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At least 145 records · Page 8

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NASA NTRS2010

Integral Battery Power Limiting Circuit for Intrinsically Safe Applications

A circuit topology has been designed to guarantee the output of intrinsically safe power for the operation of electrical devices in a hazardous environment. This design uses a MOSFET (metal oxide semiconductor field-effect transistor) as a switch to connect and disconnect power to a load. A test current is provided through a separate path to the load for monitoring by a comparator against a preset threshold level. The circuit is configured so that the test current will detect a fault in the load and open the switch before the main current can respond. The main current passes through the switch and then an inductor. When a fault occurs in the load, the current through the inductor cannot change immediately, but the voltage drops immediately to safe levels. The comparator detects this drop and opens the switch before the current in the inductor has a chance to respond. This circuit protects both the current and voltage from exceeding safe levels. Typically, this type of protection is accomplished by a fuse or a circuit breaker, but in order for a fuse or a circuit breaker to blow or trip, the current must exceed the safe levels momentarily, which may be just enough time to ignite anything in a hazardous environment. To prevent this from happening, a fuse is typically current-limited by the addition of the resistor to keep the current within safe levels while the fuse reacts. The use of a resistor is acceptable for non-battery applications where the wasted energy and voltage drop across the resistor can be tolerated. The use of the switch and inductor minimizes the wasted energy. For example, a circuit runs from a 3.6-V battery that must be current-limited to 200 mA. If the circuit normally draws 10 mA, then an 18-ohm resistor would drop 180 mV during normal operation, while a typical switch (0.02 ohm) and inductor (0.97 ohm) would only drop 9.9 mV. From a power standpoint, the current-limiting resistor protection circuit wastes about 18 times more power than the switch and the inductor configuration. In the fault condition, both the resistor and the inductor react immediately. The resistor reacts by allowing more current to flow and dropping the voltage. Initially, the inductor reacts by dropping the voltage, and then by not allowing the current to change. When the comparator detects the drop in voltage, it opens the switch, thus preventing any further current flow. The inductor alone is not sufficient protection, because after the voltage drop has settled, the inductor would then allow the current to change, in this example, the current would be 3.7 A. In the fault condition, the resistor is flowing 200 mA until the fuse blows (anywhere from 1 ms to 100 s), while the switch and inductor combination is flowing about 2 A test current while monitoring for the fault to be corrected. Finally, as an additional safety feature, the circuit can be configured to hold the switch opened until both the load and source are disconnected.

Burns, Bradley M.↗

NASA NTRS1972

Miniature intermittent contact switch

Design of electric switch for providing intermittent contact is presented. Switch consists of flexible conductor surrounding, but separated from, fixed conductor. Flexing of outside conductor to contact fixed conductor completes circuit. Advantage is small size of switch compared to standard switches.

Sword, A.↗

NASA NTRS1973

Application of the floating-potential probe for studies of low frequency oscillations in a plasma

The proper interpretation of the results obtained from measurements of the floating potential of an electrostatic probe may cause difficulties in time varying plasmas. The following limitations of the method are considered: the charge separation in the plasma, the influence of the input capacity of the measuring circuit, and the influence of the layer capacity near the probe. A detailed analysis is carried out in the cases of moving striations and ion acoustic waves. A simple measuring technique is suggested for ion acoustic studies, giving detailed information about ion density oscillations.

Dzhakov, B. Y.↗

NASA NTRS1980

Phase control system concepts and simulations

A phase control system concept for a solar power satellite is proposed which partitions the system into three major levels. The first level of phase control consists of a reference phase distribution system implemented in the form of phase distribution tree structure. The major purpose of the tree structure is to electronically compensate for the phase shift due to the transition path lengths from the center of the spacetenna to each phase control center located in each subarray. In the reference system, this is accomplished using the master slave returnable timing system technique. The second level of phase control consists of the beam steering and microwave power generating system which houses the power transponders. This transponder consists of a set of phase conjugation multipliers driven by the reference phase distribution system output and the output of a pilot spread spectrum receiver which accepts the received pilot via a diplexer connected to a separate receive horn or the subarray itself. The output of the phase conjugation circuits serve as inputs to the third level of the phase control system. The third level of phase control is associated with maintaining an equal and constant phase shift through the microwave power amplifier devices while minimizing the associated phase noise effects on the generated power beam. This is accomplished by providing a phase locked loop around each high power amplifier.

Lindsay, V. C.↗

NASA NTRS1986

Enhancing Centrifugal Separation With Electrophoresis

Separation of biological cells by coil-planet centrifuge enhanced by electrophoresis. By itself, coil-planet centrifuge offers relatively gentle method of separating cells under low centrifugal force in physiological medium that keeps cells alive. With addition of voltage gradient to separation column of centrifuge, separation still gentle but faster and more complete. Since separation apparatus contains no rotary seal, probability of leakage, contamination, corrosion, and short circuits reduced.

Herrmann, F. T.↗

NASA NTRS1993

Low impedance printed circuit radiating element

A printed circuit radiating element comprises a geometrically symmetric planar area of a conducting material separated from a ground plane by a dielectric medium. The driving point of the radiating element is at the base of a notch in one side thereof so that the driving impedance is reduced from that obtained when the element is driven at its edge. Symmetrically disposed on opposite sides of an axis of symmetry of the element along which the driving point lies are two notches which restore the electrical symmetry of the radiating element thereby to suppress higher order modes. The suppression of these higher order modes results in a radiation pattern with minimal cross-polarized energy in the principal planes and high port-to-port isolation which could not be achieved with an asymmetrical element. Two driving points may be employed with the radiating element to produce a dual linearly polarized antenna and a reactive combiner or hybrid may be employed to obtain circularly-polarized radiations. The shape of the radiating element may be square, rectangular or circular, for example, in accordance with the desired characteristics. A plurality of radiating elements may be interconnected via appropriate transmission paths to form an antenna array.

Rahm, James K.↗

NASA NTRS2018

Guideline for Single-Event Effect (SEE) Testing of System on a Chip (SOC) Devices

The use of complex single and multicore processors with significant cache memory, on-chip peripherals, memory controllers, and high speed input/output (IO) that integrate many of the parts of a traditional computer system is becoming more common in space applications. Such devices are often referred to as system on a chip devices (SOCs), even though the term is used somewhat inaccurately due to the lack of analog and mixed signal subcircuits. These devices are complex combinations of single- or multi-core processors with memory controllers, high-speed input/output (IO), and other peripheral structures that formerly would have been handled by off-chip resources. In the past the processors were tested for single event effects (SEE) separately, and the peripherals were often put into custom application-specific integrated circuits (ASICs) along with other resources required by the user. Performance and cost pressures have pushed commercial devices to incorporate many of the functional blocks into a single chip, an SOC. The NASA Electronic Parts and Packaging Program (NEPP) has been examining ways to perform SEE radiation hardness assurance (RHA) testing of these processor-centric SOCs to achieve reasonable understanding of their performance in space missions.

Guertin, Steven M.↗

NASA NTRS2017

Methods and Apparatus for Pulsed-DC Dielectric Barrier Discharge Plasma Actuator and Circuit

A plasma generating device intended to induce a flow in a fluid via plasma generation includes a dielectric separating two electrodes and a power supply. The first electrode is exposed to a fluid flow while the second electrode is positioned under the dielectric. The power supply is electrically coupled to a switch and the first and second electrodes. When the power supply is energized by repeated action of the switch, it causes a pulsed DC current between the electrodes which causes the fluid to ionize generating a plasma. The generation of the plasma induces a force with a velocity component in the fluid.

Corke, Thomas C.↗

NASA NTRS1961

Vanguard Satellite Separation Mechanisms

Early in the Vanguard program it became apparent that a thoroughly reliable means of separating the satellite packages from the third-stage rocket would be required. A completely self -contained standard mechanism was developed with redundant firing circuits for use on both test vehicles and satellite-launching vehicles. A change in the experimental objectives of the test-vehicle payload units necessitated modification of some of the standard separation mechanisms. A strap, pull-pin, girth-ring separation device was developed which employed the basic actuation of the standard mechanisms. Evidence of residual burning of the third stage made it necessary to delay separation longer than the time designed into the long-delay separation device. The standard separation mechanism was modified and integrated with the satellite command receiver system so that a ground command after third-stage burnout would cause separation. Flight performance of the various separation mechanisms proved their reliability; they performed without failure in all Vanguard launchings.

Baumann, Robert C.↗

NASA NTRS2003

120-GHz HEMT Oscillator With Surface-Wave-Assisted Antenna

Two monolithic microwave integrated circuits (MMICs) have been designed and built to function together as a source of electromagnetic radiation at a frequency of 120 GHz. One of the MMICs is an oscillator and is the highest-power 120-GHz oscillator reported thus far in the literature. The other MMIC is an end-fire antenna that radiates the oscillator signal. Although these MMICs were constructed as separate units and electrically connected with wire bonds, future oscillator/ antenna combinations could readily be fabricated as monolithic integrated units. Such units could be used as relatively high-power solid-state microwave sources in diverse applications that include automotive radar, imaging, scientific instrumentation, communications, and radio astronomy. As such, these units would be attractive alternatives to vacuum-tube oscillators, which are still used to obtain acceptably high power in the frequency range of interest. The oscillator (see figure) includes a high-electron-mobility transistor (HEMT), with gate-periphery dimensions of 4 by 37 m, in a common-source configuration. The series feedback element of the oscillator is a grounded coplanar waveguide (CPW) at the source. The HEMT is biased for class-A operation (meaning that current is conducted throughout the oscillation cycle) to maximize the output power of the oscillator. Input and output impedance-matching circuit elements are designed to maximize output power and to establish the conditions needed for oscillation. The design of the antenna takes advantage of surface waves, which, heretofore, have been regarded as highly disadvantageous because they can leak power and degrade the performances of antennas that have not been designed to exploit them. Measures taken to suppress surface waves have included complex machining of circuit substrates and addition of separate substrates. These measures are difficult to implement in standard MMIC fabrication processes. In contrast, because the design of the present antenna eliminates the need to suppress surface waves, the fabrication of the antenna is fully compatible with standard MMIC fabrication processes.

Samoska, Lorene↗

NASA NTRS2009

Large-Aperture Membrane Active Phased-Array Antennas

Large-aperture phased-array microwave antennas supported by membranes are being developed for use in spaceborne interferometric synthetic aperture radar systems. There may also be terrestrial uses for such antennas supported on stationary membranes, large balloons, and blimps. These antennas are expected to have areal mass densities of about 2 kg/sq m, satisfying a need for lightweight alternatives to conventional rigid phased-array antennas, which have typical areal mass densities between 8 and 15 kg/sq m. The differences in areal mass densities translate to substantial differences in total mass in contemplated applications involving aperture areas as large as 400 sq m. A membrane phased-array antenna includes patch antenna elements in a repeating pattern. All previously reported membrane antennas were passive antennas; this is the first active membrane antenna that includes transmitting/receiving (T/R) electronic circuits as integral parts. Other integral parts of the antenna include a network of radio-frequency (RF) feed lines (more specifically, a corporate feed network) and of bias and control lines, all in the form of flexible copper strip conductors on flexible polymeric membranes. Each unit cell of a prototype antenna (see Figure 1) contains a patch antenna element and a compact T/R module that is compatible with flexible membrane circuitry. There are two membrane layers separated by a 12.7-mm air gap. Each membrane layer is made from a commercially available flexible circuit material that, as supplied, comprises a 127-micron-thick polyimide dielectric layer clad on both sides with 17.5-micron-thick copper layers. The copper layers are patterned into RF, bias, and control conductors. The T/R module is located on the back side of the ground plane and is RF-coupled to the patch element via a slot. The T/R module is a hybrid multilayer module assembled and packaged independently and attached to the membrane array. At the time of reporting the information for this article, an 8 16 passive array (not including T/R modules) and a 2 4 active array (including T/R modules) had been demonstrated, and it was planned to fabricate and test larger arrays.

Karasik, Boris↗

NASA NTRS1988

Development of 20 GHz monolithic transmit modules

The history of the development of a transmit module for the band 17.7 to 20.2 GHz is presented. The module was to monolithically combine, on one chip, five bits of phase shift, a buffer amplifier and a power amplifier to produce 200 mW to the antenna element. The approach taken was MESFET ion implanted device technology. A common pinch-off voltage was decided upon for each application. The beginning of the total integration phases revealed hitherto unencountered hazards of large microwave circuit integration which were successfully overcome. Yield and customer considerations finally led to two separate chips, one containing the power amplifiers and the other containing the complete five bit phase shifter.

Higgins, J. A.↗

NASA NTRS1999

High-Energy Space Propulsion Based on Magnetized Target Fusion

A conceptual study is made to explore the feasibility of applying magnetized target fusion (MTF) to space propulsion for omniplanetary travel. Plasma-jet driven MTF not only is highly amenable to space propulsion, but also has a number of very attractive features for this application: 1) The pulsed fusion scheme provides in situ a very dense hydrogenous liner capable of moderating the neutrons, converting more than 97% of the neutron energy into charged particle energy of the fusion plasma available for propulsion. 2) The fusion yield per pulse can be maintained at an attractively low level (< 1 GJ) despite a respectable gain in excess of 70. A compact, low-weight engine is the result. An engine with a jet power of 25 GW, a thrust of 66 kN, and a specific impulse of 77,000 s, can be achieved with an overall engine mass of about 41 metric tons, with a specific power density of 605 kW/kg, and a specific thrust density of 1.6 N/kg. The engine is rep-rated at 40 Hz to provide this power and thrust level. At a practical rep-rate limit of 200 Hz, the engine can deliver 128 GW jet power and 340 kN of thrust, at specific power and thrust density of 1,141 kW/kg and 3 N/kg respectively. 3) It is possible to operate the magnetic nozzle as a magnetic flux compression generator in this scheme, while attaining a high nozzle efficiency of 80% in converting the spherically radial momentum of the fusion plasma to an axial impulse. 4) A small fraction of the electrical energy generated from the flux compression is used directly to recharge the capacitor bank and other energy storage equipment, without the use of a highvoltage DC power supply. A separate electrical generator is not necessary. 5) Due to the simplicity of the electrical circuit and the components, involving mainly inductors, capacitors, and plasma guns, which are connected directly to each other without any intermediate equipment, a high rep-rate (with a maximum of 200 Hz) appears practicable. 6) All fusion related components are within the current state of the art for pulsed power technology. Experimental facilities with the required pulsed power capabilities already exist. 7) The scheme does not require prefabricated fuel target and liner hardware in any esoteric form or state. All necessary fuel and liner material are introduced into the engine in the form of ordinary matter in gaseous state at room temperature, greatly simplifying their handling on board. They are delivered into the fusion reaction chamber in a completely standoff manner.

Thio, Y. C. F.↗

NASA NTRS2014

Wireless Chemical Sensor and Sensing Method for Use Therewith

A wireless chemical sensor includes an electrical conductor and a material separated therefrom by an electric insulator. The electrical conductor is an unconnected open-circuit shaped for storage of an electric field and a magnetic field. In the presence of a time-varying magnetic field, the first electrical conductor resonates to generate harmonic electric and magnetic field responses. The material is positioned at a location lying within at least one of the electric and magnetic field responses so-generated. The material changes in electrical conductivity in the presence of a chemical-of-interest.

Woodard, Stanley E.↗

NASA NTRS2016

Wireless Chemical Sensor and Sensing Method for Use Therewith

Woodard, Stanley E.↗

NASA NTRS2017

Wireless Chemical Sensing Method

Woodard, Stanley E.↗

NASA NTRS1988

Laminar-Separation Sensor

Sensor detects flow reversal in boundary layer. Laminar-separation sensor provides means for detecting laminar-separation bubble by use of very thin, surface-mounted sensor. Consists of flush array of three proximate thin films. Middle film electronically heated by means of constant-temperature anemometer (CTA). Outer films, one upstream and one downstream of middle film, incorporated into bridge circuit to respond as resistance thermometers. This sensor provides only known surface-mounted means for positively identifying pressure of laminar separation as cause of boundary-layer transition.

Holmes, Bruce J.↗

NASA NTRS1972

Intermodulation characteristics of X-band IMPATT amplifiers.

Measurement of the intermodulation products produced when two equal amplitude signals are applied to the input of an X-band IMPATT diode amplifier. A Si p(+)nn(+) IMPATT diode was operated in a double-slug-tuned reflection amplifier circuit that was tuned to provide 20 dB of small-signal gain at 9.340 GHz. The intermodulation tests consist of measurements of the magnitudes and frequencies of the amplifier output signals as a function of the input signal drive levels and frequency separations. The gain and single-frequency characteristics of the amplifier were also measured and are used along with the theoretical device and circuit admittance characteristics as a basis for explanation of the intermodulation results. A low-frequency dominance mechanism is found to exist in which the low-frequency signals are amplified more than the high-frequency signals. This mechanism becomes more significant as the amplifier drive level is increased.

Trew, R. J.↗