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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Assessment of interference to scientific instruments onboard RTG powered spacecraft caused by radiation emanating from RTG unit with application to Pioneer F/G space probes
Ionospheric electron content from Faraday rotation measurements of ATS 1 and Pioneer 7 space probe
The inner perturbing forces acting on sensors were analyzed, taking into account the technological limitations imposed on the proof mass position pickup and proof mass acquisition system. The resulting perturbing accelerations are evaluated as a function of the drag-free sensor parameters. Perturbations included gravitational attraction, electrical action, magnetic action, pressure effects, radiation effects, and action of the position pickup. These data can be used to study the laws of guidance, providing an optimization of the space probe as a whole.
A major concern in the integration of a radioisotope thermoelectric generator (RTG) with a spacecraft designed to explore the outer planets is the effect of the emitted radiation on the normal operation of scientific instruments. The necessary techniques and tools developed to allow accurate calculation of the neutron and gamma spectrum emanating from the RTG. The specific sources of radiation were identified and quantified. Monte Carlo techniques are then employed to perform the nuclear transport calculations. The results of these studies are presented. An extensive experimental program was initiated to measure the response of a number of scientific components to the nuclear radiation.
A tracking polarimeter implemented on the 64-m NASA/JPL paraboloid antenna at Goldstone, Calif., is described. Its performance is analyzed and compared with measurements. The system was developed to measure Faraday rotation in the solar corona of the telemetry carrier from the Pioneer VI spacecraft as it was occulted by the sun. It also measures rotation in the earth's ionosphere and is an accurate method of determining spacecraft orientation. The new feature of this system is its use of a pair of quarter-wave plates to allow the synthesis of a rotating feed system, while requiring the rotation of only a single section of waveguide. Since the polarization sensing is done at RF and the receiver operates essentially as a null detector, the system's accuracy is superior to other polarization tracking schemes. In addition, the antenna size and maser preamplifier provide unsurpassed sensitivity. The associated instrumentation used in the Pioneer VI experiment is also described.
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Comparison of alternative means for high data rate communication from deep space probes, and deep space navigation by orbiting spacecraft
Specific Impulse, Isp, is a measure of a rocket engine’s efficiency. It is calculated relative to the Earth’s gravitational field, where Isp = ve/ go, with go= 9.8 m/s2 and the escape velocity of the propellant, ve, in m/s. Chemical rockets have ve < 4.4x103 m/s and Isp < 450 seconds. As an alternative, the NASA Glenn Research Center developed multiple generations of Solar Electric Propulsion (SEP), high Isp, ion engines using Xe gas as a propellant. Consequently, over 100 SEP Ion Thrusters provide geo-synchronous station keeping along with deep space probes like Deep Space One and Dawn. These have ve » 2.9 x 104 m/s with Isp = 3x103 seconds. These thrusters have continuous operating lifetimes of thousands of hours allowing continuous acceleration making up for the very low thrust. Chang-Diaz’ Variable Specific Impulse Magnetoplasma Rocket (VASIMR) has the potential for four times the propellant escape velocity and four times the specific impulse1. Unfortunately, this comes at a tremendous electrical power cost, estimated at 200 kWe for maintaining the International Space Station in Low Earth Orbit (LEO). Although nuclear fission and fusion reactors2 have been suggested for powering nuclear thermal propulsion (NTP) it only doubles the Isp over chemical rockets but with comparable thrust. Instead, we propose using Lattice Confinement Fusion (LCF) reactions.
Low temperature batteries for deep space probes and extending battery usefulness by heating
Optical coupling material for deep space probes
Surveyor mission operations, and systems design engineering for Mariner, Voyager, and Surveyor space probes
Optical communications can provide high-data-rate telemetry from deep-space probes with subsystems that have lower mass, consume less power, and are smaller than their radio frequency (RF) counterparts. However, because optical communication is more a.ected by weather than is RF communication, it requires groundstation site diversity to mitigate the adverse e.ects of inclement weather on the link. An optical relay satellite is not a.ected by weather and can provide 24-hour coverage of deep-space probes. Using such a relay satellite for the deep-space link and an 8.4-GHz (X-band) link to a ground station would support high-data-rate links from small deep-space probes with very little link loss due to inclement weather. We have reviewed past JPL-funded work on RF and optical relay satellites, and on proposed clustered and linearly dispersed optical subnets. Cost comparisons show that the life cycle costs of a 7-m optical relay station based on the heritage of the Next Generation Space Telescope is comparable to that of an 8-station subnet of 10- m optical ground stations. This makes the relay link an attractive option vis- a-vis a ground-station network.
Ground-to-space laser uplinks to Earth–orbiting satellites and deep space probes serve both as a beacon and an uplink command channel for deep space probes and Earth-orbiting satellites. An acquisition and tracking point design to support a high bandwidth downlink from a 20-cm optical terminal on an orbiting Mars spacecraft typically calls for 2.5 kW of 1030-nm uplink optical power in 40 micro-radians divergent beams.2 The NOHD (nominal ocular hazard distance) of the 1030nm uplink is in excess of 2E5 km, approximately half the distance to the moon. Recognizing the possible threat of high power laser uplinks to the flying public and to sensitive Earth-orbiting satellites, JPL developed a three-tiered system at its Optical Communications Telescope Laboratory (OCTL) to ensure safe laser beam propagation through navigational and near-Earth space.
Deep space, solar probe, and out-of-ecliptic trajectories utilizing large planetary perturbations
Electronic systems designed for use in space exploration systems are expected to be exposed to harsh temperatures. For example, operation at cryogenic temperatures is anticipated in space missions such as polar craters of the moon (-223 C), James Webb Space Telescope (-236 C), Mars (-140 C), Europa (-223 C), Titan (-178 C), and other deep space probes away from the sun. Similarly, rovers and landers on the lunar surface, and deep space probes intended for the exploration of Venus are expected to encounter high temperature extremes. Electronics capable of operation under extreme temperatures would not only meet the requirements of future spacebased systems, but would also contribute to enhancing efficiency and improving reliability of these systems through the elimination of the thermal control elements that present electronics need for proper operation under the harsh environment of space. In this work, the performance of a micropower, high accuracy voltage reference was evaluated over a wide temperature range. The Analog Devices ADR3430 chip uses a patented voltage reference architecture to achieve high accuracy, low temperature coefficient, and low noise in a CMOS process [1]. The device combines two voltages of opposite temperature coefficients to create an output voltage that is almost independent of ambient temperature. It is rated for the industrial temperature range of -40 C to +125 C, and is ideal for use in low power precision data acquisition systems and in battery-powered devices. Table 1 shows some of the manufacturer s device specifications.
Gravity assisted trajectories for solar probe and deep space flyby missions
A traveling-wave tube (TWT) is an electron beam device that is used to amplify electromagnetic communication waves at radio and microwave frequencies. TWT's are critical components in deep space probes, communication satellites, and high-power radar systems. Power conversion efficiency is of paramount importance for TWT's employed in deep space probes and communication satellites. A previous effort was very successful in increasing efficiency and power at a single frequency (ref. 1). Such an algorithm is sufficient for narrow bandwidth designs, but for optimal designs in applications that require high radiofrequency power over a wide bandwidth, such as high-density communications or high-resolution radar, the variation of the circuit response with respect to frequency must be considered. This work at the NASA Glenn Research Center is the first to develop techniques for optimizing TWT efficiency and output power over a broad frequency bandwidth (ref. 2). The techniques are based on simulated annealing, which has the advantage over conventional optimization techniques in that it enables the best possible solution to be obtained (ref. 3). Two new broadband simulated annealing algorithms were developed that optimize (1) minimum saturated power efficiency over a frequency bandwidth and (2) simultaneous bandwidth and minimum power efficiency over the frequency band with constant input power. The algorithms were incorporated into the NASA coupled-cavity TWT computer model (ref. 4) and used to design optimal phase velocity tapers using the 59- to 64-GHz Hughes 961HA coupled-cavity TWT as a baseline model. In comparison to the baseline design, the computational results of the first broad-band design algorithm show an improvement of 73.9 percent in minimum saturated efficiency (see the top graph). The second broadband design algorithm (see the bottom graph) improves minimum radiofrequency efficiency with constant input power drive by a factor of 2.7 at the high band edge (64 GHz) and increases simultaneous bandwidth by 500 MHz.