Engineering Papers⌕ Search

Engineering topics

Lee, J. H.

Publications and source records attributed to Lee, J. H..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Pump performance requirement for the liquid helium orbital resupply tanker

The Liquid Helium Orbital Resupply Tanker (currently renamed to Superfluid Helium Tanker) will greatly enhance the lifetime of the space missions which require superfluid helium. The Superfluid Helium Tanker pump performance requirement is driven by the superfluid helium replenishment needs of the Space Infrared Telescope Facility (SIRTF). SIRTF is one of the space missions which will require on-orbit superfluid helium resupply in the 1990s. The Superfluid Helium Tanker will carry at least 10,000 L of superfluid helium and provide a minimum pump head of 170 torr (0 to 200 L/h) to cool SIRTF from 150 to 2 K. When the SIRTF tank starts to collect liquid, a minimum flow rate of 300 L/h with a pump head of 60 torr is required to fill the 4000-liter tank.

Lee, J. H.↗
NASA NTRS1988

Cryogenic and thermal design for the Superfluid Helium On-Orbit Transfer (SHOOT) experiment

The analysis and trade-offs of the external thermal design of the two 200-liter dewars required in the SHOOT experiment to extend space mission life by superfluid helium replenishment are discussed. Also considered are the support electronics and the optimization and prediction of the performance of the dewar and cryostat assemblies. Particular attention is given to the ground-hold and standby performance of the dewars, along with the temperature of the helium bath during high-flow-rate helium transfers.

Lee, J. H.↗
NASA NTRS1988

One-megawatt solar pumped and electrically driven lasers for space power transmission

High power lasers in space could provide power for a variety of future space missions such as spacecraft electric power requirements and laser propulsion. This study investigates four electrically pumped laser systems, krypton fluoride, copper vapor, laser diode array, and the carbon dioxide laser, all scaled to 1-MW laser output. Each system obtained its primary power from a large solar photovoltaic array which, in turn, provides power for the appropriate laser power conditioning subsystem. Each system was block-diagrammed, and the power and efficiency were found for each subsystem. The laser diode array had the highest solar-to-laser efficiency (6 percent) and smallest radiator area making it the most advantageous of the electrically driven lasers studied. This system was then compared with an iodine solar pumped laser system previously studied. The diode array had a better wavelength with regard to transmission optics mass, but it also had a heavier radiator because of its lower temperature radiator requirement. A more advanced solar pumped laser could emerge as the preferred laser system for space applications.

Deyoung, R. J.↗
NASA NTRS1987

Analytical modeling of helium II in forced flow conditions

A numerical model was developed to examine the flow behavior of He II under forced flow conditions. The model basically solves the governing equations in the two-fluid model of He II, and can be used to assess the pump requirement for transferring He II in spaceborne systems. Predictions of liquid temperature and pressure drop agree well with empirical data obtained from small scale tests. At high transfer rates, the model predicts that the forced convection dominates the Gorter-Mellink conduction in heat transfer, and the classical turbulent flow correlation is sufficient for calculating the pressure drop across the transfer line.

Ng, Y. S.↗
NASA NTRS1987

Proposed mechanistic model to simulate transfer line cool-down process using liquid helium

This paper proposes a mathematical model to simulate the cool-down behavior of a warm transfer line using liquid helium (including He II) in a microgravity environment. The thermal-hydraulic characteristics of different possible flow regimes which may occur during the cool-down process are discussed. Correlations for predicting the heat and momentum transfer rates in each flow regime are presented.

Ng, Y. S.↗
NASA NTRS1987

System implications of aperture-shade design for the SIRTF Observatory

The 1-m-aperture Space Infrared Telescope Facility (SIRTF) will operate with a sensitivity limited only by the zodiacal background. This sensitivity requirement places severe restrictions on the amount of stray light which can reach the focal plane from off-axis sources such as the sun or earth limb. In addition, radiation from these sources can degrade the lifetime of the telescope and instrument cryogenic system which is now planned for two years before the first servicing. Since the aperture of the telescope represents a break in the telescope insulation system and is effectively the first element in the optical train, the aperture shade is a key system component. The mass, length, and temperature of the shade should be minimized to reduce system cost while maximizing the telescope lifetime and stray light performance. The independent geometric parameters that characterize an asymmetrical shade for a 600 km, 28 deg orbit were identified, and the system sensitivity to the three most important shade parameters were explored. Despite the higher heat loads compared to previously studied polar orbit missions, the analysis determined that passive radiators of a reasonable size are sufficient to meet the system requirements. An optimized design for the SIRTF mission, based on the sensitivity analysis, is proposed.

Lee, J. H.↗
NASA NTRS1986

Detector arrays for low-background space infrared astronomy

The status of development and characterization tests of integrated infrared detector array technology for astronomy applications is described. The devices under development include intrinsic, extrinsic silicon, and extrinsic germanium detectors, with hybrid silicon multiplexers. Laboratory test results and successful astronomy imagery have established the usefulness of integrated arrays in low-background astronomy applications.

Mccreight, C. R.↗
NASA NTRS1986

A long-pulse amplifier for solar-pumped iodine lasers

The characteristics of a photodissociation iodine-laser amplifier pumped with a solar-simulating radiation were studied. Under long-pulse energy extraction, an energy amplification of about three and an energy storage time of longer than 500 microseconds were observed for a one meter long, 10 mm i.d. amplifier tube. The effects of elevated temperatures resulted in little reduction of the amplifier gain. These results confirm that developing an efficient chain of oscillator-amplifiers for a high-power solar-pumped iodine laser is indeed feasible.

Hwang, I. H.↗
NASA NTRS1986

Space Infrared Telescope Facility (SIRTF) observatory design

The NASA Space IR Telescope Facility (SIRTF) is a 1-m aperture, cryogenically cooled IR observatory scheduled for launch into orbit in the mid-1990s. SIRTF will operate in the 2-700 micron range and yield a 1000-fold increase in sensitivity over NASA's IRAS observatory. A low inclination orbit compatible with Space Shuttle operations will be used. Results from comparisons of a system error budget allocation for the f/24 optical configuration with recent test data indicate that a figured fused silica mirror and a blade flexure mounting system can be cooled to cryogenic temperature while meeting required wavefront tolerances for substrate deformation. An all-He cooling system will be used in the low inclination orbit.

Brooks, W. F.↗
NASA NTRS1986

Cryogenic implications of orbit selection of the Space Infrared Telescope Facility (SIRTF)

An investigation has been conducted to determine how the choice of orbit for NASA's prospective Space IR Telescope Facility (SIRTF), between polar (99-deg) and low inclination (28.5-deg) alternatives, will affect the performance of the all-superfluid He-cooled IR optics employed. While the dewar design met both the service life and 200-micron background-limited performance criteria in the case of the polar orbit mission, the alternative orbit allowed the background-limited criteria to be met only 50 percent of the time. It is accordingly recommended that the 200-micron background-limited observations be made only for a limited portion of the mission, while meeting the 100-micron limit at all times.

Lee, J. H.↗
NASA NTRS1986

Detector arrays for low-background space infrared astronomy

The status of development and characterization tests of integrated infrared detector array technology for astronomy applications is described. The devices under development include intrinsic, extrinsic silicon, and extrinsic germanium detectors, with hybrid silicon multiplexers. Laboratary test results and successful astronomy imagery have established the usefulness of integrated arrays in low-background astronomy applications.

Mccreight, C. R.↗
NASA NTRS1986

Solar-pumped photodissociation iodine laser

The scientific feasibility of a solar-pumped iodine photodissociation laser for space applications is under investigation. Recently, a 2-W CW output for more than one hour was achieved using n-C3F7I vapor as the laser material and a vortex-stabilized argon arc as the light source.

Lee, J. H.↗
NASA NTRS1985

An experimental investigation of pulsed multichannel discharge across solid insulators

An experimental study of pulsed surface flashover across a solid insulator in a vacuum is reported, with application of fast impulse voltages of a few tens of ns rise time and a few microsec tail time. Following the flashover voltage experiments, no visible degradation of the surface was found for the BaTiO3 sample, whereas for the TiO2 sample a distinct track mark could be seen where the flashover occurred. Three schemes for obtaining multichannel discharges were studied for plexiglass specimens, and results showed the number of shots to decrease as the number of channels increased.

Lakdawala, V. K.↗
NASA NTRS1985

Threshold kinetic processes for t-C4F9I

To determine the relative threshold of the lasant gas t-C4F9I in comparison to n-C3F7I, the pump energy to reach threshold for photodissociation iodine lasing is measured in a common aparatus. The comparison is made for the threshold energies in the iodide pressure range up to 50 Torr when 64-J electric input into a flashlamp is used for pumping. It is shown from the results that qualitative differences between the thresholds of the two gases result from the degree to which steady state is achieved by the time threshold is reached. The estimated recombination rate for t-C4F9I is found to be much larger than the value given by Ershov et al (1978).

Lee, J. H.↗
NASA NTRS1985

Temperature control of silica mirrors for cryogenically-cooled telescopes in space

The SIRTF (Space Infrared Telescope Facility) optical subsystem, including the primary mirror, has been modeled using lumped-parameter techniques and a thermal and cryogenic transient analysis program developed previously. Since silica mirrors have been shown to have significantly less distortion due to cryogenic cooldown, a silica primary mirror of approximately 1 m diameter is being considered. Thermal responses to variations in aperture heat load and heat sink temperature have been explored. Calculations have been made of system noise components from primary mirror spatial and temporal temperature variations. Background-limited infrared observations can be made at wavelengths out to 200 micrometers. Mirror thermal performance with and without copper wires for cooling is also considered.

Melugin, R. K.↗
NASA NTRS1984

Cryogenic and thermal design for the Space Infrared Telescope Facility (SIRTF)

The 1-meter class cryogenically cooled Space Infrared Telescope Facility (SIRTF) planned by NASA, is scheduled for a 1992 launch. SIRTF would be deployed from the Shuttle, and placed into a sun synchronous polar orbit of 700 km. The facility has been defined for a mission with a minimum initial lifetime of one year in orbit with mission extension that could be made possible through in-orbit servicing of the superfluid helium cryogenic system, and use of a thermal control system. The superfluid dewar would use an orbital disconnect system for the tank supports, and vapor cooling of the barrel baffle. The transient analysis of the design shows that the superfluid helium tank with no active feedback comes within temperature requirements for the nominal orbital aperture heat load, quiescent instrument, and chopper conditions.

Lee, J. H.↗
NASA NTRS1984

Threshold kinetics of a solar-simulator-pumped iodine laser

A model of the chemical kinetics of the n-C3F7I solar-simulator-pumped iodine laser is utilized to study the major kinetic processes associated with the threshold behavior of this experimental system. Excited-state diffusion to the cell wall is the dominant limiting factor below 5 torr. Excited-state diffusion to the cell wall is the dominant limiting factor below 5 torr. Excited-state recombination with the alkyl radical and quenching by the parent gas control threshold at higher pressures. Treatment of the hyperfine splitting and uncertainty in the pressure broadening are important factors in fixing the threshold level. In spite of scatter in the experimental data caused by instabilities in the simulator high-pressure high-pressure arc, reasonable agreement is achieved between the model and experiment. Model parameters arrived at are within the uncertainty range of values found in the literature.

Wilson, J. W.↗