422 lines
8.6 KiB
Plaintext
422 lines
8.6 KiB
Plaintext
Magellan Fact Sheet
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*** Mission Summary ***
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The Magellan spacecraft, named after the sixteenth-century
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Portuguese explorer whose expedition first circumnavigated the
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Earth, was launched May 4, 1989, and arrived at Venus on
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August 10, 1990. Magellan's solid rocket motor placed it into
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a near-polar elliptical orbit around the planet. During the
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first 8-month mapping cycle around Venus, Magellan collected
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radar images of 84 percent of the planet's surface, with
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resolution 10 times better than that of the earlier Soviet
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Venera 15 and 16 missions. Altimetry and radiometry data also
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measured the surface topography and electrical
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characteristics. During subsequent cycles the map will be
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completed, filling gaps in coverage from the first cycle and
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imaging the south polar region for the first time. Precision
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radio tracking of the spacecraft will measure Venus'
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gravitational field to show the planet's internal mass
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distribution and the forces which have created the surface
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features. Magellan's data will permit the first global
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geological understanding of Venus, the planet most like Earth
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in our solar system.
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*** Venus ***
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Distance from Sun: 1.1 x 108 km
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Orbit Period: 225 Earth days
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Radius: 6051 km
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Rotational Period (sidereal): 243 Earth days
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Average Density: 5.2 g/cm3
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Surface Gravity: .907 times that of Earth
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(8.87 m/s2)
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Surface Temperature: 850 F (730 K)
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Surface Atmospheric Pressure: 90 times that of Earth
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(90 q 2 bar)
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Atmospheric Composition: Carbon dioxide (96%); nitrogen
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(3+%); trace amounts of sulfur
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dioxide, water vapor, carbon
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monoxide, argon, helium, neon,
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hydrogen chloride, hydrogen
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fluoride
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*** Major Mission Characteristics ***
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Interplanetary Cruise: May 4, 1989, to August 10, 1990
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First Mapping Cycle: September 15, 1990 to May 15,
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1991
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Orbit Period: 3.25 hours
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Orbit Inclination: 86 degrees
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Radar Mapping Per Orbit: 37.2 minutes
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Planetary Coverage: 84%
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Extended Mission Plan: May 16, 1991 to May 15, 1993
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Cycle 2: Image the south pole region and
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gaps from Cycle 1
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Cycle 3: Fill remaining gaps and collect
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stereo imagery
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Cycle 4: Measure Venus' gravitational
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field
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*** Mission Objectives ***
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Obtain near-global radar images of Venus' surface, with
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resolution equivalent to optical imaging of 1 km per line pair
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Obtain a near-global topographic map with 50km spatial and
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100m vertical resolution
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Obtain near-global gravity field data with 700km resolution
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and 2-3 milligals accuracy
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Develop an understanding of the geological structure of the
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planet, including its density distribution and dynamics
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*** Magellan Team ***
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NASA/Solar System Exploration Division
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- Elizabeth E. Beyer, Program Manager
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- Joseph M. Boyce, Program Scientist
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- David J. Okerson, Program Engineer
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JPL
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- James F. Scott, Project Manager
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- R. Stephen Saunders, Project Scientist
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- Douglas G. Griffith, Mission Directory
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Principal Investigators
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- Radar: Gordon Pettengill (MIT)
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- Gravity: William Sjogren (JPL)
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Georges Balmino (France)
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System Contractors
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- Spacecraft: Martin Marietta/Denver
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F. McKinney, Manager
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- Radar: Hughes Aircraft
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B. Dagarin, Manager
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*** Key Spacecraft Characteristics ***
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Single radar instrument operates simultaneously (by
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interleaving) in Synthetic Aperture Radar (SAR), altimeter,
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and radiometer modes
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High Gain Antenna (3.7m diameter) is used as both the radar
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and telecommunications antenna
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X-band downlink data rate of 268.8 or 115 kbps
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Coherent X- and S-band radio subsystem used for gravity field
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measurement by precision tracking of the spacecraft's orbit
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Spacecraft on-orbit dry mass of 1035 kg
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Monopropellant hydrazine thruster system (0.9 to 445N thrust)
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Powered by solar panels with rechargeable batteries
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Three orthogonal electrically powered reaction wheels used for
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spacecraft pointing control
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*** Key Radar Characteristics ***
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Synthetic Aperture Radar (SAR)
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- Frequency 2.385 GHz
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- Peak Power 325 W
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- Pulse Length 26.5 msec
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- PRF 4400-5800 Hz
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- Swath Width 25 km (variable)
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- Data Acquisition Rate 806 kbps
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- Downlink Quantization 2 bits
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Operates in SAR, altimeter, and radiometer modes
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- SAR Resolution 150m range/150m azimuth
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- Altimeter Resolution 30m
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- Radiometer Accuracy 2 C
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Operating parameters controlled by ground command
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*** Key Scientific Results ***
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A preliminary assessment of the Magellan high-resolution
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global images is providing evidence to understand the role of
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impacts, volcanism, and tectonism in the formation of Venusian
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surface structures.
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The surface of Venus is mostly covered by volcanic materials.
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Volcanic surface features, such as vast lava plains, fields of
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small lava domes, and large shield volcanoes are common.
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There are few impact craters on Venus, suggesting that the
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surface is, in general, geologically young - less than 800
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million years old.
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The presence of lava channels over 6,000 kilometers long
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suggests river-like flows of extremely low-viscosity lava that
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probably erupted at a high rate.
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Large pancake-shaped volcanic domes suggest the presence of a
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type of lava produced by extensive evolution of crustal rocks.
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The typical signs of terrestrial plate tectonics - continental
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drift and basin floor spreading - are not in evidence on
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Venus. The planet's tectonics is dominated by a system of
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global rift zones and numerous broad, low domical structures
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called coronae, produced by the upwelling and subsidence of
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magma from the mantle.
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Although Venus has a dense atmosphere, the surface reveals no
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evidence of substantial wind erosion, and only evidence of
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limited wind transport of dust and sand. This contrasts with
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Mars, where there is a thin atmosphere, but substantial
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evidence of wind erosion and transport of dust and sand.
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*** For More Information on Data ***
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Photographic images, digital data (CD ROMs) and display
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software, and videotapes showing computer-generated flights
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over Venus are available to researchers, educators, and the
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public through the National Space Science Data Center, Goddard
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Space Flight Center, Mail Code 933.4, Greenbelt, MD 20771,
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(301) 286-6695, Fax: (301) 286-4952.
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Detailed catalog information is available to researchers funded by
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NASA's Solar System Exploration Division through the Planetary Data
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System, Geosciences Node, Earth and Planetary Remote Sensing
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Laboratory, Washington University St. Louis, MO 63130-4899,
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(314) 935-5493, Fax: (314) 935-7361.
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Photographic imagery, CD-ROMs, and videotapes are available
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for browsing at NASA's 15 Regional Planetary Image Facilities.
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For additional information, call Mary Ann Harger at the Lunar
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and Planetary Institute at (713) 486-2136 or -2172, Fax: (713)
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486-2153.
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Teachers can obtain information about Magellan, including
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copies of the videotapes, through NASA's Teacher Resource
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Centers. For more information, call the Jet Propulsion
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Laboratory's Teacher Resource Center at (818) 354-6916, Fax:
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(818) 354-8080.
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