Mariner 10. The last of Mariners
Artist's rendering of NASA's Mariner 10 spacecraft. Credit: NASA/JPL-Caltech
In 1969, NASA approved a plan to send a spacecraft to Mercury in 1973, using Venus for a gravity assist. The mission, managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California, became Mariner 10. It was the last in the highly successful Mariner series of planetary spacecraft that revealed many secrets about the inner solar system. Using gravity assist, a technique theorized for decades but never used before, under favorable conditions a spacecraft sent to one planet can use that planet’s gravitational force to essentially slingshot on to its next target. The method saved the cost of additional fuel and a larger rocket that would be necessary to launch the heavier spacecraft as well as time to get to the ultimate destination.
Mariner 10 was the first spacecraft to use this technique to reach another planet. Its orbit was determined by Italian scientist Giuseppe "Bepi" Colombo (1920–1984). The gravity assist at Venus flyby put the spacecraft into an orbit that repeatedly brought it back to Mercury every 176 days, exactly twice the time it takes the planet to orbit around the Sun. The only downside to this timing was that Mercury’s rotation period is in a 3:2 resonance with its period of revolution around the Sun, meaning that every time Mariner 10 returned to the planet, Mercury presented the same sunlit hemisphere for observation.
Mariner 10 was the first spacecraft to visit Mercury and the first to perform flybys of two planets. It was also the first mission to return to its target after an initial encounter and the first to use the solar wind as a major means of spacecraft orientation during flight. It flew by Venus and then three times by Mercury and returned the first-ever close-up images of these planets.
Mariner 10 was the first spacecraft to use this technique to reach another planet. Its orbit was determined by Italian scientist Giuseppe "Bepi" Colombo (1920–1984). The gravity assist at Venus flyby put the spacecraft into an orbit that repeatedly brought it back to Mercury every 176 days, exactly twice the time it takes the planet to orbit around the Sun. The only downside to this timing was that Mercury’s rotation period is in a 3:2 resonance with its period of revolution around the Sun, meaning that every time Mariner 10 returned to the planet, Mercury presented the same sunlit hemisphere for observation.
Mariner 10 was the first spacecraft to visit Mercury and the first to perform flybys of two planets. It was also the first mission to return to its target after an initial encounter and the first to use the solar wind as a major means of spacecraft orientation during flight. It flew by Venus and then three times by Mercury and returned the first-ever close-up images of these planets.
Artists' impression of the Mariner 10 mission. Credit: NASA/JPL-Caltech
The primary scientific objectives of the mission were to measure Mercury's environment, atmosphere, surface, and body characteristics and to make similar investigations of Venus. Secondary objectives were to perform experiments in the interplanetary medium and to obtain experience with a dual-planet gravity-assist mission.
The spacecraft structure was an eight-sided forger magnesium framework with eight electronics compartments. It measured 1.39 m diagonally and 0.457 m in depth. Two solar panels, each 2.69 m long and 0.97 m wide, were attached at the top, supporting 5.1 sq m of solar cell area. Fully deployed the spacecraft measured 8.0 m across the solar panels and 3.7 m from the top of the low-gain antenna to the bottom of the heat shield. A scan platform with two degrees of freedom was mounted on the anti-sunward face. A 5.8 m long hinged magnetometer boom extended from one of the octagonal sides of the body. Total launch mass was 502.9 kg, of this 29 kg were propellant and attitude control gas. The total mass of instruments onboard was 79.4 kg.
The rocket engine was a 222-N liquid monopropellant hydrazine motor situated below a spherical propellant tank which was mounted in the center of the framework. The nozzle protruded through a sunshade. Two sets of three pairs of orthogonal reaction nitrogen gas jets, mounted on the tips of the solar panels, were used to stabilize the spacecraft on three axes. Command and control were the responsibility of an on-board computer with a 512-word memory augmented by ground commands.
Mariner 10 carried a motor driven high-gain dish antenna, a 1.37 m diameter aluminum honeycomb-disk parabolic reflector, which was mounted on a boom on the side of the spacecraft. A low-gain omnidirectional antenna was mounted at the end of a 2.85 m boom extending from the anti-solar face of the spacecraft. Feeds enabled the spacecraft to transmit at S- and X-band frequencies; data could be transmitted at a maximum rate of 117.6 kilobits/s. The spacecraft carried a Canopus star tracker, located on the upper ring structure of the octagonal satellite, and acquisition Sun sensors on the tips of the solar panels. The interior of the spacecraft was insulated with multilayer thermal blankets at top and bottom. The sunshade was deployed after launch to protect the spacecraft on the solar-oriented side. Louvered sides on five of the eight electronics compartments also helped control the interior temperatures.
The spacecraft structure was an eight-sided forger magnesium framework with eight electronics compartments. It measured 1.39 m diagonally and 0.457 m in depth. Two solar panels, each 2.69 m long and 0.97 m wide, were attached at the top, supporting 5.1 sq m of solar cell area. Fully deployed the spacecraft measured 8.0 m across the solar panels and 3.7 m from the top of the low-gain antenna to the bottom of the heat shield. A scan platform with two degrees of freedom was mounted on the anti-sunward face. A 5.8 m long hinged magnetometer boom extended from one of the octagonal sides of the body. Total launch mass was 502.9 kg, of this 29 kg were propellant and attitude control gas. The total mass of instruments onboard was 79.4 kg.
The rocket engine was a 222-N liquid monopropellant hydrazine motor situated below a spherical propellant tank which was mounted in the center of the framework. The nozzle protruded through a sunshade. Two sets of three pairs of orthogonal reaction nitrogen gas jets, mounted on the tips of the solar panels, were used to stabilize the spacecraft on three axes. Command and control were the responsibility of an on-board computer with a 512-word memory augmented by ground commands.
Mariner 10 carried a motor driven high-gain dish antenna, a 1.37 m diameter aluminum honeycomb-disk parabolic reflector, which was mounted on a boom on the side of the spacecraft. A low-gain omnidirectional antenna was mounted at the end of a 2.85 m boom extending from the anti-solar face of the spacecraft. Feeds enabled the spacecraft to transmit at S- and X-band frequencies; data could be transmitted at a maximum rate of 117.6 kilobits/s. The spacecraft carried a Canopus star tracker, located on the upper ring structure of the octagonal satellite, and acquisition Sun sensors on the tips of the solar panels. The interior of the spacecraft was insulated with multilayer thermal blankets at top and bottom. The sunshade was deployed after launch to protect the spacecraft on the solar-oriented side. Louvered sides on five of the eight electronics compartments also helped control the interior temperatures.
A labeled diagram of the Dawn spacecraft. Credit: NASA/JPL-Caltech
Instruments on-board the spacecraft measured the atmospheric, surface, and physical characteristics of Mercury and Venus. Experiments included television photography, magnetic field, plasma, infrared radiometry, ultraviolet spectroscopy, and radio science detectors. An experimental X-band, high-frequency transmitter was flown for the first time on this spacecraft.
- two telescopes/cameras
- infrared radiometer
- ultraviolet airglow spectrometer
- ultraviolet occultation spectrometer
- two magnetometers
- charged particle telescope
- plasma analyzer
Photo of the Mariner 10 flight spare. Credit: National Air and Space Museum
Mariner 10 (also known as Mariner Venus Mercury 1973) was launched on November 3, 1973, at 05:45:00 UT from Launch Complex 36B at the Cape Canaveral, Florida, using an Atlas/Centaur launch vehicle (AC-34/Atlas 3D no. 5014D/Centaur D-1A). The spacecraft was placed in a parking orbit after launch for approximately 25 minutes, then placed in orbit around the Sun en route to Venus. The protective cover of the sunward-facing electrostatic analyzers did not open fully after launch, and these instruments, part of the Scanning Electrostatic Analyzer and Electron Spectrometer experiment, could not be used. It was also discovered that the heaters for the television cameras had failed, so the cameras were left on to prevent low temperatures from damaging the optics. The camera heaters started working on January 17, 1974, two months after launch.
Shortly after liftoff, a series of Earth and Moon observations were made. The spacecraft obtained photographs of the north polar region of the Moon where prior coverage was poor. A trajectory correction maneuver was made 10 days after launch. Immediately following this maneuver the star-tracker locked onto a bright flake of paint which had come off the spacecraft and lost lock on the guide star Canopus. An automated safety protocol recovered Canopus, but the problem of flaking paint recurred throughout the mission. The on-board computer also experienced unscheduled resets occasionally, which would necessitate reconfiguring the clock sequence and subsystems. Periodic problems with the high-gain antenna also occurred during the cruise.
Shortly after liftoff, a series of Earth and Moon observations were made. The spacecraft obtained photographs of the north polar region of the Moon where prior coverage was poor. A trajectory correction maneuver was made 10 days after launch. Immediately following this maneuver the star-tracker locked onto a bright flake of paint which had come off the spacecraft and lost lock on the guide star Canopus. An automated safety protocol recovered Canopus, but the problem of flaking paint recurred throughout the mission. The on-board computer also experienced unscheduled resets occasionally, which would necessitate reconfiguring the clock sequence and subsystems. Periodic problems with the high-gain antenna also occurred during the cruise.
The launch of the Atlas-Centaur carrying the Mariner 10 spacecraft on November 3, 1973. Credit: NASA
Mariner 10’s trajectory through the inner solar system. Credit: NASA
In January 1974, Mariner 10 made ultraviolet observations of comet Kohoutek and another mid-course correction was made on January 21. Extensive scientific observations of Venus took place over a period of about one week. The spacecraft passed Venus on February 5, 1974, at a closest range of 5,768 km at 17:01 UT. A total of 4,165 TV images were transmitted to Earth, many of which showed spectacular ultraviolet cloud formations and motions. This also marked the first time a spacecraft used a gravity assist from one planet to help it reach another.
En route to Mercury an attitude control anomaly occurred for the second time, using up attitude control gas. Some new procedures were used from that point on to orient the spacecraft, including Sun-line maneuvers and the use of solar wind on the solar panels to orient the spacecraft. A mid-course correction on March 16, 1974, refined the spacecraft’s trajectory for optimum science measurements during the first Mercury encounter. The first instruments were activated the next day and the first images of the planet were returned one week later.
En route to Mercury an attitude control anomaly occurred for the second time, using up attitude control gas. Some new procedures were used from that point on to orient the spacecraft, including Sun-line maneuvers and the use of solar wind on the solar panels to orient the spacecraft. A mid-course correction on March 16, 1974, refined the spacecraft’s trajectory for optimum science measurements during the first Mercury encounter. The first instruments were activated the next day and the first images of the planet were returned one week later.
Mariner 10 crossed the orbit of Mercury on March 29, 1974, at 20:46 UT, at a distance of about 704 km from the surface. The spacecraft continued to photograph the planet until April 3, by which time it had returned more than 2,000 images as well as a wealth of data from its other scientific instruments. At first glance, Mercury appeared very Moon-like with a heavily cratered surface. Other features such as scarps or cliffs present on Mercury are absent on the Moon and hint at the planet’s formation. Mercury also has mare or flat plain like features like the Moon and Mars. Somewhat surprisingly, Mariner 10’s magnetometer detected a weak (about 1/60th the strength of Earth’s) magnetic field. Radio tracking of the spacecraft’s trajectory revealed Mercury to be much closer to being a perfect sphere than Earth.
Five mid-course corrections were required to properly aim the spacecraft for its second encounter and also enable the third. A second encounter with Mercury occurred on September 21, 1974, at an altitude of 48,069 km. Some 500 new images of the planet were returned during the three-day encounter, and the greater distance of the flyby allowed scientists to create a series of hemisphere-wide mosaics of amazing detail. Unfortunately the lighted hemisphere was almost the same as the first encounter, so a large portion of the planet remained unimaged. The spacecraft’s ultraviolet spectrometer confirmed that Mercury has a very thin atmosphere composed mainly of helium.
Before the third and last Mercury encounter, Mariner 10, already running low on attitude control fuel, rolled out of communication with Earth. Controllers scrambled to get time on tracking antennas to regain control of the spacecraft and succeeded just in time for the encounter. The encounter occurred on March 16, 1975, at an altitude of 327 km, the closest to Mercury, with additional photography and magnetic field measurements. Because of the failure of a tape recorder and restrictions in the rate of data reception, only the central quarter of each of 300 high-resolution images was received during this encounter.
Five mid-course corrections were required to properly aim the spacecraft for its second encounter and also enable the third. A second encounter with Mercury occurred on September 21, 1974, at an altitude of 48,069 km. Some 500 new images of the planet were returned during the three-day encounter, and the greater distance of the flyby allowed scientists to create a series of hemisphere-wide mosaics of amazing detail. Unfortunately the lighted hemisphere was almost the same as the first encounter, so a large portion of the planet remained unimaged. The spacecraft’s ultraviolet spectrometer confirmed that Mercury has a very thin atmosphere composed mainly of helium.
Before the third and last Mercury encounter, Mariner 10, already running low on attitude control fuel, rolled out of communication with Earth. Controllers scrambled to get time on tracking antennas to regain control of the spacecraft and succeeded just in time for the encounter. The encounter occurred on March 16, 1975, at an altitude of 327 km, the closest to Mercury, with additional photography and magnetic field measurements. Because of the failure of a tape recorder and restrictions in the rate of data reception, only the central quarter of each of 300 high-resolution images was received during this encounter.
Artist's impression of Mariner 10 flyby of Mercury. Credit: NASA
Engineering tests were continued until March 24, 1975, when the supply of attitude-control gas was depleted and mission controllers sent a signal to turn the spacecraft off, terminating the mission.
Overall, Mariner 10 returned over 2,700 pictures during its three Mercury flybys that covered nearly half of the planet’s surface. Some of the images showed detail as small as 100 meters wide. Perhaps the most impressive surface feature was the Caloris basin, characterized by a set of concentric rings and ridges and about 2,500 kilometers in diameter.
Mariner 10 results showed a Hadley-type circulation existed in Venus' atmosphere and showed that Venus had at best a weak magnetic field, and the ionosphere interacted with the solar wind to form a bow shock. At Mercury, it was confirmed that Mercury had no atmosphere and a cratered, dormant Moon-like surface was shown in the images. Mercury was shown to have a small magnetic field and a relatively large iron-rich core. The total cost of the Mariner 10 mission was roughly $100 million. The mission was the last visit to Mercury by a robotic probe for more than 30 years.
Mariner 10 results showed a Hadley-type circulation existed in Venus' atmosphere and showed that Venus had at best a weak magnetic field, and the ionosphere interacted with the solar wind to form a bow shock. At Mercury, it was confirmed that Mercury had no atmosphere and a cratered, dormant Moon-like surface was shown in the images. Mercury was shown to have a small magnetic field and a relatively large iron-rich core. The total cost of the Mariner 10 mission was roughly $100 million. The mission was the last visit to Mercury by a robotic probe for more than 30 years.
Photo gallery from the mission
This mosaic of Moon's north pole composed of 22 frames acquired in orange, clear, UV, and UV-polarized wavelengths by Mariner 10. Credit: NASA/JPL/Northwestern University
The Earth and Moon were imaged by Mariner 10 from 2.6 million km while completing the first ever Earth-Moon encounter by a spacecraft capable of returning high resolution digital color image data. These images have been combined to illustrate the relative sizes of the two bodies. Credit: NASA/JPL/Northwestern University
Layers of haze above the clouds of Venus. Credit: NASA/JPL-Caltech
A false color composite image of Venus created by combining images taken using orange and ultraviolet spectral filters on the spacecraft's imaging camera. These were used for the red and blue channels of the color image, respectively, with the green channel synthesized by combining the other two images. The images used to create this view were acquired by Mariner 10 on Feb. 7 and 8, 1974, a couple of days after the spacecraft's closest approach to Venus on Feb. 5. Credit: NASA/JPL-Caltech/Kevin M. Gill
Mariner 10's first image of Mercury acquired on March 24, 1974. This picture was acquired from a distance of 5,380,000 km from the surface of Mercury. Credit: NASA/JPL/USGS
Discovery Scarp photographed by Mariner 10 during its first encounter with Mercury.
Credit: NASA/JPL/Northwestern University
Credit: NASA/JPL/Northwestern University
Mercury's south pole photographed by Mariner 10 during its second close flyby of the planet September 21, 1974.
Credit: NASA/JPL/Northwestern University
References:
Dunne, James A.; Burgess, Eric. The Voyage of Mariner 10: Mission to Venus and Mercury (NASA SP-424). National Aeronautics and Space Administration Scientific and Technical Information Office. Washington, D.C. 1978
Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. Washington, DC: NASA History Program Office, 2018. ISBN 978-1-62683-042-4
Uri, John. 45 Years Ago: Mariner 10 First to Explore Mercury. NASA, Johnson Space Center
NASA Solar System Exploration: Mariner 10
NASA.
NSSDCA: Mariner
10
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