Search Results

Electronic components including switches that can operate at elevated temperatures in excess of 200 °C are under development for applications such as the More Electric Aircraft. SiC is utilized to build high temperature switches, but limitations in fabrication techniques have stunted the development of SiC based devices. Other wide band gap materials such as diamond offer the promise of meeting the high temperature requirements. A new class of high voltage, high power, high temperature diamond switches was developed under a Phase II STTR program from the US Air Force. A 1000 V, 156 A diamond switch was operated at temperatures up to 375 °C to demonstrate the validity of these switches for More Electric Aircraft applications. Designs for a practical switch were completed. Such a 1000 V/1000 A diamond switch operating at 400 °C would have a <5 V forward voltage drop.

This paper presents trade studies that address the use of the thermionic/AMTEC cell - a cascaded, high-efficiency, static power conversion concept that appears well-suited to space power applications. Both the thermionic and AMTEC power conversion approaches have been shown to be promising candidates for space power. Thermionics offers system compactness via modest efficiency at high heat rejection temperatures, and AMTEC offers high efficiency at modes heat rejection temperature. From a thermal viewpoint, the two are ideally suited for cascaded power conversion: thermionic heat rejection and AMTEC heat source temperatures are essentially the same. In addition to realizing conversion efficiencies potentially as high as 35-40%, such a cascade offers the following perceived benefits: Survivability - capable of operation in the Van Allen belts. Simplicity - static conversion, no moving parts. Long lifetime - no inherent life-limiting mechanisms identified.

As part of the DoD/NASA Lithium-Ion and More-Electric Aircraft (MEA) development programs, in-house life-testing and performance characterization of lithium-ion batteries of sizes 1-20 amp-hours (Ah) were performed. Using AC impedance spectroscopy, the impedance behavior of lithium-ion cells with respect to temperature, cycle number, electrode, and state-of-charge was determined. Cell impedance is dominated by the positive (cathode) electrode, increases linearly with cycle number, and exponentially increases with decreasing temperature. From cell performance testing, we have seen the cell behavior is extremely sensitive to the ambient temperature. Preliminary battery performance results as well as AC impedance and life cycle test results are presented below.

A research and development program is being conducted at the Saft Advanced Technologies Division in Hunt Valley, Maryland, to double the energy density of a thermal battery. A baseline battery has been developed with lithium/iron disulfide chemistry to meet a set of military requirements. A study of transition metal fluoride cathodes to replace iron disulfide is in progress for an improved battery. Development of a lithium/copper(II) fluoride (CUF2) couple is proceeding by iterative testing of single cells. LiAl/CuF2 cells have produced 227 Wh/kg. This exceeds the specific energy of state-of-the-art cells with iron disulfide by nearly 40%. The copper fluoride cells average 2.44 volts when discharged at a current density of 200 mA/cm2.

Molten salts are ionic, nonflammable, nonvolatile liquids with high ionic conductivity, oxidation voltage greater than 5 V vs. Li and high thermal stability (>300°C). So far the application of molten salts in batteries has been limited to those operating at relatively high temperature (>150°C). Rechargeable lithium-ion and lithium batteries have attained wide acceptance in both commercial and military applications. However, most of the solvents used in these cells are volatile and flammable; hence, they represent a significant safety hazard, especially, when operated at higher temperatures. Therefore the application of molten salts as electrolytes in lithium and lithium-ion cells containing LiMn2O4 (cathode) was investigated. The preliminary results show that rechargeable lithium and lithium-ion cells can be constructed and operated using molten salts as electrolytes. Test cells were cycled at ambient temperature and at higher temperature (55°C).

U. S. Army developed the Nickel Metal Hydride (NMH) BB-390 battery, Lithium ion battery BB-2847 and two hours charger for PM Night Vision thermal devices and PM Sincgar radios. The BB-390 can provide 240 watts (10 Amperes at 24 Volts) of power for transmit for the radios. The BB-390 battery replaced the BB-590 nickel Cadmium battery. The BB-390 battery contains 40 “A” size cells and provided up to two times the capacity over the nickel cadmium battery with same weight. During charging the BB-390 NMH battery, the battery will heat up to as high as 57 C. This NMH battery contains 10 thermos devices for protection during both charge and discharge. The BB-2847 lithium ion battery contains 6 each 18650, It provides 26 watt-hours These batteries are protected from external short as well as overdischarge.

Lithium ion conductivity of a lithium compound is known to be influenced by an inert, non-lithium ion conductor additive. This paper reports an investigation of the effects of boron nitride (BN) addition to the conductivity of lithium iodide (Lil). The Lil:BN stoichiometry and heat treatment parameters (temperature and time) have been used as variables. It will be shown that lithium conductivity is strongly dependent upon heat treatment parameters. The activation energy for lithium ion transport also decreases with the addition of BN. Further analysis of activation energy data suggests that lithium ion motion takes place through interfacial regions of Lil and BN phases.

The objective of this paper is to design and fabricate a micro-cooler to provide integral cooling to electronics or Microelectromechanical Systems (MEMS) type components utilizing current MEMS technologies. A three-port capillary pumped loop (CPL) was analyzed and fabricated from silicon and quartz for this purpose. An analytical study of the device is presented in support of this design. This proves the feasibility of such a device, and thus the rationale for continuing its development.

A 20 watt thermophotovoltaic (TPV) battery substitute system is being developed that will provide higher storage capacity and lower weight than the batteries currently used for many military missions. It can also be instantaneous recharged by refueling with propane. The TPV battery substitute incorporates several advanced design features. These include: an evacuated and sealed enclosure for the emitter and photovoltaic (PV) cells to minimize unwanted convection heat transfer from the emitter to the PV cells; a selective tungsten emitter with a well matched gallium antimonide PV cell receiver, spectral control optical filters to recycle non-convertible radiant energy, and a silicon carbide thermal recuperator to recover thermal energy from the exhaust gases. The design of the system and fabrication of the components are discussed.

Active magnetic bearings (AMBs) while offering many unique design and operational advantages for high speed rotor systems, still require that backup bearings be included to protect and/or catch the rotor in the event of a failure in the AMB. A Zero Clearance Auxiliary Bearing (ZCAB) has recently been conceived and tested. The ZCAB incorporates a series of interconnected rollers that move radially inward when activated until the shaft is contacted by all rollers and the initial clearance is eliminated. Besides centering the shaft in the AMB and ZCAB clearance circles, the ZCAB design minimizes the potential for destructive backward whirl and introduces external damping for reduced sensitivity to unbalance and other rotor system vibrations. This paper presents the results of a preliminary ZCAB design study for a light-weight, high-speed rotor system and test results for a prototype ZCAB.

NASA requires lightweight rechargeable batteries for future missions to Mars and the outer planets that are capable of operating at low temperatures. Due to the attractive performance characteristics, lithium-ion batteries have been identified as the battery chemistry of choice for a number of future applications, including Mars Rovers and Landers. Under an Interagency program, lithium-ion cells of varying capacity are being developed for NASA and DOD applications. JPL, in collaboration with Wright Patterson Laboratory (Air Force), is currently evaluating a number of lithium-ion cells varying in capacity from 3 Ah to 50 Ah for future aerospace applications. The Mars Lander and Rover applications require a rechargeable, high energy density system capable of operation at temperatures as low as -20°C.

BlueStar Advanced Technology Corporation (BATC), under contract to the USAF, is developing large Li ion cells and batteries which will satisfy the performance requirements of future Mars Lander and Rover missions. The present scenario for the Lander mission calls for a 28-V, 25-Ah battery which will discharge at the C/5 to C rate and be charged at the C/5 to C/2 rate. The mission requires > 500 cycles at a 50% depth of discharge and an operating temperature of -20°C to + 45°C. The Rover mission calls for a 14-V, 7-Ah battery which will operate in the temperature range -30°C to + 45°C with all other requirements being identical to that of the Lander. Cell designs, characteristics and test data will be presented as well as preliminary battery designs.

Yardney Technical Products is developing a high energy density Li-ion cell tailored for NASA's Extravehicular Mobility Unit battery. The goal of the program is to develop a Li-ion technology which offers long storage and cycle life in a system which provides energy density and exercise performance comparable to the current 6.7kg Zn-AgO battery. The Zinc-Silver Oxide cells which are most commonly used in this application provide 400 Wh/l with a 32 cycle life at 26.6Ah and 1.55V with a rated wet life of 425 days. To improve the energy density of the Li-ion cells we have focused on improving the energy density of its components. In addition to using thin metal foil current collectors, the energy density of the cathode material was improved by utilizing a high capacity Co doped nickel oxide material. Further efforts have focused on developing a more energy dense carbonaceous anode material. The results of this effort are reviewed.

Li-ion cells were cycled as part of a program to assess commercial technologies for space applications. Cells showing capacity loss were disassembled and compared with new cells using scanning electron microscopy (SEM) x-ray diffraction (XRD), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to determine the underlying cause for the capacity loss. Results indicate a loss of lithium from the cathode and a thicker, non-active, fluorine-rich layer on the surface of the anode.

A summary of the past and present activities of EPT in the quest to develop the lithium-ion technology for spacecraft applications is presented. Specific technical challenges addressed are rate capability and along with maintained or improved performance (specific energy and cycle life). Preliminary investigations show the LiNiCoO2//MCMB system was found to have a higher rate capability than the LiCoO2//EP-G3 chemistry. Further investigation on the processing and interface effects is necessary to confirm the findings.

Very little published data exist for the lithium ion chemistry showing that it will meet the rigors of GEO or LEO satellites. This paper reveals that the graphite/LiNiO2 chemistry has achieved 133,000 discharges at 30% DOD in 18650 cells. Full scale 40 Ah cell data predicts ∼ 4000 cycles for 60% DOD and above 100,000 cycles for 20 and 30% DOD.

Since the late 1980s Super NiCd™ Batteries have been used by Hughes Space and Communications, Co. (HSC), NASA, TRW, Lockheed Martin Space and Missiles Group, and Johns Hopkins University Applied Physics Laboratory. In early flight programs with the technology, some capacity losses on long-term storage were experienced, but recently batteries with storage up to five years prior to launch are yielding within 2-3% of prestrorage capacity and are demonstrating managable performance in orbit.

With the launch of the Deep Space One Mission spacecraft, the NASA Solar-Electric-Propulsion Technology Applications Readiness Program (NSTAR) began flight validation of its xenon ion propulsion system. The NSTAR system includes a 30-cm diameter ion thruster, a xenon tankage and feed system, a power processing unit, and a digital control and interface unit. Since program inception in 1995 two flight power processors have been built, tested, and integrated. The test program consisted of acceptance and qualification testing at the system level plus solar vacuum testing at the spacecraft level. In addition to the ground test program, in-flight acceptance testing was successfully completed before year-end 1998. Further a multi-year mission profile test is planned to begin early this year at the Jet Propulsion Laboratory ion engine vacuum test facility.

The Hall Effect Thrusters (HET's), which are presently available in a broad range of power levels, are recognized as an economic, efficient, and effective means to perform numerous propulsion functions for commercial and military satellite applications. Also, the HET technology is the preferred alternative for future constellations of LEO satellites, and several GEO applications. Power Processing Units (PPU's) for electric thrusters are very complex custom designs which require long and expensive development and qualification cycles. The core element of a HET PPU is its Discharge Power Supply (DPS) which processes more than 95% of the input power. Traditional DPS designs cannot easily accommodate parametric changes, and for severe thermal and EMI issues must be overcome high power applications. These custom approaches require lengthy developments, lack proven “heritage”, are costly.

A Hall Thruster discharge power converter breadboard was successfully developed. The converter is rated at 400 Watts, with a maximum output of 350 Volts or 1.25 Amps. Both voltage and current are real time continuously adjustable from zero to their respective maximums. An arbitrary number of these converters can be paralleled, offering modularity, redundancy and power scaling for application on a range of Hall thrusters from few a hundred watts to several kilowatts. Operational stability and an overall efficiency of 92% was demonstrated over a broad power range, first on a resistive load and then on Busek's 200 Watt Hall thruster. The design, construction and test results are described in this paper with particular attention to the dynamic interaction of the converter and the thruster.