Title: Electric propulsion reliability: statistical analysis of on-orbit anomalies and comparative analysis of electric versus chemical propulsion failure rates,
Abstract: With a few hundred spacecraft launched to date with electric propulsion (EP),
it is possible to conduct an epidemiological study of EP on orbit reliability.
The first objective of the present work was to undertake such a study and
analyze EP track record of on orbit anomalies and failures by different
covariates. The second objective was to provide a comparative analysis of EP
failure rates with those of chemical propulsion. After a thorough data
collection, 162 EP-equipped satellites launched between January 1997 and
December 2015 were included in our dataset for analysis. Several statistical
analyses were conducted, at the aggregate level and then with the data
stratified by severity of the anomaly, by orbit type, and by EP technology.
Mean Time To Anomaly (MTTA) and the distribution of the time to anomaly were
investigated, as well as anomaly rates. The important findings in this work
include the following: (1) Post-2005, EP reliability has outperformed that of
chemical propulsion; (2) Hall thrusters have robustly outperformed chemical
propulsion, and they maintain a small but shrinking reliability advantage over
gridded ion engines. Other results were also provided, for example the
differentials in MTTA of minor and major anomalies for gridded ion engines and
Hall thrusters. It was shown that: (3) Hall thrusters exhibit minor anomalies
very early on orbit, which might be indicative of infant anomalies, and thus
would benefit from better ground testing and acceptance procedures; (4) Strong
evidence exists that EP anomalies (onset and likelihood) and orbit type are
dependent, a dependence likely mediated by either the space environment or
differences in thrusters duty cycles; (5) Gridded ion thrusters exhibit both
infant and wear-out failures, and thus would benefit from a reliability growth
program that addresses both these types of problems.