Engineering topics

Farmer, J. T.

Publications and source records attributed to Farmer, J. T..

6 records

NASA NTRS2013

Development and Testing of a Variable Conductance Thermal Acquisition, Transport, and Switching System

This paper describes the development and testing of a scalable thermal control architecture for instruments, subsystems, or systems that must operate in severe space environments with wide variations in sink temperature. The architecture is comprised by linking one or more hot-side variable conductance heat pipes (VCHPs) in series with one or more cold-side loop heat pipes (LHPs). The VCHPs provide wide area heat acquisition, limited distance thermal transport, modest against gravity pumping, concentrated LHP startup heating, and high switching ratio variable conductance operation. The LHPs provide localized heat acquisition, long distance thermal transport, significant against gravity pumping, and high switching ratio variable conductance operation. Combining two variable conductance devices in series ensures very high switching ratio isolation from severe environments like the Earth's moon, where each lunar day spans 15 Earth days (270 K sink, with a surface-shielded/space viewing radiator) and each lunar night spans 15 Earth days (80-100 K radiative sink, depending on location). The single VCHP-single LHP system described herein was developed to maintain thermal control of International Lunar Network (ILN) anchor node lander electronics, but it is also applicable to other variable heat rejection space missions in severe environments. The LHPVCHP system utilizes a stainless steel wire mesh wick ammonia VCHP, a Teflon wick propylene LHP, a pair of one-third square meter high  radiators (one capillary-pumped horizontal radiator and a second gravity-fed vertical radiator), a half-meter of transport distance, and a wick-bearing co-located flow regulator (CLFR) to allow operation with a hot (deactivated) radiator. The VCHP was designed with a small reservoir formed by extending the length of its stainless steel heat pipe tubing. The system was able to provide end-to-end switching ratios of 300-500 during thermal vacuum testing at ATK, including 3-5 W/K ON conductance and 0.01 W/K OFF conductance. The test results described herein also include an in-depth analysis of VCHP condenser performance to explain VCHP switching operation in detail. Future multi-VCHP/multi-LHP thermal management system concepts that provide scalability to higher powers/longer transport lengths are also discussed in the paper.

Bugby, D. C.↗

NASA NTRS2008

Heater Development, Fabrication, and Testing: Analysis of Fabricated Heaters

Thermal simulators (highly designed heater elements) developed at the Early Flight Fission Test Facility (EFF-TF) are used to simulate the heat from nuclear fission in a variety of reactor concepts. When inserted into the reactor geometry, the purpose of the thermal simulators is to deliver thermal power to the test article in the same fashion as if nuclear fuel were present. Considerable effort has been expended to mimic heat from fission as closely as possible. To accurately represent the fuel, the simulators should be capable of matching the overall properties of the nuclear fuel rather than simply matching the fuel temperatures. This includes matching thermal stresses in the pin, pin conductivities, total core power, and core power profile (axial and radial). This Technical Memorandum discusses the historical development of the thermal simulators used in nonnuclear testing at the EFF-TF and provides a basis for the development of the current series of thermal simulators. The status of current heater fabrication and testing is assessed, providing data and analyses for both successes and failures experienced in the heater development and testing program.

Bragg-Sitton, S. M.↗

NASA NTRS1986

System impacts of solar dynamic and growth power systems on space station

Concepts for the 1990's space station envision an initial operational capability with electrical power output requirements of approximately 75 kW and growth power requirements in the range of 300 kW over a period of a few years. Photovoltaic and solar dynamic power generation techniques are contenders for supplying this power to the space station. A study was performed to identify growth power subsystem impacts on other space station subsystems. Subsystem interactions that might suggest early design changes for the space station were emphasized. Quantitative analyses of the effects of power subsystem mass and projected area on space station controllability and reboost requirements were conducted for a range of growth station configurations. Impacts on space station structural dynamics as a function of power subsystem growth were also considered.

Farmer, J. T.↗

NASA NTRS1986

Space Station momentum control and reboost requirements for two power generation concepts

Results are presented of dynamic structural analyses of 75 and 300 kW versions of a solar dynamic (SD) power supply for the Space Station (MSS). The SD is being seriously considered as an alternative to solar panels due to lower areal and mass requirements and higher efficiencies. The functioning principle is to use parabolic concentrators to focus sunlight on a heat engine to boil liquids to drive a turbine. Potential problems are foreseen in terms of the torques which would be experienced by the MSS and the subsequent orbital stability effects. The stability would be altered by changing aerodynmaic drag, altered moment of inertia and angular momentum and the altered center of mass location. The problem is exacerbated by the need to first equip the MSS with solar panels while the SD technology is developed. The analysis shows that the attitude control system will need to be redesigned and resized to accommodate MSS growth with either power system. The effects of the rotating parts of the SD system can be minimized, but further studies are required to determine the effects on the pointing accuracy of the SD, which must be 10 times as precise as that needed by a photovoltaic array.

Farmer, J. T.↗

NASA NTRS1983

Interactive systems analysis of four structural concepts for a Land Mobile Satellite System

Weight and structural analysis data were generated for four structural concepts for a Land Mobile Satellite System (LMSS) using the Interactive Design and Evaluation of Advanced Spacecraft (IDEAS) computer-aided design and analysis program. Structural concepts analyzed included the wrapped radial rib, box ring, tetrahedral truss, and hoop column. Estimates of total spacecraft weight, structural natural frequencies and modal shapes were determined and compared for several loading conditions for each concept. Spacecraft-induced and environmental effects on antenna performance (surface accuracy, defocus and boresight offset) are quantified.

Ferebee, M. J., Jr.↗

NASA NTRS1982

Weight and structural analysis of four structural concepts for a land mobile satellite system

The present study is concerned with a Land Mobile Satellite System (LMSS) which can provide mobile communications for commercial and government applications in nonmetropolitan areas of the continental U.S. and Canada as an augmentation to existing and planned terrestrial systems. The satellite system would provide 'narrow band' telecommunications services, thin-route fixed telephone and data services in the 806-890 MHz band, and continuous emergency beacon monitoring in the 406-406.1 MHz band. It is pointed out that a satellite system operating in concert with terrestrial cellular systems could provide truly ubiquitous mobile communications services in the U.S. and Canada. A single shuttle shuttle launch could place the LMSS spacecraft in geosynchronous orbit over the continental U.S. in 1995 with a 10-year lifetime. Attention is given to the structural concepts, a weight analysis, and a structural analysis.

Ferebee, M. J.↗