Modeling Ionosphere Environments: Creating an ISS Electron Density Tool

The International Space Station (ISS) maintains an altitude typically between 300 km and 400 km in low Earth orbit (LEO) which itself is situated in the Earth's ionosphere. The ionosphere is a region of partially ionized gas (plasma) formed by the photoionization of neutral atoms and molecules in the upper atmosphere of Earth. It is important to understand what electron density the spacecraft is/will be operating in because the ionized gas along the ISS orbit interacts with the electrical power system resulting in charging of the vehicle. One instrument that is already operational onboard the ISS with a goal of monitoring electron density, electron temperature, and ISS floating potential is the Floating Potential Measurement Unit (FPMU). Although this tool is a valuable addition to the ISS, there are limitations concerning the data collection periods. The FPMU uses the Ku band communication frequency to transmit data from orbit. Use of this band for FPMU data runs is often terminated due to necessary observation of higher priority Extravehicular Activities (EVAs) and other operations on ISS. Thus, large gaps are present in FPMU data. The purpose of this study is to solve the issue of missing environmental data by implementing a secondary electron density data source, derived from the COSMIC satellite constellation, to create a model of ISS orbital environments. Extrapolating data specific to ISS orbital altitudes, we model the ionospheric electron density along the ISS orbit track to supply a set of data when the FPMU is unavailable. This computer model also provides an additional new source of electron density data that is used to confirm FPMU is operating correctly and supplements the original environmental data taken by FPMU

Space Weather Impacts on Spacecraft Design and Operations in Auroral Charging Environments

Spacecraft in low altitude, high inclination (including sun-synchronous) orbits are widely used for remote sensing of the Earth s land surface and oceans, monitoring weather and climate, communications, scientific studies of the upper atmosphere and ionosphere, and a variety of other scientific, commercial, and military applications. These systems are episodically exposed to environments characterized by a high flux of energetic (approx.1 to 10 s kilovolt) electrons in regions of very low background plasma density which is similar in some ways to the space weather conditions in geostationary orbit responsible for spacecraft charging to kilovolt levels. While it is well established that charging conditions in geostationary orbit are responsible for many anomalies and even spacecraft failures, to date there have been relatively few such reports due to charging in auroral environments. This presentation first reviews the physics of the space environment and its interactions with spacecraft materials that control auroral charging rates and the anticipated maximum potentials that should be observed on spacecraft surfaces during disturbed space weather conditions. We then describe how the theoretical values compare to the observational history of extreme charging in auroral environments and discuss how space weather impacts both spacecraft design and operations for vehicles on orbital trajectories that traverse auroral charging environments

Bounding Extreme Spacecraft Charging in the Lunar Environment

Robotic and manned spacecraft from the Apollo era demonstrated that the lunar surface in daylight will charge to positive potentials of a few tens of volts because the photoelectron current dominates the charging process. In contrast, potentials of the lunar surface in darkness which were predicted to be on the order of a hundred volts negative in the Apollo era have been shown more recently to reach values of a few hundred volts negative with extremes on the order of a few kilovolts. The recent measurements of night time lunar surface potentials are based on electron beams in the Lunar Prospector Electron Reflectometer data sets interpreted as evidence for secondary electrons generated on the lunar surface accelerated through a plasma sheath from a negatively charged lunar surface. The spacecraft potential was not evaluated in these observations and therefore represents a lower limit to the magnitude of the lunar negative surface potential. This paper will describe a method for obtaining bounds on the magnitude of lunar surface potentials from spacecraft measurements in low lunar orbit based on estimates of the spacecraft potential. We first use Nascap-2k surface charging analyses to evaluate potentials of spacecraft in low lunar orbit and then include the potential drops between the ambient space environment and the spacecraft to the potential drop between the lunar surface and the ambient space environment to estimate the lunar surface potential from the satellite measurements

Improving Communications in the Courtroom Symposium (Welcoming Remarks and Statement of the Issues)

Symposium: Improving Communications in the Courtroo

Improving Communications in the Courtroom Symposium (Welcoming Remarks and Statement of the Issues)

Symposium: Improving Communications in the Courtroo

Climatology of Deep O+ Dropouts in the Night-Time F-Region in Solar Minimum Measured by a Langmuir Probe Onboard the International Space Station

The Floating Potential Measurement Unit (FPMU) onboard the International Space Station includes a Wide sweeping Langmuir Probe (WLP) that has been operating in the F-region of the ionosphere at ∼400 km since 2006. While traditional Langmuir probe estimates include critical plasma parameters like electron density and temperature, we have also extracted the O+ percentage from the total ion constituents. This O+ composition dataset from the recent minimum in the Solar Cycle 24 reveals orbits with dropouts in O+ to below 80% of the total background ion density at ISS orbital altitudes. The observed O+ percentages during these dropouts are much lower than the values predicted by the International Reference Ionosphere 2016 (IRI2016) empirical model. In this paper, we present the climatology of these O+ dropouts with their dependency on season, local time and geographical location. The results show that the lowered O+ percentages are more significant in the winter hemispheres and are routinely observed for orbits in the pre-sunrise periods. The patterns in O+ dropouts can be explained in part from the lowering of the O+/H+ transition height during solar minimum along with patterns in neutral wind variation