Electrical anomalies on spacecraft due to hypervelocity impacts
One of the main challenges in satellite design is dealing with the threat from the space environment. Numerous spacecraft anomalies are reported on a regular basis and in most of these cases, it is extremely difficult to diagnose the cause of these anomalies/failures. Hypervelocity impacts from meteoroids and orbital debris has recently emerged as possible catalysts for electrical anomalies observed on spacecraft. In this paper, we present a case study and statistical analysis of hypervelocity impact-induced electrical anomalies. We present data showing anomalous currents in the power distribution system on the JASON-1 satellite following a hypervelocity impact. A statistical analysis is carried out using 2413 anomalies from the Ascend satellite anomaly database and 5033 anomalies from the anomaly database maintained in the 1990s by the National Geophysical Data Center (NGDC). We find that there is no correlation between the flux of shower meteoroids and incidence of anomalies. For geostationary satellites, we use NASA's Meteoroid Engineering Model to calculate the flux of sporadic meteoroids at different locations in the orbit and find that the incidence rate of anomalies is significantly higher in regions with high average meteoroid flux. These results serve as a strong indicator of electrical damage caused by electromagnetic emissions from meteoroid impacts.
Microscopic ejecta measurements from hypervelocity impacts on aluminum and powdered regolith targets
Abstract Meteoroids and space debris pose a two-fold threat to spacecraft due to the risk of both mechanical damage from the impact and electrical damage from the impact-generated plasma, which produces electromagnetic emissions. Analysis of impact products, however, has the potential to provide useful information about planetary rings and small solar system bodies, such as asteroids and comets. Understanding the plasma dynamics and radiation mechanism is essential to addressing the impact threat and extracting science data from impacts. Charge attachment to condensed-phase debris may lead to a dusty plasma under certain conditions, so interpreting hypervelocity impacts requires knowledge of both the nature of the plasma and of the ejecta. We address the latter with measurements of the microscopic ejecta distribution produced by light gas gun impacts on solid aluminum and powdered regolith simulant targets. We examine both the size and shape of the ejecta using thin-film witness plates and find that the size distributions of microscopic ejecta follow power laws. Observations from the powdered regolith simulant match well with disruption experiments of solid basalt, while measurements from the aluminum impacts diverge from extrapolations based on studies of macroscopic debris. Analysis of the ejecta shape shows a transition from smooth to irregularly shaped ejecta at the material grain size, and the shape of debris may provide insight on the phase of the ejected material. Based on our results, we predict a significant number of secondary impacts on plasma sensors due to ejecta, even at considerable distance from the target, supporting the hypothesis that charged dust affects plasma measurements in the ejecta curtain.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.