Engineering topics
Publications and source records attributed to Lee, K..
This paper will propose one vision for an interstellar program. It will include a discussion of mission concepts as well as technological requirements for accomplishing those missions.
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The Space Shuttle Main Engine (SSME) Fuel Flowmeter is located in the duct between the low and high pressure fuel turbopumps. In the flowmeter the rotation rate of a 4-blade rotor positioned downstream of two flow straighteners is employed to measure the engine fuel flow rate and thereby control the engine mixture ratio via the engine controller. Hence, inaccurate operation of the flowmeter could have serious consequences for SSME engine operation and performance, forcing, for example, tanking of extra fuel to allow for inaccurate flowmeter measurement. Since the current flight flowmeter configuration was incorporated into the SSME in the early eighties, some anomalies in flowmeter behavior have been observed. The initial flowmeter incorporated an "egg crate" design for the two flow straighteners which turn the duct flow to make it more uniform and parallel after it has come out of the 90 degree bend just upstream of the flowmeter.
Anomalous behavior manifested in the apparent SSME fuel flowmeter constant which relates the rotor speed to the engine flowrate has been shown to be the result of wakes of the upstream hexagonal web flow straightener periodically stalling the rotor blades, thereby changing the lift on the blades and the rotation speed of the rotor. Moreover, an unsteady, two-dimensional computational fluid dynamics model of the flowmeter has shown this wake-induced stall disappearing as the straightener-rotor distance is doubled, in accord with the existing SSME flowmeter database for the previous "egg crate" flowmeter. These observations have led to a new flowmeter design which has been shown in three-dimensional CFD computations (consistent with both the previous two-dimensional analyses and with existing correlations for airfoil stall) to be much less susceptible to stalling instabilities.
We present results of developments of low noise millimeter wave receivers for space applications utilizing InP HEMT monolithic microwave integrated circuts (MMICs).
Improved navigational technology (such as the Microwave Landing System and the Global Positioning System) installed in modern aircraft will enable air traffic controllers to better utilize available airspace. Consequently, arrival traffic can fly approaches to parallel runways separated by smaller distances than are currently allowed. Previous simulation studies of advanced navigation approaches have found that controller workload is increased when there is a combination of aircraft that are capable of following advanced navigation routes and aircraft that are not. Research into Air Traffic Control automation at Ames Research Center has led to the development of the Center-TRACON Automation System (CTAS). The Final Approach Spacing Tool (FAST) is the component of the CTAS used in the TRACON area. The work in this paper examines, via simulation, the effects of FAST used for aircraft landing on closely spaced parallel runways. The simulation contained various combinations of aircraft, equipped and unequipped with advanced navigation systems. A set of simulations was run both manually and with an augmented set of FAST advisories to sequence aircraft, assign runways, and avoid conflicts. The results of the simulations are analyzed, measuring the airport throughput, aircraft delay, loss of separation, and controller workload.
We report on resistivity and chemical stability of Cr/Au bilayers deposited by sputtering on three kinds of substrates: alumina, aluminum nitride and aluminum nitride coated alumina. The insertion loss of Cr/Au microstrip lines fabricated on these three substrates was low and stable after 100 cycles in the -65 degree C to 125 degree C temperature range.
Commercial and government communication, radar, and information systems face the challenge of cost and mass reduction via the application of advanced packaging technology. A majority of both government and industry support has been focused on low frequency digital electronics.
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A 20 GHz active receive slot array has been developed for operation in the downlink frequency band of NASA's Advanced Communication Technology Satellite (ACTS) for the ACTS Mobile Terminal (AMT) project. The AMT is to demonstrate voice and data communication between a mobile terminal in Los Angeles, California, and a fixed terminal in Cleveland, Ohio, via the ACTS satellite.
A new millimeter-wave package architecture with supporting electrical, mechanical and material science experiment and analysis is presented.
JPL has developed several mobile-vehicular antenna systems for satellite service throughout the last decade. The frequency bands cover UHF through Ka-band, and the antennas vary from high-gain with automatic satellite-tracking to omni-directional.
Structural models are usually tested by comparing their response with that of a reference structure (an actual structure or a more refined model) to a limited number of arbitrary loads. This test is not always reliable because the loads are arbitrary. An antioptimization-based method is proposed to test structural models. This method compares a structural model with a reference model or an actual structure under the worst loading case that maximizes the error in the model. Specifically, the method identifies the loading case that maximizes the difference between the responses of two models of the same structure using optimization. This method can be used to design experiments in order to validate a structural model. It can also be applied to identify damage in a structure by determining the load that maximizes the difference in the behavior of the damaged and the intact structure. The proposed method is illustrated by applying it to a plate and an automotive structure.
Microscopic dissipation processes in quasi-perpendicular shocks are studied by two-dimensional plasma simulations in which electrons and ions are treated as particles moving in self-consistent electric and magnetic fields. Cross-field currents induce substantial turbulence at the shock front reducing the reflected ion fraction, increasing the bulk ion temperature behind the shock, doubling the average magnetic ramp thickness, and enhancing the upstream field aligned electron heat flow. The short scale length magnetic fluctuations observed in the bow shock are probably associated with this turbulence.
Colonies of L. patella were collected from inshore water adjacent to small islets near Babelthaup Island, Republic of Palau, for the purpose of studying Prochloron symbionts. Examination of the algal symbionts after fixing, dehydrating, and embedment in Epon, showed Prochloron's central body to consist of a granular ground substance with a few electron-dense inclusions and to be enclosed by prominent photosynthetic membranes. Also found around the central body were thylakoids in a concentric pattern. After comparing the results with those of former studies, it was suggested that Prochloron morphology is host specific. Finally the network of host tissue extensions that entraps the symbionts was noted as possibly being a site for metabolic exchange.
The evolution of collisionless, quasi-parallel shocks (the angle between the shock normal and the upstream magnetic field being less than 45 deg) is examined using two dimensional particle simulations. Reflected ions upstream from the shock are observed with average guiding center velocity and gyrational energy which agree well with the prediction of simple specular reflection. Strong ion heating through the shock ramp is apparently caused by large amplitude whistler turbulence. A flux of suprathermal electrons is also the magnetic field direction. Much stronger ion heating occurs in the shock than electron heating. The relevance of this work to the earth's bow shock is discussed.
A hydraulic output system for the RE-1000 free piston stirling engine (FPSE) was designed. The hydraulic output system can be readily integrated with the existing hot section of RE-1000 FPSE. The system has two simply supported diaphragms which separate the engine gas from the hydraulic fluid, a dynamic balance mechanism, and a novel, null center band hydraulic pump. The diaphragms are designed to endure more than 10 billion cycles, and to withstand the differential pressure load as high as 14 MPa. The projected thermodynamic performance of the hydraulic output version of RE-1000 FPSE is 1.87 kW at 29/7 percent brake efficiency.