Many satellite operators continue to violate long-established guidelines for end-of-life disposal of their spacecraft, both for larger satellites in geostationary orbit and the many smaller satellites in low Earth orbit. A rule of thumb for low-orbiting satellites: A spacecraft at 600 kilometers or above needs to have a propulsion system or an orbit-drag unit to assure it falls into the atmosphere within 25 years, as the guidelines provide. For geostationary satellites, the guidelines call for the repositioning of retired spacecraft several hundred kilometers above the geostationary belt. For medium-Earth-orbit satellites, where the U.S., Russian, Chinese and European navigation constellations operate: It’s complicated and guidelines aren’t yet clear. Credit: IADC
PARIS — Less than half of the large geostationary-orbit satellites taken out of service in 2015 were properly disposed of, meaning placed into graveyard orbits above the geostationary arc, an international debris-monitoring panel said Feb. 1.
During the same year, one-third of all low-orbiting satellites, meaning orbits lower than 2,000 kilometers in altitude, were incorrectly disposed of, the group said.
In a presentation to the United Nations Committee on the Peaceful Uses of Outer Space, the Inter-Agency Space Debris Coordination Committee (IADC) — whose 13 agency members include all the world’s major space powers — said the situation in low Earth orbit is especially worrisome.
IADC refuses to adopt ‘naming and shaming’ policy
IADC policy is not to identify the satellites that did not follow the rules. Holger Krag, who is head of he European Space Agency’s space debris office and presented the IADC report, said the subject is occasionally debated at IADC but as yet has has found no consensus.
The performance of owners of retiring geostationary satellites in 2015 is remarkably poor — 60 percent of these satellites were either moved an insufficient distance from the geostationary arc or were just switched off while on the orbital highway.
In 2014, 75 percent of geostationary satellite retirements were in compliance with the guideline stipulating that satellites be placed into graveyard orbits around 300 kilometers above geostationary orbit, which is 36,000 kilometers above the equator. The idea is to keep them out of geostationary orbit for at least 200 years. The precise retirement orbit needed to assure that depends on a satellite’s mass and surface area.
No improvement in smallsat respect for debris mitigation procedures
Krag said the expected increased compliance by operators of small satellites in low orbit should be showing up in the annual data. But it’s not.
Unlike geostationary-orbit satellites, which are usually large and expensive, satellites in low orbit have a wide variety of owners, especially as the cost of building and launching a satellite weighing just a few kilograms has come down in recent years.
Also unlike geostationary-satellite operators, some smallsat owners have the option of launching into orbits so low that the satellites will naturally fall out of orbit within 25 years of retirement, as per international guidelines.
The problem is for satellites orbiting at 600 kilometers or higher. These spacecraft need on-board propulsion or an orbit-drag mechanism to force to lower altitudes that permit them to respect the 25-year rule.
According to IADC, 43 percent of low-orbiting satellites retired in 2015 were at altitudes permitting natural orbit decay within 25 years.
But 36 percent of the low-orbit population operated in higher orbits requiring special deorbit measures that either they did not have or did not use. The remaining 21 percent of satellites did what was necessary to correctly lower their orbits.
A dozen companies are planning constellations of hundreds, even thousands, of relatively small satellites in low Earth orbit, but with orbits too high to permit natural deorbiting. This has raised concerns among orbital debris specialists.
In a separate presentation to the UN, NASA said it’s not so much the numbers of satellites that raises concerns as the fact that they will need to be equipped with extremely reliable end-of-life propulsion or orbit-drag systems to put them into lower orbits.
Krag agreed. In a Feb. 2 interview, he said many of the planned constellation operators have taken a strong interest in debris mitigation. The problem, he said, is that even a small percentage of failures in orbit will leave hundreds of satellites stranded.
“It is clear that significant improvements in the reliability of the disposal function at end of life will be needed for the new constellations compared with that
currently demonstrated by space systems on orbit,” IADC said in its presentation.
Krag added: “The problem is the numbers. If you have a 90 percent reliability on a constellation of 3,000 satellites, that leaves 300 failures.”