Date of Award
Doctor of Philosophy (PhD)
Mechanical and Aerospace Engineering
Robert A. Frederick, Jr.
Jason T. Cassibry
D. Keith Hollingsworth
Nuclear propulsion., Space vehicles--Nuclear power plants., Water., Ammonia.
Recently, the NASA Artemis Program has pushed for a return to the Moon with In-Situ resource utilization (ISRU) being the central focus to sustainably achieve this goal. Nuclear Thermal Propulsion (NTP) is one of the considered propulsion systems for Mars missions under this program which can theoretically use any propellant provided that significant core degradation does not occur. The propellant of choice for NTP is hydrogen. However, water and ammonia are both found on the Moon and are much more dense than liquid hydrogen, do not require post processing such as electrolysis, and can be used directly by NTP. Using a NASA Design Reference Architecture, Alternative propellant NTP (A-NTP) engine models were developed to numerically examine water and ammonia A-NTP engines. The performance parameters of these engines were used for vehicle analysis for Mars missions and a Lunar ascent/descent mission. Other engines that were modeled for comparison included chemical engines that use hydrogen and oxygen as well as methane and oxygen, hydrogen in NTP (H-NTP), and Liquid oxygen Augmented Nuclear Thermal Rocket (LANTR). The vehicle analysis provided the necessary parameters to develop Lunar infrastructure requirements which were used to estimate the total cost of the architecture and cost per mission. Economies of scale were also analyzed by examining multiple vehicles performing together simultaneously. When operating the A-NTP engines at the maximum rated power level of the reactor, it was found that water doubled the thrust while ammonia increased the thrust by 70% from the H-NTP reference. The primary factors limiting the operational life of the engine were the maximum temperature of the cladding for water of 1400 K for sustained operation and 2400 K for up to 5 hours of operation, and the maximum temperature for the nuclear fuel of 2850 K for ammonia. Different material temperatures were set to match the time it took to utilize all the U-235 energy resource with the material operating time limits which resulted in compromising between specific impulse and engine life. For missions requiring changes in velocity lower than 4500 m/s, water A-NTP infrastructures are comparable to H-NTP infrastructures while ammonia A-NTP infrastructures were the costliest since ammonia is scarce relative to water in the Lunar surface. As mining occurs on the Moon, ammonia will always build up as an excess resource and Supplemental Vehicles using ammonia A-NTP engines can increase the total number of missions for a given infrastructure. However, the number of required Lunar launches to retank the Supplemental Vehicle for a Mars mission can drive the cost per mission up higher than just using the non-A-NTP vehicles and venting the excess resources.
Nikitaev, Dennis, "Implications of alternative in-situ propellants used in nuclear thermal propulsion engines" (2021). Dissertations. 231.