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We nearly lost Fermi: The problem of orbital debris


May 2, 2013

The Fermi Gamma-ray Space Telescope has a near-collision with Cosmos 1805

The Fermi Gamma-ray Space Telescope has a near-collision with Cosmos 1805

Image Gallery (7 images)

Julie McEnery is NASA's Project Scientist for the Fermi Gamma-ray Space Telescope. When she checked her email on March 29, 2012, she was startled to find an automatically generated message stating that in six days, her half-billion-plus dollar satellite was going to cross paths with Cosmos 1805, a Soviet-era spy satellite. The predicted encounter had the two satellites occupying the same coordinates only 30 milliseconds apart. Not only that, but Cosmos was in an orbit moving nearly perpendicular to Fermi such that their collision would be equivalent to tons of high explosives. Essentially total destruction.

Launched into low Earth orbit in 2008, Fermi is a space observatory that performs gamma-ray astronomy observations of the heavens. It measures about 1.8 m (4.6 ft) square by 2.9 m (9.2 ft) high, with solar wings that extend to give Fermi a total width of about 15 m (50 ft). Fermi is not a light satellite, having a mass of 4,300 kg (9,500 lb).

Fermi's instrumentation was developed to study astrophysical and cosmological phenomena, such as active galactic nuclei, pulsars, gamma-ray bursts, other high-energy sources and dark matter. While its formal mission was to last five years, the spacecraft was designed to continue operations for a full ten years.

In the other corner we have Cosmos 1805 – a Russian Tselina D military communications satellite intended to monitor military naval signals. Launched from the Plesetsk cosmodrome in 1986, it was intended for an active lifetime of six months, but since no one was worrying about limiting orbital debris in those days, it is still in orbit nearly 30 years later. The satellite weighs 1,400 kg (3,080 lb) and is in a nearly polar orbit, so that its orbit crosses that of Fermi nearly perpendicularly.

The two objects, speeding toward each other at a net velocity of 11 km/s (7 miles/s) were expected to miss each other by a mere 210 m (700 ft). While a miss is as good as a mile, satellite operators have learned that they can't be too careful. In 2009, the Iridium 33 communications satellite and Cosmos 2251 collided about 800 km (500 miles) over Siberia, leaving some 1,500 kg (3,300 lb) of small metal pieces strewn over an ever widening volume of space. Before the collision, the satellite tracking reports predicted a miss of 584 m (1,900 ft).

So the decision was made that Fermi would dodge the oncoming Cosmos 1805. Ironically, this would be accomplished with a one second pulse on the de-orbit thrusters that were designed to push Fermi out of orbit at the end of its life so it would burn up in the atmosphere and not pose a threat to other satellites.

Although intended to get Fermi out of harm's way, this maneuver is not without its own dangers. The procedure involves halting Fermi's scanning of the skies, orienting the satellite along its direction of motion, folding and parking the solar panels, and tucking away its high gain communication antenna. Then, once the (untested) thrusters had been fired, the process of making Fermi safe for the maneuver had to be reversed. A single glitch had the potential to render Fermi unusable, explaining why the decision to maneuver was not taken lightly.

As it happened, all went swimmingly with the burn on April 3 and Fermi was back doing scientific observations within an hour of the maneuver. The following day, Fermi and Cosmos 1805 missed colliding by 10 km (6 miles), a much more comfortable distance than the length of two football fields.

Today, maneuvers to avoid satellite collisions have become a routine requirement. Despite this, the amount of space debris continues to increase. Not all of it can be detected, and very few of the pieces in orbit still have maneuvering capability. This was underlined on the ISS this past Monday, when Commander Chris Hatfield noticed that a small bit of debris had punched a hole in one of the space station's solar panels.

Space debris has the potential, through a chain reaction known as a Kessler syndrome, to render near-Earth space impassible, perhaps for centuries. Such a fate may still be avoided, although some aerospace experts believe that a Kessler syndrome is nearly unavoidable at this point. It seems that the space nations of the world must get serious about the space debris problem, while we can still get into space.

The following video shows how Fermi avoided possible destruction.

Source: NASA

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer. All articles by Brian Dodson

Given the legal and propulsion requirements for cleaning up the space junk, I don't see how the Kessler syndrome can be avoided. On the bright side, we could rename the Kessler syndrome the 'Planetary Defense Shield' and count on it to prevent aliens from attacking Earth from orbit.


The good news is that small objects in low earth orbit are still inside the far reaches of the upper atmosphere, and thus experience minute amounts of atmospheric drag. They'll deorbit on their own within a few years' time. The tinier the debris, the more susceptible it is to drag.

So you don't have to worry about a popped rivet staying in orbit forever like a perpetual stray bullet.

Jon A.

The users of disposable launcher should take space debris into account for their launches not just for avoiding collisions on the way up but for taking down bits of debris on the way back down. Granted they can't bring down Cosmos 1805 with a well timed propellent dump but every little bit helps and it should be possible to catch 1cm pieces by having them punch into an empty tank but not have enough energy to punch out the other side.


I can remember back in the 1960's the effort that went into eliminating the debris from cable assemblies that were cut when launch vehicles went through stage separation.


The asteroid mining tech ideas can be used to take out the old satellites net them into a hunter satellite that kicks the old sat down and then leap froggs to the next object to be decommissioned.

Joseph Mertens

Totally agree with Joseph Mertens. We could take the idea a step further. In tune with International Space Station, an effort is the need of hour for all the space faring nations to pool resources and send space cleaning missions. All such nations are already facing the menace. Once a concerted effort is taken, the space can be made squeaking clean for future endeavours. The effort may however need a sincerely correct info from all those countries that have previously sent unannounced satellites into space. On the brighter side, since the sats have served their purpose whats the harm in telling. Else they can send 'anonymous' letters with the required info................ heh, heh ,heh

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