David W. Plachta

An Updated Zero Boil-Off Cryogenic Propellant Storage Analysis Applied to Upper Stages or Depots in a LEO Environment

Previous efforts have shown the analytical benefits of zero boil-off (ZBO) cryogenic propellant storage in launch vehicle upper stages of Mars transfer vehicles for conceptual Mars Missions. However, recent NASA mission investigations have looked at a different and broad array of missions, including a variety of orbit transfer vehicle (OTV) propulsion concepts, some requiring cryogenic storage. For many of the missions, this vehicle will remain for long periods (greater than one week) in low earth orbit (LEO), a relatively warm thermal environment. Under this environment, and with an array of tank sizes and propellants, the performance of a ZBO cryogenic storage system is predicted and compared with a traditional, passive-only storage concept. The results show mass savings over traditional, passive-only cryogenic storage when mission durations are less than one week in LEO for oxygen, two weeks for methane, and roughly 2 months for LH2. Cryogenic xenon saves mass over passive storage almost immediately.

Cryogenic propulsion with zero boil-off storage applied to outer planetary exploration

§This paper describes a study of the potential application of cryogenic propulsion systems using liquid oxygen and hydrogen propellants to planetary spacecraft. A conceptual liquid oxygen/ liquid hydrogen propulsion stage designs were developed. Mission-level assessments of the impacts of adopting cryogenic propulsion with the latest in zero boil off cryogenic storage techniques were made. Results are presented for the three missions studied: Titan Explorer, Mars Sample Return Earth Return Vehicle, and Comet Nucleus Sample Return. Thermal analysis results show that it is possible to store LOX/LH 2 at reasonable tank pressures using only passive radiation cooling when the field of view of propellant tanks can be kept clear of warm planetary bodies. This situation is typical of interplanetary cruise, spacecraft orbiting bodies with low effective blackbody temperatures, and spacecraft with very short stay times near the target planet, asteroid, or comet. Passive storage was accomplished using a combination of sun shades, spacecraft configuration considerations, spacecraft pointing constraints, and the low conductance Passive Orbit Displacement Strut (PODS). Actively cooled designs use cryocoolers and mechanically pumped fluid loops to reject heat from the propellant tanks. From the results of the mission studies performed in this study, it appears that the applicability of cryogenic propulsion (specifically pump-fed LOX / LH 2 systems) is limited for missions in the Discovery and New Frontiers class or for unmanned exploration of Mars. Significant benefits were found for missions that share the following two characteristics: 1) Very large 8V requirements (over 3000 m/s) and 2) No requirement to store the propellants for an extended period in a low orbit about a planetary body. The large dry mass fraction of the cryogenic system, as conceived, reduced or outweighed the benefits from high Isp performance for missions with lower delta-V or which required active cooling.

Mastering Cryogenic Propellants

AbstractThe National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) began experimentation with cryogenic propellants in the early 1950s to understand the potential of these high-performance propellants for use in liquid propellant rocket engines. Supporting these tests required learning how to both design cryogenic systems and develop procedures to safely and reliably work with cryogenic fuels and oxidizers. This early work led to the development of a skill set that has been core to the center ever since. When NASA was formed and the exploration missions were defined, it became clear that the ability to use cryogenic propellants in the thermal and microgravity environment of space was critical to mission success, and the agency was tasked with enabling this capability. To support development of the Centaur upper stage and the Saturn S-IVB stage, GRC researchers and engineers initiated extensive technology development for the in-space application of cryogenic fluid management (CFM)...

CRYOGENIC PROPELLANT BOIL-OFF REDUCTION SYSTEM

Lunar missions under consideration would benefit from incorporation of high specific impulse propellants such as LH2 and LO2, even with their accompanying boil-off losses necessary to maintain a steady tank pressure. This paper addresses a cryogenic propellant boil-off reduction system to minimize or eliminate boil-off. Concepts to do so were considered under the In-Space Cryogenic Propellant Depot Project. Specific to that was an investigation of cryocooler integration concepts for relatively large depot sized propellant tanks. One concept proved promising—it served to efficiently move heat to the cryocooler even over long distances via a compressed helium loop. The analyses and designs for this were incorporated into NASA Glenn Research Centers Cryogenic Analysis Tool. That design approach is explained and shown herein. Analysis shows that, when compared to passive only cryogenic storage, the boil-off reduction system begins to reduce system mass if durations are as low as 40 days for LH2, and 14 days ...

Long Term Space Storage and Delivery of Cryogenic Propellants for Exploration

In support of the NASA’s Exploration Technology Development Program, Ball Aerospace & Technologies Corp. (Ball Aerospace), in conjunction with NASA GRC and JSC, performed design, analysis, and comparative analyses on a cryogenic propellant storage and delivery system that would provide acceptable quality Liquid Oxygen (LOX) and Liquid Methane (LCH4) propellant for a cryogenically fueled CEV Service Module (SM). Cryogenic propellants for both the Reaction Control System (RCS) and Orbital Maneuvering System (OMS) thrusters were baselined for the Crew Exploration Vehicle (CEV) in the Exploration Systems Architecture Study (ESAS). The goal of this study was the characterization and optimization of a cryogenic propellant storage and delivery subsystem that would meet the Lunar Return Mission requirements for the cryogenically fueled CEV SM. This mission required that LOX and LCH4 be stored for a period of 241.5 days after launch, including 180 days in Low Lunar Orbit (LLO). For this mission Ball Aerospace analyzed the impact of various SM configurations on the storage of these cryogenic propellants, including thruster operational constraints, tank geometries and thermal coupling, pressurant effects, delivery subsystems interactions and operational requirements. Both passive and active cooling approaches were optimized during this effort.

ANALYSIS OF CONTINUOUS HEAT EXCHANGERS FOR CRYOGENIC BOIL-OFF REDUCTION

Cryogenic boil-off reduction systems (CBRS) employing continuous heat exchangers in pressurized helium distributed cooling networks for active thermal control of large surfaces such as propellant tank walls and light-weight radiation shields have been studied for some time. Usually, very simple and intuitive relations are used to derive such quantities as the pressure drop across the network and the required flow rate for a given heat load. Here, detailed thermal-fluid and heat transfer relations for such systems are formulated and then studied term by term in order to determine the conditions under which various approximations to them may reasonably be made. It is found that in most applications of interest, use of the simplified relations is justifiable.

Large scale demonstration of liquid hydrogen storage with zero boiloff

Cryocooler and passive insulation technology advances have substantially improved prospects for zero boiloff (ZBO) cryogenic storage. Therefore, a cooperative effort by NASA’s Ames Research Center, Glenn Research Center, and Marshall Space Flight Center (MSFC) has been implemented to develop ZBO concepts for in-space cryogenic storage. Described herein is one program element, a large-scale ZBO demonstration using the MSFC Multipurpose Hydrogen Test Bed (MHTB). A commercial cryocooler is interfaced with the existing MHTB spray-bar mixer and insulation system in a manner that enables a balance between incoming and extracted thermal energy. The testing is scheduled for the summer of 2001. In this paper the test objectives, test set-up, and test procedures are presented.

Feasibility of Scavenging Propellants from Lander Descent Stage to Supply Fuel Cells and Life Support

A feasibility study consisting of both analytical and experimental work was performed to determine if the lunar lander vehicle can use residual propellants remaining in the descent stage tanks after landing to provide reactants to the fuel cell power system and oxygen to life support for a 7-day sortie mission. Initial results indicate that the residual hydrogen will last approximately 19 days at the poles and 15 days at the equator. The residual oxygen will last 21 days at the poles and more than 16.5 days at the equator. Excess hydrogen will need to be vented during the mission to prevent tank over-pressurization, while heat must be added to the oxygen tank at the poles. Tests performed on a liquid oxygen tank pressurized with helium demonstrate that the helium concentrations in the ullage gas can be reduced significantly with venting. Tests on a flow-through fuel cell stack indicate that they can tolerate significant amounts of helium contamination in the reactants without permanent

Cryogenic Boil-Off Reduction System Testing

Cryogenic propellants such as liquid hydrogen (LH2) and liquid oxygen (LO2) are a part of NASAs future space exploration due to the high specific impulse that can be achieved using engines suitable for moving 10s to 100s of metric tons of payload mass to destinations outside of low earth orbit. However, the low storage temperatures of LH2 and LO2 cause substantial boil-off losses for missions with durations greater than several days. The losses can be greatly reduced by incorporating high performance cryocooler technology to intercept heat load to the propellant tanks and by the integration of self-supporting multi-layer insulation. The active thermal control technology under development is the integration of the reverse turbo- Brayton cycle cryocooler to the propellant tank through a distributed cooling network of tubes coupled to a shield in the tank insulation and to the tank wall itself. Also, the self-supporting insulation technology was utilized under the shield to obtain needed tank applied LH2 performance. These elements were recently tested at NASA Glenn Research Center in a series of three tests, two that reduced LH2 boil-off and one to eliminate LO2 boil-off. This test series was conducted in a vacuum chamber that replicated the vacuum of space and the temperatures of low Earth orbit. The test results show that LH2 boil-off was reduced 60% by the cryocooler system operating at 90K and that robust LO2 zero boil-off storage, including full tank pressure control was achieved.

ZBO Cryogenic Propellant Storage Applied to a Mars Sample Return Mission Concept

Zero Boil‐Off (ZBO) Cryogenic Propellant Systems were designed and analyzed for a Mars sample return mission. JPL designed the spacecraft, and NASA GRC/ARC and contractors designed the cryogenic storage systems. The performance of those systems are compared to traditional storable propellant propulsion systems. The cryogenic storage system modeling included cryocoolers, heat pipes, a radiator, shadowing, MLI, foam, and tank internal components. Model descriptions and tools developed are shown, along with the systems performances and masses. Models show that the ZBO systems applied to cryogenic propellants are beneficial to the Mars mission.