The ''Magellan'' spacecraft was a
robotic
Robotics is the interdisciplinary study and practice of the design, construction, operation, and use of robots.
Within mechanical engineering, robotics is the design and construction of the physical structures of robots, while in computer s ...
space probe
Uncrewed spacecraft or robotic spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input, such as remote control, or remote guidance. They may also be autonomous, in which th ...
launched by
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
on May 4, 1989. Its mission objectives were to map the surface of
Venus
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...
by using
synthetic-aperture radar and to measure the planetary
gravitational field
In physics, a gravitational field or gravitational acceleration field is a vector field used to explain the influences that a body extends into the space around itself. A gravitational field is used to explain gravitational phenomena, such as ...
.
The ''Magellan'' probe was the first interplanetary mission to be launched from the
Space Shuttle
The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...
, the first one to use the
Inertial Upper Stage
The Inertial Upper Stage (IUS), originally designated the Interim Upper Stage, was a Multistage rocket, two-stage, Solid-propellant rocket, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for ...
booster, and the first spacecraft to test
aerobraking as a method for circularizing its orbit. ''Magellan'' was the fifth successful NASA mission to Venus, and it ended an eleven-year gap in U.S. interplanetary probe launches.
History
Beginning in the late 1970s, scientists advocated for a radar mapping mission to Venus. They first sought to construct a spacecraft named the ''
Venus Orbiting Imaging Radar'' (VOIR), but it became clear that the mission would be beyond the budget constraints during the ensuing years. The VOIR mission was canceled in 1982.
A simplified radar mission proposal was recommended by the Solar System Exploration Committee, and this one was submitted and accepted as the Venus Radar Mapper program in 1983. The proposal included a limited focus and a single primary scientific instrument. In 1985, the mission was renamed ''Magellan'', in honor of the sixteenth-century Portuguese explorer
Ferdinand Magellan
Ferdinand Magellan ( – 27 April 1521) was a Portuguese explorer best known for having planned and led the 1519–22 Spanish expedition to the East Indies. During this expedition, he also discovered the Strait of Magellan, allowing his fl ...
, known for his exploration, mapping, and circumnavigation of the Earth.
The objectives of the mission included:
* Obtain near-global radar images of the Venusian surface with a resolution equivalent to optical imaging of per line pair. (''primary'')
* Obtain a near-global
topographic map
In modern mapping, a topographic map or topographic sheet is a type of map characterized by large- scale detail and quantitative representation of relief features, usually using contour lines (connecting points of equal elevation), but histori ...
with spatial and vertical resolution.
* Obtain near-global
gravity field
In physics, a gravitational field or gravitational acceleration field is a vector field used to explain the influences that a body extends into the space around itself. A gravitational field is used to explain gravitational phenomena, such as ...
data with resolution and two to three
milligals of accuracy.
* Develop an understanding of the geological structure of the planet, including its density distribution and dynamics.
Spacecraft design

The spacecraft was designed and built by the
Martin Marietta
The Martin Marietta Corporation was an American company founded in 1961 through the merger of Glenn L. Martin Company and American-Marietta Corporation. In 1995, it merged with Lockheed Corporation to form Lockheed Martin.
History
Martin Marie ...
Company,
and the
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center (FFRDC) in La Cañada Flintridge, California, Crescenta Valley, United States. Founded in 1936 by Cali ...
(JPL) managed the mission for NASA. Elizabeth Beyer served as the program manager and Joseph Boyce served as the lead program scientist for the NASA headquarters. For JPL, Douglas Griffith served as the ''Magellan'' project manager and R. Stephen Saunders served as the lead project scientist.
Hughes Aircraft Company
The Hughes Aircraft Company was a major American aerospace and defense contractor founded on February 14, 1934 by Howard Hughes in Glendale, California, as a division of the Hughes Tool Company. The company produced the Hughes H-4 Hercules air ...
's Space and Communications Group designed and built the spacecraft's synthetic aperture radar.
To save costs, most of the ''Magellan'' probe was made up of
flight spare parts and reused design elements from other spacecraft:
;Reuse Type Legend:
The main body of the spacecraft, a spare one from the Voyager missions, was a 10-sided aluminum
bus
A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a motor vehicle that carries significantly more passengers than an average car or van, but fewer than the average rail transport. It is most commonly used ...
, containing the computers, data recorders, and other subsystems. The spacecraft measured 6.4 meters tall and 4.6 meters in diameter. Overall, the spacecraft weighed 3,445 kilograms.
Attitude control and propulsion

The spacecraft's
attitude control
Spacecraft attitude control is the process of controlling the orientation of a spacecraft (vehicle or satellite) with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, ...
(orientation) was designed to be three-axis stabilized, including during the firing of the
Star 48B solid rocket motor (SRM) used to place it into orbit around Venus. Prior to ''Magellan'', all spacecraft SRM firings had involved spinning spacecraft, which made control of the SRM a much easier task. In a typical spin mode, any unwanted forces related to SRM or nozzle mis-alignments are cancelled out. In the case of ''Magellan'', the spacecraft design did not lend itself to spinning, so the resulting propulsion system design had to accommodate the challenging control issues with the large Star 48B SRM. The Star 48B, containing 2,014 kg of solid propellant, developed a thrust of ~89
kN (20,000 lbf) shortly after firing; therefore, even a 0.5% SRM alignment error could generate side forces of 445 N (100 lbf). Final conservative estimates of worst-case side forces resulted in the need for eight 445 N thrusters, two in each quadrant, located out on booms at the maximum radius that the Space Shuttle Orbiter Payload Bay would accommodate (4.4-m or 14.5-ft diameter).
The actual propulsion system design consisted of a total of 24 monopropellant
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydraz ...
thrusters fed from a single 71cm (28 in) diameter titanium tank. The tank contained 133 kg (293 lb) of purified hydrazine. The design also included a pyrotechnically-isolated external high pressure tank with additional helium that could be connected to the main tank prior to the critical Venus orbit insertion burn to ensure maximum thrust from the 445 N thrusters during the SRM firing. Other hardware regarding orientation of the spacecraft consists of a set of
gyroscopes
A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining Orientation (geometry), orientation and angular velocity. It is a spinning wheel or disc in ...
and a
star scanner.
Communications

For communications, the spacecraft included a lightweight graphite/aluminum, 3.7-meter
high-gain antenna
A directional antenna or beam antenna is an antenna that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction ...
left over from the
Voyager Program
The Voyager program is an American scientific program that employs two interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable planetary alignment to explore the two gas giants Jupiter ...
and a medium-gain antenna spare from the
Mariner 9
Mariner 9 (Mariner Mars '71 / Mariner-I) was a robotic spacecraft that contributed greatly to the exploration of Mars and was part of the NASA Mariner program. Mariner 9 was launched toward Mars on May 30, 1971, from Spaceport Florida Launch Comp ...
mission. A low-gain antenna attached to the high-gain antenna was also included for contingencies. When communicating with the
Deep Space Network
The NASA Deep Space Network (DSN) is a worldwide Telecommunications network, network of spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA' ...
, the spacecraft was able to simultaneously receive commands at 1.2
kilobits/second in the
S-band
The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave band of the electromagnetic spectrum covering frequencies from 2 to 4 gigahertz (GHz). Thus it crosses the convention ...
and transmit data at 268.8 kilobits/second in the
X-band
The X band is the designation for a band of frequency, frequencies in the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is set at approximately 7.0� ...
.
Power
''Magellan'' was powered by two square
solar arrays, each measuring 2.5 meters across. Together, the arrays supplied 1,200 watts of power at the beginning of the mission. However, over the course of the mission the solar arrays gradually degraded due to frequent, extreme temperature changes. To power the spacecraft while occulted from the Sun, twin 30 amp-hour, 26-cell,
nickel-cadmium batteries were included. The batteries recharged as the spacecraft received direct sunlight.
Computers and data processing
The computing system on the spacecraft was partially modified equipment from the
''Galileo''. There were two
ATAC-16 computers forming one redundant system, located in the attitude-control subsystem, and four
RCA 1802 microprocessors, as two redundant systems, to control the command and data subsystem (CDS). The CDS was able to store commands for up to three days, and also to autonomously control the spacecraft if problems were to arise while mission operators were not in contact with the spacecraft.
For storing the commands and recorded data, the spacecraft also included two multitrack
digital tape recorders, able to store up to 225
megabytes
The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes ...
of data until contact with the Earth was restored and the tapes were played back.
Scientific instruments
Thick and opaque, the
atmosphere of Venus
The atmosphere of Venus is the very dense layer of gases surrounding the planet Venus. Venus's atmosphere is composed of 96.5% carbon dioxide and 3.5% nitrogen, with other chemical compounds present only in trace amounts. It is much denser and ho ...
required a method beyond optical survey, to map the surface of the planet. The resolution of conventional
radar
Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...
depends entirely on the size of the antenna, which is greatly restricted by costs, physical constraints by launch vehicles and the complexity of maneuvering a large apparatus to provide high resolution data. ''Magellan'' addressed this problem by using a method known as
synthetic aperture, where a large antenna is imitated by processing the information gathered by ground computers.
The ''Magellan''
high-gain parabolic antenna, oriented 28°–78° to the right or left of
nadir
The nadir is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface.
The direction opposite of the nadir is the zenith.
Et ...
, emitted thousands of
microwave
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
pulses per second that passed through the clouds and to the surface of Venus, illuminating a swath of land. The Radar System then recorded the brightness of each pulse as it reflected back off the side surfaces of rocks, cliffs, volcanoes and other geologic features, as a form of
backscatter. To increase the imaging resolution, ''Magellan'' recorded a series of data bursts for a particular location during multiple instances called, "looks". Each "look" slightly overlapped the previous, returning slightly different information for the same location, as the spacecraft moved in orbit. After transmitting the data back to Earth,
Doppler modeling was used to take the overlapping "looks" and combine them into a continuous, high resolution image of the surface.
Radar System (RDRS)


The Radar System (RDRS) functioned in three modes:
synthetic aperture radar
Synthetic-aperture radar (SAR) is a form of radar that is used to create two-dimensional images or 3D reconstruction, three-dimensional reconstructions of objects, such as landscapes. SAR uses the motion of the radar antenna over a target regi ...
(SAR),
altimetry
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water.
T ...
(ALT), and
radiometry
Radiometry is a set of techniques for measurement, measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power (physics), power in space, as opposed to phot ...
(RAD). The instrument cycled through the three modes while observing the surface geology, topography, and temperature of Venus using the 3.7-meter parabolic,
high-gain antenna
A directional antenna or beam antenna is an antenna that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction ...
and a small
fan-beam antenna, located just to the side.
– In the ''Synthetic Aperture Radar'' mode, the instrument transmitted several thousand long-wave, 12.6-centimeter
microwave
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
pulses every second through the high-gain antenna, while measuring the
doppler shift
The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...
of each hitting the surface.
– In ''Altimetry'' mode, the instrument interleaved pulses with SAR, and operating similarly with the altimetric antenna, recording information regarding the elevation of the surface on Venus.
– In ''Radiometry'' mode, the high-gain antenna was used to record microwave radiothermal emissions from Venus. This data was used to characterize the surface temperature.
The data was collected at 750 kilobits/second to the tape recorder and later transmitted to Earth (10 Bit per second * 365 *4 * 24 * 60 = 21 Mbit (maximum) = 85 Foto (maximum) ) to be processed into usable images, by the Radar Data Processing Subsystem (RDPS), a collection of ground computers operated by JPL.
The
principal investigator for this instrument was Gordon Pettengill from
MIT
The Massachusetts Institute of Technology (MIT) is a private research university in Cambridge, Massachusetts, United States. Established in 1861, MIT has played a significant role in the development of many areas of modern technology and sc ...
.
Experiments
Magellan returned data to perform three so called experiments:
* Synthetic Aperture Radar (SAR), already covered above while discussion the RDRS instrument;
* Gravimetry, consisting on detailed measurements of the Venus gravitational field,
with the principal investigator being Georges Balmino from
Centre National d'Etudes Spatiales;
* Magellan Radio Science Occultation Experiment (ROCC), consisting on measurements of the atmospheric density and radio occultation data on the atmospheric profile. The principal investigator was Jon M. Jenkins from
NASA Ames Research Center
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laborat ...
.
Gallery
File:Magellan diagramm.png, alt=Annotated diagram of Magellan, Annotated diagram of ''Magellan''
File:Magellan - Magellan Spacecraft in Preflight Checkout at Kennedy Space Center.png, alt=Magellan during pre-flight checkout, ''Magellan'' during pre-flight checkout
File:Magellan Preparations.jpg, alt=Magellan being fixed into position inside the payload bay of Atlantis prior to launch, ''Magellan'' being fixed into position inside the payload bay of ''Atlantis'' prior to launch
Mission profile
Launch and trajectory
''Magellan'' was launched on May 4, 1989, at 18:46:59 UTC by the
National Aeronautics and Space Administration
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the United States's civil space program, aeronautics research and space research. Established in 1958, it su ...
from
KSC Launch Complex 39B at the
Kennedy Space Center
The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the NASA, National Aeronautics and Space Administration's (NASA) ten NASA facilities#List of field c ...
in Florida, aboard
Space Shuttle ''Atlantis'' during mission
STS-30. Once in orbit, the ''Magellan'' and its attached
Inertial Upper Stage
The Inertial Upper Stage (IUS), originally designated the Interim Upper Stage, was a Multistage rocket, two-stage, Solid-propellant rocket, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for ...
booster were deployed from ''Atlantis'' and launched on May 5, 1989 01:06:00 UTC, sending the spacecraft into a Type IV
heliocentric orbit
A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun ...
where it would circle the
Sun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
1.5 times, before reaching Venus 15 months later on August 10, 1990.
Originally, the ''Magellan'' had been scheduled for launch in 1988 with a trajectory lasting six months. However, due to the
Space Shuttle ''Challenger'' disaster in 1986, several missions, including
''Galileo'' and ''Magellan'', were deferred until shuttle flights resumed in September 1988. ''Magellan'' was planned to be launched with a liquid-fueled,
Centaur G upper-stage booster, carried in the cargo bay of the Space Shuttle. However, the entire Centaur G program was canceled after the ''Challenger'' disaster, and the ''Magellan'' probe had to be modified to be attached to the less-powerful
Inertial Upper Stage
The Inertial Upper Stage (IUS), originally designated the Interim Upper Stage, was a Multistage rocket, two-stage, Solid-propellant rocket, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for ...
. The next best opportunity for launching occurred in October 1989.
Further complicating the launch however, was the launching of the ''Galileo'' mission to Jupiter, one that included a fly-by of Venus. Intended for launch in 1986, the pressures to ensure a launch for ''Galileo'' in 1989, mixed with a short launch-window necessitating a mid-October launch, resulted in replanning the ''Magellan'' mission. Wary of rapid shuttle launches, the decision was made to launch ''Magellan'' in May, and into an orbit that would require one year, three months, before encountering Venus.
File:STS-30 launch.jpg, alt=Launch of STS-30 on May 4, 1989, Launch of STS-30 on May 4, 1989
File:Atlantis and Magellan (3).jpg, The spacecraft in a deployment position in Atlantis' payload bay
File:Magellan deploy.jpg, alt=Deployment of Magellan with Inertial Upper Stage booster, Deployment of ''Magellan'' with Inertial Upper Stage
The Inertial Upper Stage (IUS), originally designated the Interim Upper Stage, was a Multistage rocket, two-stage, Solid-propellant rocket, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for ...
booster
File:Magellan - trajectory.png, alt=Trajectory of Magellan to Venus, Trajectory of ''Magellan'' to Venus
Orbital encounter of Venus
On August 10, 1990, ''Magellan'' encountered Venus and began the orbital insertion maneuver which placed the spacecraft into a three-hour, nine minute, elliptical orbit that brought the spacecraft 295-kilometers from the surface at about 10 degrees North during the
periapsis
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values.
Apsides perta ...
and out to 7762-kilometers during
apoapsis
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values.
Apsides perta ...
.
During each orbit, the space probe captured radar data while the spacecraft was closest to the surface, and then transmitted it back to Earth as it moved away from Venus. This maneuver required extensive use of the reaction wheels to rotate the spacecraft as it imaged the surface for 37-minutes and as it pointed toward Earth for two hours. The primary mission intended for the spacecraft to return images of at least 70 percent of the surface during one Venusian day, which lasts 243 Earth days as the planet slowly spins. To avoid overly-redundant data at the highest and lowest latitudes, the ''Magellan'' probe alternated between a ''Northern-swath'', a region designated as 90 degrees north latitude to 54 degrees south latitude, and a ''Southern-swath'', designated as 76 degrees north latitude to 68 degrees south latitude. However, due to periapsis being 10 degrees north of the equatorial line, imaging the South Pole region was unlikely.
Mapping cycle 1
*''Goal: Complete primary objective.''
*''September 15, 1990 – May 15, 1991''
The primary mission began on September 15, 1990, with the intention to provide a "left-looking" map of 70% of the Venusian surface at a minimum resolution of 1-kilometer/
pixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...
. During cycle 1, the altitude of the spacecraft varied from 2000-kilometers at the north pole, to 290-kilometers near periapsis. Upon completion during May 15, 1991, having made 1,792 orbits, ''Magellan'' had mapped approximately 83.7% of the surface with a resolution between 101 and 250-meters/pixel.
Mission extension
Mapping cycle 2
*''Goal: Image the south pole region and gaps from Cycle 1.''
*''May 15, 1991 – January 14, 1992''
Beginning immediately after the end of cycle 1, cycle 2 was intended to provide data for the existing gaps in the map collected during first cycle, including a large portion of the southern hemisphere. To do this, ''Magellan'' had to be reoriented, changing the gathering method to "right-looking". Upon completion during mid-January 1992, cycle 2 provided data for 54.5% of the surface, and combined with the previous cycle, a map containing 96% of the surface could be constructed.
Mapping cycle 3
*''Goal: Fill remaining gaps and collect stereo imagery.''
*''January 15, 1992 – September 13, 1992''
Immediately after cycle 2, cycle 3 began collecting data for stereo imagery on the surface that would later allow the ground team to construct, clear, three-dimensional renderings of the surface. Approximately 21.3% of the surface was imaged in stereo by the end of the cycle on September 13, 1992, increasing the overall coverage of the surface to 98%.
File:Magellan - cycle 3 map - 1299006020759454362.039599.jpg, alt=Mosaic of the stereo data collected during cycle 3, Map of the stereo imaging collected by ''Magellan'' during cycle 3
File:GulaMons SifMons northeast.jpg, alt=Eistla Regio featuring Gula Mons reprojected in 3D from stereo data, Eistla Regio featuring Gula Mons reprojected in 3D from stereo data
File:Venus - 3D Perspective View of Maat Mons.jpg, alt=Reprojection of Maat Mons, Reprojection of Maat Mons, with vertical exaggeration
File:Venus dome 3D.jpg, alt=Volcanic dome observed from reprojecting stereo data, Volcanic dome in Alpha Regio observed from reprojecting stereo data
Mapping cycle 4
*''Goal: Measure Venus' gravitational field.''
*''September 14, 1992 – May 23, 1993''

Upon completing cycle 3, ''Magellan'' ceased imaging the surface. Instead, beginning mid-September 1992, the ''Magellan'' maintained pointing of the high-gain antenna toward Earth where the
Deep Space Network
The NASA Deep Space Network (DSN) is a worldwide Telecommunications network, network of spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA' ...
began recording a constant stream of telemetry. This constant signal allowed the DSN to collect information on the gravitational field of Venus by monitoring the velocity of the spacecraft. Areas of higher gravitation would slightly increase the velocity of the spacecraft, registering as a
Doppler shift
The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...
in the signal. The space craft completed 1,878 orbits until completion of the cycle on May 23, 1993; a loss of data at the beginning of the cycle necessitated an additional 10 days of gravitational study.
Mapping cycle 5
*''Goal: Aerobraking to circular orbit and global gravity measurements.''
*''May 24, 1993 – August 29, 1994''
At the end of the fourth cycle in May 1993, the orbit of ''Magellan'' was circularized using a technique known as
aerobraking. The circularized orbit allowed a much higher resolution of gravimetric data to be acquired when cycle 5 began on August 3, 1993. The spacecraft performed 2,855 orbits and provided high-resolution gravimetric data for 94% of the planet, before the end of the cycle on August 29, 1994.
=Aerobraking
=
*''Goal: To enter a circular orbit''
*''May 24, 1993 – August 2, 1993''
Aerobraking had long been sought as a method for slowing the orbit of interplanetary spacecraft. Previous suggestions included the need for
aeroshells that proved too complicated and expensive for most missions. Testing a new approach to the method, a plan was devised to drop the orbit of ''Magellan'' into the outermost region of the
Venusian atmosphere. Slight friction on the spacecraft slowed the velocity over a period, slightly longer than two months, bringing the spacecraft into an approximately circular orbit with periapse altitude at 180 km and apoapse altitude at 540 km, down from an apoapse altitude at 8467 km.
The method has since been used extensively on later interplanetary missions.
Mapping cycle 6
*''Goal: Collect high-resolution gravity data and conduct radio science experiments.''
*''April 16, 1994 – October 13, 1994''
The sixth and final orbiting cycle was another extension to the two previous gravimetric studies. Toward the end of the cycle, a final experiment was conducted, known as the "Windmill" experiment to provide data on the composition of the upper atmosphere of Venus. ''Magellan'' performed 1,783 orbits before the end of the cycle on October 13, 1994, when the spacecraft entered the atmosphere and disintegrated.
=Windmill experiment
=
*''Goal: Collect data on atmospheric dynamics.''
*''September 6, 1994 – September 14, 1994''
In September 1994, the orbit of ''Magellan'' was lowered to begin the "Windmill experiment". During the experiment, the spacecraft was oriented with the solar arrays broadly perpendicular to the orbital path, where they could act as paddles as they impacted molecules of the upper-Venusian atmosphere. Countering this force, the thrusters fired to keep the spacecraft from spinning. This provided data on the basic oxygen gas-surface interaction. This was useful for understanding the impact of upper-atmospheric forces which aided in designing future Earth-orbiting satellites, and methods for aerobraking during future planetary spacecraft missions.
Results
*Study of the ''Magellan'' high-resolution global images is providing evidence to better understand
Venusian geology and the role of impacts,
volcanism
Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...
, and tectonics 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
Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
- continental drift and basin floor spreading - are not evident 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.
''Magellan'' created the first (and currently the best) near-photographic quality, high resolution radar mapping of the planet's surface features. Prior Venus missions had created low resolution radar globes of general, continent-sized formations. ''Magellan'', however, finally allowed detailed imaging and analysis of craters, hills, ridges, and other geologic formations, to a degree comparable to the visible-light photographic mapping of other planets.
File:Maxwell Montes of planet Venus.jpg, alt=Maxwell Montes, highest point on Venus, Maxwell Montes
Maxwell Montes is a mountain range on the planet Venus, of which Skadi Mons is the List of tallest mountains in the Solar System, highest.
General description
Located on Ishtar Terra, the more northern of the planet's two major highlands, Ma ...
, highest point on Venus
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...
File:Bahet and Onatah Coronae PIA00461.jpg, alt=Coronae as seen in the Fortuna region of Venus, Volcanoes as seen in the Fortuna region of Venus
File:Aphrodite Terra on Venus.jpg, alt=Aphrodite Terra, a rugged landscape, Aphrodite Terra
Aphrodite Terra is one of the three continental regions on the planet Venus, the others being Ishtar Terra and Lada Terra. It is named for Aphrodite, the Greek equivalent of the goddess Venus, and is found near the equator of the planet. Aphro ...
, a rugged landscape
File:Addams crater on Venus.jpg, alt=Addams crater, Addams Addams is a patronymic surname of English origin from the given name Adam. There are other spellings. Notable people with the surname include:
* Calpernia Addams (born 1971), American transgender author, actress, and activist
* Christian Hejnal Ad ...
crater
File:Alpha Regio.jpg, alt=Pancake domes visible in Alpha Regio, Pancake domes visible in Alpha Regio
File:Mgn f45n019 1.gif, alt=A meandering lava channel from Fortuna Tessera to Sedna Planitia, A meandering lava channel from Fortuna Tessera to Sedna Planitia
File:Venusvulkan Tick-Typ.jpg, alt=An unusual volcanic edifice in the Eistla region, An unusual volcanic edifice in the Eistla region
File:Isabella Crater PIA00480.jpg, alt=175-kilometer Isabella crater, 175-kilometer Isabella crater
Scientists
The
Magellan project was set up so that the initial images and data from the Magellan probe were only for use and study by a team of principal investigators from a variety of universities and institutions, and by the
Magellan Project Science Team. These scientists were responsible for validating the data, contributing input for spacecraft acquisition of data, and interpreting the data results for their release to the public. Data was shared with three visiting Soviet scientists (
Alexander Basilevsky, Effaim Akim and Alexander Zacharov), a first, and sensitive issue, for NASA at the time considering the
Cold War
The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...
was just coming to a close.
The Magellan Project Science room became notorious for its hanging of long thermal print strips of image data (FBIDRs) along the walls of a spacious room. This was the first form in which the imagery of the surface of Venus was seen due to the long, narrow swathes acquired by the spacecraft. Significant guests during the mission's operation included
Margaret Thatcher
Margaret Hilda Thatcher, Baroness Thatcher (; 13 October 19258 April 2013), was a British stateswoman who served as Prime Minister of the United Kingdom from 1979 to 1990 and Leader of the Conservative Party (UK), Leader of th ...
.
After the initial investigation stage Magellan's full data set was released for public consumption.
Project Science Team
The Magellan Project Science Team consisted of Dr. R. Stephen Saunders, the Project Scientist;
Dr. Ellen Stofan, the Deputy Project Scientist; research assistants Tim Parker,
Dr. Jeff Plaut, and Annette deCharon; and Project Science Aide, Gregory Michaels.
Other Magellan scientists were involved with the mission's science including
principal investigators and three visiting Soviet scientists.
End of mission

On September 9, 1994, a press release outlined the termination of the ''Magellan'' mission. Due to the degradation of the power output from the solar arrays and onboard components, and having completed all objectives successfully, the mission was to end in mid-October. The termination sequence began in late August 1994, with a series of orbital trim maneuvers which lowered the spacecraft into the outermost layers of the
Venusian atmosphere to allow the Windmill experiment to begin on September 6, 1994. The experiment lasted for two weeks and was followed by subsequent orbital trim maneuvers, further lowering the altitude of the spacecraft for the final termination phase.
On October 11, 1994, moving at a velocity of 7 kilometers/second, the final orbital trim maneuver was performed, placing the spacecraft 139.7 kilometers above the surface, well within the atmosphere. At this altitude the spacecraft encountered sufficient ram pressure to raise temperatures on the solar arrays to .
On October 13, 1994 at 10:05:00 UTC, communication was lost when the spacecraft entered
radio occultation
Radio occultation (RO) is a remote sensing technique used for measuring the physical properties of a planetary atmosphere or ring system. Satellites carrying onboard GNSS-Radio occultation instruments include CHAMP, GRACE and GRACE-FO, MetOp an ...
behind Venus. The team continued to listen for another signal from the spacecraft until 18:00:00 UTC, when the mission was determined to have concluded. Although much of ''Magellan'' was expected to vaporize due to atmospheric stresses, some amount of wreckage is thought have hit the surface by 20:00:00 UTC.
Communication with the ''Magellan'' spacecraft was lost early Wednesday morning, following an aggressive series of five Orbit Trim Maneuvers (OTMs) on Tuesday, October 11, which took the orbit down into the upper atmosphere of Venus. The Termination experiment (extension of September "Windmill" experiment) design was expected to result in final loss of the spacecraft due to a negative power margin. This was not a problem since spacecraft power would have been too low to sustain operations in the next few weeks due to continuing solar cell loss.
Thus, a final controlled experiment was designed to maximize mission return. This final, low altitude was necessary to study the effects of a carbon dioxide atmosphere.
The final OTM took the periapsis to where the sensible drag on the spacecraft was very evident. The solar panel temperatures rose to 126 deg. C. and the attitude control system fired all available Y-axis thrusters to counteract the torques. However, attitude control was maintained to the end.
The main bus voltage dropped to 24.7 volts after five orbits, and it was predicted that attitude control would be lost if the power dropped below 24 volts. It was decided to enhance the Windmill experiment by changing the panel angles for the remaining orbits. This was also a preplanned experiment option.
At this point, the spacecraft was expected to survive only two orbits.
''Magellan'' continued to maintain communication for three more orbits, even though the power continued to drop below 23 volts and eventually reached 20.4 volts. At this time, one battery went off-line, and the spacecraft was defined as power starved.
Communication was lost at 3:02 am PDT just as ''Magellan'' was about to enter an Earth occultation on orbit 15032. Contact was not re-established. Tracking operations were continued to 11:00 am but no signal was seen, and none was expected. The spacecraft should land on Venus by 1:00 pm PDT Thursday, October 13, 1994.
See also
*
List of missions to Venus
*
Venus Express
*
Venera 15
*
Venera 16
References
External links
''Magellan'' homepage''Magellan'' Mission Profileby NASA's Solar System Exploration
NASA Space Science Data Coordinated Archive*Radar System (RDRS) data
{{DEFAULTSORT:Magellan (Spacecraft)
Missions to Venus
NASA space probes
Destroyed space probes
Orbiters (space probe)
Spacecraft launched by the Space Shuttle
Spacecraft launched in 1989
Space radars
Space synthetic aperture radar
Space radar altimeters
Articles containing video clips