Eugina D. Mendez Ramos
(Advisor: Dimitri Mavris)

will defend a doctoral thesis entitled,

Enabling Conceptual Design and Analysis of Cryogenic In-Space Vehicles through the Development of an Extensible Boil-Off Model

On

Wednesday, March 24 at 2:00 p.m.
Via BlueJeans: https://bluejeans.com/626306470

Abstract
During the conceptual design process, the standard approach for estimating propellant losses due to boil-off is to divide the thermal load on the tank by the enthalpy of vaporization of the propellant. This provides a simple method for estimating the propellant losses that can easily integrated into the vehicle sizing process. However, the majority of designers implement this method not knowing what the underlying assumptions are and how they impact the design.

The above approach is based on a theoretical model that assumes that the heat entering the tank is directly responsible for evaporation of the liquid propellant at the interface. By ascribing all of the incoming heat towards the evaporation process, the model assumes the worst-case scenario, since in an actual tank only a portion of the incoming heat contributes to boil-off. Due to the simplicity and corresponding low fidelity that is used when representing the boil-off process, the model has the potential to significantly overestimate boil-off, and thus the propellant losses. The uncertainty in the propellant losses is then propagated throughout the vehicle during the sizing process through the propellant mass requirements.

In order to increase the fidelity in boil-off predictions, more of the physical effects responsible for the boil-off phenomenon must be captured. This necessitates modeling of the heat and mass transfer processes within the propellant tank. Numerous cryogenic propellant tank models exist in literature; however, those exhibiting the desired level of fidelity are too complex and are more suitable once the design space has been narrowed down, and there is more turnaround time between design iterations.

The primary objective of this research is to improve conceptual design and analysis of in-space vehicles through the development of a simplified cryogenic propellant tank model capable of providing higher-fidelity boil-off estimates. The proposed model allows for rapid evaluation of various tank geometries and utilizes direct venting as the method of pressure control. This latter capability is absolutely necessary if the model is to be applicable to future long-term missions. To demonstrate the benefits provided by the higher-fidelity model, it is incorporated in the sizing process of a relevant system – the descent stage of the Human Landing System – and compared with the results when the same system is sized using the standard approach.

Committee

• Prof. Dimitri Mavris – School of Aerospace Engineering (advisor)
• Prof. Daniel Schrage – School of Aerospace Engineering
• Prof. Jechiel Jagoda – School of Aerospace Engineering
• Dr. Bradford Robertson – School of Aerospace Engineering
• Dr. Thomas Percy – Integrated Performance Lead, Human Lander System Program, NASA Marshall Space Flight Center