Reply to comment by Joseph E. Mazur and T. Paul O'Brien on “Analysis of GEO spacecraft anomalies: Space weather relationships”

Abstract

[1] The authors welcome the comment from J. E. Mazur and T. P. O'Brien [Mazur and O'Brien, 2012] on our recently published study [Choi et al., 2011]. In our paper, we investigated the geostationary Earth orbit (GEO) satellite anomalies archived by Satellite News Digest (SND) during 1997-2009 in order to search for possible influences of space weather on the anomaly occurrences. There were good relationships between geomagnetic activity (as measured by the Kp index) and anomaly occurrences of the GEO satellites; the satellite anomalies occurred mainly in the midnight-to-morning sector, and the anomalies were found more frequently in spring and fall than in summer and winter. A comparison of the SND data with data from Los Alamos National Laboratory satellites showed that low-energy (<100 keV) electrons exhibit behavior similar to that of spacecraft anomalies and implied that the spacecraft charging may be a primary contributor to the GEO spacecraft anomalies reported on the SND Web site (http://www.sat-index.co.uk).[2] Mazur and O'Brien [2012] point out that some anomalies used in our analysis were not obviously caused by space weather effects. In fact, we intentionally used all of the GEO satellite anomalies listed on the SND Web site in order to exclude a subjective selection effect. Our event list, chosen from the SND database, represented major satellite anomalies that had significant financial impacts. There were numerous minor satellite anomalies reported from many agencies, and we want to emphasize that their tendency was similar to that of our event list. While the number of events may not be large enough to analyze local time dependence, when the anomalies reported by SND from 2010 to 2011 (indicated in Figure 1 by star symbols) are included, it is very clear that the anomaly occurrences are more frequent at nighttime than during the daytime.[3] Mazur and O'Brien [2012] also mention the relationship between GEO satellite anomalies and charging effects. Internal charging may be concerned with high-energy electrons and independent of its local time, while external charging is related to low-energy electrons and dependent on its local time. As we noted in Choi et al. [2011], the flux of 100 keV electrons on GEO orbit shows nonuniform distribution on the local time, yet these electrons don't have enough energy to penetrate satellite walls and charge internal components. At this moment, we don't fully understand the mechanism by which charged particles bring about the anomalies.[4] We support the proposal made by Mazur and O'Brien[2012] that an agency be established to maintain adequate and open anomaly and abnormality lists containing all information about events. We also anticipate that our paper will serve as encouragement to all the agencies concerned to make their anomaly data publicly available and to investigate an occurrence mechanism of spacecraft anomaly. References

Spacecraft surface charging induced by severe environments at geosynchronous orbit

“…Even though modern satellites have benefited from the analysis of past flight anomalies and losses (Koons et al, ), surface charging remains a source of problems (Ferguson, ; Minow & Parker, ). A statistical analysis of the 95 commercial satellite anomalies provided by the Satellite News Digest (SND) website in the period of 1997–2009 showed the anomalies have a strong correlation with geomagnetic activity as monitored by the Kp index (Choi et al, ; Choi et al, ). Even though Mazur and O'Brien () indicated that a number of these anomalies were not related to the environment, the combined detailed analysis of Los Alamos National Laboratory (LANL) GEO spacecraft data made by Choi et al () and by Thomsen et al () indicated that anomalies are more likely to occur a) during higher values of Kp index, b) in the local time between premidnight through dawn; c) during the equinox seasons; d) during the declining phase of the solar cycle.…”

Statistical properties of the surface‐charging environment at geosynchronous orbit

“…Recently, Choi et al . [, ] have identified a large set of spacecraft anomalies that occurred at geosynchronous orbit between 1997 and 2009, as reported in the Satellite News Digest. They presented a table of 95 anomalies of various types, including 32 for which event times (and therefore spacecraft locations) were known.…”

“…Because of the Kp and seasonal dependence, and especially the local time dependence, Choi et al . [, ] concluded that the majority of satellite anomalies in their compilation were attributable to surface charging effects. For comparison with the statistical anomaly occurrence rates, they also analyzed Los Alamos energetic electron fluxes from geosynchronous orbit in the energy ranges of 50–75 keV, 225–315 keV, and 1.9–3.1 MeV.…”