Space Power and Transportation
Electric Propulsion and Solar Electric Direct-Drive Propulsion
Russian T-100 thruster
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Electric Propulsion is a type of propulsion used in the space environment. This type of propulsion system uses an electrically powered thruster that ionizes and accelerates gaseous propellants carried onboard such as Xenon, generating thrust. The thruster we currently are using is a Russian T-100 SPT-type Hall Effect Thruster (HET). Due to their relatively high efficiency, Hall thrusters are being used on more and more spacecraft for many applications including station-keeping for ear-Earth communications, and as primary propulsion to the Moon and beyond. At SRI we are obtaining the needed electric energy from a 600 V triple-junction solar cell array and applying it directly to the HET's anode drive circuit. This method is sometimes referred to as ‘Direct-Drive'. The Direct-Drive approach may help reduce the need for high voltage conversion electronics making large, high power propulsion systems simpler, producing a mass and cost savings.
Pulsed Inductive Thrusters
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PT-1 thruster |
Farad thruster |
SRI at Auburn University is the home of two advanced pulsed inductive thruster research programs. Both the Farad thruster and PT-1 thruster are the only lab operational thruster of each design in the world. The programs are a cooperative research effort between Space Research Institute, Radiance Technologies, NASA Marshall Space Flight Center, and the University of South Alabama. These projects offer unique research opportunities for Auburn graduate and undergraduate students. Almost all the design, fabrication, and testing is done by AU engineering students employed by Radiance and SRI.
Stretched Lens Array
Full scale SLASR panel. This module can produce 3.75 kW and weighs only 10 kg
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Auburn University is working with Entech Solar to test and promote the Stretched Lens Array (SLA). The SLA is a solar array that uses refractive concentrator technology to collect and convert solar energy into useful electricity with efficiencies of greater than 27%. It is durable, lightweight, cost effective, radiation resistant, capable of reliable high voltage operation, and is inherently designed to withstand electrostatic discharge. The Stretched Lens Array (SLA) offers unprecedented performance (>80 kW/m3 stowed power, >300 W/m2 areal power, and >300 W/kg specific power) and cost-effectiveness (50-75% savings in $/W compared to conventional solar arrays). Ground testing of the SLA is essential to help prove the reliability of space operation and consists of lens material testing for UV/VUV, high voltage corona testing, and hypervelocity impact testing. SLA's demonstrated high performance and radiation tolerance, coupled with its substantial mass and cost advantages, will lead to many applications, both government and commercial missions. More information can be found at the SLA web site.
Plasma Blasting
A plasma blasting system uses low average power to charge a capacitor bank which is then discharged in a very short pulse at very high current to break solid substances. A prototype system has been tested successfully to break rocks and fracture steel reinforced concrete cylinders. This system was originally developed as a demonstration of a potential tool for use on the Moon or Mars. Because of the system's low vibration, reduced noise and almost no flying rock, it would be a viable option to explosives, especially where environmental and safety restrictions are concerned. It also has potential uses in terrestrial applications including rescue-excavation scenarios.
Hypervelocity Impact Facility
Hypervelocity gun being fired
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In 1988, an experimental test facility was constructed at SRI to test the environmental effects of hypervelocity micrometeroid impacts on materials. The Hypervelocity Impact Facility (HYPER) is a unique, one of a kind facility that has continued to evolve and has gone through numerous upgrades as an extremely affordable space debris simulator. Utilizing a particle acceleration technique referred as plasma-drag, HYPER can accelerate particles upwards to 13 km/s. A wide variety of particle stimulants ranging in size from less than 100 micron to above 200 micron can be used. Using two separate chambers separated by a flight tube, very clean impact environments can be established in the target sample region. Test target samples can also be emplaced in different environmental conditions which include: cryogenic or high temperatures, in-situ LEO-like plasma, electrically biased, and active electrical current flow. An ultra-high speed electronic camera can record each individual impact event allowing for specific impact energy data correlation.
Satellite Reliablity
Sustained arc on the EOS-AM1 solar array test article in a simulated spaceplasma in the Lewis Plasma Interactions Facility demonstrates how space plasma can cause satellite solar array failures
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Auburn University has completed a detailed statistical analysis of satellite solar array anomalies to find out what is reality versus what is perception to better face the challenge of solar array anomalies on orbit. On any satellite, the solar array is exposed to the harshest environment compared to the other systems and payloads; therefore, it is not surprising to find in the last ten years 117 satellite solar array anomalies have been reported with 12 satellites being retired due to solar array failure. Solar arrays are vital to satellite mission success; however, solar array anomalies continue to occur, thus making them unreliable and costly liabilities. Information gained from this study will help the satellite industry to better understand the challenges faced by solar arrays in the space environment and enable new designs to inherently guard against those anomalies. A solar array that can withstand the hazards of the space environment and is continually reliable is imperative in order to reverse the increases in insurance costs and restore international confidence in U.S. satellites.
Radiation Analysis
Radiation surrounding the earth
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The destructive radiation effects of the Van Allen Belts have limited the number of satellites in near earth orbits of 3,000-7,000 km. These are optimal orbits for earth observation and radar missions, but the lifetime of satellites is so reduced due to the natural radiation hazard that it has not been cost effective to use these orbits. New research is being done at the Space Research Institute at Auburn University to analyze and optimize solar cells and arrays in high radiation environments to overcome these difficulties. The European Space Agency's program SPENVIS, which incorporates the NASA AP-8 and AE-8 models, has been used for all radiation calculations. The SPENVIS models provide the 1 MeV equivalent electron radiation doses for given orbits and durations. This data can then be converted into the power remaining after the chosen orbital duration. End-of-life specific power and areal power density can be calculated with knowledge of array parameter information to determine the overall effect of radiation on solar arrays. This can help determine which arrays to use in high radiation missions such as spiral-up solar electric propulsion missions, earth resources survey, radar observations, etc.
Thermal-Vacuum tests of CubeSats
Cubesat thermal vacuum chamber
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When developers of CubeSat projects are conducting acceptance and qualification tests, they must lease time in expensive aerospace testing facilities to carry out their thermal vacuum tests. A prototype of a small thermal chamber for thermal vacuum tests of CubeSats was designed at SRI. It can be used in a small vacuum chamber as small as 1cu ft. so the CubeSat developers can do the thermal-vacuum tests at their own facility greatly reducing costs of testing.
Liquid Sheet Radiator
Liquid Sheet Radiators are devices with a capability of disposing large heat fluxes in space at a very low mass. The interest on such devices to reject heat from Free Piston Stirling Engine is that they could be coupled directly into the Stirling Convertor power system. A liquid sheet generator head with adjustable slit thickness for a Liquid Sheet Radiator (LSR) was built and tested. Simulations of the Liquid Sheet Generator Head (LSGH) were carried out using CFD software.
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