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Journal Article

Compliance with High-Intensity Radiated Fields Regulations - Emitter's Perspective

NASA's Deep Space Network (DSN) uses high-power transmitters on its large antennas to communicate with spacecraft of NASA and its partner agencies. The prime reflectors of the DSN antennas are parabolic, at 34m and 70m in diameter. The DSN transmitters radiate Continuous Wave (CW) signals at 20 kW - 500 kW at X-band and S-band frequencies. The combination of antenna reflector size and high frequency results in a very narrow beam with extensive oscillating near-field pattern. Another unique feature of the DSN antennas is that they (and the radiated beam) move mostly at very slow sidereal rate, essentially identical in magnitude and at the opposite direction of Earth rotation.
Technical Paper

Selection of an Effective Architecture for a Precursor Mission to Callisto

One startling realization that's come from NASA's explorations of the satellites of Jupiter and Saturn is that the so-called “habitable zone” around our Sun may not be restricted to Earth's vicinity. The Galileo mission found conditions that might support life on two Jovian moons-Europa & Callisto. This raises the possibility of habitable zones elsewhere near the outer planets. Consideration of human missions beyond Mars, likely to occur sometime beyond the year 2040, exceeds the horizon of even the most advanced planning activities within NASA. During the next 25 to 30 years, robotic spacecraft are envisioned to explore several moons of outer planets, especially Europa and Titan. Since Callisto lies well outside Jupiter's radiation belt, and there is evidence of water ice there is a compelling rationale to send human explorers to that Jovian moon.
Technical Paper

Tunable Diode Lasers (TDL) for Spectroscopy and Environmental Monitoring

The current status of III-V semiconductor diode lasers emitting between 1 -5 μm wavelengths to be used as light sources for absorption spectroscopy is reviewed. The emission wavelength of the laser is chosen to coincide with the primary absorption line of a molecule or one of its many overtones. The lasers, with a single longitudinal mode emission, are wavelength tuned over several angstroms by modulating the drive current of the device. This sweeping of the wavelength leads to the nomenclature tunable diode laser or TDL. Single mode distributed feedback (DFB) strained layer InGaAs(P) lasers grown on InP substrates with emission wavelengths from 1.2 to 2.06 μm have been developed at JPL, and several devices will be used for planetary atmospheric studies for the first time.
Technical Paper

JOVIAN ICY MOON EXCURSIONS: Radiation Fields, Microbial Survival and Bio-contamination Study

The effects of both the cosmic ray heavy ion exposures and the intense trapped electron exposures are examined with respect to impact on cellular system survival on exterior spacecraft surfaces as well as at interior (shielded) locations for a sample mission to Jupiter’s moons. Radiation transport through shield materials and subsequent exposures are calculated with the established Langley heavy ion and electron deterministic codes. In addition to assessing fractional DNA single and double strand breaks, a variety of cell types are examined that have greatly differing radio-sensitivities. Finally, implications as to shield requirements for controlled biological experiments are discussed.
Technical Paper

Improved Electrical Properties of n-Type SiGe Alloys

The effect of changes in the carrier concentration and mobility for heavily doped n-type SiGe on the electrical power factor has been investigated. It has been shown that power factors of 37-40 μV/cm-K2 can be achieved with carrier concentrations of 2.0 - 2.5 × 1020 cm-3 and mobilities of 38-40 cm2/V-sec. Many samples with suitable carrier concentration do not have high mobilities and some rationale for this behavior is presented. Initial results are presented on fabrication of n-type samples from ultra-fine powders. The emphasis in this work is to achieve thermal conductivity reductions by adding inert particles to scatter mid-frequency phonons.