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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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NASA NTRS1991

Magellan - Early results from the Venus mapping mission

Some results obtained with the Magellan Venus Radar Mapper are presented. Mapping was initiated on October 26, 1990 and has completed over 714 orbits of image data, covering 40 percent of the surface of Venus. Mapping began at 330 deg east longitude, mapping from the north pole to about 78 deg south latitude. Included are the regions of Ishtar Terra, Sedna, Guinevere and Lavinia Planitiae, and Lada Terra. Features discernable from the mapping include high and lowland plains, evidence of volcanic activity, and impact craters from 6 km to over 50 km across. Some Magellan scientific discoveries are listed, including evidence of a predominant role of ballistic volcanism, extensive and intensive tectonics, a moderate rate of volcanic and tectonic resurfacing, and a low rate of weathering and wind erosion. Other discoveries concerning techntonics, volcanism, impact cratering, and exogenous resurfacing are also listed. Magellan image coverage is discussed, and a chronology of the development of VOIR and Magellan is provided.

Saunders, R. S.↗
NASA NTRS1992

Contribution of Doppler and interferometric tracking during the Magellan approach to Venus

On May 4, 1989, the Magellan spacecraft began its 463 day and 1.3 billion km earth to Venus interplanetary cruise. Magellan's Venus approach trajectory required prediction accuracy of 6.1 seconds in arrival time and 126 km in the position of closest approach to achieve a desired Venus orbit. Data collection from Magellan's SAR required an elliptical orbit with an inclination between 84 deg and 86 deg to the Venus equator, a period between 3.1 and 3.3 hours, a periapsis altitude within 275 km and 325 km and a latitude of periapsis between 0 deg and 10 deg North. Predictions of Magellan's arrival time and closest approach to Venus were derived from cruise trajectories determined exclusively from coherent two-way Doppler using both S-band (2.3 GHz) uplink/downlink and X-band (8.4 GHz) uplink/downlink and X-band spacecraft-quasar interferometric delay data. Analysis of data reduction strategies employing various data arc lengths and data combinations shows that interferometric tracking data, used in conjunction with Doppler, improved trajectory solution accuracy and robustness.

Graat, E. J.↗
NASA NTRS1992

Magellan mission summary

Magellan started mapping the planet Venus on September 15, 1990, and after one cycle (one Venus day or 243 earth days) had mapped 84 percent of the planet's surface. This returned an image data volume greater than all past planetary missions combined. Spacecraft problems were experienced in flight. Changes in operational procedures and reprogramming of onboard computers minimized the amount of mapping data lost. Magellan data processing is the largest planetary image-processing challenge to date. Compilation of global maps of tectonic and volcanic features, as well as impact craters and related phenomena and surface processes related to wind, weathering, and mass wasting, has begun. The Magellan project is now in an extended mission phase, with plans for additional cycles out to 1995. The Magellan project will fill in mapping gaps, obtain a global gravity data set between mid-September 1992 and May 1993, acquire images at different view angles, and look for changes on the surface from one cycle to another caused by surface activity such as volcanism, faulting, or wind activity.

Saunders, R. S.↗
NASA NTRS1992

SAR data processing for the Magellan prime mission

The Magellan prime mission involves mapping the planet of Venus once around its rotational axis. The Magellan synthetic aperture radar (SAR) data processing facility processes all SAR data collected by the Magellan spacecraft into image data on an orbit-by-orbit basis. About 1700 million bits of radar data were collected. A complete description of the Magellan SAR Data Processing Facility is provided with emphasis on key design features of the data processors that satisfied the project data processing requirements. A summary of the attained data processing performance is included, as well as a brief discussion of some of the constraints and considerations regarding the applicability of the processors to meeting the data processing goals anticipated for the follow-on mission phases (i.e., cycles II, III, and beyond).

Leung, K.↗
NASA NTRS1992

An analysis of the focusing performance of Magellan SAR image data

Synthetic aperture radar (SAR) focusing can be achieved either based on accurate ephemeris data or on an autofocusing process. For the Magellan project, such a decision must be made in the early phase of Magellan SAR system design. The analysis of the emphemeris requirement is complicated. The analysis given by the author leads to the conclusion that empheris data obtained from the Magellan navigation system provide sufficient accuracy to meet the Magellan image resolution requirement.

Jin, Michael Y.↗
NASA NTRS1992

Implementation and performance of the Magellan digital correlator subsystem

The Magellan synthetic aperture radar (SAR) produces Venus surface images from data collected by the SAR carried on board the Magellan spacecraft. The core of the primary Magellan SAR processor is the digital correlator subsystem (DCS). The pipeline DSC architecture enables the Magellan primary SAR processor (PSP) to achieve real-time data processing capability. The implementation and performance of the DSC are described. Hardware (H/W) constraints that influenced the processing algorithm design are highlighted.

Chen, M.↗
NASA NTRS1993

Global Magellan-image map of Venus at full resolution

During its first 243-day mapping cycle, the Magellan spacecraft succeeded in imaging 84 percent of the surface of Venus at resolutions on the order of 100 meters; subsequent cycles have increased the total coverage to over 97 percent and provided redundant coverage of much of the planet with differing viewing geometries. Unfortunately, this full-resolution global dataset is in the form of thousands of individual orbit tracks (F-BIDR's) whose length-to-width ratio of nearly 1000:1 makes them minimally useful unless mosaicked. The Magellan project produced full-resolution mosaics (F-MIDR's) only for selected regions on the planet, whereas a global set of mosaics was made only at threefold degraded resolution (C1-MIDR's). Furthermore, although the F-MIDR's, which are approximately equidimensional, are much better suited for scientific interpretation than the F-BIDR's, they are still an unwieldy dataset: over 1500 quadrangles, each showing a region only about 600 km on a side, would be required to cover the entire planet. The USGS has therefore undertaken to produce and distribute a global, full resolution set of mosaics of the Magellan image data in a format that will be efficient for both hardcopy and digital use. The initial motivation was that it would provide an efficient means of verifying the integrity of the F-BIDR's to be archived on computer-compatible tape at the USGS Flagstaff facility. However, the resulting product, known as the FMAP, should also serve as an important resource for future scientific interpretation. It will offer several advantages beyond global coverage at full resolution. The first, alluded to above, is its division of the planet's surface to minimize the number of quadrangles and maximize their area, subject to the limits on the number of pixels imposed by state-of-the-art digital recording media and hardcopy output devices. The second, the use of improved 'cosmetic' processing techniques, will greatly reduce tonal discontinuities between component F-BIDR's in the FMAP compared to the standard Magellan mosaic products. Finally, wherever possible, the FMAP will incorporate data that were unavailable (e.g., because of processing delays) when the standard MIDR products were created, as well as data that were reprocessed to improve their radiometric or geometric quality.

Kirk, R. L.↗
NASA NTRS1993

Magellan Mission

The Magellan spacecraft was launched from Cape Kennedy on 4 May 1989 and was inserted into orbit around Venus on 10 Aug. 1990. The Magellan spacecraft carries a radar instrument that makes synthetic aperture radar (SAR) images of the surface, measures the altitude of the Venusian surface directly below the spacecraft, and obtains radiometric observations of the surface. Radar and radiometric observations of the Venusian surface commenced on 15 Sep. 1990 and continued until 15 Sep. 1992. Gravity observations began on 24 Sep. 1992 and will continue until late May 1993. The radar observations produced SAR images and surface topography for 99 percent of the surface. These radar observations support the objective of improving the knowledge of the geological history of Venus by analysis of surface morphology and the processes that control them. The gravity observations that are being conducted now support the Magellan objective of improving the knowledge of the geophysics of Venus, principally its density distribution and dynamics. Also, Magellan generated more digital planetary image data than all previous planetary missions.

Thompson, Thomas W.↗
NASA NTRS1994

Venus surface roughness and Magellan stereo data

Presented are results of some studies to develop tools useful for the analysis of Venus surface shape and its roughness. Actual work was focused on Maxwell Montes. The analyses employ data acquired by means of NASA's Magellan satellite. The work is primarily concerned with deriving measurements of the Venusian surface using Magellan stereo SAR. Roughness was considered by means of a theoretical analyses based on digital elevation models (DEM's), on single Magellan radar images combined with radiometer data, and on the use of multiple overlapping Magellan radar images from cycles 1, 2, and 3, again combined with collateral radiometer data.

Maurice, Kelly E.↗
NASA NTRS1998

Magellan Aerodynamic Characteristics During the Termination Experiment Including Thruster Plume-Free Stream Interaction

Results are presented on the aerodynamic characteristics of the Magellan spacecraft during the October 1994 Termination Experiment, including the effects of the thruster engine exhaust plumes upon the molecular free stream around the spacecraft and upon the aerodynamics coefficients. As Magellan passed through the Venusian atmosphere, the solar arrays were turned in opposite directions relative to the free stream creating a torque on the spacecraft. The spacecraft control system was programmed to counter the effects of this torque with attitude control engines to maintain an inertially fixed attitude. The orientation and reaction engine telemetry returned from Magellan are used to create a model of the aerodynamic torques. Geometric models of the Magellan spacecraft are analyzed with the aid of both free molecular and Direct Simulation Monte Carlo codes. The simulated aerodynamic torques determined are compared to the measured torques. The Direct Simulation Monte Carlo method is also used to model the attitude engine exhaust plumes, the free stream disturbance caused by these plumes, and the resulting torques acting on the spacecraft compared to no-exhaust plume cases. The effect of the exhaust plumes was found to be sufficiently large that thrust reversal is possible.

Cestero, Francisco J.↗
NASA NTRS2019

Complex Organic Molecules in the Star-Forming Regions of the Magellanic Clouds

The Large and Small Magellanic Clouds (LMC and SMC), gas-rich dwarf companions of the Milky Way, are the nearest laboratories for detailed studies on the formation and survival of complex organic molecules (COMs) under metal-poor conditions. To date, only methanol, methyl formate, and dimethyl ether have been detected in these galaxiesall three toward two hot cores in the N113 star-forming region in the LMC, the only extragalactic sources exhibiting complex hot-core chemistry. We describe a small and diverse sample of the LMC and SMC sources associated with COMs or hot-core chemistry, and compare the observations to theoretical model predictions. Theoretical models accounting for the physical conditions and metallicity of hot molecular cores in the Magellanic Clouds have been able to broadly account for the existing observations, but they fail to reproduce the dimethyl ether abundance by more than an order of magnitude. We discuss future prospects for research in the eld of complex chemistry in the low- metallicity environment. The detection of COMs in the Magellanic Clouds has important implications for astrobiology. The metallicity of the Magellanic Clouds is similar to that of galaxies in the earlier epochs of the universe; thus, the presence of COMs in the LMC and SMC indicates that a similar prebiotic chemistry leading to the emergence of life, as it happened on Earth, is possible in low-metallicity systems in the earlier universe.

Sewilo, Marta M.↗
NASA NTRS1993

Beyond Aerobraking: Designing the Magellan Global Gravity Experiment

The orbit of the Magellan spacecraft was circularized during a 70 day aerobraking phase, which ended on August 3, 1993. Shrinking the orbit apoapsis from 8467 km down to 541 km was required to obtain meaningful gravity science data at high and moderate latitudes. Aerobraking was the only way to reach this nearly-circular orbit, since the amount of propellant on board Magellan was at least an order of magnitude too small to circularize propulsively. This paper will describe the gravity science experiment which drove the final design of the nearly-circular orbit. Magellan is currently in a 541 by 197 km altitude orbit around the planet Venus. This paper will also briefly describe the Magellan mission history, and then describe the design tradeoffs which went into picking the desired nearly-circular orbit.

Austin, Rick S.↗
NASA NTRS1994

Automatic DEM Generation Using Magellan Stereo Data

The Magellan radar instrument collected a large volume of radar stereo images during its two years of operation. In order to make full use of this data an automatic means of generating digital elevation models is required. Because of Magellan's unique orbital geometry and radar image formation algorithm a number of modifications to the standard stereo processing scheme are required. This paper outlines a stereo algorithm suitable for Magellan data.

magellan radar images radar stereo images digital ↗
NASA NTRS2014

Dust and Gas in the Magellanic Clouds from the Heritage Herschel Key Project. I. Dust Properties and Insights into the Origin of the Submm (Submillimeter) Excess Emission

The dust properties in the Large and Small Magellanic Clouds are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 micromillimeters. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a powerlaw emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models we investigate the origin of the submillimeter excess; defined as the submillimeter (submm) emission above that expected from SMBB models fit to observations < 200 micromillimeters. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 micromillimeters submillimeter excesses of 27% and 43% for the Large and Small Magellanic Clouds, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our fitting results show that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellar medium (ISM) were condensed into dust. This indicates that the submillimeter excess is more likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3 plus or minus 1.7) x 10 (sup 5) and (8.3 plus or minus 2.1) x 10 (sup 4) solar masses for the Large and Small Magellanic Clouds, respectively. We find significant correlations between the submillimeter excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlations.

Magellanic↗
NASA NTRS1982

The carbon abundance in the Magellanic Clouds from IUE observations of H II regions

Results are given of observations of the UV spectra of several H II regions in the Magellanic Clouds, with emphasis on obtaining the carbon abundance from the UV lines of C II, C III, and C IV. The observations and results are described, and theoretical model calculations are presented of the H II regions and the relative abundances of H, He, C, N, O, S, Cl, and Ar computed from the UV and visual spectra. In addition, the abundance results for the Magellanic Clouds are compared with the sun, the Orion Nebula, and galactic planetary nebulae. In comparison with solar abundances, carbon is found to be depleted relative to hydrogen in the Magellanic Clouds by an amount larger than that of nitrogen and oxygen in the SMC and by an amount between that of nitrogen and oxygen in the LMC. It is noted that the results are consistent with a scenario that nitrogen and oxygen have greater primary yields in massive stars than carbon, which may be produced predominantly in less massive stars (such that C/N and C/O in galaxies are initially very low and subsequently increase with evolution). Subsequently, the C/N ratio may decrease as secondary production of nitrogen in less massive stars becomes significant.

Dufour, R. J.↗
NASA NTRS1984

Ages of intermediate-age Magellanic Cloud star clusters

Ages of intermediate-age Large Magellanic Cloud star clusters have been estimated without locating the faint, unevolved portion of cluster main sequences. Six clusters with established color-magnitude diagrams were selected for study: SL 868, NGC 1783, NGC 1868, NGC 2121, NGC 2209, and NGC 2231. Since red giant photometry is more accurate than the necessarily fainter main-sequence photometry, the distributions of red giants on the cluster color-magnitude diagrams were compared to a grid of 33 stellar evolutionary tracks, evolved from the main sequence through core-helium exhaustion, spanning the expected mass and metallicity range for Magellanic Cloud cluster red giants. The time-dependent behavior of the luminosity of the model red giants was used to estimate cluster ages from the observed cluster red giant luminosities. Except for the possibility of SL 868 being an old globular cluster, all clusters studied were found to have ages less than 10 to the 9th yr. It is concluded that there is currently no substantial evidence for a major cluster population of large, populous clusters greater than 10 to the 9th yr old in the Large Magellanic Cloud.

Flower, P. J.↗
NASA NTRS1987

Magellan attitude and articulation control subsystem closed loop testing

In the spring of 1989, the Magellan spacecraft will embark on a two-year mission to map the surface of the planet Venus. Guiding it there will be the Attitude and Articulation Control Subsystem (AACS). To ensure reliable operations the AACS is being put through a rigorous test program at Martin Marietta Denver Aerospace. Before Magellan ever leaves the Space Shuttle bay from which it is to be launched, its components will have flown a simulated spaceflight in a ground-based lab. The primary objectives of the test program are to verify form, fit, and function of the AACS, particularly subsystem external interfaces and functional operation of the flight software. This paper discusses the Magellan Closed Loop Test Systems which makes realistic tests possible by simulating the dynamic and 'visual' flight environment for AACS components in the lab.

Olschansky, David G.↗
NASA NTRS1989

Space Shuttle to deploy Magellan planetary science mission

The objectives of Space Shuttle Mission STS-30 are described along with major flight activities, prelaunch and launch operations, trajectory sequence of events, and landing and post-landing operations. The primary objective of STS-30 is to successfully deploy the Magellan spacecraft into low earth orbit. Following deployment, Magellan will be propelled to its Venus trajectory by an Inertial Upper Stage booster. The objectives of the Magellan mission are to obtain radar images of more than 70 percent of Venus' surface, a near-global topographic map, and near-global gravity field data. Secondary STS-30 payloads include the Fluids Experiment Apparatus (FEA) and the Mesoscale Lightning Experiment (MLE).

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