PARIS – United Launch Alliance (ULA) Delta 4 program managers have launched an investigation to determine the source of an unexpectedly large trail of debris that came off the vehicle’s upper stage following November’s launch of a U.S. Air Force meteorological satellite.
The successful deployment mission also demonstrated, for the first time, a maneuver that permitted the upper stage to exit a heavily used orbit and to remove the risk of a future uncontrolled atmospheric re-entry.
Because the Delta 4 Medium had more power than needed to place the Air Force satellite into its 850-kilometer polar orbit, the excess was used to propel the upper stage out of orbit and into the
Pacific Ocean
within two hours of launch.
Delta 4 second stages typically weigh around 3,000 kilograms. If left in their drop-off orbits, they would circle the Earth for months or years before re-entering the atmosphere at a time and place under no one’s control.
“How often we can conduct this maneuver and deorbit the stage in the future depends on the performance margin we have for future missions,” said Mark Wilkins, Delta program vice president at ULA. “We will do it whenever we have the appropriate performance margin.”
What was not planned for this launch was the ejection of at least 62 pieces of debris from the second stage sometime between the separation of the Air Force satellite and the deorbit maneuver.
Delta 4 program managers had mounted a camera above the second-stage engine to monitor performance and had recorded what they thought was a standard amount of debris – around 12 pieces of what are presumed to be graphite epoxy stiffeners used when the second-stage engine nozzle is extended.
The Delta 4 second stage is powered by a Pratt & Whitney Rocketdyne RL10B-2 motor with an extendible nozzle.
But radar that are part of the U.S. Space Surveillance Network detected 62 pieces of debris of unknown origin, according to an analysis of the data performed by the NASA Orbital Debris Program Office, located at Johnson Space Center in Houston.
Wilkins said ULA will employ other radar to verify the amount of debris left and to fill out the still-patchy image provided by the Space Surveillance Network.
“We hope to have a better idea of this in April from the supplemental radar data so that we can understand what they are seeing,” Wilkins said Jan. 23. “It could be foam from the thermal blankets; we’re not sure.”
Also unclear is whether the same phenomenon has occurred in the previous six Delta 4 launches. This was the third time the Medium configuration was used. Wilkins said it is possible that more radar were trained on the November launch than on previous missions, and thus more debris was registered.
NASA’s Orbital Debris Program Office said it recorded eight breakups of spent rocket stages and satellites in orbit during the last eight months of 2006 – more than in any year since 1993. Most of the resulting debris will deorbit quickly, but some pieces will remain in orbit for years.
One of the most spectacular of these debris-creating events was the breakup of a 7,000-kilogram Russian Earth observation satellite, launched into low Earth orbit in September.
NASA’s orbital-debris review for 2006 said these Russian satellites, which operate at altitudes of between 200 and 350 kilometers, are customarily blown up on command at the end of their operational lives – typically no more than four months after launch.
Detonating these satellites spews debris up and down, with a debris trail as high as 1,100 kilometers, according to the NASA debris office. In the case of the satellite detonated Nov. 28, pieces of debris were created in orbits as high as 850 kilometers. All of them had fallen out of orbit by late December, according to NASA.
