29 Jun 2011

 

 

 

 

 

Space junk near miss with the ISS

 

Yesterday the International Space Station risked a collision with a small unidentified object, a piece of so-called "space junk". According to NASA spokesman Stephanie Schierholz, the size of the object is unknown, but given that at the altitude of the ISS (about 350 km above our heads) the orbital velocities are around 10 km/s, even an object a few centimetres across becomes a lethal bullet.
Having ample warning of the potential danger, 18 minutes before the passage of the fragment the 6 members of the ISS crew took shelter in a Soyuz craft docked to the station, where they remained for about one and a half hours, before continuing with their normal activities. Data collected by the US Space Surveillance Network indicate that the object passed by at only 250 metres from the ISS, something that has sparked further debate on the continual production of space debris.
In 54 years of space exploration there have been about 4600 launches, that together with controversial destruction of satellites in orbit, have produced tens of millions of fragments of metal, plastic, glass and any other material used in the space industry. Of these, 16,000 are bigger than 10 cm, while 500,000 exceed 1 cm, all capable of seriously damaging multi-million dollar space missions and putting the lives of astronauts at risk.
Thanks to agreements between the major space agencies, the region of space in which the ISS orbits is kept free of debris as far as possible, but the passage of fragments on intersecting orbits or that are on decaying orbits due to atmospheric braking cannot be totally eliminated.
Fragments that orbit below 600 km undergo significant braking and so remain in circulation only for a few years. More persistent however, are those that orbit between 800 and 1000 km, whose orbital decay takes decades. Worse still are those above 1000 km, that will be around for centuries or millennia. An awkward legacy to leave for the future...

 

by Michele Ferrara & Marcel Clemens

credit: NASA/EOS