are fairly daunting,” says Wein, “but if we could get high compliance this problem could stay under control.”

The fees would be used to compensate for operational spacecraft destroyed in future collisions, and partially fund research and development into space debris mitigation technologies.

What’s happening in low earth orbit (LEO) is an example of environmental economics says Wein, with the region representing a renewable resource. Compared to the length of time man has been contributing to ocean pollution, space is just beginning to suffer from man’s encroachment. Taking action now will protect communication satellites today as well as protect a resource.

(Source: Stanford Graduate School of Business. The research appears in the March 2009 issue of Stanford Knowledgebase, the free monthly information source for thoughts, ideas and research at the Stanford Graduate School of Business)