Catastrophic collisions in orbit: an inevitability?
The latest research into the condition of the Low Earth Orbit (LEO) has shown that missions into space could soon become so hazardous that we will have no choice but to suspend space programmes. Unless mitigation strategies can be put in place, the amount of junk in the LEO is in danger of becoming so large that it will be dangerous to send people into space, and given the risk, uneconomical for companies or governments even to send up new satellites.
It is somewhat ironic that in the same year that the Dutch organisation Mars One has mooted the possibility of sending people on a trip to Mars, a report entitled Stability of the Future LEO Environment has been presented which suggests a trip to Mars, or even only as far as our own orbit, may soon be a practical impossibility.
The report is the culmination of two years’ work conducted by six separate agencies. The disturbing aspect of the report is that not that some of the conclusions of the different agencies paint a dire picture, but that all six have reached the same conclusions.
The report was commissioned by the Inter-Agency Space Debris Coordination Committee (IADC), an international governmental forum for the worldwide coordination of activities related to the issues of man-made and natural debris in space.
The primary purposes of the IADC are to exchange information on space debris research activities between member space agencies, to facilitate opportunities for cooperation in space debris research, to review the progress of ongoing cooperative activities, and to identify debris mitigation options.
In 2009 the IADC initiated a project to investigate the projected growth of the LEO debris population. Independent research was carried out by six IADC member agencies: the Italian Space Agency (ASI); the European Space Agency (ESA); the Indian Space Research Organisation (ISRO); the Japan Aerospace Exploration Agency (JAXA); the US National Aeronautics and Space Administration (NASA); and the United Kingdom Space Agency (UKSA). The results from the six agencies’ work were collated to form the final report, and despite the fact that all agencies based some of their work on favourable assumptions, the conclusions are troubling.
Each agency used a different model to analyse the LEO and predict the likely changes to the environment. Even though different models were used, all the agencies assumed 90% compliance with commonly-adopted mitigation measures (under which nations launching new objects into space commit to removing them from orbit within 25 years of the end of their useful life). In reality compliance falls well short of 90% as, according to a book published by the US National Research Council, Limiting Future Collision Risk to Spacecraft: An Assessment of NASA’s Meteoroid and Orbital Debris Programs, waivers are sometimes granted during the planning stages of missions to allow this condition to be overlooked. They also ignored the risks of future explosions in space due to ruptured fuel cells, canisters and batteries which have been a major source of debris in past. Furthermore, all agencies based their calculations on the initial population figure from 2009 provided by the ESA, which while accepted is also generally considered to be conservative.
- “We’re certainly not at 90% compliance with the 25-year rule yet, and we see explosion events on average about three times a year.”
Dr Hugh Lewis, presenting the IADC report 6th European Conference on Space Debris in Darmstadt, Germany.
Even using these favourable assumptions, the agencies expect the LEO debris population to increase by an average of approximately 30% in the next 200 years, and they believe catastrophic collisions will continue to occur every five to nine years.
- Models used by the different agencies
- ASI: Space Debris Mitigation long-term analysis program (SDM)
- ESA: Debris Environment Long-Term Analysis model (DELTA)
- ISRO: KS Canonical Propagation model (KSCPROP)
- JAXA: LEO Debris Evolutionary Model (LEODEEM)
- NASA: LEO-to-GEO Environment Debris model (LEGEND)
- UKSA: Debris Analysis and Monitoring Architecture for the Geosynchronous Environment (DAMAGE)
Source: Astrium UK
As can be seen from the graphs, there is an astonishing correlation between the different models. The IADC report, with input from the participating agencies, made two key recommendations.
The first is that there needs to be greater compliance with mitigation measures, such as the 25-year rule. The 90% compliance assumption made in the simulations is certainly higher than the current reality, and the IADC is keen to push for 100%. If the international space community cannot reach this level soon, the IADC warns, future debris population growth will be far worse than the study results suggest, and it will make future management of the orbital environment much more difficult.
The second recommendation to stabilise the LEO environment is to invest in more aggressive measures, such as active debris removal. Remediation of the environment after more than 50 years of space activities is complex, difficult, and will likely require a tremendous amount of resources and international cooperation, the IADC points out. The report advises the international community to increase efforts to investigate the benefits of environment remediation, explore various options, and support the development of the most cost-effective technologies.
In our November 2012 issue of Courcy’s Future Threats we discussed various technologies currently being researched with the purpose of cleaning up the LEO. All the most promising solutions share the goal of de-orbiting debris (rather than collecting it, or sending it into space). The most significant are: a space harpoon, where a chaser satellite approaches the debris, fires the harpoon, then forces it down through the atmosphere; a space grapple, which would work in a similar way to the harpoon; space sail technology, where a satellite would approach the debris in the same manner and attach sails which would then cause the debris to de-orbit through increased drag from the upper atmosphere; a space net, also for dragging debris down; and a ground based laser that would cause the debris to change course and enter the atmosphere.
Space sail technology is already in use on some satellites, but is not (currently) the most promising of these technologies for removing debris. For large pieces of debris the harpoon, being developed by the British firm Astrium UK, is the furthest advanced. When we discussed the technology last year it was being test fired over a distance of two metres at an easy target. It has now reached a stage where it is being test fired over a range of 10 metres, which is realistically about the same distance as would be the case in space, at a target rotating as a piece of debris would.
The on-the-ground test harpoon is about 60cm in total length. A space harpoon would not need the winged stabilizer. Source: Astrium UK
The harpoon is currently the most likely option for de-orbiting large pieces of debris, usually defined as being over 10cm in diameter, but there is also a huge amount of debris smaller than that. Even though a piece of debris is small it can do a huge amount of damage, as the average speed of a piece of detritus is 12km/s. If a small piece of metal strikes a lightly shielded satellite or manned spacecraft at that speed, the results could still be catastrophic. It is difficult to know how many pieces of small debris are in the LEO as our ability to track them is limited, but as our monitoring technology improves we are finding more and more. For removing these pieces of debris the ground based space laser.
Dr Claude Phipps, a leading authority on space technology, has suggested a solution he terms the Laser Orbital Debris Removal (LODR) system, an Earth based laser system that would decelerate the targeted debris and cause it to fall out of orbit. Highlighting the danger posed by the millions of pieces of small debris (1-10cm diameter), and the importance of removing them as soon as possible, Dr. Phipps suggests this is more capable of removing smaller pieces than other grappling devices. Critics have also drawn attention to the problem of aiming this device and tracking the targets, but Dr Phipps suggests an answer to this problem would be to deploy a “pusher laser” to illuminate and track the target before firing.
One of the biggest advantages of this system is the price. It is estimated that the LODR could remove small objects for a few thousand dollars each and large objects would cost in the region of $1 million. This is significantly less than the cost of launching vessels into space to hunt the debris. NASA believes that, with recent advances in laser and mirror technology, this system could be made operational in two years.
The LODR would be very useful, but as part of a suite of solutions rather than the only one. The LODR is ideal for small pieces of debris, but it would require several pulses to de-orbit larger objects.
If some of these technologies can be brought into operation it is possible that the LEO can be cleaned up enough to allow ongoing orbital missions, but these measures are not enough on their own. Unless the space-faring community as a whole commits to complying with good practice measures, such as the 25-year rule, the amount of debris in the LEO will continue to increase faster than it can be removed. Without agreement and compliance on these measures de-orbiting of some of the existing debris will just kick the can down the road.
As can be seen from the graphs, there is an astonishing correlation between the different models. The IADC report, with input from the participating agencies, made two key recommendations.
The first is that there needs to be greater compliance with mitigation measures, such as the 25-year rule. The 90% compliance assumption made in the simulations is certainly higher than the current reality, and the IADC is keen to push for 100%. If the international space community cannot reach this level soon, the IADC warns, future debris population growth will be far worse than the study results suggest, and it will make future management of the orbital environment much more difficult.
The second recommendation to stabilise the LEO environment is to invest in more aggressive measures, such as active debris removal. Remediation of the environment after more than 50 years of space activities is complex, difficult, and will likely require a tremendous amount of resources and international cooperation, the IADC points out. The report advises the international community to increase efforts to investigate the benefits of environment remediation, explore various options, and support the development of the most cost-effective technologies.
In our November 2012 issue of Courcy’s Future Threats we discussed various technologies currently being researched with the purpose of cleaning up the LEO. All the most promising solutions share the goal of de-orbiting debris (rather than collecting it, or sending it into space). The most significant are: a space harpoon, where a chaser satellite approaches the debris, fires the harpoon, then forces it down through the atmosphere; a space grapple, which would work in a similar way to the harpoon; space sail technology, where a satellite would approach the debris in the same manner and attach sails which would then cause the debris to de-orbit through increased drag from the upper atmosphere; a space net, also for dragging debris down; and a ground based laser that would cause the debris to change course and enter the atmosphere.
Space sail technology is already in use on some satellites, but is not (currently) the most promising of these technologies for removing debris. For large pieces of debris the harpoon, being developed by the British firm Astrium UK, is the furthest advanced. When we discussed the technology last year it was being test fired over a distance of two metres at an easy target. It has now reached a stage where it is being test fired over a range of 10 metres, which is realistically about the same distance as would be the case in space, at a target rotating as a piece of debris would.
[PICTURE]
[CAPTION: The on-the-ground test harpoon is about 60cm in total length. A space harpoon would not need the winged stabilizer. Source: Astrium UK]
The harpoon is currently the most likely option for de-orbiting large pieces of debris, usually defined as being over 10cm in diameter, but there is also a huge amount of debris smaller than that. Even though a piece of debris is small it can do a huge amount of damage, as the average speed of a piece of detritus is 12km/s. If a small piece of metal strikes a lightly shielded satellite or manned spacecraft at that speed, the results could still be catastrophic. It is difficult to know how many pieces of small debris are in the LEO as our ability to track them is limited, but as our monitoring technology improves we are finding more and more. For removing these pieces of debris the ground based space laser.
Dr Claude Phipps, a leading authority on space technology, has suggested a solution he terms the Laser Orbital Debris Removal (LODR) system, an Earth based laser system that would decelerate the targeted debris and cause it to fall out of orbit. Highlighting the danger posed by the millions of pieces of small debris (1-10cm diameter), and the importance of removing them as soon as possible, Dr. Phipps suggests this is more capable of removing smaller pieces than other grappling devices. Critics have also drawn attention to the problem of aiming this device and tracking the targets, but Dr Phipps suggests an answer to this problem would be to deploy a “pusher laser” to illuminate and track the target before firing.
One of the biggest advantages of this system is the price. It is estimated that the LODR could remove small objects for a few thousand dollars each and large objects would cost in the region of $1 million. This is significantly less than the cost of launching vessels into space to hunt the debris. NASA believes that, with recent advances in laser and mirror technology, this system could be made operational in two years.
The LODR would be very useful, but as part of a suite of solutions rather than the only one. The LODR is ideal for small pieces of debris, but it would require several pulses to de-orbit larger objects.
If some of these technologies can be brought into operation it is possible that the LEO can be cleaned up enough to allow ongoing orbital missions, but these measures are not enough on their own. Unless the space-faring community as a whole commits to complying with good practice measures, such as the 25-year rule, the amount of debris in the LEO will continue to increase faster than it can be removed. Without agreement and compliance on these measures de-orbiting of some of the existing debris will just kick the can down the road.