Last month, on 20 January, two of our colleagues were interviewed by the National Spanish Radio about space debris. Following on from this event we are going to publish a series of blog posts on this burning issue.
In recent months uncontrolled satellite re-entries have hit the news three times. The first was the American satellite UARS which re-entered the atmosphere over the Pacific Ocean on 24 September 2011. Shortly afterwards, on 23 October 2011, the German X-ray telescope ROSAT did likewise over the Bay of Bengal (Indian Ocean). More recently, on 15 January 2012, the Russian satellite Phobos-Grunt, originally programmed for a complete Mars mission, careened down over the Pacific Ocean.
On their re-entry through the atmosphere these bus-sized objects break up progressively into smaller and smaller fragments, some of which might reach the earth’s surface. Nonetheless the likelihood of one of these rogue objects killing anyone is remote; we should not forget that most of the Earth is covered by water and there are also large land areas that are uninhabited.
As well as these large satellites, other space junk is continually re-entering the atmosphere, though it normally breaks up completely on the way down without posing any threat to people.
At present there are about 1,000 operational satellites of various types in orbit (telecommunications, navigation, earth observation, scientific and military research). As well as these missions there are another 15,000 to 20,000 listed and monitored uncontrolled objects in space. There are also about 300,000 objects ranging from 1 cm to 10 cm in size that could destroy another satellite, and millions of even smaller objects (less than 1 cm) that slip below the radar but still pose a huge risk. All these earth-orbiting objects not belonging to active missions are lumped together under the term “space debris”. Space debris is made up by objects as varied as large rocket chunks and old satellites, remains of explosions or collisions and tiny particles.
PROBABILITY OF PHYSICAL HARM
As we have already pointed out, many objects re-enter the earth’s atmosphere every day. Most break up on re-entry and never reach the ground. Few are the objects big enough to survive the whole break-up process and actually come to ground.
Even debris that does not break up completely on re-entry is very unlikely to cause physical harm to anyone on earth (odds of 1 in a million) and there has only been one known case of impact with humans to date.
PROBABILITY OF COLLISION WITH A SATELLITE
The real risk, however, stems from the probability of collisions between different objects in space. The upshot of such collisions might be mission loss, exponential growth of space debris and consequent increase of the collision risk in a vicious circle, which could in last instance make it difficult to access the Space environment in the future.
The likelihood of collisions between two space objects is still low but is continually increasing with the growth of space debris itself, especially in the more saturated areas (low almost polar orbits, from 800–1000 km high, and equatorial and geostationary orbits at a height of 36,000 km).
Space debris is a growing concern. The more uncontrolled objects that are out there, the greater the likelihood of catastrophic collisions, causing not only the loss of one-off missions but also a collisional cascading chain known as the Kessler Syndrome. This would exponentially increase collision risk and pose a serious hazard for future space missions, especially manned ones.
Satellite operators are therefore becoming increasingly alarmed, especially after the collision between an operational satellite of the Iridium constellation (satellite telephony) with a decommissioned Russian satellite in February 2009.
Consider these telling facts: NASA now has to make over 10 satellite maneuvers a year to avoid collisions; ESA has to maneuver its most important satellite ENVISAT more than once a year and the International Space Station has had to be maneuvered and the crew evacuated to a safety pod on several occasions due to space-debris near misses.
DETECTION, OBSERVATION AND MONITORING OF SPACE DEBRIS
The state of space debris is monitored from space surveillance systems that detect and keep an eye on orbiting objects. This involves powerful radars (for near earth objects) and telescopes (for higher orbits). These systems can list and monitor orbiting objects above a certain size (over 10 cm in low orbits and 1m in high orbits).
Several countries now systematically monitor space debris:
- The USA runs a worldwide military Space Surveillance Network to list these objects. Part of this information is published (sometimes of a degraded quality and never for missions considered to be critical to its interests).
- Russia also has a (more limited) space surveillance capacity but publishes no information on the matter.
- Since 2009 Europe has been working busily towards its own Space Surveillance and Tracking capability. Spain as a country is currently the main contributor and its space industry is playing a crucial role in developing the system. GMV in particular is participating in and leading several ESA projects in this area.
In upcoming posts I’ll be talking about how the space debris problem might be mitigated and the junk removed.
I hope this has been of interest to you. Feel free to leave your comments below.
Author: Alberto Águeda Maté
Las opiniones vertidas por el autor son enteramente suyas y no siempre representan la opinión de GMV
The author’s views are entirely his own and may not reflect the views of GMV