Whitney Lohmeyer

Communication satellite power amplifiers: current and future SSPA and TWTA technologies

Summary This study captures the state of current satellite transponder technology, specifically, solid-state power amplifiers (SSPAs) and traveling wave tube amplifiers (TWTAs), and describes expected future advances, including GaN SSPAs. The findings of five previous SSPA and TWTA studies, including the 1991 European Space and Technology Center study, the 1993 National Aeronautics and Space Administration study, and three Boeing studies conducted in 2005, 2008, and 2013, are tabulated and summarized. The results of these studies are then compared with new analyses of two validated sources of amplifier data: a commercially licensed database, Seradatas Spacetrak, and a publicly available database, Gunters Space Page. The new analyses consider a total of 18,902 amplifiers (6428 TWTAs, 2158 SSPAs, and 10,316 unspecified amplifiers) onboard 565 communications satellites launched from 1982 to 2016. This new study contains the largest number of satellites and amplifiers to date and compares output power, redundancy, and bandwidth capabilities. We find an increase in output power from the 1993 study of >200% for Ku-band TWTAs and C-band SSPAs, and >1000% increase for C-band TWTAs. The ratio of operational to redundant amplifiers is 10 times higher for TWTAs than SSPAs, and the majority of amplifiers over the past 30 years operate with bandwidth less than 100 MHz. A second analysis is conducted using failure records and telemetry of 16 geostationary satellites equipped with 659 amplifiers: 535 SSPAs and 124 TWTAs. We find that <2% of TWTAs and 5% of SSPAs experience anomalies. Overall, this research was performed to update and clarify how the power and bandwidth needs and redundancy trends of the SatCom community have evolved over the past 30 years. Copyright

Causal relationships between solar proton events and single event upsets for communication satellites

In this work, we analyze a historical archive of single event upsets (SEUs) maintained by Inmarsat, one of the worlds leading providers of global mobile satellite communications services. Inmarsat has operated its geostationary communication satellites and collected extensive satellite anomaly and telemetry data since 1990. Over the course of the past twenty years, the satellites have experienced more than 226 single event upsets (SEUs), a catch-all term for anomalies that occur in a satellites electronics such as bit-flips, trips in power supplies, and memory changes in attitude control systems. While SEUs are seemingly random and difficult to predict, we correlate their occurrences to space weather phenomena, and specifically show correlations between SEUs and solar proton events (SPEs). SPEs are highly energetic protons that originate from solar coronal mass ejections (CMEs). It is thought that when these particles impact geostationary (GEO) satellites they can cause SEUs as well as solar array degradation. We calculate the associated statistical correlations that each SEU occurs within one day, one week, two weeks, and one month of 10 MeV SPEs between 10 - 10,000 particle flux units (pfu). However, we find that SPEs are most prevalent at solar maximum and that the SEUs on Inmarsats satellites occur out of phase with the solar maximum. Ultimately, this suggests that SPEs are not the primary cause of the Inmarsat SEUs. A better understanding of the causal relationship between SPEs and SEUs will help the satellite communications industry develop component and operational space weather mitigation techniques as well as help the space weather community to refine radiation models.

Quantifying the average and the likelihood of increases in space weather indices and in situ measurements during Solar Cycles 20–23

It is known that space weather harshly affects spacecraft performance, yet spacecraft operations and understanding the cause of anomalies can be challenging due to the complexity of environmental metrics. In this work, we analyse five metrics and in-situ measurements (Kp, Dst, and AE index, and high-energy proton and electron flux) throughout Solar Cycles 20–23 (1964 to 2008), and provide a baseline for the environment during the phases of the solar cycles (maximum, minimum, declining or ascending). We define increased activity as activity greater than two median absolute deviations (MADs) above the average activity for each phase. MAD is used, rather than standard deviation, because it is more resilient to outliers. The average and MAD values are tabulated in Table 3 to Table 6. We determine the probability that increased activity occurs 3, 14 or 30 days before a random day to distinguish between increased/quiet activities and to aid in correlating intensifications of the environment and anomalous satell...

Correlation of GEO Comsat Anomalies and Space Weather Phenomena for Improved Satellite Performance and Risk Mitigation

Citation Lohmeyer, Whitney, and Daniel Baker. “Correlation of GEO Comsat Anomalies and Space Weather Phenomena for Improved Satellite Performance and Risk Mitigation.” In 30th AIAA International Communications Satellite System Conference (ICSSC), September 24-27, 2012, Ottawa, CANADA. American Institute of Aeronautics and Astronautics, 2012. As Published http://dx.doi.org/10.2514/6.2012-15083 Publisher Aerospace Research Central

Deep Dielectric Charging and Spacecraft Anomalies

Abstract This is an overview of deep dielectric charging on spacecraft. Spacecraft anomalies and failures may occur after exposure to energetic (MeVs) electron environments. These anomalies and failures typically occur with a delay time of days to weeks because it requires significant time for large charge density to accumulate on or in shielded spacecraft materials. This chapter discusses the relationship between deep dielectric charging and such spacecraft anomalies and failures. Deep dielectric charging and subsequent electrical discharging are not only related to severe space environment conditions in the vicinity of the spacecraft, but also depend on the spacecraft material properties which may change slowly in space as materials age from exposure to the space environment.

Does Spacecraft Potential Depend on the Ambient Electron Density

In this paper, we address the question of whether spacecraft potential depends on the ambient electron density. In Maxwellian space plasmas, the onset of spacecraft charging does not depend on the ambient electron density. The balance of electron currents causes the incoming electrons to balance with the outgoing secondary electrons. The onset is controlled by the critical or anticritical temperature of the ambient electrons, but not the electron density. Above the critical temperature, charging to negative potential occurs. If the energy of the incoming electrons increases to well beyond the second crossing point of the secondary electron yield (SEY), the value of SEY decreases to well below unity. When the secondary electron current is negligible compared with the primary electron current, the spacecraft potential is governed solely by the balance of the incoming electrons and the sum of the currents of the repelled electrons and the attracted ions. In neutral space plasma, the electron and ion charges cancel each other. But if the space plasma deviates from being neutral, then the densities can have effect on the spacecraft potential. If the ambient plasma deviates significantly from equilibrium, a non-Maxwellian electron distribution may result. For a kappa distribution, one can show that the spacecraft charging level is independent of the ambient electron density. For a double Maxwellian distribution, the spacecraft charging level depends on the electron densities. For a conducting spacecraft charging in sunlight, the charging level is low and positive. It also depends on the ambient electron density. For a dielectric spacecraft in sunlight, the high-level negative-voltage charging on the shadowed side may extend to the sunlit side and block the photoelectrons trying to escape from the sunlit side. In this case, the charging level does not depend on ambient electron density. Using coordinated environmental and spacecraft charging data obtained from the Los Alamos National Laboratory geosynchronous satellites, we showed some results confirming that spacecraft potential is indeed often independent of the ambient electron density.