Magellan (spacecraft)

The Magellan spacecraft, also referred to as the Venus Radar Mapper, was a 1,035-kilogram (2,282 lb) 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 probe was the first interplanetary mission to be launched from the Space Shuttle, the first one to use the Inertial Upper Stage booster for launching, 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.

Magellan
Magellan - artist depiction
Artist's depiction of Magellan at Venus
Mission typeVenus orbiter
OperatorNASA / JPL
COSPAR ID1989-033B
SATCAT no.19969
Websitewww2.jpl.nasa.gov/magellan/
Mission duration4 years, 5 months, 8 days, 13 hours, 18 minutes
Spacecraft properties
ManufacturerMartin Marietta
Hughes Aircraft
Launch mass3,449 kilograms (7,604 lb)
Dry mass1,035 kilograms (2,282 lb)
Powerabout 1,030 watt
Start of mission
Launch dateMay 4, 1989, 18:47:00 UTC
RocketSpace Shuttle Atlantis
STS-30 / IUS
Launch siteKennedy LC-39B
End of mission
DisposalControlled entry into Venus
Decay dateOctober 13, 1994, 10:05:00 UTC
Orbital parameters
Reference systemCytherocentric
Semi-major axis4,028.5 kilometers (2,503.2 mi)
Eccentricity0.39177
Pericytherion295 kilometers (183 mi)
Apocytherion7,762 kilometers (4,823 mi)
Inclination85.5°
Period3.26 hours
Venus orbiter
Orbital insertionAugust 10, 1990, 17:00:00 UTC
Mgnlogo3 small

Legacy insignia for the Magellan mission, commemorating the deorbit of the spacecraft in 1994.  

History

Beginning in the late 1970s, scientists pushed 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, known for his exploration, mapping, and circumnavigation of the Earth.[1][2][3]

The objectives of the mission included:[4]

  • 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

Magellan - spacecraft bus
The spacecraft bus that formed the main body of Magellan

The spacecraft was designed and built by the Martin Marietta Company,[5] and the Jet Propulsion Laboratory (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.[1]

To save costs, most of the Magellan probe was made up of spare parts from various missions, including the Voyager program, Galileo, Ulysses, and Mariner 9. The main body of the spacecraft, a spare one from the Voyager missions, was a 10-sided aluminum bus, 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 1,035 kilograms and carried 2,414 kilograms of propellant for a total mass of 3,449 kilograms.[2][6]

Attitude control and propulsion

Magellan - attitude and propulsion
Thrusters, Star 48 booster and the internal components of the Forward Equipment Module

The spacecraft's attitude control (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 ~89,000 Newton (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 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 and a star scanner.[2][3][6][7]

Communications

Magellan - antennas
Positions of the three antennas

For communications, the spacecraft included a lightweight graphite/aluminum, 3.7-meter high-gain antenna left over from the Voyager Program and a medium-gain antenna spare from the Mariner 9 mission. A low-gain antenna attached to the high-gain antenna, was also included for contingencies. When communicating with the Deep Space Network, the spacecraft was able to simultaneously receive commands at 1.2 kilobits/second in the S-band and transmit data at 268.8 kilobits/second in the X-band.[2][3][6][7]

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.[2][6]

Computers and data processing

The computing system on the spacecraft, partially modified equipment from the Galileo, included two ATAC-16 computers, as 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.[8]

For storing the commands and recorded data, the spacecraft also included two multitrack digital tape recorders, able to store up to 225 megabytes of data until contact with the Earth was restored and the tapes were played back.[2][6][7]

Scientific instruments

Magellan - diagram of atimetry and SAR data gathering
Orientation while collecting data
Magellan - data gathering diagram
Orbital path for collecting RDRS data
Magellan - imagery for VRM and from past missions
Comparison to previous missions

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 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.[9][10]

The Magellan high-gain parabolic antenna, oriented 28°–78° to the right or left of nadir, emitted thousands of microwave pulses 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.[9][10][11]

Radar System (RDRS)
Magellan - radar electronics

Magellan - burst rate diagram - orig
The Radar System functioned in three modes: synthetic aperture radar (SAR), altimetry (ALT), and radiometry (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 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 pulses every second through the high-gain antenna, while measuring the doppler shift 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 to be processed into usable images, by the Radar Data Processing Subsystem (RDPS), a collection of ground computers operated by JPL.[9][12][13][14]

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,[15] measurements of the atmospheric density, and radio occultation data on the atmospheric profile.

Gallery

Magellan diagramm

Annotated diagram of Magellan

Magellan - Magellan Spacecraft in Preflight Checkout at Kennedy Space Center

Magellan during pre-flight checkout

Magellan at Kennedy Space Center

Magellan with its Star 48B solid rocket motor undergoing final checks at the Kennedy Space Center

Magellan Preparations

Magellan being fixed into position inside the payload bay of Atlantis prior to launch

Mission profile

STS-30 launch

Launch of STS-30 on May 4, 1989

Magellan deploy

Deployment of Magellan with Inertial Upper Stage booster

Magellan - trajectory

Trajectory of Magellan to Venus

Magellan - cycle 3 map - 1299006020759454362.039599

Map of the stereo imaging collected by Magellan during cycle 3

GulaMons SifMons northeast

Eistla Regio featuring Gula Mons reprojected in 3D from stereo data

Venus - 3D Perspective View of Maat Mons

Reprojection of Maat Mons, with vertical exaggeration

Venus dome 3D

Volcanic dome in Alpha Regio observed from reprojecting stereo data

Maxwell Montes of planet Venus

Maxwell Montes, highest point on Venus

Bahet and Onatah Coronae PIA00461 scaled down

Volcanoes as seen in the Fortuna region of Venus

Aphrodite Terra on Venus

Aphrodite Terra, a rugged landscape

Addams crater on Venus

Addams crater

Alpha Regio

Pancake domes visible in Alpha Regio

Mgn f45n019 1

A meandering lava channel from Fortuna Tessera to Sedna Planitia

Venusvulkan Tick-Typ

An unusual volcanic edifice in the Eistla region

Isabella Crater PIA00480

175-kilometer Isabella crater

Magellan to Venus
Magellan orbit
Artistic depiction of the orbiter cycle
Magellan - mapping phase
Diagram of the mapping cycle
Magellan - geometry of the orbit
Mapping cycles
The highly elliptical orbit of Magellan allowed the high-gain antenna to be used for radar data and communicating with Earth
Magellan - mapping phase
Magellan - geometry of the orbit
Magellan - cycle 1 map - 1298972763463430062.580622
Mosaic of the "left-looking" data collected during cycle 1
Magellan - cycle 2 map - 1299005988110004007.109767
Mosaic of the "right-looking" data collected during cycle 2
Rendered animation of Venus rotating using data gathered by Magellan
Magellan Venus globes
Five global views of Venus by Magellan
Magellan - end of mission poster - mgnlogo2
A poster designed for the Magellan end of mission
1994 in science

The year 1994 in science and technology involved many significant events, listed below.

7336 Saunders

7336 Saunders, provisional designation 1989 RS1, is a stony asteroid and near-Earth object of the Amor group, approximately 0.5 kilometers in diameter.

The asteroid was discovered on 6 September 1989, by American astronomer Eleanor Helin at Palomar Observatory in California, United States. It was named for JPL-project scientist R. Stephen Saunders.

Asteria Regio

Asteria Regio is a region on the planet Venus. It is bordered on the southeast by Phoebe Regio. It is located in the Hecate Chasma (v28) quadrangle.

Cleopatra (crater)

Cleopatra, initially called Cleopatra Patera, is an impact crater on Venus, in Maxwell Montes.

Cleopatra is a double-ring impact basin about 100 kilometers (62 mi) in diameter and 2.5 kilometers (1.6 mi) deep. A steep-walled, winding channel a few kilometers wide (Anuket Vallis) breaks through the rough terrain surrounding the crater rim. A large amount of lava originating in Cleopatra flowed through this channel and filled valleys in Fortuna Tessera. Cleopatra is superimposed on the structures of Maxwell Montes and appears to be undeformed, indicating that Cleopatra is relatively young. The crater is named after Egyptian queen Cleopatra VII.

Danilova (crater)

Maria Danilova, Russian ballet dancer, (b. 1793) is honored by the impact crater Danilova on Venus.

Devana Chasma

Devana Chasma is a weak extensional rift zone on Venus, with a length of 4000 km, a width of 150–250 km, and a depth reaching 5 km. Most of the faults are facing north-south. The rift is located in Beta Regio, a 3000 km rise created by volcanic activity. Mantle plumes rising from the bottom are the reason behind the formation of the rift zone. The slow extension rates in the rift may be driven by the same reason.

Ganis Chasma

Ganis Chasma is a group of rift zones on the surface of the planet Venus. Bright spots detected by the Venus Monitoring Camera on the European Space Agency's Venus Express in the area suggest that there may be active volcanism on Venus.

Geodynamics of Venus

NASA's Magellan spacecraft mission discovered that Venus has a geologically young surface with a relatively uniform age of 500±200 Ma (million years). The age of Venus was revealed by the observation of over 900 impact craters on the surface of the planet. These impact craters are nearly uniformly distributed over the surface of Venus and less than 10% have been modified by plains of volcanism or deformation. These observations indicate that a catastrophic resurfacing event took place on Venus around 500 Ma, and was followed by a dramatic decline in resurfacing rate. The radar images from the Magellan missions revealed that the terrestrial style of plate tectonics is not active on Venus and the surface appears to be immobile at the present time. Despite these surface observations, there are numerous surface features that indicate an actively convecting interior. The Soviet Venera landings revealed that the surface of Venus is essentially basaltic in composition based on geochemical measurements and morphology of volcanic flows. The surface of Venus is dominated by patterns of basaltic volcanism, and by compressional and extensional tectonic deformation, such as the highly deformed tesserae terrain and the pancake like volcano-tectonic features known as coronae. The planet's surface can be broadly characterized by its low lying plains, which cover about 80% of the surface, 'continental' plateaus and volcanic swells. There is also an abundance of small and large shield volcanoes distributed over the planet's surface. Based on its surface features, it appears that Venus is tectonically and convectively alive but has a lithosphere that is static.

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. The combined company became a leader in chemicals, aerospace, and electronics. In 1995, it merged with Lockheed Corporation to form Lockheed Martin.

October 12

October 12 is the 285th day of the year (286th in leap years) in the Gregorian calendar. 80 days remain until the end of the year.

Outline of Venus

The following outline is provided as an overview of and topical guide to Venus:

Venus – second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period (243 days) of any planet in the Solar System and rotates in the opposite direction to most other planets. It has no natural satellite. It is named after the Roman goddess of love and beauty. It is the second-brightest natural object in the night sky after the Moon, reaching an apparent magnitude of −4.6, bright enough to cast shadows. Because Venus orbits within Earth's orbit it is an inferior planet. Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun, and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 92 times that of Earth, or roughly the pressure found 900 m (3,000 ft) underwater on Earth.

Phoebe Regio

Phoebe Regio is a regio on the planet Venus. It lies to the southeast of Asteria Regio. It is 2,852 kilometres (1,772 mi) in diameter and is the principal feature of the V41 quadrangle, to which it gave its name. Four Soviet landers, Venera 11, Venera 12, Venera 13 and Venera 14, landed on the eastern side of Phoebe Regio and performed various scientific measurements.

Ruth (Venusian crater)

Ruth is an impact crater on Venus. The crater, based on data provided by the Magellan spacecraft, has an estimated diameter of 18.5 kilometres (11.5 mi) and an elevation of 6,051.365 kilometres (3,760.144 mi).

STS-30

STS-30 was the 29th NASA Space Shuttle mission and the fourth mission for Space Shuttle Atlantis. It was the fourth shuttle launch since the Challenger Disaster and the first shuttle mission since the disaster to have a female astronaut on board. The mission launched from Kennedy Space Center, Florida, on 4 May 1989, and landed four days later on 8 May. During the mission, Atlantis deployed the Venus-bound Magellan probe into orbit.

STS-34

STS-34 was a NASA Space Shuttle mission using Atlantis. It was the 31st shuttle mission overall, and the fifth flight for Atlantis. STS-34 launched from Kennedy Space Center, Florida, on 18 October 1989, and landed at Edwards Air Force Base, California, on 23 October. During the mission, the Jupiter-bound Galileo probe was deployed into space.

Scalloped margin dome

A scalloped margin dome is a type of volcanic dome, found on Venus, that has experienced collapse and mass wasting such as landslides on its perimeter. The margins of these domes have arcuate headscarps or 'scallops' separated by ridges that are a consequence of adjoining scallops. Sometimes debris or slumping can be found at the bottom of these scarps or scattered many tens of kilometers away. Many examples show no debris at all. The center of these domes is often, but not always, a depression. There is another theory that the radial ridges of scalloped margin domes are volcanic dikes.

During the first month of data from the Magellan spacecraft, the first of these features was found to the northeast of Alpha Regio, on Venus. It was one of the largest of these domes and therefore stood out. The strange feature was originally dubbed by the Magellan Project Science Team The Tick, because the many radiating ridges resembled the legs of a tick. Its concavity was likely confused as domelike as a tick's body, instead of the actuality which is that it is a bowl-shaped depression. Through the first year of Magellan image data The Tick was thought to be a unique feature until an aide to the science team catalogued inconspicuous similar features all over Venus. This resulted in referring to the features as 'ticks' which was later changed to 'scalloped margin domes'.

Yvonne Cagle

Yvonne Darlene Cagle (born April 24, 1959) is an American astronaut and Manager.

  Begin Venus primary mission operations

Time Event  

1990-08-10
Venus orbital insertion maneuver.
1990-09-15
Begin mapping cycle 1
1991-05-15
Phase stop
  Begin Venus extended mission operations

Time Event  

1991-05-16
Begin mapping cycle 2
1992-01-24
Begin mapping cycle 3
1992-09-14
Begin mapping cycle 4
1993-05-26
Begin testing aerobraking maneuver to place Magellan into an almost circular orbit.
1993-08-16
Begin mapping cycle 5
1994-04-16
Begin mapping cycle 6
1994-04-16
Begin "Windmill" experiment
1994-10-12
Phase stop
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