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Christie, R. J.

Publications and source records attributed to Christie, R. J..

5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Thermal Acoustic Oscillation: Causes, Detection, Analysis, and Prevention

Thermal Acoustic Oscillations (TAO) can occur in cryogenic systems and produce significant sources of heat. This source of heat can increase the boil off rate of cryogenic propellants in spacecraft storage tanks and reduce mission life. This paper discusses the causes of TAO, how it can be detected, what analyses can be done to predict it, and how to prevent it from occurring.The paper provides practical insight into what can aggravate instability, practical methods for mitigation, and when TAO does not occur. A real life example of a cryogenic system with an unexpected heat source is discussed, along with how TAO was confirmed and eliminated.

Cryogenics↗
NASA NTRS2011

Broad Area Cooler Concepts for Cryogenic Propellant Tanks

Numerous studies and ground tests have shown that broad area cooling (also known as distributed cooling) can reduce or eliminate cryogenic propellant boil-off and enable long duration storage in space. Various combinations of cryocoolers, circulators, heat exchangers and other hardware could be used to build the system. In this study, several configurations of broad area cooling systems were compared by weighing hardware combinations, input power requirements, component availability, and Technical Readiness Level (TRL). The preferred system has a high TRL and can be scaled up to provide cooling capacities on the order of 150W at 90K

Christie, R. J.↗
NASA NTRS1982

Vibration analysis of three guyed tower designs for intermediate size wind turbines

Three guyed tower designs were analyzed for intermediate size wind turbines. The four lowest natural frequencies of vibration of the three towers concepts were estimated. A parametric study was performed on each tower to determine the effect of varying such tower properties as the inertia and stiffness of the tower and guys, the inertia values of the nacelle and rotor, and the rotational speed of the rotor. Only the two lowest frequencies were in a range where they could be excited by the rotor blade passing frequencies. There two frequencies could be tuned by varying the guy stiffness, the guy attachment point on the tower, the tower and mass stiffness, and the nacelle/rotor/power train masses.

Christie, R. J.↗
NASA NTRS1974

The economic value of remote sensing of earth resources from space: An ERTS overview and the value of continuity of service. Volume 6: Land use. Part 2: The role of ERTS in the establishment and updating of a nationwide land cover information system

The utility of an ERS system as an effective tool in land use management is analyzed. The cost effectiveness of satellites as a component of an ERS system is presented based on various projected levels of demand. It is indicated that a cost savings potential of $7.9 to $37.1 million annually is attributable to the inclusion of ERS-like satellites in the ERTS system.

Christie, R. J.↗