Engineering topics

Feller, Jeffrey R.

Publications and source records attributed to Feller, Jeffrey R..

4 records

NASA NTRS2015

Reduced Boil-Off System Sizing

NASA is currently developing cryogenic propellant storage and transfer systems for future space exploration and scientific discovery missions by addressing the need to raise the technology readiness level of cryogenic fluid management technologies. Cryogenic propellants are baselined in many propulsion systems due to their inherently high specific impulse; however, their low boiling points can cause substantial boil-off losses over time. Recent efforts such as the Reduced Boil-off Testing and the Active Thermal Control Scaling Study provide important information on the benefit of an active cooling system applied to LH2 propellant storage. Findings show that zero-boil off technologies can reduce overall mass in LH2 storage systems when low Earth orbit loiter periods extend beyond two months. A significant part of this mass reduction is realized by integrating two stages of cooling: a 20 K stage to intercept heat at the tank surface, and a 90 K stage to reduce the heat entering the less efficient 20 K stage. A missing element in previous studies, which is addressed in this paper, is the development of a direct method for sizing the 90 K cooling stage. Such a method requires calculation of the heat entering both the 90 K and 20 K stages as compared to the overall system masses, and is reliant upon the temperature distribution, performance, and unique design characteristics of the system in question. By utilizing the known conductance of a system without active thermal control, the heat being intercepted by a 90 K stage can be calculated to find the resultant lift and mass of each active thermal control stage. Integral to this is the thermal conductance of the cooling straps and the broad area cooling shield, key parts of the 90 K stage. Additionally, a trade study is performed to show the ability of the 90 K cooling stage to reduce the lift on the 20 K cryocooler stage, which is considerably less developed and efficient than 90 K cryocoolers.

Cryogenic fluid management↗

NASA NTRS2014

Tank Applied Testing of Load-Bearing Multilayer Insulation (LB-MLI)

The development of long duration orbital cryogenic storage systems will require the reduction of heat loads into the storage tank. In the case of liquid hydrogen, complete elimination of the heat load at 20 K is currently impractical due to the limitations in lift available on flight cryocoolers. In order to reduce the heat load, without having to remove heat at 20 K, the concept of Reduced Boil-Off uses cooled shields within the insulation system at approximately 90 K. The development of Load-Bearing Multilayer Insulation (LB-MLI) allowed the 90 K shield with tubing and cryocooler attachments to be suspended within the MLI and still be structurally stable. Coupon testing, both thermal and structural was performed to verify that the LB-MLI should work at the tank applied level. Then tank applied thermal and structural (acoustic) testing was performed to demonstrate the functionality of the LB-MLI as a structural insulation system. The LB-MLI showed no degradation of thermal performance due to the acoustic testing and showed excellent thermal performance when integrated with a 90 K class cryocooler on a liquid hydrogen tank.

Thermal Insulation↗

NASA NTRS2014

Cryogenic Boil-Off Reduction System Testing

Cryogenic propellants such as liquid hydrogen (LH2) and liquid oxygen (LO2) are a part of NASA's future space exploration due to the high specific impulse that can be achieved using engines suitable for moving 10's to 100's 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.

Propellant Storage↗

NASA NTRS2012

Methane Lunar Surface Thermal Control Test

NASA is considering propulsion system concepts for future missions including human return to the lunar surface. Studies have identified cryogenic methane (LCH4) and oxygen (LO2) as a desirable propellant combination for the lunar surface ascent propulsion system, and they point to a surface stay requirement of 180 days. To meet this requirement, a test article was prepared with state-of-the-art insulation and tested in simulated lunar mission environments at NASA GRC. The primary goals were to validate design and models of the key thermal control technologies to store unvented methane for long durations, with a low-density high-performing Multi-layer Insulation (MLI) system to protect the propellant tanks from the environmental heat of low Earth orbit (LEO), Earth to Moon transit, lunar surface, and with the LCH4 initially densified. The data and accompanying analysis shows this storage design would have fallen well short of the unvented 180 day storage requirement, due to the MLI density being much higher than intended, its substructure collapse, and blanket separation during depressurization. Despite the performance issue, insight into analytical models and MLI construction was gained. Such modeling is important for the effective design of flight vehicle concepts, such as in-space cryogenic depots or in-space cryogenic propulsion stages.

Plachta, David W.↗