Magellan Probe
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The ''Magellan'' spacecraft was a
robotic Robotics is an interdisciplinarity, interdisciplinary branch of computer science and engineering. Robotics involves design, construction, operation, and use of robots. The goal of robotics is to design machines that can help and assist human ...
space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; or ent ...
launched by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
of the United States, on May 4, 1989, to map the surface of
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
by using
synthetic-aperture radar Synthetic-aperture radar (SAR) is a form of radar that is used to create two-dimensional images or three-dimensional reconstructions of objects, such as landscapes. SAR uses the motion of the radar antenna over a target region to provide fine ...
and to measure the planetary
gravitational field In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenome ...
. The ''Magellan'' probe was the first interplanetary mission to be launched from the
Space Shuttle The Space Shuttle is a retired, partially 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. Its official program na ...
, the first one to use the
Inertial Upper Stage The Inertial Upper Stage (IUS), originally designated the Interim Upper Stage, was a two-stage, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for raising payloads from low Earth orbit to h ...
booster, and the first spacecraft to test
aerobraking Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the atmosphere at the low point of the orbit (periapsis). The resulting drag slows the spacecraft. Aerobraking is ...
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 Venus Orbiting Imaging Radar (VOIR; also called Venus Orbital Imaging Radar) was a planned 1983 U.S. spacecraft mission to Venus that was primarily intended to use a microwave imaging radar to perform mapping of the Venusian surface. The goal was t ...
'' (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 ( or ; pt, Fernão de Magalhães, ; es, link=no, Fernando de Magallanes, ; 4 February 1480 – 27 April 1521) was a Portuguese explorer. He is best known for having planned and led the 1519 Spanish expedition to the East ...
, 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 1.0 km per line pair. (''primary'') * Obtain a near-global topographic map with 50 km spatial and 100 m vertical resolution. * Obtain near-global gravity field data with 700 km 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 Company, and the
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
(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 Hughes Tool Company. The company was known for producing, among other produ ...
'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 Flight or flying is the process by which an object moves through a space without contacting any planetary surface, either within an atmosphere (i.e. air flight or aviation) or through the vacuum of outer space (i.e. spaceflight). This can be a ...
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 road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
, 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 Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...
(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 toxic unless handled in solution as, for example, hydrazine ...
thrusters fed from a single 71 cm (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 and angular velocity. It is a spinning wheel or disc in which the axis of rotat ...
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 which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance ...
left over from the
Voyager Program The Voyager program is an American scientific program that employs two robotic interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to Flyby (spacef ...
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 LC-36B at Cape Canaveral Air ...
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 American spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that suppo ...
, 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 conventional ...
and transmit data at 268.8 kilobits/second in the
X-band The X band is the designation for a band of 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 rather indefinitely set at approxim ...
.


Power

''Magellan'' was powered by two square
solar arrays A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and c ...
, 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 The COSMAC (Complementary Symmetry Monolithic Array Computer) is an 8-bit microprocessor family introduced by RCA. It is historically notable as the first CMOS microprocessor. The first production model was the two-chip CDP1801R and CDP1801U, w ...
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.http://www2.jpl.nasa.gov/magellan/guide4.html#4.11 The Magellan Venus Explorer's Guide, Chapter 4 – The Magellan Spacecraft – Computing and Software 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 o ...
of data until contact with the Earth was restored and the tapes were played back.


Scientific instruments

Thick and opaque, the atmosphere of Venus required a method beyond optical survey, to map the surface of the planet. The resolution of conventional
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
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 (, ; ar, نظير, naẓīr, counterpart) 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 direc ...
, emitted thousands of
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
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 In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, a ...
. 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.


Other science

In addition to the radar data, Magellan collected several other types of scientific measurements. These included detailed measurements of the Venus gravitational field, measurements of the atmospheric density, and radio occultation data on the atmospheric profile.


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 at Kennedy Space Center.jpg, alt=Magellan with its Star 48B solid rocket motor undergoing final checks at the Kennedy Space Center, ''Magellan'' with its
Star 48B The Star 48 is the largest of a family of solid rocket motors used by many space propulsion and launch vehicle stages. It is used almost exclusively as an upper stage. It was developed primarily by Thiokol Propulsion and is now, after several m ...
solid rocket motor undergoing final checks at the Kennedy Space Center 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 civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding th ...
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 National Aeronautics and Space Administration's (NASA) ten field centers. Since December 1968 ...
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 two-stage, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for raising payloads from low Earth orbit to h ...
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 i ...
where it would circle the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
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 two-stage, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for raising payloads from low Earth orbit to h ...
. 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 two-stage, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for raising payloads from low Earth orbit to h ...
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 (astronomy), primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two ...
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. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...
. During each orbit, the space probe captured radar data while the spacecraft was closest to the surface, and then transmit 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 image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...
. 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 Gula Mons is a volcano in western Eistla Regio on Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to ...
reprojected in 3D from stereo data File:Venus - 3D Perspective View of Maat Mons.jpg, alt=Reprojection of Maat Mons, Reprojection of
Maat Mons Maat Mons is a massive shield volcano on the planet Venus and the planet's second-highest mountain and highest volcano. It rises above the mean planetary radius at , and nearly 5 km above the surrounding plains. It is named after the Egyp ...
, with
vertical exaggeration Vertical exaggeration (VE) is a scale that is used in raised-relief maps, plans and technical drawings (cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section ...
File:Venus dome 3D.jpg, alt=Volcanic dome observed from reprojecting stereo data, Volcanic dome in
Alpha Regio Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , which ...
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 American spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that suppo ...
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 or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...
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 Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the atmosphere at the low point of the orbit (periapsis). The resulting drag slows the spacecraft. Aerobraking is ...
. 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
aeroshell An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spacecraft vehicle from pressure, heat, and possible debris created by drag during atmospheric entry (see blunt body theory). Its main components consist of a heat ...
s 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 The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of Supercritical carbon dioxide, supercritical carbon dioxide and is much denser and hotter than atmosphere of Earth, that of Earth. The temperature at the ...
. 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 or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called ...
, 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 (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...
- 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. ''Magellan'''s global radar map currently remains as the most detailed Venus map in existence, although the upcoming NASA
VERITAS Veritas is the name given to the Roman virtue of Honesty, truthfulness, which was considered one of the main virtues any good Roman should possess. The Greek goddess of truth is Aletheia (Ancient Greek language, Ancient Greek: ). The German phi ...
and
Roskosmos The State Space Corporation "Roscosmos" (russian: Государственная корпорация по космической деятельности «Роскосмос»), commonly known simply as Roscosmos (russian: Роскосмос) ...
Venera-D Venera-D (russian: Венера-Д, ) is a proposed Russian space mission to Venus that would include an orbiter and a lander to be launched in 2029. The orbiter's prime objective is to perform observations with the use of a radar. The lander, ba ...
probes will carry a radar that can achieve a much higher resolution compared to the radar used by ''Magellan''. Both probes are expected to launch in 2029. File:Maxwell Montes of planet Venus.jpg, alt=Maxwell Montes, highest point on Venus,
Maxwell Montes Maxwell Montes is a mountain massif on the planet Venus, of which a peak ( Skadi Mons) is the highest point on the planet's surface. General description Located on Ishtar Terra, the more northern of the planet's two major highlands, Maxwell ...
, highest point on
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
File:Bahet and Onatah Coronae PIA00461 scaled down.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. Aphrod ...
, a rugged landscape File:Addams crater on Venus.jpg, alt=Addams crater,
Addams Addams is a patronymic surname of English people, English origin from the given name Adam (name), Adam. There are other spellings. Notable people with the surname include: *Calpernia Addams (born 1971), American transgender author, actress, and act ...
crater File:Alpha Regio.jpg, alt=Pancake domes visible in Alpha Regio, Pancake domes visible in
Alpha Regio Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , which ...
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 Sedna Planitia is a large lowland area of Venus, south of Ishtar Terra. It is thought to be lava-covered and similar to a lunar mare The lunar maria (; singular: mare ) are large, dark, basaltic plains on Earth's Moon, formed by ancient aster ...
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 Isabella may refer to: People and fictional characters * Isabella (given name), including a list of people and fictional characters * Isabella (surname), including a list of people Places United States * Isabella, Alabama, an unincorpor ...
crater


Scientists

The
Magellan Ferdinand Magellan ( or ; pt, Fernão de Magalhães, ; es, link=no, Fernando de Magallanes, ; 4 February 1480 – 27 April 1521) was a Portuguese explorer. He is best known for having planned and led the 1519 Spanish expedition to the East ...
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 The ''Magellan'' spacecraft was a robotic space probe launched by NASA of the United States, on May 4, 1989, to map the surface of Venus by using synthetic-aperture radar and to measure the planetary gravitational field. The ''Magellan'' p ...
. 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 is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...
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 Prime Minister of the United Kingdom from 1979 to 1990 and Leader of the Conservative Party (UK), Leader of the Conservative Party from 1975 to 1990. S ...
. 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 The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of Supercritical carbon dioxide, supercritical carbon dioxide and is much denser and hotter than atmosphere of Earth, that of Earth. The temperature at the ...
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 126 degrees Celsius. 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. Atmospheric radio occultation Atmospheric radio occultation relies on the detection of a change in a radio ...
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 There have been 46 (including gravity-assist flybys) space missions to the planet Venus. Missions to Venus constitute part of the exploration of Venus. List As of 2020, the Soviet Union, United States, European Space Agency and Japan have con ...
*
Venus Express ''Venus Express'' (VEX) was the first Venus exploration mission of the European Space Agency (ESA). Launched in November 2005, it arrived at Venus in April 2006 and began continuously sending back science data from its polar orbit around Venus. ...
*
Venera 15 Venera 15 (russian: Венера-15 meaning ''Venus 15'') was a spacecraft sent to Venus by the Soviet Union. This uncrewed orbiter was to map the surface of Venus using high resolution imaging systems. The spacecraft was identical to Venera 16 ...
*
Venera 16 Venera 16 (russian: Венера-16 meaning ''Venus 16'') was a spacecraft sent to Venus by the Soviet Union. This uncrewed orbiter was to map the surface of Venus using high resolution imaging systems. The spacecraft was identical to Venera 1 ...


References


External links


''Magellan'' homepage''Magellan'' Mission Profile
b
NASA's Solar System Exploration
*https://web.archive.org/web/20070126122448/http://library.thinkquest.org/J0112188/magellan_probe.htm
NASA Space Science Data Coordinated Archive
{{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