Engineering topics
Lin, R.
Publications and source records attributed to Lin, R..
Terahertz Radiometer for Outer Planet and Moon Atmospheres (TROPA)
We are developing a prototype instrument platform to demonstrate the feasibility of a wideband spectrometer for planetary applications under a three-year NASA research program. This development focuses on three specific areas needing advancement. First, the terahertz portion consists of an optical bench with dual heterodyne Schottky-mixer based receivers, one for each band. The beams entering the horns of the two receivers are de-multiplexed from the input beam by a polarizing beam splitter. The blocks containing the 560 and 1200 GHz mixer are more highly integrated than previous space instruments to reduce mass and volume. The receivers take a fundamental pump frequency near 30 GHz and multiply up to the submillimeter range. Second, a rapid-tuning, low-phase noise, and low-power 33 GHz range LO synthesizer is being prototyped. The low phase noise requirement is needed because of the factor of 36 multiplication to reach 1200 GHz, giving a requirement that the integrated phase noise from 100 kHz up be less than 0.6 degrees. The synthesizer will require about 6 watts. Finally, we are developing an advanced polyphase filter back-end spectrum analyzer with a bandwidth of 750 MHz, and power consumption of about 3 Watts and 4096 channels. This system is based on a simple three-chip architecture, having a commercial 1.5 GS/s analog-to-digital converter, an ASIC to do the filtering and an advanced FPGA for data processing and control.
An Integrated 520-600 GHz Sub-Harmonic Mixer and Tripler Combination Based on GaAs MMIC Membrane Planar Schottky Diodes
We present here the design, development and test of an integrated sub-millimeter front-end featuring a 520-600 GHz sub-harmonic mixer and a 260-300 GHz frequency tripler in a single cavity. Both devices used GaAs MMIC membrane planar Schottky diode technology. The sub-harmonic mixer/tripler circuit has been tested using conventional machined as well as silicon micro-machined blocks. Measurement results on the metal block give best DSB mixer noise temperature of 2360 K and conversion losses of 7.7 dB at 520 GHz. Preliminary results on the silicon micro-machined blocks give a DSB mixer noise temperature of 4860 K and conversion losses of 12.16 dB at 540 GHz. The LO input power required to pump the integrated tripler/sub-harmonic mixer for both packages is between 30 and 50 mW
Verification of Spectral Purity in the HIFI Local Oscillator
No abstract available
An Integrated 520-600 GHz Sub-Harmonic Mixer and Tripler Combination Based on GaAs MMIC Membrane Planar Schottky Diodes
We present here the design, development and test of an integrated sub-millimeter front-end featuring a 520-600 GHz sub-harmonic mixer and a 260-300 GHz frequency tripler in a single cavity. Both devices used GaAs MMIC membrane planar Schottky diode technology. The sub-harmonic mixer/tripler circuit has been tested using conventional machined as well as silicon micro-machined blocks. Measurement results on the metal block give best DSB mixer noise temperature of 2360 K and conversion losses of 7.7 dB at 520 GHz. Preliminary results on the silicon micro-machined blocks give a DSB mixer noise temperature of 4860 K and conversion losses of 12.16 dB at 540 GHz. The LO input power required to pump the integrated tripler/sub-harmonic mixer for both packages is between 30 and 50 mW.
The DYNAMO Orbiter Project: High Resolution Mapping of Gravity/Magnetic Fields and In Situ Investigation of Mars Atmospheric Escape
Dynamo is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for Dynamo of 120-130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere, and water, from the planet. There is much room for debate on the importance of current atmosphere escape processes in the evolution of the Martian atmosphere, as early "exotic" processes including hydrodynamic escape and impact erosion are traditionally invoked to explain the apparent sparse inventory of present-day volatiles. Yet, the combination of low surface gravity and the absence of a substantial internally generated magnetic field have undeniable effects on what we observe today. In addition to the current losses in the forms of Jeans and photochemical escape of neutrals, there are solar wind interaction-related erosion mechanisms because the upper atmosphere is directly exposed to the solar wind. The solar wind related loss rates, while now comparable to those of a modest comet, nonetheless occur continuously, with the intriguing possibility of important cumulative and/or enhanced effects over the several billion years of the solar system's life. If the detailed history of the Martian internal field could be traced back, and the current escape processes could be understood well enough to model the expected stronger losses under early Sun conditions, one could go a long way toward constraining this part of the mysterious history of Mars' atmosphere.
An All Solid-State 640 GHz Subharmonic Mixer
This paper reports on the first all solid-state two-diode subharmonically pumped (SHP) mixer operating at 640 GHz.
Accelerated Lifetime Testing and Failure Analysis of Quartz Based GaAs Planar Schottky Diodes
Accelerated lifetime tests have been performed on intergrated planar GaAs Schottky diodes that were bonded to quartz substrates up-side-down with a heat-cured epoxy.
An observation of annihilation radiation from the Galactic center region
Results are reported from observations of the 511 MeV annihilation gamma-ray line from the Galactic center, made on May 22, 1989 with a high-resolution gamma-ray spectrometer on board a balloon launched from Alice Springs (Australia). The observations were made at about 4 gm/sq cm atmospheric depth for 6 hrs in a series of target and background pointings lasting 20 min each. The results obtained from multiparameter Gaussian fits to the data were as follows: 511 keV flux = 0.00089 + or - 0.00027 ph/sq cm per sec-rad, line width of about 1.1 keV, and less than 3.2 keV FWHM at 95 percent confidence.
An observation of the Galactic center region with the HEXAGONE high resolution gamma-ray spectrometer
The Galactic center region was observed for 6 hours on May 22, 1989 from a high altitude balloon with the HEXAGONE high resolution gamma-ray spectrometer. The instrument had a 285 sq/cm array of cooled germanium detectors with an energy resolution of 2.2 keV at 511 keV and an 18 deg FWHM field of view. The 511 keV gamma-rays from electron-positron annihilation and 1809 keV gamma-rays from the radioactive decay of Al-26 were observed to have fluxes of 8.9 x 10 exp -4 and 1.9 x 10 exp -4 ph/cm-s, respectively. Continuum emission was detected from 20 to 800 keV and preliminary results have been obtained for the spectrum. Below 120 keV this is well described by power law with a slope of -2.6. In the 120-250 keV band the spectrum contains a broad linelike feature. This is interpreted as the result of Compton backscattering of about 511 keV photons from a compact source of electron-positron annihilation radiation.
NASA's Precision Segmented Reflectors (PSR) project
The PSR project representing a step toward developing the technology base needed to support future advanced astrophysics missions is described. The project is focused on producing high precision lightweight panels, large structures with proven erectability and accuracy, and lightweight and low power controls capable of achieving a high degree control of accuracy. Panels of sizes from 0.4 to 0.9 meter are fabricated to verify various design concepts for improving panel surface accuracy; in particular, a 0.4 meter panel is fabricated and refinished to a high degree of accuracy.
Solar High-energy Astrophysical Plasmas Explorer (SHAPE). Volume 1: Proposed concept, statement of work and cost plan
The concept of the Solar High-Energy Astrophysical Plasmas Explorer (SHAPE) is studied. The primary goal is to understand the impulsive release of energy, efficient acceleration of particles to high energies, and rapid transport of energy. Solar flare studies are the centerpieces of the investigation because in flares these high energy processes can be studied in unmatched detail at most wavelenth regions of the electromagnetic spectrum as well as in energetic charged particles and neutrons.
Spectrophotovoltaic orbital power generation, phase 2
A subscale model of the spectral splitting concentrator system with 10" aperture is defined and designed. The model is basically a scaled down version of Phase 1 design with an effective concentration ratio up to 1000:1. The system performance is predicted to be 21.5% for the 2 cell GaAs/Si system, and 20% for Si/GaAs at AM2 using realistic component efficiencies. Component cost of the model is projected in the $50K range. Component and system test plans are also detailed.
Spectrophotovoltaic orbital power generation
A system with 1000 : 1 concentration ratio is defined, using a cassegrain telescope as the first stage concentration (270 x) and compound parabolic concentrators (CPC) for the second stage concentration of 4.7 x for each spectral band. Using reported state of the art (S.O.A.) solar cells device parameters and considering structural losses due to optics and beamsplitters, the efficiencies of one to four cell systems were calculated with efficiencies varying from approximately 22% to 30%. Taking into account cost of the optics, beamsplitter, radiator, and the cost of developing new cells the most cost effective system is the GaAs/Si system.
A broad look at solar physics adapted from the solar physics study of August 1975
The current status of our knowledge of the basic mechanisms involved in fundamental solar phenomena is reviewed. These include mechanisms responsible for heating the corona, the generation of the solar wind, the particle acceleration in flares, and the dissipation of magnetic energy in field reversal regions, known as current sheets. The discussion covers solar flares and high-energy phenomena, solar active regions; solar interior, convection, and activity; the structure and energetics of the quiet solar atmosphere; the structure of the corona; the solar composition; and solar terrestrial interactions. It also covers a program of solar research, including the special observational requirements for spectral and angular resolution, sensitivity, time resolution, and duration of the techniques employed.
Thermal/acoustical aircraft insulation material
Attempts made to improve the acoustical properties of low density Fiberfrax foam, an aircraft insulation material, are reported. Characterizations were also made of the physical and thermal properties. Two methods, optimization of fiber blend composition and modification of the foam fabrication process, were examined as possible means of improving foam acoustics. Flame impingement tests were also made; results show performance was satisfactory.