Alexander L. Bogorad

Interaction of Charged Spacecraft with Electric Propulsion Plume: On Orbit Data and Ground Test Results

On-orbit observations and ground tests demonstrate interaction between charged spacecraft and electrothermal thruster-generated plasma. On-orbit measurements and test results are presented for plasma diagnostics and solar array performance during long-term exposure of flight solar panel. The long-term performance of a flight 70 V 2mtimes4 m GEO solar array exposed to a 2 kW arcjet plasma environment was studied

On-Orbit Error Rates of RHBD SRAMs: Comparison of Calculation Techniques and Space Environmental Models With Observed Performance

SEU data for more than 250 equivalent on-orbit SRAM device years is compared with upset rate calculations using various environmental models and contributions of both direct ionization and nuclear interactions.

Shielding Effectiveness and Closeout Methods for Composite Spacecraft Structural Panels

Increasingly, the latest spacecraft designs utilize partially conducting composite materials such as graphite epoxy or carbon-loaded Kevlar panels. These materials provide significant weight and mechanical advantages compared to conventional metallic structures, but their radio-frequency (RF) shielding properties are not well understood. In order to maintain a specified level of electromagnetic shielding on the spacecraft, it is necessary to use these composites and other materials to construct complex electromagnetic interference closeouts where harnesses, propulsion lines, RF cables, and waveguides penetrate the spacecraft Faraday cage. Shielding effectiveness measurements of these composite materials with standard seams and penetrations were performed. Closeout methodology was based on best commercial practices and included materials such as metallic mesh screen, double-sided metal-clad dielectric, conductive thermal blankets, and metallic foil tape with conductive adhesive. The test was conducted using standard methods inside a MIL-STD-461E anechoic chamber. Results demonstrated that the spacecraft composite structure with closeouts typical for commercial spacecraft can provide greater than 40 dB of shielding effectiveness from 200 MHz to 10 GHz and greater than 30 dB of shielding effectiveness from 10 to 40 GHz.

Spacecraft Charging Monitoring at GEO: Natural and Electric Propulsion Environment Measurements

Surface charging sensors are used on spacecraft to characterize the potential difference between a sample material surface relative to spacecraft common ground. A review has been performed of data collected over a period representative of a typical spacecraft lifetime from more than 10 such sensors aboard 6 Lockheed Martin built satellites operated by SES and INTELSAT which employ the use of electric propulsion systems at geosynchronous altitudes. Data are used to study the effects on surface charging caused by the electric propulsion plasma / GEO plasma correlative environment. Data are also used to review the performance of the sensors, characterize worst-case charging conditions experienced by the vehicles, and evaluate the frequency of severe charging events over the mission lifetimes.

Charging of Composites in Space Environment: Ground Test Data

Results of an extensive ground test routine, during which the charging characteristics of numerous composites commonly used in spacecraft design, are presented for plasmas representative of spacecraft exterior and shielded locations at GEO.

Total Ionizing Dose and Dose Rate Effects in Candidate Spacecraft Electronic Devices

Total dose tests of common devices reveal unexpected dose rate sensitivity. Devices from the same vendor procured to SMD versus military specifications exhibit substantially different dose rate effects. Behavior and critical parameters are compared and discussed.

Influence of Solar Cell Shape, Interconnect Shape, and Coverglass Coatings on Solar Array Arcing Parameters

Arc inception voltage studies have been performed on several common solar cell types. Results yielded quantitatively significant findings indicating specific designs are susceptible to arc inception at bias voltages readily achievable at near Earth orbits.

On-Orbit SEU Rates of UC1864 PWM: Comparison of Ground Based Rate Calculations and Observed Performance

More than 10 years of on-orbit UC1864 SEU data are compared with typical upset rate calculation methodologies and GCR environments. Results suggest that the most common calculation methods overestimate upset rates by at least 2×. Mitigation techniques are also verified via direct in orbit observations.

Spacecraft Charging, Plume Interactions, and Space Radiation Design Considerations for All-Electric GEO Satellite Missions

The use of electric propulsion (EP) for geostationary Earth orbit (GEO) stationkeeping and geostationary transfer orbit offers satellite operators the opportunity to reduce mission costs and to increase revenue by enabling a higher dry mass to orbit compared with traditional chemical or EP systems. The penalty for such benefits comes, initially, in the form of an increased time-to-orbit whereby the low-thrust transfer orbit duration will range from a few months, at best, to possibly one year or more. During the low-thrust transfer, the spacecraft will experience prolonged exposure to the portions of the trapped radiation belts to which the GEO spacecraft otherwise would not be subjected-most notably the inner belt and slot region. Further, the spacecraft will also experience on the order of 105 h of high-density high-energy plume plasma-a more challenging operational environment compared with that typically applied to the GEO spacecraft. Applicable environments are introduced, an overview of specific operational effects is provided, and design guidelines are highlighted.

On-Orbit Total Dose Measurements From 1998 to 2007 Using pFET Dosimeters

An updated review of on-orbit measurements for multiple pFET dosimeters at GEO for 1998-2007 time period indicates excellent sensor performance over a range of dose rates and yields valuable information regarding space environment model (AE-8, AE-9, IGE-2006, and POLE)/transport tool validation.