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NASA NTRS1987

A compilation system for Venus radar mission (Magellan)

A synthetic aperture radar (SAR) compilation system was developed for extraction of topographic information of Venus from stereoradar imagery to be obtained from the Magellan mission. The system was developed for an AS-11AM analytical stereoplotter. Extensive tests were made on this compilation software by using stereo images from various radar systems, both spaceborne and airborne. Maps were compiled and the precision of planimetry and contour measurement was evaluated. Digital data of some models were also collected for processing orthophoto or perspective views by using the original radar images.

Wu, Sherman S. C.↗
NASA NTRS1990

Distribution of tessera terrain on Venus - Prediction for Magellan

Tessera terrain is the dominant tectonic unit in the northern hemisphere of Venus and is characterized by complex sets of intersecting structural trends and distinctive radar properties due to a high degree of meter and sub-meter scale (5 cm to 10 m) roughness. Based on these distinctive radar properties, a prediction of the global distribution of tessera can be made using Pioneer Venus (PV) reflectivity and roughness data. Where available, Benera 15/16 and Arecibo images and PV diffuse scattering data were used to evaluate the prediction. From this assessment, it is concluded that most of the regions with prediction values greater than 0.6 (out of 1) are likely to be tessera, and are almost certain to be techonically deformed.

Bindschadler, D. L.↗
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 NTRS1993

Preliminary analysis of Dione Regio, Venus: The final Magellan regional imaging gap

In Sep. 1992, the Magellan spacecraft filled the final large gap in its coverage of Venus when it imaged an area west of Alpha Regio. F-BIDR's and some test MIDR's of parts of this area were available as of late December. Dione Regio was imaged by the Arecibo observatory and a preliminary investigation of Magellan images supports the interpretations made based on these earlier images: Dione Regio is a regional highland on which is superposed three large, very distinct volcanic edifices. The superior resolution and different viewing geometry of the Magellan images also clarified some uncertainties and revealed fascinating details about this region.

Keddie, S. T.↗
NASA NTRS1990

Consequences of a hydrous mantle for Venus tectonics - Predictions for Magellan

The consequences of a Venus mantle enriched in water relative to the earth are considered. If the moon-forming impact hypothesis is correct, earth may have lost substantial volatiles. Venus, however, experienced no such impact and is therefore likely to be relatively more water-rich. It is demonstrated that a higher abundance of water in the Venus mantle has the effect of inhibiting the rise of crust-forming melts and volatiles to the surface, which results in a thin stable crust, a dry, stiff upper mantle, and restricted magmatism. Conduction through a shallow thermal lithosphere dominates the removal of heat from the interior, and flow in the mantle is strongly coupled to the surface deformation. Current observations of Venus are consistent with this model. A review of the consequences of this model makes it possible to make predictions for the Magellan radar images.

Williams, David R.↗
NASA NTRS1991

Impact craters on Venus - Initial analysis from Magellan

The general features of impact craters are described emphasizing two aspects: the effect of the atmosphere on crater and ejecta morphology and the implications of the distribution and appearance of the craters for the volcanic and tectonic resurfacing history of Venus. Magellan radar images reveal 135 craters about 15 km in diameter containing central peaks, multiple central peaks, and peak rings. Craters smaller than 15 km exhibit multiple floors or appear in clusters. Surface flows of material initially entrained in the atmosphere are characterized. Zones of low radar albedo originated from deformation of the surface by the shock or pressure wave associated with the incoming meteoroid surround many craters. A spectrum of surface ages on Venus ranging from 0 to 800 million years indicates that Venus must be a geologically active planet.

Phillips, Roger J.↗
NASA NTRS1991

Precise tracking of the Magellan and Pioneer Venus orbiters by same-beam interferometry

Results of a demonstration of same-beam interferometry, the simultaneous tracking of two spacecraft in orbit about a distant planet by widely separated earth-based radio antennas, are presented with regard to the Magellan and Pioneer 12 orbiters at Venus. Signals from both spacecraft fall within the same beamwidth of the tracking antennas. The plane-of-sky position difference between spacecraft is precisely determined by double-differenced phase measurements. This data type complements line-of-sight Doppler and improves orbital accuracy by up to an order of magnitude. The predicted error is dominated by solar plasma fluctuations, and is 15.1 psec for a 5-min integration. The rms of the residuals is less than this by about 25 percent. The shape of the spectrum computed from residuals is consistent with that derived from a model of solar plasma fluctuations. Same-beam interferometry is expected to enhance tracking accuracy and efficiency for proposed multiple missions to Mars.

Border, James S.↗
NASA NTRS1987

Magellan - Communicating with a spacecraft at Venus

NASA's Magellan mission scheduled for launch in April 1989, using the Space Shuttle/Innertial Upper Stage configuration, will put a single spacecraft in orbit around Venus in order to map the planet's surface with SAR. The SAR's resolution will be enough to furnish surface details, and such geological features as tectonics, volcanic activity, surface faulting, and water and wind erosion. Attention is presently given to the telecommunications system that will be needed to transmit the 3.4 trillion bits of data which the SAR will acquire during the course of this mission.

Burow, Nathan A.↗
NASA NTRS1990

Tectonics of Lakshmi Planum, Venus - Tests for Magellan

The origin of Lakshmi Planum and its surrounding mountain belts remains an important unresolved element in the global tectonic framework of Venus. From the perspective of gravity signature and potential driving forces, the mantle upwelling model is the simplest, and its principal failure, that it cannot produce radial shortening on the uplift periphery, may be resolved if the lithosphere is laterally heterogeneous. The preferred model consists of a hot mantle plume rising beneath a preexisting block of tessera. The lithosphere is weakened at this hotter and presumably thicker crust, and the outward near-surface flow is attenuated at the peripheral discontinuity in lithospheric strength. Crustal thickening and mountain belt formation occur there. Several criteria are proposed to test this 'tessera-plume' model together with its competitors at the higher resolution in both imaging and gravity afforded by the Magellan mission.

Grimm, Robert E.↗
NASA NTRS1994

Evidence for Active Hotspots on Venus from Analysis of Magellan Gravity Data

Teh 500 My average crater retension for Venus ahs raised questions about the present-day level of tectonic activity. In this study we examine the relationship between the gravity and topography of four large volcanic swells, Beta, Atla, Bell, and Western Eistla Regiones, for clues about their stage of evolution.

hotspots↗
NASA NTRS1995

Wind-Related Features and Processes on Venus Summary of Magellan Results

A search of Magellan synthetic aperture radar images covering about 98% of the venusian surface shows that aeolian features occur at all longitudes and latitudes. A global data base for wind streaks, the most common type of aeolian feature, was developed. For each of the 5970 streaks in the data base, information was compiled on location, streak type, radar backscatter, dimensions, azimuth, orientation with respect to local slope, and type of landform with which it is associated. In addition, streaks occurring in association with parabolic ejecta deposits were designated type P streaks, which constitute about 31% of the data base. Wind streak azimuths were analyzed to assess wind patterns at the time of their formation. Both hemispheres show strong westward and equatorward trends in azimuths, consistent with Hadley circulation and inferred upper atmospheric westward zonal winds. When type P streaks (those considered to result from transient impact events) were removed, the westward component was greatly reduced, suggesting that the upper zonal winds do not extend to the surface. The presence of equator-oriented streaks at high latitudes suggests that Hadley circulation extends to the poles. A field of possible yardangs found southwest of Mead Crater strikes NE-SW and occupies plains situated in a shallow topographic depression. Analysis of non-type P streaks in the area suggests that equatorward winds are funneled through the depression and are responsible for the erosion of the terrain to form the yardangs. Dune deposits are limited on Venus. Two dune fields were identified (Aglonice and Fortuna-Meshkenet) which total in area about 18,300 square km. Microdunes are proposed for some southern hemisphere areas which show distinctive radar reflectivities. Bragg scattering and/or subpixel reflections from the leeward faces of microdune bedforms could account for the unusual radar backscatter cross sections.

Greeley, Ronald↗
NASA NTRS1995

Wind-Related Features and Processes on Venus: Summary of Magellan Results

A search of Magellan synthetic aperture radar images covering approximately 98% of the venusian surface shows that aeolian features occur at all longitudes and latitudes. A global data base for wind streaks, the most common type of aeolian feature, was developed. For each of the 5970 streaks in the data base, information was compiled on location, streak type, radar backscatter, dimensions, azimuth, orientation with respect to local slope, and type of landform with which it is associated. In addition, streaks occurring in association with parabolic ejecta deposits were designated type P streaks, which constitute about 31% of the data base. Wind streak azimuths were analyzed to assess wind patterns at the time of their formation. Both hemispheres show strong westward and equatorward trends in azimuths, consistent with Hadley circulation and inferred upper atmospheric westward zonal winds. When type P streaks (those considered to result from transient impact events) were removed, the westward component was greatly reduced, suggesting that the upper zonal winds do not extend to the surface. The presence of equator-oriented streaks at high latitudes suggests that Hadley circulation extends to the poles. A field of possible yardangs found southwest of Mead Crater strikes NE-SW and occupies plains situated in a shallow topographic depression. Analysis of non-type P streaks in the area suggests that equatorward winds are funneled through the depression and are responsible for the erosion of the terrain to form the yardangs. Dune deposits are limited on Venus. Two dune fields were identified (Aglonice and Fortuna-Meshkenet) which total in area about 18,300 sq km. Microdunes are proposed for some southern hemisphere areas which show distinctive radar reflectivities. Bragg scattering and/or subpixel reflections from the leeward faces of microdune bedforms could account for the unusual radar backscatter cross sections.

Greeley, Ronald↗
NASA NTRS1991

Solar system exploration in the 1990's and beyond

Exploration of Venus by Magellan and Pioneer Venus continues. Additionally, Galileo's Venus-earth-earth gravity assist trajectory to Jupiter has already provided targets of opportunity at Venus and at earth. Additional opportunities exist during the October 29, 1991, flyby of the asteroid Gaspra, the second earth gravity assist on December 8, 1992, and the flyby of the asteroid Ida on October 18, 1993. A fully successful mission through entry of the Jupiter atmospheric probe is anticipated in 1995/1996. The buildup of the Mars Observer spacecraft for a September 1992 launch is accelerating, and the development of the CRAF spacecraft and the orbiter for the NASA-ESA Cassini mission to Saturn is proceeding. Strategic plans to continue this ambitious program include early initiation of a phased program to detect other planetary systems; start of a program of low-cost, near-earth missions beginning with a near-earth asteroid rendezvous; continuation of moon-Mars exploration using sequentially launched single experiment Lunar Scouts and clusters of small landers to build up a Mars network of 16 stations; and finally, start of a major mission late in the century to explore Neptune and/or Pluto.

Huntress, Wesley T., Jr.↗
NASA NTRS1993

Venus gravity: New Magellan low altitude data

Acquisition of a new high quality gravity data set has begun. The data set presently covers one third of the Venusian longitude. Better spatial resolution is obtained from a 60th degree and order spherical harmonic solution. Plans for aerobraking in May 1993 into a near circular orbit will provide excellent data for higher latitude regions.

Sjogren, W. L.↗
NASA NTRS2016

Venera-D: Technology Implications

The Venera-D concept mission being developed by the Joint Russian US Science Definition Team (JSDT) is an exciting concept for exploring Venus and is based largely successful approach of heritage Soviet Veneras and VEGA missions. The desired science of Venera-D seeks to build on the results on these missions and also missions by other nations such as the American Mariners, Pioneer Venus, and Magellan missions, ESAs Venus Express, and the current Japanese Akatsuki mission. A number of elements comprise the potential full mission concept. Core elements of the mission include a long lived orbiter (3 years) and a short duration ( 2 hour) but powerful lander. Several other mission elements are possible depending on mission constraints which include cost limitations. Other possible elements include some form of mobile aerial platform, such as a balloon, long lived dropsonde(s), and sub-satellite. One can image the diverse maturity of technologies that will be needed to support the various elements of the Venera-D mission concept. Given the long heritage and recent orbiting missions, little technology challenges are expected for the orbiter. However it has been several decades since humanity has placed a functioning lander on the Venus surface or spent time floating in the Venus atmosphere so the technology challenges will be of greater concern. This briefing presents some of the results of the Venera-D technology sub-group.

Venera-D↗
NASA NTRS1991

Magellan - Initial analysis of Venus surface modification

Images of the Venus surface provided by the Magellan mission make it possible to see the fine-scale features diagnostic of weathering, erosion, and deposition. These include ejecta deposits extending up to 1000 km to the west of several impact craters, windblown deposits, features containing both obstacles and a source of particulate material, and evidence for degradation by atmosphere-surface interactions and mass movements. Initial Magellan observations pertaining to the nature, rate, and history of surficial processes are analyzed. Emphasis is placed on radar imaging, but results from radiometry and altimetry observations are also discussed.

Arvidson, R. E.↗