Cubesats provide a valuable, low-cost research space platform for institutions, universities, laboratories and space agencies, but could their use create a new hazard for the increasingly crowded orbital environment?
According to space debris expert Hugh Lewis, of the University of Southampton, the use of cubesats and the relaxed attitude to space collision hazards could increase the likelihood of space assets encountering the small satellites in the future.
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Speaking at the 65th International Astronautical Congress in Toronto today (Sept. 30), Lewis outlined some of the problems associated with cubesat use. For starters, most cubesats cannot maneuver themselves while orbiting Earth, so should a collision scenario be predicted, they cannot be commanded to dodge out of the way. Also, some of the organizations using cubesats have insufficient plans for de-orbiting their orbital assets, meaning many defunct cubesats will remain in orbit long after their operational lifetimes.
Cubesats are still considered a low impact risk, but concern is growing for the lack of attention that is being paid to guidelines that specify a 25 year orbital lifetime. Over a third of all cubesats launched (approximately 160 between the years 2003 and 2013) are expected to remain in orbit long past this 25 year benchmark. And as cubesats are launched into higher and higher orbits, their orbital lifetimes increase, becoming a long-term issue for future generations.
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"To reduce the risks, some effort is needed to engage with the growing small satellite community," said Lewis. "All space users, not just those in the CubeSat community, who are taking the right steps should be encouraged to continue and, ultimately, lead on sustainable practices and debris mitigation activities.
"Those who are not yet engaged with this approach should be encouraged to do so. It's probably a matter of changing their perceptions of the risks and helping them to understand that there is a collective responsibility to ensure that outer space activities are sustainable so that future generations have the same opportunities to use space as we do."
Although they do represent the tiny tip of the space junk iceberg, cubesats have been involved in over 360,000 close approaches of less than 5 kilometers with other orbiting objects, according to a University of Southampton press release. Using a sophisticated computer model called "Debris Analysis and Monitoring Architecture to the Geosynchronous Environment" (DAMAGE), Lewis' team have, perhaps unsurprisingly, predicted that cubesats will be responsible for millions of orbital near-misses, with a handful of these orbital encounters resulting in collisions, by 2043.
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A "handful" may not sound like a serious issue, but considering each orbital collision can generate thousands of pieces of debris and each piece of debris can hit other orbital assets, the risk of a cascading collision risk becomes clear. This dangerous scenario is known as "Kessler syndrome" which could render certain orbital altitudes unusable in the future.
As far as space junk goes, the cubesat contribution remains fairly tiny, but better regulation of anything we launch into space, cubesat or otherwise, is needed if we are to safeguard the future use of Earth orbit.
"By far the greatest risk comes from those with long lifetimes at altitudes of about 750 km," warns Lewis. "If CubeSats continue to be launched into long-lived orbits without any means of disposing of them, then they will contribute to the growing space debris hazard. This is not a responsible or sustainable practice, in my view. However, if efforts are made to limit the lifetimes - as some are already doing - then the risks will be reduced."
Source: University of Southampton