PARIS — One of every five cubesats launched between 2003 and 2014 is in violation of international guidelines calling for satellites to deorbit – by force of nature or their on-board systems – within 25 years of retirement, NASA said.
Depending on how the data is read, the United States is both the biggest single offender and a better-than-average participant in the cubesat business when measured by orbital debris-mitigation practices, NASA said.
In the July 2015 issue of Orbital Debris Quarterly News, produced by the NASA Orbital Debris Program Office at the Johnson Space Center in Houston, the agency provides fodder to both sides of the debate over whether the increasingly popular cubesats are a threat to orbital-highway safety.
Cubesat is a term measuring a satellite’s approximate size and mass. A 1-unit cubesat is a 10-centimeter cube weighing about 1 kilogram. Most launched so far are in the 1- to 3-unit size, but the industry is expanding so rapidly that these early trends may not endure.
Most cubesats have no on-board propulsion. Many cubesat owners are obliged to take such launch opportunities as are available to them, even though their spacecraft, as secondary payloads, must accept whatever orbit is required for the rocket’s main customer.
This is why cubesat owners are often unable to tell regulators, or other satellite owners, exactly what their operating orbit will be when they announce their programs.
Having to hitch a ride to orbit however they can get it, cubesat owners have said they sometimes face a Hobson’s choice of scrapping their entire mission or accepting a launch to an orbit in which their spacecraft will remain for many decades after operational lives of two years or so.
Orbital debris experts calculate how long a satellite will remain in orbit by its orbital parameters and by the satellite’s area-to-mass ratio, which provides indications of how quickly its orbit will decay naturally from the drag of the residual atmosphere in low Earth orbit.
Using data from the U.S. Air Force’s Joint Space Operations Center at Vandenberg Air Force Base, California, NASA counts 231 cubesats launched between 2003 and the end of 2014, not including 44 lost in launch failures.
Sixty-one percent of these satellites are U.S.-owned. Twelve of these U.S. spacecraft are in orbits from which they will not reenter the atmosphere within 25 years and are thus in violation of international guidelines. Another 26 have satellite and orbital characteristics that make it impossible to determine how long they will remain in orbit.
While their numbers are much smaller, non-U.S. cubesats have performed worse than their U.S. counterparts when measured by atmospheric reentry dates: More than one-third of the 90 non-U.S. cubesats will remain in orbit more than 25 years after they stop functioning, NASA says.
Cubesats operating in orbits with perigees below 600 kilometers in altitude will usually meet the 25-year rule. Orbits between 600 and 700 kilometers “are on the boundary” and may or may not meet the guideline, NASA says. The International Space Station, which is serving as a platform for cubesat launches, flies at around 400 kilometers in altitude, meaning satellites launched from there will almost invariably deorbit within 25 years.
Above 700 kilometers, “all cubesats display longer in-orbit lifetimes and non-compliant residence times,” according to NASA.
There is no known case of a cubesat, dead or alive, colliding with another object in low Earth orbit. But the effervescence of the cubesat industry — and more generally, the current production rate of small satellites — is such that the situation in low Earth orbit is likely to be much different in five years.
Recognizing the problem — and wanting to avoid being freighted with even well-meaning regulatory burdens if debris concerns become more pressing — some cubesat owners are designing debris-mitigation into their satellites.
Adding on-board propulsion is currently out of the question for many cubesat programs given the additional manufacturing and launch-cost increases this would entail. But they can add lightweight hardware to their satellites that would deploy on retirement, increasing the area-to-mass ratio and acting as an orbital brake, forcing the satellite down to where it reenters the atmosphere more quickly.
This 2011 video shows U.K.-based Clyde Space’s first test of a stored energy deployment system for a dragsail, or aerobrake, that can be used to de-orbit cubesats at the end of their missions.