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One symptom of optical damage in Ti-diffused LiNbO3 directional-coupler switch reversed by temporarily raising input illumination to higher-thannormal power level. Healing phenomenon used to restore normal operation, increase operating-power rating, and stabilize operating characteristics at lower powers. Higher operating power is tolerated after treatment.
An overload protection system for a power inverter utilized a first circuit for monitoring current to the load from the power inverter to detect an overload and a control circuit to shut off the power inverter, when an overload condition was detected. At the same time, a monitoring current inverter was turned on to deliver current to the load at a very low power level. A second circuit monitored current to the load, from the monitoring current inverter, to hold the power inverter off through the control circuit, until the overload condition was cleared so that the control circuit may be deactivated in order for the power inverter to be restored after the monitoring current inverter is turned off completely.
A 30 kW class arcjet Power Conditioning Unit, PCU, was built and tested during this Phase 2 SBIR contract. The PCU is an improved version of two previously developed PCU's. All of these units are 3-phase, 20 kHz buck regulators with current mode feed back to modulate the duty cycle to control the arcjet current at any selected operating point. The steady state control can assure arcjet stability despite the negative dynamic resistance of the arc discharge. The system also has a circuit to produce a high voltage start pulse to breakdown the gas and initiate the arc. The start pulse is formed by temporarily switching a short current path across the output terminals with a special solid state switching array. The switches then open rapidly, and the energy stored in the output inductors of the buck regulator produces a pulse of approximately 2500 V for approximately 500 nsec. The system was tested and modified until the transition to steady operation occurred after start up with a very small surge current overshoot. The system also can withstand a direct short circuit across the output without damage. The automatic feed back control simply reduces the duty cycle to hold the current at the set point. When the short is removed the full power output is immediately restored. This latest version arcjet PCU is conduction cooled to remove waste heat by conduction to the base plate. This unit is closer to flight a type of design than the previous functional bread boards. Waste heat is small because the PCU has a very high efficiency, 296 percent. The PCU was extensively tested with resistor loads to simulate operation with an arcjet. The unit was tested with ammonia arcjets at the Jet Propulsion Laboratory. Approximately 400 hours of testing were completed, with several starts. Many hours were also demonstrated with resistive loads. Some testing with hydrogen arcjets was also carried out at NASA LeRC. This system concept is now the design base for the ATTD program.
Isochronal and isothermal annealing studies were conducted on 0.1 and 2 ohm centimeter n(+)/p silicon cells after irradiation by 1 MeV electrons at fluences of 10 to the 14th power, 5 times 10 to the 14th power, and 10 to the 15th power per square centimeter. For the 0.1 ohm centimeter cells, reverse annealing was not observed in the isochronal data. However, reverse annealing was observed between approximately 200 and 325 C in the isochronal data of the 2 ohm centimeter cells. Isothermal annealing of 0.1 ohm centimeter cells at 500 C restored pre-irradiation maximum power P sub max within 20 minutes at fluence = 10 to the 14th power, in 180 minutes at fluence = 5 times 10 to the 14th power and to 92 percent of pre-irradiation P sub max in 180 minutes for fluence = 10 to the 15th power. Annealing at 450 C was found inadequate to restore 0.1 ohm centimeter cell performance within reasonable times for all fluence levels. By comparison, at 450 C, the P sub max of 2 ohm centimeter cells was restored within 45 minutes, for the two highest fluence levels, while for the lowest fluence, restoration was completed within 15 minutes. Spectral response data indicate that, for both resistivities, degradation occurs predominantly in the cells p-type base region.
The main purpose of this program was to determine the life characteristics of nine space-qualified, metal-ceramic CO2 lasers. Lifetimes ranged between about 400 hours to over 2000 hours (the limit of testing) with a high degree of consistency in like groups. In all cases the tubes which had failed could be restored to near their original power by doubling the cathode current for 30 minutes. Periodic rejuvenation allowed operation for the full 2000 hours on all tubes. The failure mechanism appears to involve formation of NiO and C on the nickel cathode emission surface with subsequent absorption of tube gases.
Topics covered include: Lighting the Way for Quicker, Safer Healing; Discovering New Drugs on the Cellular Level; Hydrogen Sensors Boost Hybrids; Today s Models Losing Gas?; 3-D Highway in the Sky; Popping a Hole in High-Speed Pursuits; Monitoring Wake Vortices for More Efficient Airports; From Rockets to Racecars; All-Terrain Intelligent Robot Braves Battlefront to Save Lives; Keeping the Air Clean and Safe--An Anthrax Smoke Detector; Lightning Often Strikes Twice; Technology That's Ready and Able to Inspect Those Cables; Secure Networks for First Responders and Special Forces; Space Suit Spins; Cooking Dinner at Home--From the Office; Nanoscale Materials Make for Large-Scale Applications; NASA s Growing Commitment: The Space Garden; Bringing Thunder and Lightning Indoors; Forty-Year-Old Foam Springs Back With New Benefits; Experiments With Small Animals Rarely Go This Well; NASA, the Fisherman's Friend; Crystal-Clear Communication a Sweet-Sounding Success; Inertial Motion-Tracking Technology for Virtual 3-D; Then Why Do They Call Earth the Blue Planet?; Valiant 'Zero-Valent' Effort Restores Contaminated Grounds; Harnessing the Power of the Sun; Water and Air Measures That Make 'PureSense'; Remote Sensing for Farmers and Flood Watching; Pesticide-Free Device a Fatal Attraction for Mosquitoes Making the Most of Waste Energy Washing Away the Worries About Germs Celestial Software Scratches More Than the Surface A Search Engine That's Aware of Your Needs Fault-Detection Tool Has Companies 'Mining' Own Business; Software to Manage the Unmanageable; Tracking Electromagnetic Energy With SQUIDs; Taking the Risk Out of Risk Assessment; Satellite and Ground System Solutions at Your Fingertips; Structural Analysis Made 'NESSUSary'; Software of Seismic Proportions Promotes Enjoyable Learning; Making a Reliable Actuator Faster and More Affordable; Cost-Cutting Powdered Lubricant NASA s Radio Frequency Bolt Monitor: A Lifetime of Spinoffs Going End to End to Deliver High-Speed Data; Advanced Joining Technology: Simple, Strong, and Secure; Big Results From a Smaller Gearbox; Low-Pressure Generator Makes Cleanrooms Cleaner; and The Space Laser Business Model.
The organizational structure and facilities available at the Marshall Space Flight Center are described and the role of the Center in NASA program management is demonstrated in a review of the Center's past history and current development projects. Particular attention is given to space shuttle and the space transportation system; the preparation of experiments and management of Spacelab missions; and the development of the space telescope. Energy related activities discussed include the automatic guidance and control of the longwall shearing machine for coal extraction, systems for the solar heating and cooling of buildings, and the design of the solar power satellite. Products developed by Center personnel highlighted include the power factor controller to reduce electrical consumption by motors and the image enhancement process being used to restore early historical photographs. A free flying solar power source to increase mission duration of the orbiter and its payloads; techniques for the orbital assembly of large space structures; facilities for materials processing in space; the orbit transfer vehicle, solar electric propulsion systems; and the preparation of science and applications payloads are also described.
Assessment of Analog Electronics for Lunar Power Hibernation Non-nuclear robotic spacecraft on the Moon may not reliably operate past the first lunar day due to the subsequent long lunar night with an extreme low temperature range of 50K-100K. To address this concern, the NASA Glenn Research Center is developing a lunar power hibernation protocol that could enable spacecraft to passively survive the lunar night without any additional heating source and then reactivate at lunar dawn. Low cost lunar robotic missions could extend their mission lifetime from a single lunar cycle to potentially many months, thus greatly extending science data gathering and return on investment for commercial missions. This approach centers on evidence that lithium-ion battery cells can recover to full operation after being subjected to cryogenic temperatures. Exploiting this battery capability requires that all spacecraft electronics, including power system and avionics, passively tolerate the extreme cold without degradation. Key elements in the power system will also need to be capable of actively operating in the extreme cold to perform the functions required to restore the system to full operation after solar power returns at lunar dawn. This presentation provides an assessment of extreme-cold tolerance and operational capability of analog electronics where choices in semiconductor material, device type, and circuit fabrication technology has a dramatic impact on circuit behavior and reliability at low temperatures.
The Dawn mission is part of NASA's Discovery Program and has as its goal the scientific exploration of the two most massive main-belt asteroids, Vesta and Ceres. The Dawn spacecraft was launched from the Cape Canaveral Air Force Station on September 27, 2007 on a Delta-II 7925H-9.5 (Delta-II Heavy) rocket that placed the 1218-kg spacecraft onto an Earth-escape trajectory. On-board the spacecraft is an ion propulsion system (IPS) developed at the Jet Propulsion Laboratory which will provide a total ?V of 11.3 km/s for the heliocentric transfer to Vesta, orbit capture at Vesta, transfer between Vesta science orbits, departure and escape from Vesta, heliocentric transfer to Ceres, orbit capture at Ceres, and transfer between Ceres science orbits. Fullpower thrusting from December 2007 through October 2008 was used to successfully target a Mars gravity assist flyby in February 2009 that provided an additional ?V of 2.6 km/s. Deterministic thrusting for the heliocentric transfer to Vesta resumed in June 2009 and concluded with orbit capture at Vesta on July 16, 2011. An additional 210 hours of IPS thrusting was used to enter the first Vesta science orbit, called Survey orbit, on August 3, 2011 at an altitude of approximately 2,735 km. To date the IPS has been operated for 23,621 hours, consumed approximately 252 kg of xenon, and provided a delta-V of approximately 6.7 km/s. The IPS performance characteristics are very close to the expected performance based on analysis and testing performed pre-launch. The only significant issue in over the almost four years of IPS operations in flight was the temporary failure of a valve driver board in the Digital Control and Interface Unit-1 (DCIU-1), resulting in a loss of thrust of approximately 29 hours. Thrusting operations resumed after switching to DCIU-2, and power cycling conducted after orbit capture restored DCIU-1 to full functionality. After about three weeks of Survey orbit operations the IPS will be used to transfer the spacecraft to the other planned science orbit altitudes. After approximately one year of science operations the IPS will be used for escape from Vesta and then for thrusting to Ceres with a planned arrival date at Ceres in February 2015. This paper provides an overview of Dawn's mission objectives and the results of Dawn IPS mission operations through the start of science operations at Vesta.
The ACS Repair (ACS-R) team includes contributors from NASA's Goddard Space Flight Center, Ball Aerospace, and Teledyne Imaging Sensors; It determined that all of the capabilities of the ACS could be restored and created a concept for the ACS-R component of SN4. ACSR will restore the WFC of ACS by replacing the existing CCD Electronics Box (CEB) with the CEB-Replacement (CEB-R) and providing power from a new Low Voltage Power Supply Replacement (LVPS-8). The new LVPS-R will also attempt to restore the HRC function by providing power through the original power bus. In this presentation, we faeus on the concept and technical aspects of the ACS-R.
Phase-diverse speckle (PDS) is a novel imaging technique intended to overcome the degrading effects of atmospheric turbulence on fine-resolution imaging. As its name suggests, PDS is a blend of phase-diversity and speckle-imaging concepts. PDS reconstructions on solar data were validated by simulation, by demonstrating internal consistency of PDS estimates, and by comparing PDS reconstructions with those produced from well accepted speckle-imaging processing. Several sources of error in data collected with the Swedish Vacuum Solar Telescope (SVST) were simulated: CCD noise, quantization error, image misalignment, and defocus error, as well as atmospheric turbulence model error. The simulations demonstrate that fine-resolution information can be reliably recovered out to at least 70% of the diffraction limit without significant introduction of image artifacts. Additional confidence in the SVST restoration is obtained by comparing its spatial power spectrum with previously-published power spectra derived from both space-based images and earth-based images corrected with traditional speckle-imaging techniques; the shape of the spectrum is found to match well the previous measurements. In addition, the imagery is found to be consistent with, but slightly sharper than, imagery reconstructed with accepted speckle-imaging techniques.
Large-scale applications of high-power lasers are considered (special experiments are described to confirm the feasibility of these applications) to achieve also large-scale environmental advantages. The possibility of producing electric energy by Laser-Solar Power Satellites in the near future is discussed. A full-scale experimental L-SPS satellite is suggested as a module of a global space energy network. Electric power of about 10 MW at the surface of the Earth is achievable as a result of energy conversion of laser radiation. L-SPS is based on the greatest advantages of present optics and laser techniques. Specialized-scale experiments are carried out and described. L-SPS project could provide real electricity for consumers not later than by highly developed fusion techniques, and the environmental aftereffects are quite favorable. A new method of power supply for satellites is suggested, based on the connection of an on-board electric circuit directly with the ground-based power grid by means of laser beams.
Propulsion systems that utilize hypergolic propellants have been used to power space vehicles since the beginning of the space program. Liquid methane and oxygen propulsion systems have emerged as an alternative and have proven to be more environmentally friendly. The incorporation of liquid methane/liquid oxygen (LOX) into the propulsion system has demonstrated an increase in engine performance, as well as a reduction in the volume, size and complexity of the system. Consequently, reducing the total mass of the vehicle which is a crucial aspect that is considered when planning space missions to both the Moon and Mars [1]. Project Morpheus has made significant advancements in liquid oxygen/liquid methane propulsion system technologies by incorporating a LOX/methane propulsion system to a vertical test bed. The vehicle consisted of a 5,000 lb main engine and four 20 lb remote control system (RCS) engines that utilize liquid methane/LOX as its propellant [1]. The vehicle completed successful flight testing at Kennedy Space Center in 2014 which marked the completion of the Morpheus project. Subsequent projects utilizing Morpheus' vertical test bed have been developed to make further advancements. One of the subsequent projects consisted of the addition of a smaller 2,000 lb main engine and a cold helium heat exchanger which would make it possible for a pressurant tank systems to be send to Mars or the Moon by significantly decreasing the overall mass and volume of the pressurant tank. The hot fire tests of the integrated system with the smaller main engine and cold helium heat exchanger were successful at sea level, but further studies are being conducted to better understand how the vertical test bed will behave under thermal-vacuum conditions. For this reason, the integrated vehicle will be taken to Plum Brook to be tested in a chamber capable of simulating these conditions. To ensure that the vehicle will function properly under vacuum conditions, testing will be first completed at the component level. During this process, the igniter of the main engine and the RCS thrusters will be tested under a vacuum. To complete the testing of the components, the test setup first needed to be finalized. The CryoCart is being used to feed the propellants to the test article. The CryoCart is a movable test set-up that was developed in 2009 to provide a mobile platform for testing oxygen/methane systems with hot-fire capability up to 100 lbf. The CryoCart consists of three different systems: Oxygen, Methane, and liquid Nitrogen. The Oxygen and Methane systems are placed into two different carts while the liquid nitrogen system is mainly located in the methane cart. Over the years, the CryoCart has been utilized for different projects and has undergone deterioration. For this reason, a new phase has been developed to rebuild it to working conditions once again. During my internship, I was aiding in the construction and restoration of the CryoCart. In the initial stages of the process, I updated the fluid and electrical schematics for the oxygen, methane, and test article systems. The original CryoCart consisted of an electrical panel that utilized electromechanical relays and a terminal to drive the igniter power and signal, as well as the main fuel and oxygen valves. This electrical panel connected to the CryoCart through various wire harnesses that could be found exiting from the CryoCart. First, it was determined how these harnesses connected to the electromechanical relays so that they worked correctly. Once the electrical system was understood, an alternative for the electromechanical relays and the Molex connectors used throughout the system was sought since these components can often prove to be unreliable. Solid State relays and MIL connectors were purchased to serve as replacements. Upon arrival of the parts, crimping and wiring was completed to install the new solid state relays and MIL connectors. During the replacement of the relays and connectors, system checks of the electrical system were ran to ensure that the system was working correctly. While completing system checks, the pressure transducers that were not functioning properly were also replaced and any issue with the wiring or signal was addressed. Once the electrical components were replaced, the restoration of the fluid system began. Parts of the tubing in the CryoCart had to be rebuild and often consisted of sizing, cutting, bending, filing, and sanding the tubing to prepare it to be flared. Many components had to be proof-tested to bring their certifications up to date, and several components had to be replaced. Various flex hoses, valves, and fittings were send to the Clean Lab because they were new, dirty, or had gone through proof-testing. Once they arrived from the cleaning lab they had to be put back to the system and leak checks and functional tests were conducted. In the Nitrogen system, the copper tubing located in the Oxygen cart was rebuild and Aerogel insulation was added to this section. A new gaseous nitrogen system was added to the CryoCart to purge the vacuum tube which will serve as the test chamber. Once the CryoCart was completed, construction of parts of the vacuum tube began. A flange was manufactured with welded fittings to hold the line of the vacuum pump as well as some extra fittings which will serve as extra inlets used to introduce fluid lines to the vacuum tube. Stress analysis was ran in this flange to ensure that it would not fail under vacuum conditions. The fluid lines leading from the air side of the vacuum to the test article were also constructed and added to the mount that had already been manufactured. Three different sets of tubing were constructed to accommodate the seven different RCS thruster and the main engine igniter that are going to be tested. Full electrical system checks were completed to ensure that all the wire harnesses and valves were functioning. Upon the completion of the CryoCart and the vacuum tube, hot fire testing for the RCS thrusters and the main engine igniter are going to begin. During this time any issues encountered with the engines or igniter will be addressed to ensure that the components function under vacuum conditions. After successful completion of testing, the vertical test bed, Morpheus, will be rebuilt and prepared to be sent to Plum Brook. In Plum Brook, the vehicle will be tested in the thermal-vacuum chamber to demonstrate that integrated lox-methane propulsion system operation in space-like conditions. This internship has allowed me the opportunity to gain valuable hands on experience and to develop skills that will aid in my education as well as in the workforce, while at the same time helping me determine that I would like to further pursue a career in propulsion engineering.
The conventional (no-offset) quadriphase modulation technique suffers from the fact that hardlimiting will restore the frequency sidelobes removed by proper filtering. Thus, offset keyed quadriphase modulation techniques are often proposed for satellite communication with bandpass hardlimiting. A unified theory is developed which is capable of describing the power spectral density before and after the hardlimiting process. Using the in-phase and the quadrature phase channel with arbitrary pulse shaping, analytical results are established for generalized quadriphase modulation. In particular MSK, OPSK or the recently introduced overlapped raised cosine keying all fall into this general category. It is shown that for a linear communication channel, the power spectral density of the modulated signal remains unchanged regardless of the offset delay. Furthermore, if the in phase and the quadrature phase channel have identical pulse shapes without offset, the spectrum after bandpass hardlimiting will be identical to that of the conventional QPSK modulation. Numerical examples are given for various modulation techniques. A case of different pulse shapes in the in phase and the quadrature phase channel is also considered.
In recent years, wildfires in New Mexico’s Gila National Forest have become increasingly common and more severe. Wildfires can have powerful impacts on hydrology and soil stability, including erosion, flooding, and debris-flows that threaten lives and infrastructure downstream. Vegetation restoration treatments like seeding and mulching can mitigate these effects and facilitate ecosystem recovery. Understanding the effectiveness of various restoration methods is vital to planning a cost-effective and successful post-fire recovery strategy. The immediate response to a fire on US Forest Service land is coordinated by a Burned Area Emergency Response (BAER) team, a group responsible for mitigating immediate post-fire risks to human life, property, and critical natural and cultural resources. This study created a proof-of-concept methodology for a decision-support tool designed to help BAER teams identify the restoration treatments most likely to succeed in a given burned area. Leveraging random forest regression, Google Earth Engine, and Landsat 7 and 8 Earth observations, this study modeled vegetation recovery after the 2013 Silver Fire for seeded areas, seeded/mulched areas, and untreated areas. Treatment type and initial burn severity were the largest drivers of vegetation recovery across the landscape. Seeded/mulched areas showed higher recovery levels than untreated areas three months post-fire, but by four years post-fire, treated and untreated areas displayed similar recovery levels. To produce a robust predictive tool for the Gila National Forest, the model should be trained on many more fires and incorporate post-fire weather conditions into the process. Such a model will help partners ensure efficient resource use and plan effective post-fire restoration strategies.
A battery charger design for the NASA Earth Observing System (EOS) space platform has been developed and tested. The authors discuss the design of the battery charger power state and its current and voltage control loops. In addition to restoring energy to the batteries, this charger regulates the spacecraft bus voltage during the posteclipse transition period. The battery charger design and analysis were facilitated by use of the pulse-width-modulated (PWM) switch model and the new continuous-time model for current-mode control. Analyses of the battery charger small-signal behavior are compared to hardware measurements to verify modeling accuracy.
The concept of a solar-cell array for a solar power satellite is developed to permit evaluation of its economic feasibility for generating power for delivery to public utilities on earth. Gallium arsenide solar cells were considered but it could not be assured that the world gallium resources could support constructions of two solar power satellites per year. Therefore, for preliminary design an array blanket made from 5 by 10 cm silicon solar cells, 50 microns thick, and electrostatically bonded between borosilicate glass sheets was adopted. In annealing experiments, a radiated 50 microns thick cell was restored to its initial performance in a 500 C. Solar-cell efficiency effects significantly the solar power satellite mass, which varies from 90,000 metric tons for 20 percent cells to 120,000 metric tons for 12 percent cells. The anticipated cost of delivered power, based on 1977 dollars, varies from 4 cents per kWh with 18 percent cells, to 5 cents per kWh for 12 percent efficient cells.
Method for adjusting electric-motor torque output to accomodate various loads utilizes phase-lock loop to control relay connected to starting circuit. As load is imposed, motor slows down, and phase lock is lost. Phase-lock signal triggers relay to power starting coil and generate additional torque. Once phase lock is recoverd, relay restores starting circuit to its normal operating mode.