For the natural particulate environment, it is critical to determine just how smaller, faster meteoroids might create mission-degrading and mission-terminating failures. Significant debate and ongoing research are focused on the possibility that particulate-catalyzed electrical failures may contribute measurably to the compendium of satellite anomalies. Strong data from experimentation show that plasma is produced during a hypervelocity impact event. At meteoroid velocities such free charges near a spacecraft might be expected to cause electrostatic discharge (ESD) and electromagnetic pulse (EMP) events (for additional detail on these phenomena, see Chapter 4, “The Meteoroid Environment and Its Effects on Spacecraft”). In addition, ground-based experiments have shown that significant plasma is produced when a particle impacts a satellite even at speeds typically associated with orbital debris (around 7 km/s). The electrical anomalies resulting from either a debris or a meteoroid impact remain poorly characterized.1
Although it will be difficult to determine the contribution to anomalies from meteoroids versus orbital debris, it is important to gain an understanding of that balance to provide a forcing function for future research and operational procedures. This issue is also discussed in Chapter 3, “Orbital Debris Modeling and Simulation.”
Just as the Orbital Debris Program Office works to significantly increase measurements of the sub-5-mm population through returned samples and of the 1- to 10-cm population through Haystack measurement campaigns, developing standard processes for recording, analyzing, reporting, and sharing satellite anomalies will provide a rich source of information not only on the environment flux but also on the effects on satellite systems of impacts by particles in the 5 mm to 10 cm size range.
An examination performed on a limited set of records for the past 20 years for satellite anomalies identified discrepancies in the available data that may make any post facto analysis of limited use, and it is essential that NASA now prepare for the future and establish a means to change this situation going forward. Many physical phenomena are reported indirectly but are crucial for determining the impactor that caused an anomaly: sudden pointing direction change, sudden drop in current from solar arrays, discrete voltage changes on instruments or power system, and so on can all be used to diagnose an anomaly.
Previous analyses have focused on the probability of impact equating to a probability of physical damage, yet it is possible that an impact itself may not be the only causative mechanism for failure. The impact may directly create an EMP or be the catalyst for an electrostatic discharge, as hypothesized above for fast meteoroids.
The difficult chore of writing and promulgating a standard process for satellite anomaly recording, analyzing, reporting, and sharing could leverage the successful migration of debris mitigation guidelines into international standards. This new effort can also leverage the current outreach and international dialog in which ODPO participates at the Inter-Agency Space Debris Coordination Committee, the United Nations, and other such organizations.
Databases already exist that contain spacecraft anomalies. An example is the Aerospace Corporation’s Space System Engineering Database (SSED).2 The SSED provides valuable data related to satellite failures and anomalies; however, it does not provide sufficient coverage or fidelity to permit the development of causative relationships with MMOD particulate environments. Attempts to use existing databases have produced results suggesting that a statistical relationship might exist between certain types of failures and the MMOD environment, but its insufficiency makes the information in the databases conclusive.3
Development of standard processes for characterizing satellite anomalies will also provide a database that will complement the continued measurement campaign in this size range, which in turn will support the continued refinement of MEM, ORDEM, and BUMPER. Predicted flux levels of orbital debris in the 5 mm to 10 cm size range and for meteoroids (10–11 g) in the 100 µm to 1 cm size range can be correlated with the actual number of satellite anomalies, creating a tighter linkage between environment definition and satellite operations.
1 See D.A. Crawford, and P.H. Schultz, Electromagnetic properties of impact-generated plasma, vapor and debris, International Journal of Impact Engineering 23:169-180, 1999; and Burchell et al., 1996.
2 See J.F Binkley, Aerospace Corporation, “The Space System Engineering Database (SSED),” demonstration, available at http://klabs.org/mapld04/tutorials/mishaps/intro_aerospace.htm.
3 D. McKnight, W. Riley, I. Shukry, and A.Shukry, Correlation of spacecraft anomalies to the debris environment, Proceedings of SPIE 2813:185-196, 1996.