We wish to correct a misconception that has appeared in the last two issues of Space News and was attributed to NASA [“Envisat To Pose Big Orbital Debris Threat for 150 Years, Experts Say,” July 26, page 4, and “Dealing with Envisat,” editorial, Aug. 2, page 18].
The editorial asserted that “NASA estimates that even if all space launch activity were to come to an immediate halt, the amount of orbital debris would continue to rise for 50 or so years due to collisions and break-ups among stuff that’s already up there.” This is not a proper interpretation of NASA studies.
Our work on the future evolution of the orbital debris environment, which appeared in Science (Jan. 20, 2006) and other subsequent publications, shows a steady increase in orbital debris creation from accidental collisions for centuries to come. The original analysis indicated that if all launches ceased immediately, the total population would remain approximately fixed for several decades as the generation of collisional debris was offset by natural orbital decay of low-altitude objects. After that period, collision fragments would dominate the environment and force the total debris population to increase at a nonlinear rate. The detrimental effects of the Chinese anti-satellite test in 2007 and the accidental collision between U.S. and Russian satellites in 2009 have only made matters worse.
The assumption of no future launches was chosen to place a lower bound on the future orbital debris population; in reality, the increase in the Earth’s satellite population will be more dramatic unless remediation efforts — i.e., removal of large resident space objects — are initiated.
Nicholas L. Johnson
Jer-Chyi Liou
NASA Orbital Debris Program Office
Lyndon
B. Johnson Space Center, Houston
