14 DAY TRIAL // Officials at NASA have just completed a large review of data collected by the US Space Surveillance Network (SSN) on space junk or space debris in Earth's orbit. They conclude that the International Space Station (ISS) will most likely not have to carry out any collision-avoidance maneuvers in 2014.
The maneuvers involve firing up the station's onboard thrusters, as well as the motors on the two Russian-built Soyuz capsules, in order to raise or lower the space lab's altitude. This process is very complex, and involves an accurate knowledge of the trajectories space debris will follow.
The SSN features a widespread network of ground- and space-based sensors, which is capable of mapping the positions and trajectories of tens of thousands of space debris at any time. Data produced by this organization is essential for planning the ISS flight trajectory over several months.
The orbital laboratory is encased in what NASA experts call the Pizza Box, a flat, rectangular and imaginary box that extends 1.5 kilometers in depth by 50 kilometers in width and 50 kilometers in length (1 mile deep by 30 miles across by 30 miles long).
As soon as an object's trajectory is determined as having a high chance of penetrating the Pizza Box, astronauts aboard the space station are notified, and they carry out orbital-boosting or -lowering maneuvers, taking the ISS out of harm's way.
This may seem a bit paranoid at first, but there are well over 50,000 pieces of space junk in Earth's orbit, of which roughly 10,000 are large enough to cause serious damage to the station, regardless of its impact shields. Space debris travel at an average speed of 28,163 kilometers (17,500 miles) per hour.
Previous years saw the ISS relocating in its orbit many times, but oddly enough no avoidance burns will be carried out this year. This change in trend does not reflect a decrease in the space junk problem, but rather highlights the unpredictable nature of these debris clouds.
In over 15 years of space flight, the ISS has boosted or lowered its orbit to avoid collisions with space junk a total of 16 times. On three occasions, warning from Mission Control came too late to take any meaningful actions. An additional maneuver failed, with the ISS becoming stuck in its orbit.
In order for the station to be moved, experts at Mission Control have to determine that there is more than a 1-in-10,000 chance that a foreign object will impact the ISS. No such threats are estimated for this year, Space News reports.