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Magellan Fact Sheet
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MISSION SUMMARY
The Magellan spacecraft, named after the sixteenth-century Portuguese
explorer whose expedition first circumnavigated the Earth, was
launched May 4, 1989, and arrived at Venus on August 10, 1990.
Magellan's solid rocket motor placed it into a near-polar elliptical
orbit around the planet. During the first 8-month mapping cycle around
Venus, Magellan collected radar images of 84 percent of the planet's
surface, with resolution 10 times better than that of the earlier
Soviet Venera 15 and 16 missions. Altimetry and radiometry data also
measured the surface topography and electrical characteristics.
During the extended mission, two further mapping cycles from May 15,
1991 to September 14, 1992 brought mapping coverage to 98% of the
planet, with a resolution of approximately 100m.
Precision radio tracking of the spacecraft will measure Venus'
gravitational field to show the planet's internal mass distribution
and the forces which have created the surface features. Magellan's
data will permit the first global geological understanding of Venus,
the planet most like Earth in our solar system.
[A global view of Venus]
_A global view of Venus made from a mosaic of radar imagery from the
Magellan spacecraft. This computer-generated globe shows the planet from
above the equator at 180 degrees longitude. It shows the coverage of Venus
during Magellan's highly successful first mapping cycle, completed in 1991.
Magellan continues to gather data that will influence our understanding of
terrestrial planets for years to come._
VENUS
Distance from Sun: 1.1 x 10^8 km
Orbit Period: 225 Earth days
Radius: 6051 km
Rotational Period (sidereal): 243 Earth days
Average Density: 5.2 g/cm3
Surface Gravity: 0.907 times that of Earth (8.87 m/s2)
Surface Temperature: 850 F (730 K)
Surface Atmospheric Pressure: 90 times that of Earth (90 +- 2 bar)
Atmospheric Composition: Carbon dioxide (96%); nitrogen (3+%); trace
amounts of sulfur dioxide, water vapor, carbon
monoxide, argon, helium, neon, hydrogen chloride,
hydrogen fluoride
MAJOR MISSION CHARACTERISTICS
Interplanetary Cruise: May 4, 1989, to August 10, 1990
First Mapping Cycle: September 15, 1990 to September 15, 1991
Orbit Period: 3.25 hours
Orbit Inclination: 86 degrees
Radar Mapping Per Orbit: 37.2 minutes
Planetary Coverage: 98%
Extended Mission: September 15, 1991
Cycle 2: Image the south pole region and gaps from Cycle 1
Cycle 3: Fill remaining gaps and collect stereo imagery
Cycle 4: Measure Venus' gravitational field
Cycle 5: Aerobraking to circular orbit and global gravity measurements
MISSION OBJECTIVES
* Obtain near-global radar images of Venus' surface, with resolution
equivalent to optical imaging of 1 km per line pair.
* Obtain a near-global topographic map with 50km spatial and 100m
vertical resolution.
* Obtain near-global gravity field data with 700km resolution and 2-3
milligals accuracy.
* Develop an understanding of the geological structure of the planet,
including its density distribution and dynamics.
MAGELLAN TEAM
NASA/Solar System Exploration Division
* Elizabeth E. Beyer, Program Manager
* Joseph M. Boyce, Program Scientist
* David J. Okerson, Program Engineer
JPL
* James F. Scott, Project Manager
* R. Stephen Saunders, Project Scientist
* Douglas G. Griffith, Mission Directory
Principal Investigators
* Radar: Gordon Pettengill (MIT)
* Gravity: William Sjogren (JPL), Georges Balmino (France)
System Contractors
* Spacecraft: Martin Marietta/Denver, F. McKinney, Manager
* Radar: Hughes Aircraft, B. Dagarin, Manager
Key Spacecraft Characteristics
* Single radar instrument operates simultaneously (by interleaving)
in Synthetic Aperture Radar (SAR), altimeter, and radiometer modes.
* High Gain Antenna (3.7m diameter) is used as both the radar and
telecommunications antenna.
* X-band downlink data rate of 268.8 or 115 kbps.
* Coherent X- and S-band radio subsystem used for gravity field
measurement by precision tracking of the spacecraft's orbit.
* Spacecraft on-orbit dry mass of 1035 kg.
* Monopropellant hydrazine thruster system (0.9 to 445N thrust).
* Powered by solar panels with rechargeable batteries.
* Three orthogonal electrically powered reaction wheels used for
spacecraft pointing control.
Key Radar Characteristics
* Synthetic Aperture Radar (SAR)
+ Frequency: 2.385 GHz
+ Peak Power: 325 W
+ Pulse Length: 26.5 microsec
+ PRF: 4400-5800 Hz
+ Swath Width: 25 km (variable)
+ Data Acquisition Rate: 806 kbps
+ Downlink Quantization: 2 bits
* Operates in SAR, altimeter, and radiometer modes
+ SAR Resolution: 150m range/150m azimuth
+ Altimeter Resolution: 30m
+ Radiometer Accuracy: 2 degree C
Sample Magellan SAR data showing surface features
_Sample Magellan SAR data in false color showing surface of Venus_
KEY SCIENTIFIC RESULTS
Study of the Magellan high-resolution global images is providing
evidence to understand the role of impacts, volcanism, and tectonism
in the formation of Venusian surface structures.
The surface of Venus is mostly covered by volcanic materials. Volcanic
surface features, such as vast lava plains, fields of small lava
domes, and large shield volcanoes are common.
There are few impact craters on Venus, suggesting that the surface is,
in general, geologically young - less than 800 million years old.
The presence of lava channels over 6,000 kilometers long suggests
river-like flows of extremely low-viscosity lava that probably erupted
at a high rate.
Large pancake-shaped volcanic domes suggest the presence of a type of
lava produced by extensive evolution of crustal rocks.
The typical signs of terrestrial plate tectonics - continental drift
and basin floor spreading - are not in evidence on Venus. The planet's
tectonics is dominated by a system of global rift zones and numerous
broad, low domical structures called coronae, produced by the
upwelling and subsidence of magma from the mantle.
Although Venus has a dense atmosphere, the surface reveals no evidence
of substantial wind erosion, and only evidence of limited wind
transport of dust and sand. This contrasts with Mars, where there is a
thin atmosphere, but substantial evidence of wind erosion and
transport of dust and sand.
Sample Magellan SAR data showing surface features
_Sample Magellan SAR data showing surface features_
FOR MORE INFORMATION ON DATA
Photographic images, digital data [1]CD-ROMs and display software, and
videotapes showing computer-generated flights over Venus are available
to researchers, educators, and the public through the National Space
Science Data Center, Goddard Space Flight Center, Mail Code 633,
Greenbelt, MD 20771, (301) 286-6695, Fax: (301) 286-1771.
Detailed catalog information is available to researchers funded by
NASA's Solar System Exploration Division through the Planetary Data
System, Geosciences Node, Earth and Planetary Remote Sensing
Laboratory, Washington University St. Louis, MO 63130-4899, (314)
935-5493, Fax: (314) 935-7361, e-mail: request@nssdca.gsfc.nasa.gov.
Sample Magellan SAR data showing surface features
_Sample Magellan SAR data showing surface features_
Photographic imagery, CD-ROMs, and videotapes are available for
browsing at NASA's 15 Regional Planetary Image Facilities. For
additional information, call Mary Ann Harger at the Lunar and
Planetary Institute at (713) 486-2136 or -2172, Fax: (713)486-2153.
Teachers can obtain information about Magellan, including copies of
the videotapes, through NASA's Teacher Resource Centers. For more
information, call the Jet Propulsion Laboratory's Teacher Resource
Center at (818) 354-6916, Fax: (818) 354-8080.
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For questions about Planetary data at the NSSDC, please conta
ct:
David Williams, dwilliams@nssdca.gsfc.nasa.gov, (301)441-4197
NSSDC/Hughes STX, Suite 400, 7701 Greenbelt Rd.
Greenbelt, MD 20770 USA
[NSSDC logo]
________________________________________________________
Syed S. Towheed, Towheed@nssdca.gsfc.nasa.gov, (301)286-4136
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, USA
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SPACECRAFT: MAGELLAN
Spacecraft Information
======================
Launch Date : 1989-05-04
Instrument Host Name : MAGELLAN
Instrument Host Type : SPACECRAFT
Mission Information
===================
Mission Start Date : 1989-05-04
Mission Stop Date : UNK
Mission Alias Name : VENUS RADAR MAPPER (VRM)
Targets
=======
VENUS
Instruments
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RADAR SYSTEM
Spacecraft Description
======================
The design of the Magellan spacecraft was driven by the need
for a low-cost, high-performance vehicle. Some of the
Magellan spacecraft components were already in existence or
at least designed. Protoflight spacecraft were available
from storage at no cost. These include the 3.7 meter
diameter, high-gain antenna (HGA), the spacecraft bus,
propulsion system components, thermal control louvers, and
much of the radio subsystem. The stockpile of flight spares
for the Galileo spacecraft provided Magellan's command and
data system, tape recorders, attitude control processor,
power subsystem and propulsion components. Further elements
were drawn from other projects and from NASA standard
designs. Only about 30% (by mass) of the Magellan spacecraft
was especially designed for the mission, primarily the radar
electronics and the solar panels. The spacecraft system was
built by Martin Marietta Corporation. The spacecraft system
is composed of the structure, thermal control, power,
attitude control, propulsion, command data and data storage,
and telecommunications subsystems. The spacecraft structure
is composed of four major sections: High-Gain Antenna (HGA),
Forward Equipment Module (FEM), Spacecraft Bus (including
the solar array), and the Orbit Insertion Stage. The
High-Gain antenna is used as the antenna for the SAR and as
the primary antenna for the telecommunications system. The
radar electronics, the reaction wheels, and various other
spacecraft subsystem components are contained within the
Forward Equipment Module, located between the bay and the
HGA. The spacecraft bus is a ten sided structure that
contains remainder of the spacecraft subsystem components
including the solar panel array, star scanner, medium-gain
antenna (MGA), rocket engine modules (REMs), command, data
and data storage (CDDS) subsystem, attitude control
monopropellant tank, and a nitrogen tank for providing
propellant pressurization. The orbit insertion stage
contains a STAR-48 solid rocket motor (SRM) that is used to
provide the impulse required to perform the Venus Orbit
Insertion (VOI) maneuver. Thermal control of the spacecraft
is accomplished by a combination of louvers, thermal
blankets, passive coatings, and heat dissipating elements.
The nominal operating temperature for the spacecraft
components is between -5 and +40 degrees Centigrade. The
thermal control subsystem maintains these components at the
appropriate temperatures for all orientations of the
spacecraft orbit and sun- line and for all spacecraft
operating modes. Electrical power is supplied by two large
solar panels with a total area of 12.6 square meters. This
array is capable of producing a minimum power of 1029 W at
the end of the nominal mission, and has a single degree of
freedom about the solar array axis to allow tracking of the
Sun despite the changing Earth-Sun-spacecraft geometry
during the mission. A dedicated sun sensor optimizes power
production. Bus voltage regulation is controlled by the
power control unit (PCU) with a shunt regulator for
diverting excess power from the solar arrays to maintain
power as raw power (28-35 v), regulated power at 28 vDC
+/-0.56 vDC, and as AC at 2.4 KHz through the inverter. Two
30 amp-hour, 26-cell nickel cadmium batteries provide power
during times of solar occultation, and allow normal
spacecraft operations independent of real-time solar
illumination. These batteries are sized to allow a degraded
mission in the event that one of them fails. The attitude of
the Magellan spacecraft is controlled through the use of
reaction wheels, with monopropellant rocket motors being
used to periodically desaturate the reaction wheels. During
both the interplanetary cruise and the orbital portions of
the mission, attitude reference is provided by an inertial
reference unit (IRU) which is updated each orbit using
celestial references. During the mapping phase of the orbit,
the spacecraft is initially oriented with the HGA pointing
down toward Venus, with the exact attitude being a function
of the spacecraft altitude. During the downlink transmission
phase of the orbit, the spacecraft is oriented with the HGA
slightly off the Earth-line. The low gain antenna (LGA) is
mounted coaxially with the HGA and does not require pointing
since it has an omnidirectional beam pattern. The altimeter
horn (ALTA) has been positioned so that a portion of the
fan-shaped beam always points in the nadir direction during
the mapping phase of an orbit. The Magellan propulsion
subsystem consists of two parts. The first, a Star 48 SRM,
provides the impulse for VOI. Following that maneuver, the
empty casing and parts of its support structure were ejected
from the spacecraft. The second part consists of
monopropellant hydrazine thrusters that were used for
trajectory correction maneuvers (TCMs) during interplanetary
cruise, thrust vector control (TVC) during VOI, orbit trim
maneuvers during the mapping mission, and attitude control
when the action wheels are being desaturated. The rocket
motors are clustered in modules located on the end of
outrigger booms in order to increase their moment arm and
thus decrease attitude control propellant requirements.
Twelve 0.9-N (Newton) and four 22-N rocket motors are used
for attitude control, with thrust being provided by eight
445-N rocket motors or by the 0.9-N motors for small TCMs.
All engines point in the -Z direction, with the exception of
the roll motors. The 0.9-N motors were used for tip-off
control following separation of the inertial upper stage
(IUS), reaction wheel desaturation, roll control for all
times other than VOI, to back up any failed reaction wheels,
and for small TCMs or orbit trim maneuvers (OTMs). The 22-N
motors were used for roll control during VOI. The 445-N
motors were used for controlling the spacecraft rotational
axis during VOI, and to provide impulses during all
propulsive maneuvers. The monopropellant motors also
provided the impulses needed to trim the VOI maneuver. The
command, data and data storage (CDDS) system is responsible
for receiving uplink commands via the radio frequency
subsystem (RFS) and controlling the spacecraft in response
to those commands. It is also responsible for controlling
the acquisition and storage of scientific data and sending
that data, along with supplemental engineering data, to the
RFS for downlink transmission to Earth. The commands are
sent to the spacecraft as time-event pairs for storage and
later execution, and also in the form of blocks which the
CDDS later expands into spacecraft executable commands. In
the Venus orbit phase, commands for up to three days of
radar operations are stored. The provision also exists to
receive and execute discrete commands sent up from the
ground. Engineering data is nominally transmitted to Earth
over a real-time S-band link. During those times when
real-time link is not possible, the data is tape recorded
and played back via the X-band high-rate link. The SAR data
are nominally stored on two multi-track digital tape records
(DTRs) for later playback over the high-rate X-band link.
There is no provision for real-time transmission of the SAR
data. Data storage capacity of the two DTRs is approximately
1.8 billion bits. These DTRs are primarily used for
recording SAR data, although low- rate engineering data can
be stored on these devices, interleaved with the SAR data,
during times when those data cannot be transmitted to Earth
over a real-time link. The recorded data stream will
alternately be switched between these two DTRs so that the
data will not be lost during the DTR track change. The
Magellan telecommunications subsystem contains all the
hardware necessary to maintain communications between Earth
and the spacecraft. The subsystem contains the radio
frequency subsystem, the LGA, MGA, and HGA. The RFS performs
the functions of carrier transponding, command detection and
decoding, and telemetry modulation. The spacecraft is
capable of simultaneous X-band and S- band uplink and
downlink operations. The S-band operates at a transmitter
power of 5 W, while the X-band operates at a power of 22 W.
Uplink data rates are 31.25 and 62.5 bps (bits per second)
with downlink data rates of 40 bps (emergency only), 1200
bps (real-time engineering rate), 115.2 kbps (kilobits per
second) (radar downlink backup), and 268.8 kbps (nominal).
Platform Descriptions
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Platform SPACECRAFT
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The radar system is mounted onto the spacecraft.
Reference
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Journal: JOURNAL OF GEOPHYSICAL RESEARCH
Publication Date: 1990-06-10
Reference Key ID: SAUNDERSETAL1990
Authors
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GORDON H. PETTENGILL
LESLIE J. PIERI
R. STEPHEN SAUNDERS
RAYMOND E. ARVIDSON
W. L. SJOGREN
WILLIAM T. K. JOHNSON
Citation
--------
Saunders, R.S., G.H. Pettengill, R.E. Arvidson, W.L.
Sjogren, W.T.K. Johnson, L. Pieri, The Magellan Venus Radar
Mapping Mission, Journal of Geophysical Research, 1990, Vol
95, pp. 8339-8335
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