Engineering topics
Conroy, David
Publications and source records attributed to Conroy, David.
Flight Plasma Diagnostics for High-Power, Solar-Electric Deep-Space Spacecraft
NASA’s Asteroid Redirect Robotic Mission (ARRM) mission concept plans included a set of plasma and space environment instruments, the Plasma Diagnostic Package (PDP), to fulfill ARRM requirements for technology extensibility to future missions. The PDP objectives were divided into the classes of 1) Plasma thruster dynamics, 2) Solar array-specific environmental effects, 3) Plasma environmental spacecraft effects, and 4) Energetic particle spacecraft environment. A reference design approach and interface requirements for ARRM’s PDP was generated by the PDP team at JPL and GRC. The reference design consisted of redundant single-string avionics located on the ARRM spacecraft bus as well as solar array, driving and processing signals from multiple copies of several types of plasma, effects, and environments sensors distributed over the spacecraft and array. The reference design sensor types were derived in part from sensors previously developed for USAF Research Laboratory (AFRL) plasma effects campaigns such as those aboard TacSat-2 in 2007 and AEHF-2 in 2012. ARRM project leadership also encouraged the PDP team to convene a team of topical subject matter experts from across the country to review and confirm the reference design and to consider effective alternatives and/or enhancements to the reference design. This activity was proposed and accepted as an interactive, informal JPL “A-team” study and a cadre of 25 participants gathered in early 2017 for discussions. The outcome of the two-day A-team study was that the PDP reference design would allow the most important induced-environment unknowns to be measured in the appropriate space environment. Another outcome addressed technology developments of new or improved space plasma environmental sensors. The A-team study concluded that selected developments would lead to improved measurements that could efficiently provide important and otherwise unavailable information about plasma thruster operation in the space environment as well as the plasma induced spacecraft environment. Specifically, the A-team group recommended greater sensor diversity, by inclusion of deployed sensor capabilities in the thruster plume, or by occasional gimbaling of the thruster(s) toward the sensor arrays. The A-team also recommended developing high-speed probes, optical plasma probes, energy selective probes, and direct erosion/deposition sensors, among others; and recommended the inclusion of cameras as well as, since ARRM was to be recovered in cis-lunar orbit by a crewed mission, astronaut assessments of thruster induced environments and collection of sample coupons. Overall, the PDP A-team study provided a clear, consensus supported validation of the reference design PDP approach and pointed out important directions for future flight plasma sensor development.
Flight Plasma Diagnostics for High-Power, Solar-Electric Deep-Space Spacecraft
NASA's Asteroid Redirect Robotic Mission (ARRM) project plans included a set of plasma and space environment instruments, the Plasma Diagnostic Package (PDP), to fulfill ARRM requirements for technology extensibility to future missions. The PDP objectives were divided into the classes of 1) Plasma thruster dynamics, 2) Solar array-specific environmental effects, 3) Plasma environmental spacecraft effects, and 4) Energetic particle spacecraft environment. A reference design approach and interface requirements for ARRM's PDP was generated by the PDP team at JPL and GRC. The reference design consisted of redundant single-string avionics located on the ARRM spacecraft bus as well as solar array, driving and processing signals from multiple copies of several types of plasma, effects, and environments sensors distributed over the spacecraft and array. The reference design sensor types were derived in part from sensors previously developed for USAF Research Laboratory (AFRL) plasma effects campaigns such as those aboard TacSat-2 in 2007 and AEHF-2 in 2012.
Water Contaminant Mitigation in Ionic Liquid Propellant
Appropriate system and operational requirements are needed in order to ensure mission success without unnecessary cost. Purity requirements applied to thruster propellants may flow down to materials and operations as well as the propellant preparation itself. Colloid electrospray thrusters function by applying a large potential to a room temperature liquid propellant (such as an ionic liquid), inducing formation of a Taylor cone. Ions and droplets are ejected from the Taylor cone and accelerated through a strong electric field. Electrospray thrusters are highly efficient, precise, scaleable, and demonstrate low thrust noise. Ionic liquid propellants have excellent properties for use as electrospray propellants, but can be hampered by impurities, owing to their solvent capabilities. Of foremost concern is the water content, which can result from exposure to atmosphere. Even hydrophobic ionic liquids have been shown to absorb water from the air. In order to mitigate the risks of bubble formation in feed systems caused by water content of the ionic liquid propellant, physical properties of the ionic liquid EMI-Im are analyzed. The effects of surface tension, material wetting, physisorption, and geometric details of the flow manifold and electrospray emitters are explored. Results are compared to laboratory test data.