Henry B. Garrett

Aerospace: Neutralizing charged-up spacecraft: Electrical charge gathered from space plasma can cause malfunctions or failure, but techniques for minimizing its effects are available

Electrical charge gathered from space plasma can cause malfunctions or failure, but techniques for minimizing its effects are available. This article concentrates on the effects of spacecraft charging on unmanned operations.

Comparison of Single Event Upset Effects on the Clementine and Cassini Solid State Data Recorders—A Study in Data Mining

As part of an on-going “data mining” effort, the response to single event upsets (SEU) of the Clementine 2.1 Gb Solid State Data Recorder (SSDR) was compared to that of the two Cassini 2.5 gigabit (2.1 Gb usable for data) Solid State Recorders (SSRs) to see what lessons could be learned. Both systems were evaluated for their sensitivities to SEUs before flight. Estimates of the in-situ environments for the two missions allow evaluation of the ability of SEU models and ground tests to predict flight performance using actual data. The DRAMS that make up the solid state recorders, despite having different manufacturers, appear to have similar SEU cross-sections. This similarity has permitted a comparison of the effects of the ambient environments on the systems for two very different missions (lunar versus Saturn). Initial results from previous studies had revealed a nearly constant background upset rate for both systems of ~71 bit flips/day for the SSDR and ~280 for the SSRs due to the Galactic Cosmic Ray background. While there was no obvious correlation with a solar proton event recorded by Clementine on 20-21 February 1994 nor with trapped protons during its brief passage through the Earth’s radiation belts, the Cassini SSRs showed pronounced responses to both solar proton event and Saturn trapped radiation environments. This difference is explained here by applying the proton cross-sections measured for Cassini to the Clementine observations—the new results show that the protoninduced upset rates would have been too low to be observed by Clementine. This study completes the original Clementine SSDR analyses and, in the process, demonstrates agreement between the Cassini SSR upsets and the JPL SATRAD proton radiation model. Finally, the lunar orbit variations in the SSDR upset rates observed by Clementine are reevaluated using a new methodology—the pronounced lunar orbit altitude dependence is shown to fit the expected variation in GCR fluxes due to lunar shielding.

Active electrostatic flight for airless bodies

The environment near the surface of asteroids, comets, and the Moon is electrically charged due to the Suns photoelectric bombardment and lofting dust, which follows the Sun illumination as the body spins. Charged dust is ever present, in the form of dusty plasma, even at high altitudes, following the solar illumination. If a body with high surface resistivity is exposed to the solar wind and solar radiation, sun-exposed areas and shadowed areas become differentially charged. The E-Glider (Electrostatic Glider) is an enabling capability for operation at airless bodies, a solution applicable to many types of in-situ missions, which leverages the natural environment. This platform directly addresses the “All Access Mobility” Challenge, one of the NASAs Space Technology Grand Challenges. Exploration of comets, asteroids, moons and planetary bodies is limited by mobility on those bodies. The lack of an atmosphere, the low gravity levels, and the unknown surface soil properties pose a very difficult challenge for all forms of know locomotion at airless bodies. This E-Glider levitates by extending thin, charged, appendages, which are also articulated to direct the levitation force in the most convenient direction for propulsion and maneuvering. The charging is maintained through continuous charge emission. It lands, wherever it is most convenient, by retracting the appendages or by firing a cold-gas thruster, or by deploying an anchor. Preliminary calculations indicate that a 1 kg mass can be electrostatically levitated in a microgravity field with a 2 m diameter electrostatically inflated ribbon structure at 19kV, hence the need for a “balloon-like” system. The wings could be made of very thin Au-coated Mylar film, which are electrostatically inflated, and would provide the lift due to electrostatic repulsion with the naturally charged asteroid surface. Since the E-glider would follow the Suns illumination, the solar panels on the vehicle would constantly charge a battery. Further articulation at the root of the lateral strands or inflated membrane wings, would generate a component of lift depending on the articulation angle, hence a selective maneuvering capability which, to all effects, would lead to electrostatic (rather than aerodynamic) flight.

Radiation Environment Model of Protons and Heavier Ions at Jupiter

We performed an in depth study of the methods used to review the geometric factors (GF) and sensitivity to charge particles of the Energetic Particle Detector instrument on board the Galileo Spacecraft. Monte Carlo simulations were performed to understand the interactions of electrons and ions (i. e., protons and alphas) with the sensitive regions of the instrument. The DC0 and B0 channels were studied with the intention of using them to update the jovian proton radiation model. The results proved that the B0 is a clean proton chanel without any concerns for contamination by heavier ions and electrons. In contrast, DC0 was found to be contaminated by electrons. Furthermore, we also found out that the B2 channel is a clean alpha particle channel (in other words, no contamination by electrons and/or protons).

Special Issue on Spacecraft Charging Technology 2012

The 32 papers in this special issue were originally presented at the 11th Spacecraft Charging Technology Conference. held in Albuquerque, NM, in September 2010.