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Sean Greenhalge

Publications and source records attributed to Sean Greenhalge.

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2026

Parameterization of Nuclear Electric Propulsion Trajectories for Outer Solar System Science Missions Methodology

This manuscript addresses the methodology used to create a database of low thrust missions to outer planets. This database utilizes previous work modeling NEP systems to determine the maximum delivered mass to outer planets based on a range of mission parameters, such as time of flight, launch vehicle, and power system mass. Trajectories were selected which best utilized NEP benefits. Additionally, a discussion on the database outputs for missions to Saturn is included, such as time of flight based on trajectory type and maximum payload, given a specific launch vehicle. The purpose of this work was to create a basis for future mission design, and a tool to investigate general trends across mission options.

Outer Planets↗
NASA NTRS2023

Parametric Modeling of NTP Engine Performance for a Crewed Mars Mission

Nuclear thermal propulsion (NTP) has been studied extensively for use on a crewed mission to Mars, and NASA and DARPA are partnering in the development and demonstration of an NTP engine as part of the DRACO project. The specific impulse and thrust achieved by an engine in the context of a mission determines the propellant amount required to close the mission and the size of the vehicle required. An NTP engine has a slower start-up/shut-down transient than traditional chemical engines and requires post-firing cooling, and thus the average Isp for a burn is a function of the power ramp-up rate and the duration of the burn. An initial demonstration engine may target a lower Isp than the 900 sec that has been extensively studied by NASA. This paper shows the effect on the mission closure and vehicle sizing of the transient ramp rate performance and of lower than 900 sec specific impulse. Ammonia is considered as an alternate NTP propellant, with mission performance estimated.

NTP↗
NASA NTRSDate not supplied

Capabilities of Single Launch NTP and Chemical Spacecrafts for Cis-Lunar Tug Missions

Renewed interest in the region between the Earth and the moon suggests that a tug operating between these two destinations will be most likely required in the near future. This report details a parametric spacecraft model which sizes a nuclear thermal propulsion or chemical propulsion spacecraft and compares their payload transport capabilities for missions to the moon. A spacecraft sized to fit in a single launch vehicle is assumed, and six launch vehicles are investigated. Maximum spacecraft payload mass and minimum mission transit time are compared between nuclear and chemical propulsion spacecrafts. For vehicles sized to the maximum capability of a launch vehicle, payloads of at least five metric tons are possible with either propulsion option; with nuclear thermal propulsion able to provide additional mass or reduced transit time when the spacecraft is sized to the maximum capability of the heaviest-lift launch vehicles. Transit times to the moon with a five-ton payload could be reduced by at least 0.2 days with a nuclear propulsion system.

Cis-lunar tug↗
NASA NTRSDate not supplied

Capabilities of Single Launch NTP and Chemical Spacecrafts for Cis-Lunar Tug Missions

Renewed interest in the region between the Earth and the moon suggests that a tug operating between these two destinations will be most likely required in the near future. This report details a parametric spacecraft model which sizes a nuclear thermal propulsion or chemical propulsion spacecraft and compares their payload transport capabilities for missions to the moon. A spacecraft sized to fit in a single launch vehicle is assumed, and six launch vehicles are investigated. Maximum spacecraft payload mass and minimum mission transit time are compared between nuclear and chemical propulsion spacecrafts. For vehicles sized to the maximum capability of a launch vehicle, payloads of at least five metric tons are possible with either propulsion option; with nuclear thermal propulsion able to provide additional mass or reduced transit time when the spacecraft is sized to the maximum capability of the heaviest-lift launch vehicles. Transit times to the moon with a five-ton payload could be reduced by at least 0.2 days with a nuclear propulsion system.

Cis-lunar tug↗
NASA NTRSDate not supplied

Concept of Operations of Cryogenic Fluid Management for Nuclear Thermal Propulsion

Cryogenic Fluid Management (CFM) is a critical capability for a hydrogen NTP vehicle for a crewed mission to Mars. AMA has investigated the concept of operations for zero boiloff CFM systems and provided feasibility assessment for a zero-boiloff CFM system based on gravity-independent technologies. This includes identification of CFM-critical mission stages, modelling of CFM operational modes in steady state and transient conditions, thermal analysis of the NTP vehicle and CFM systems, hydrogen leakage analysis, and system margins and fault tolerance. This work illustrates the feasibility of a zero boiloff mission with a set of technology performance assumptions.

cryogenic fluid management↗
NASA NTRSDate not supplied

Key Performance Parameters for an Operational CIS-Lunar NTP Vehicle

Nuclear Thermal Propulsion (NTP) is in active development by NASA and DARPA. This paper presents an investigation into the effects of different values of key performance parameters (KPPs) of an NTP engine in the context of payload delivery missions between Earth and Lunar orbits. The high Isp afforded by NTP combined with the relatively large engine mass is best applied to missions where the payload mass is large and required ΔV high. Two missions considered are the round-trip Earth to Moon tug and a NRHO to low Lunar orbit tug. Chemical propulsion vehicles can generally achieve higher propellant mass fractions, similar payload mass and similar ΔV performance on these missions. When re-use of the vehicle is considered, the reduced propellant mass required by an NTP vehicle begins to add up over multiple refilling launches and trades more favorably. Analysis illustrates the impact of variation in NTP engine performance values, especially Isp, engine mass and thrust, on performance and the comparison to chemical propulsion. NTP transient and cooldown effects on the vehicle performance are examined. A variety of launch vehicles and hydrogen and ammonia NTP propellants are included in the analyses, and cryogenic fluid management system effects are accounted for.

NTP↗