PARIS — The October launch of a U.S. meteorological satellite and six microsatellites was a model of how mission managers can minimize the production of orbital debris, NASA said.
The post-mission performance of the United Launch Alliance Delta 2 rocket’s upper stage, the design of the main payload — the Suomi National Polar-orbiting Partnership (NPP) satellite — and the placement of the six tiny cubesats all were done to avoid adding to the substantial orbital debris population.
In a mid-January assessment, NASA’s Orbital Debris Program Office at the Johnson Space Center in Houston said NPP is equipped with a propulsion system that will ensure a controlled re-entry into the Earth’s atmosphere after it is retired.
The six cubesats, weighing just a few kilograms each, are too small to carry similar end-of-life gear.
If left in the same 820-kilometer orbit as NPP, they would not re-enter the atmosphere within 25 years and thus not meet the guidelines established by the Inter-Agency Debris Coordination Committee (IADC). IADC’s 12 members are the space agencies of the world’s principal spacefaring nations, including NASA.
To solve the problem, the Delta 2 upper stage placed NPP into its target orbit and then was restarted to carry the cubesats into an elliptical orbit with a perigee of 460 kilometers and an apogee of 815 kilometers.
NASA estimates that at this location, the cubesats will fall into the atmosphere within 25 years, thus respecting the IADC guidelines, which are not binding.
That left the Delta 2 upper stage. Rocket stages account for about 11 percent of the 16,000 debris fragments that NASA tracks using U.S. Air Force ground radars. Their population has not been decreasing in recent years despite attempts by many launch vehicle operators to incorporate debris-mitigating technologies into their designs.
One such technique is to use a restartable upper stage that can reorient itself, after dropping off its satellite payload, into a position to lower its orbit to allow for a quick atmospheric re-entry.
The Delta 2 upper stage performed this maneuver, using a final burn of its engine to drop its orbit to 180 kilometers by 715 kilometers. The stage was destroyed on re-entry into the Earth’s atmosphere Nov. 29, NASA said — just 32 days after launch.
