(October 30) The Little Things that go Bump in the Night: Space Debris from the Bottom Up

While now days we tend to think of “space debris” as collisions between large spacecraft, the truth is that the distribution of space debris ranges from the micrometer size particles to objects the size of the ISS or even a derelict rocket booster. Indeed, a 1 m² surface in LEO can experience 100 impacts visible to the eye in a typical 5 year mission (e.g., the Hubble WFPC). To understand the true range of threats and take steps to mitigate their effects we need to consider the whole mass/velocity range of “debris” and, in addition, include the meteoroid environment in any potential impact studies — the so called MMOD (micrometeoroid and orbital debris) environment. In this short talk, I will first describe the Earth debris and meteoroid environments that currently threaten spacecraft operations. I will then describe simple methods for estimating collision probabilities with emphasis on particles of 1 g or smaller as these can in principle be protected against (that is, larger masses are very difficult to shield and maneuvering is currently the only known mitigation). The physics of hypervelocity impacts will be covered and methods for shielding a spacecraft from the effects of those impacts will then be briefly discussed. To conclude, the overall objective of the talk will be to provide an overview of the range of hypervelocity impact threats posed by the space debris and meteoroids, describe the physics of those impacts, estimate probabilities for an impact, and discuss possible methods of shielding and damage mitigation.

Dr. Garrett has a doctorate in Space Physics and Astronomy. He has over 150 publications on the space environment and its effects with specific emphasis in the areas of atmospheric physics, the low earth ionosphere, radiation, micrometeoroids, space plasma environments, and effects on materials and systems in space. While on active duty in the Air Force he served as Project Scientist for the highly successful SCATHA program which studied the effects of charging on spacecraft. For this he was awarded the Harold Brown Award, the Air Force’s highest scientific award. In 1992, he was selected for a joint DoD/NASA assignment at the Pentagon as part of the Ballistic Missile Defense Organization where he acted as the Deputy Program Manager for the Clementine Lunar Mission and Program Manager for the Clementine InterStage Adapter Satellite (ISAS). For contributions to these missions, he was awarded NASA's Medal for Exceptional Engineering Achievement. After a 30 years career in the USAF Reserves, he retired in 2002 as a full Colonel and was awarded the AF Legion of Merit. During his 40 year career at JPL, he has been responsible for defining the space environment and its effects on reliability for many NASA missions. He has also published several textbooks on the space environment and its impact on spacecraft design and reliability. Dr. Garrett is an international consultant on the terrestrial and interplanetary space environments and spacecraft reliability having worked for INTELSAT, L’Garde, NASDA, LORAL, CNES, and other organizations. In 2006 Dr. Garrett received NASA’s Exceptional Service Medal for “his achievements in advancing the understanding of space environments and effects.” Recently, Dr. Garrett co-authored with Mr. Albert Whittlesey the primary NASA standard on spacecraft surface and internal charging for earth missions. Dr. Garrett retired from full time duties at JPL in 2017 but continues in an emeritus position. He was made a Fellow of the AIAA in 2019.