High-power Solar Electric Propulsion Research Articles

Low-thrust trajectory design for near-Earth asteroid supply delivery and resource transportation mission using high-power solar electric propulsion

This paper presents the low-thrust (LT) trajectory design for near-Earth asteroid (NEA) supply delivery and resource transportation mission using high-power Solar Electric Propulsion (SEP). NEA low-thrust roundtrip accessibility is investigated through a numerical approach and new knowledge of the mass transportation capability of SEP systems in NEA missions is provided. A number of powerful deep neural networks (DNNs) were trained and optimized for 60 kW, 150 kW, 300 kW and 500 kW SEP-based LT trajectory design. DNNs are used as the surrogate of the conventional optimization process. A new low thrust trajectory roundtrip opportunity search algorithm is developed, which integrates the DNN models and allows an efficient roundtrip search process. Compared to the conventional approach, the DNN-based search algorithm reduces the search time by 99.96%. The SEP mass transportation capabilities were numerically studied. It was found the 60 kW SEP can deliver 5 tons of supply to up to 40% of NEAs. Considering refueling on NEAs, the accessible NEAs can be further increased by 16.2%. It is suggested that the 150 kW, 300 kW, 500 kW SEP to be used to transport 10–30 tons, 30–70 tons, 70–120 tons resources from NEAs respectively. These mass ranges ensure about 4,000 or more targets to be accessible. In all the case studies, the roundtrip accessible boundaries were constructed using polynomial regression. These boundaries were numerically obtained, which could be useful for mission designers to rapidly determine the LT roundtrip accessibility of newly found NEAs.

High Voltage Solar Array Development for Space and Thruster-Plume Plasma Environments

High-power solar arrays are in development by the National Aeronautics and Space Administration (NASA) for near-term high-power solar electric propulsion (SEP) missions. These high-voltage (HV) solar arrays use deployable flexible blanket configurations and need to be able to operate in the plasma environment of high-power Hall thrusters operating at tens of kilowatts of power. Array voltages of 300–800 V are desired both to minimize the copper bus mass in the system and to potentially operate the SEP Hall thrusters directly at high specific impulse without an in- series power processing unit. Coupons with multiple strings of solar cells (SCs) have been tested to high positive and negative biases in a plasma environment representative of the edge of Hall thruster plumes. Proper encapsulation of the exposed metals and triple points is required to avoid excessive current collection and arc initiation. Fully encapsulated test coupons have been successfully been tested at highest anticipated thruster plume plasma densities at voltages from 600 to 1000 V, which enables both very high power arrays and direct drive configurations for SEP missions.

Solar electric propulsion orbital debris ferry, vehicle concept and reference mission

The hazards of orbital debris in Low Earth Orbit (LEO) are well understood and concepts for Active Debris Removal (ADR) have been proposed in the literature, yet no mission has been launched to date. This is in part due to the lack of baseline space vehicle concepts. To give a point of departure design, a Solar Electric Propulsion (SEP) orbital debris ferry concept and operations approach has been developed. This concept provides a feasible solution to ADR that is currently ready for a demonstration mission. This approach uses a single space vehicle to independently and autonomously rendezvous with multiple LEO debris objects, secure, and ferry them to a sufficiently low disposal orbit. This mission architecture is enabled by flight-proven, relatively high-power SEP technologies and Autonomous Rendezvous and Docking (AR&D) algorithms and systems. The high Specific Impulse (Isp) of SEP enables low propellant requirements for removal of many debris objects with a single vehicle, and results in a low cost per target removed. Results from system sizing, low-thrust trajectory analysis, AR&D simulation, conceptual vehicle design, a concept of operations, and an implementation approach are provided. Results show that the SEP orbital debris ferry is a relatively low-cost and low-risk solution to mitigate the threat of orbital debris.

Breakthrough capability for UVOIR space astronomy: Reaching the darkest sky

We describe how availability of new solar electric propulsion (SEP) technology can substantially increase the science capability of space astronomy missions working within the near-UV to far-infrared (UVOIR) spectrum by making dark sky orbits accessible for the first time. We present a proof of concept case study in which SEP is used to enable a 700kg Explorer-class observatory payload to reach an orbit beyond where the zodiacal dust limits observatory sensitivity. The resulting scientific performance advantage relative to a Sun–Earth L2 point orbit is presented and discussed. We find that making SEP available to astrophysics Explorers can enable this small payload program to rival the science performance of much larger long development-time systems. We also present flight dynamics analysis which illustrates that this concept can be extended beyond Explorers to substantially improve the sensitivity performance of heavier (7000kg) flagship-class astrophysics payloads such as the UVOIR successor to the James Webb Space Telescope by using high power SEP that is being developed for the Asteroid Redirect Robotics Mission.

Experimental Investigation of a Direct-Drive Hall Thruster and Solar Array System

Studies of high-power solar electric propulsion systems (i.e., tens to hundreds of kilowatts) suggest that significant mass savings may be realized by implementing direct-drive power systems. The National Direct-Drive Testbed was established to address issues associated with implementation of direct drive, and experimental results at power levels up to 10 kW are reported here. Hall thruster operation and control were shown to be simple and no different from that for operation on conventional power supplies. Thruster oscillations were the same as those for conventional power supplies, did not adversely affect solar array operation, and were independent of filter capacitance from 8 to . Solar array current and voltage oscillations were very small compared to their mean values and showed a modest dependence on capacitor size. Significantly, no instabilities or anomalous behavior were observed in the thruster or power system at any operating condition investigated, including near and at the array peak power point. Thruster startup using the anode propellant flow as the power “switch” was shown to be simple and reliable, with system transients mitigated by the proper selection of filter capacitance size. A simple electrical circuit model was developed and is shown to have good agreement with the experimental data.