David Hanks’s research while affiliated with Aerojet Rocketdyne and other places

View Video Presentation: https://doi.org/10.2514/6.2022-4373.vid Aerojet Rocketdyne (AR) has long had a vision for providing propulsion that permits exploration and extensive travel capability across the Solar System. AR’s history and current efforts include providing propulsion and power for NASA’s far-reaching exploration goals and science missions. These include propulsion for the return to the moon with the Space Launch System (SLS), battery and power systems for the International Space Station (ISS), propulsion for Mars landers, and power for Mars rovers (e.g., Perseverance) and propulsion to power deep space missions like New Horizon. AR has continued the race in developing advanced propulsion systems that help the USA and NASA advance their goal of getting humans to Mars by working on a High-Assay Low Enriched Uranium (HALEU) Nuclear Thermal Propulsion (NTP) system. Current mission studies are focused on Mars missions in the late 2030’s and beyond. NTP engine requirements (e.g., thrust size, Isp) have been connected to those current studies that have been on-going since 2019. Those studies have shown a wide range of thrust sizes (e.g., 12,500 to 25,000-lbf) which can close the architecture and vehicle design using a nuclear fuel material that is capable of high temperature (e.g., peak temperatures between 2,800 to 3,000-deg K) operation to achieve a specific impulse (Isp) at or above 900 seconds. Although Mars missions dominate where NTP shows high pay-off, cis-lunar missions where NTP can support faster 2-3 day missions and more cargo mass also show payoff versus typical chemical propulsion systems. The HALEU NTP designs continue to use hydrogen propellant as the coolant and can use either a Ceramic-Metallic, Ceramic-Ceramic, or Carbide based fuel. The new approach in 2021 for the NTP fuel arrangement utilizes discrete cylindrical assemblies in the moderator block. The grouping is optimized for achieving criticality, which produces the required power level but is similar to the previous approach of using hexagonal (prismatic form) fuel elements with hydrogen flowing in channels within the fuel assembly. Current work has extended the fuel and core designs beyond NTP fuels initially analyzed between 2017 to 2020 and have started looking at other fuels with Carbide material approaches since 2021. Engine design trades are still on going to identify the optimum core/engine system operating characteristics. The NTP design trades that are continuing rely heavily on thermodynamic cycle modeling that includes the neutronic design attributes of the fuel and how it operates within a reactor core design. This paper presents a discussion on the methods for NTP modeling of the engine system for both steady state and transient operation, examining start, shutdown and post-cool down operations. In addition to steady state and transient modeling architectures, the implications of capturing component design influences on the NTP design is discussed.

Aerojet Rocketdyne is working with NASA, the Department of Energy, and other industry to define a more affordable path to nuclear propulsion and power use for lunar, Mars and broader solar system exploration missions. Aerojet Rocketdyne's (AR) recent work builds on the legacy design, analysis, and testing knowledge gained from the Rover/NERVA (Nuclear Engine for Rocket Vehicle Applications) to create a feasible Low Enriched Uranium (LEU) design that has been shown to provide high thrust capability (e.g., 25,000 lbf) for faster trajectories and a higher specific impulse (Isp) (e.g., 850 to 900 seconds) than can be achieved with chemical propulsion (e.g., 460 seconds) systems. Some evolutionary approaches with carbide fuel may be able to provide over 1,000 seconds of specific impulse. Evolving and modernizing Nuclear Thermal Propulsion (NTP) engine designs to use LEU reactor fuel has proven to be feasible, and affordable approaches to manufacturing and testing are being pursued using an organized technology maturity plan (TMP) with NASA oversight. LEU NTP engine and reactor development activity is proceeding in 2019 and architecture analysis is showing NTP will provide enabling benefits for multiple solar system missions. Making LEU NTP practical for use in Lunar and Mars missions is foremost and is the expected first use of the engine system. Later missions can evolve using the NASA Space Launch System (SLS) and LEU NTP stages to send orbiters to the gas giants and to the interstellar medium. This paper discusses and provides background on the analysis and results from the work that is proceeding on developing a LEU NTP system. It is expected that this propulsion system can be used for lunar tugs, crewed and cargo missions to Mars and as a rapid transfer space transport stage.

Studies of Nuclear Thermal Propulsion (NTP) over the past several decades, and updated most recently with the examination of Low Enriched Uranium (LEU), have shown nuclear propulsion is an enabling technology to reach beyond this planet and establish permanent human outposts at Mars or rapidly travel to any other solar system body. The propulsion needed to propel human spacecraft needs high thrust to operate withinthe deep gravity well of a planet and provide high propulsive efficiency for rapid travel and reduced total spacecraft mass. NTP can provide the thrust to move a spacecraft between orbits, can operate as a dual-mode system that provides power and propulsion capability, provides a strong architectural benefit to human and robotic exploration missions, and provides a path toward reusable in-space transportation systems. NTP provides smaller vehicle systems due to its specific impulse (ISP) being twice that of the best cryogenic liquid rocket propulsion and can thus provide reduced trip times for round-trip missions from Earth to Mars. Aerojet Rocketdyne (AR) is working with NASA, other government agencies, and other industry partners to improve the design and reduce the cost of NTP engine systems. Current NTP designs focus on thrust sizes between 15,000-lbf (~67-kN) and 25,000-lbf (~111-kN). AR in 2019 has examined various reactor cores and enhancements to optimize LEU NTP designs. The enhancements improve the mission architecture robustness and provide more design margin for Mars vehicles across many mission opportunities, trip times, and mission types. The LEU NTP design can offer mission architecture stages or elements that can be used for both Lunar and deep space exploration missions. The NTP designs enable packaging of various NTP stage designs (e.g., crew Mars vehicle stage elements, cargo stage derivatives, a deep space stage with payload, Lunar stage elements) on the NASA SLS Block 2 using the 8.4-meter fairing. The primary LEU core designs studied, for the above-mentioned missions, have relied on liquid hydrogen for the propellant and coolant and use Zirconium Hydride within a structural element as the neutron moderator. Several designs have been examined that use Beryllium Oxide with the fuel elements in the core to eliminate the structural elements. The LEU NTP engine systems studied have typically been used only for the primary delta-V burns (e.g., earth escape, planetary capture, planetary escape, earth return capture). LEU NTP engine systems have also been examined using a the LEU reactor fuel element and moderator element approach to perform orbital maneuvering system (OMS) burns during the mission simply by permitting the reactor to keep operating at very low power levels during the entire mission. This paper will discuss the various engine system and mission design trades performed in 2019 for Mars and lunar missions when using a single NTP or a cluster of NTP engines.