A small impact chip on an ISS window was caused by flying debris – perhaps a paint flake or tiny metal fragment flying it very high speed – a photo taken by British astronaut Tim Peake shows. The European Space (ESA) station says one of the hazards astronauts face is space debris travelling at up to 17,500 mph (28,163 km/h).
According to ESA and NASA, the tiny chip on the window, which has a diameter of 7 mm (0.0275 of an inch) is not a danger to the ISS (International Space Station) crew members.
The chip was gouged out by flying debris on one of the windows of the Cupola module, which has big bay windows so that the astronauts can see outside. One of the space station’s two robotic work stations that Major Peake and colleagues use to manipulate the large robotic arm that can be seen through the right window is housed there.
An impact chip on an ISS window. According to ESA: “even a 1 cm nut can hit with the energy of an exploding hand grenade. Impact by larger debris at orbital velocity can cause a catastrophic break-up – meaning destruction of a spacecraft.” (Image: European Space Agency. Credit: Major Tim Peake)
The Cupola module is connected to the underside (nadir side) of the ISS, from which crew members get a full panoramic view of Earth.
Major Peake posted an image of the impact chip on one of Cupola’s windows on Twitter last Friday, and wrote “Often asked if @Space_Station is hit by space debris. Yes – this chip is in a Cupola window, glad it is quadruple glazed!”
Windows sometimes get hit
ESA says the windows on the space station, which are made of borosilicate-glass and fused-silica, are sometimes struck by very small pieces of space debris, often called ‘space junk’ – and there is an awful lot of it orbiting our planet.
ISS has extensive reinforced shielding around all vital technical and crew areas so that minor collisions pose no threat.
There are literally millions of fragments of space debris orbiting the Earth. It is surprising there have not been several catastrophic collisions with our spacecraft, experts say. (Image: European Space Agency)
While we can protect astronauts and crucial technical equipment from small debris impacts, there is nothing to prevent a catastrophe if the ISS were hit by medium-to-large sized fragments.
A small chip like the one in the image is minor and of little concern. However, larger fragments of debris crashing into the space station pose a serious and possibly lethal threat.
According to ESA, a fragment of space junk up to one centimeter across could disable a critical flight system on a satellite or put an instrument out of action.
Any pieces bigger than 1 cm would most likely penetrate right through the ISS crew module shields. Any object larger than 10 cm would smash the whole spacecraft into pieces if certain parts of the space station were hit.
Regarding the dangers of space junk, Head of ESA’s Space Debris Office, Holger Krag, said:
“ESA is at the forefront of developing and implementing debris-mitigation guidelines, because the best way to avoid problems from orbital debris is not to cause them in the first place.”
“These guidelines are applied to all new missions flown by ESA, and include dumping fuel tanks and discharging batteries at the end of a mission, to avoid explosions, and ensuring that satellites reenter the atmosphere and safely burn up within 25 years of the end of their working lives.”
As well as the hazard in space, larger debris objects that reenter Earth’s atmosphere in an uncontrolled way, such as old satellites, rocket bodies and large fragments, can pose risks to humans on the ground, because they can be too big to burn up completely. (Image: European Space Agency)
Lots of space debris orbiting Earth
NASA tracks more than 500,000 pieces of space debris orbiting our planet. The fragments travel at incredibly high speed, more than seven times faster than a bullet when it is fired from an M16 rifle. A 55 grain bullet travels at 2,250 mph or 3,300 feet per second when it is fired from an M16 rifle. Compare that to the 17,500 mph (28,163 km/h), or 25,666 feet per second, for the average piece of space junk.
Regarding space debris and the danger to the ISS and other spacecraft, NASA makes the following comment:
“The rising population of space debris increases the potential danger to all space vehicles, but especially to the International Space Station, space shuttles and other spacecraft with humans aboard.”
“NASA takes the threat of collisions with space debris seriously and has a long-standing set of guidelines on how to deal with each potential collision threat. These guidelines, part of a larger body of decision-making aids known as flight rules, specify when the expected proximity of a piece of debris increases the probability of a collision enough that evasive action or other precautions to ensure the safety of the crew are needed.”
Even relatively small fragments of space debris can cause significant damage to our spacecraft.
Types of space debris
There are two types of space debris, or potentially dangerous objects in space, as far as our spacecraft are concerned.
1. Natural (meteoroid) particles: objects which fly through space at very high speed and orbit our Sun.
2. Artificial (man-made) particles: fragments from objects we have made which orbit the Earth. They are often called orbital debris. Examples include non-functional spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris.
There are more than 20,000 fragments larger than a softball (rounders or cricket ball) in orbit around Earth. There are over half-a-million fragments that are bigger than a marble, and several million smaller ones.
While we are able to track all fragments marble-sized and bigger, we cannot monitor the smaller ones.
Even very small fragments travelling at more than 17,000 mph can damage parts of a spacecraft and go straight through humans on a spacewalk.
Tim Peake’s spacewalk. Whenever astronauts go out on a spacewalk, they are exposed to the risk of flying space debris going right through them at 17,000 mph. We cannot track the very small fragments, which could also kill them, i.e. they could hit a human and we would not know they were coming. (Image: European Space Agency)
Nicholas Johnson, NASA chief scientist for orbital debris, said:
“In fact, a number of space shuttle windows have been replaced because of damage caused by material that was analyzed and shown to be paint flecks. The greatest risk to space missions comes from non-trackable debris.”
NASA, ESA and Russia’s space agency Roscosmos say they are surprised there are so few disastrous impacts in space, given how much debris is flying around out there.
Guidelines for hazardous space debris
Space agencies such as NASA, ESA and Roscosmos have a set of guidelines that are used to determine whether a fragment of debris represents a threat to one of its spacecraft.
— Tim Peake (@astro_timpeake) May 12, 2016
“Debris avoidance manoeuvres are planned when the probability of collision from a conjunction reaches limits set in the space shuttle and space station flight rules.”
“If the probability of collision is greater than 1 in 100,000, a manoeuvre will be conducted if it will not result in significant impact to mission objectives. If it is greater than 1 in 10,000, a maneuver will be conducted unless it will result in additional risk to the crew.”
Manoeuvres to avoid space junk impacts are generally small and are done from one to four hours before the estimated moment of collision.
If the ISS crew want to move the space station out of the path of an incoming fragment, it can use the thrusters of the Russian Progress supply ship, if one is docked at the space station. When there is no supply ship attached to ISS, the thrusters on the Russian Zvezda service module may be used.
As a last resort, crew members on ISS can get into the Soyuz space capsules and wait and see whether a collision occurs. If one does, they can rapidly detach from the ISS and try to get back to Earth.
Video – Five bizarre ways to clean up space junk
Space junk poses a serious risk for the lives of astronauts and the state of our equipment in space. This Scientific American Space Lab video looks at some of the strangest proposals put forward to combat the ever-growing cloud of space junk.