Artist's impression of the Mariner 10 mission
|Mission type||Planetary exploration|
|Operator||NASA / JPL|
|Mission duration||1 year, 4 months, 12 days|
|Manufacturer||Jet Propulsion Laboratory|
|Launch mass||502.9 kilograms (1,109 lb)|
|Power||820 watts (at Venus encounter)|
|Start of mission|
|Launch date||November 3, 1973, 05:45:00UTC|
|Rocket||Atlas SLV-3D Centaur-D1A|
|Launch site||Cape Canaveral LC-36B|
|End of mission|
|Deactivated||March 24, 1975|
|Flyby of Venus|
|Closest approach||February 5, 1974|
|Distance||5,768 kilometers (3,584 mi)|
|Flyby of Mercury|
|Closest approach||March 29, 1974|
|Distance||704 kilometers (437 mi)|
|Flyby of Mercury|
|Closest approach||September 21, 1974|
|Distance||48,069 kilometers (29,869 mi)|
|Flyby of Mercury|
|Closest approach||March 16, 1975|
|Distance||327 kilometers (203 mi)|
Mariner 10 was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program (Mariner 11 and 12 were allocated to the Voyager program and redesignated Voyager 1 and Voyager 2).
The mission objectives 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. Mariner 10's science team was led by Bruce C. Murray at the Jet Propulsion Laboratory.
- 1 Design and trajectory
- 2 Instruments
- 3 Departing the Earth–Moon system
- 4 Cruise to Venus
- 5 Venus flyby
- 6 First Mercury flyby
- 7 Second Mercury flyby
- 8 Third Mercury flyby
- 9 End of mission
- 10 Discoveries
- 11 Mariner 10 Commemoration
- 12 See also
- 13 References
- 14 External links
Design and trajectory
Mariner 10 was the first spacecraft to make use of an interplanetary gravitational slingshot maneuver, using Venus to bend its flight path and bring its perihelion down to the level of Mercury's orbit. This maneuver, inspired by the orbital mechanics calculations of the Italian scientist Giuseppe Colombo, put the spacecraft into an orbit that repeatedly brought it back to Mercury. Mariner 10 used the solar radiation pressure on its solar panels and its high-gain antenna as a means of attitude control during flight, the first spacecraft to use active solar pressure control.
The components on Mariner 10 can be categorized into four groups based on their common function. The solar panels, power subsystem, attitude control, and computer kept the spacecraft operating properly during the flight. The navigational system, including the hydrazine rocket, would keep Mariner 10 on track to Venus and Mercury. Several scientific instruments would collect data at the two planets. Finally, the antennas would transmit this data to the Deep Space Network back on Earth, as well as receive commands from Mission Control. Mariner 10's various components and scientific instruments were attached to a central hub, which was roughly the shape of an octagonal prism. The hub stored the spacecraft's internal electronics. The Mariner 10 spacecraft was manufactured by Boeing. NASA set a strict limit of $98 million for Mariner 10's total cost, which marked the first time the agency subjected a mission to an inflexible budget constraint. No overruns would be tolerated, so mission planners carefully considered cost efficiency when designing the spacecraft's instruments. The mission ended up about $1 million under budget.
Attitude control is needed to keep a spacecraft’s instruments and antennas aimed in the correct direction. Mariner 10 determined its attitude using two optical sensors, one pointed at the Sun, and the other at a bright star, usually Canopus. Nitrogen gas thrusters were used to adjust Mariner 10’s orientation along three axes. The spacecraft’s electronics were intricate and complex: it contained over 32,000 pieces of circuitry, of which resistors, capacitors, diodes, microcircuits, and transistors were the most common devices. Commands for the instruments could be stored on Mariner 10’s computer, but were limited to 512 words. The rest had to be broadcast by the Mission Sequence Working Group from Earth.
The flyby past Mercury posed major technical challenges for scientists to overcome. Due to Mercury's proximity to the Sun, Mariner 10 would have to endure 4.5 times more solar radiation than when it departed Earth—compared to previous Mariner missions, spacecraft parts needed extra shielding against the heat. Thermal blankets and a sunshade were installed on the main body. After evaluating different choices for the sunshade cloth material, mission planners chose beta cloth, a combination of aluminized Kapton and glass-fiber sheets treated with Teflon. However, solar shielding was unfeasible for some of Mariner 10's other components. Mariner 10's two solar panels needed to be kept under 115 °C. Covering the panels would defeat their purpose of producing electricity. The solution was to add an adjustable tilt to the panels, so the angle at which they faced the sun could be changed. Engineers considered folding the panels toward each other, making a V-shape with the main body, but tests found this approach had the potential to overheat the rest of the spacecraft. The alternative chosen was to mount the solar panels in a line and tilt them along that axis, which had the added benefit of increasing the efficiency of the spacecraft’s nitrogen jet thrusters, which could now be placed on the panel tips. The panels could be rotated a maximum of 76 degrees. Additionally, Mariner's 10 hydrazine rocket nozzle had to face the Sun to function properly, but scientists rejected covering the nozzle with a thermal door as an undependable solution. Instead, a special paint was applied to exposed parts on the rocket so as to reduce heat flow from the nozzle to the delicate instruments on the spacecraft.
Accurately performing the gravity assist at Venus posed another hurdle. Mariner 10's trajectory had to pass 400 kilometres (250 mi) of the critical point or closer to later arrive at Mercury. To ensure that the necessary course corrections could be made, mission planners tripled the amount of hydrazine fuel Mariner 10 would carry, and also equipped the spacecraft with more nitrogen gas for the thrusters than the previous Mariner mission had held. These upgrades proved crucial in enabling the second and third Mercury flybys.
Even so, the mission still lacked the ultimate safeguard: a sister spacecraft. It was common for probes to be launched in pairs, with complete redundancy to guard against the failure of one or the other. The budget constraint ruled this option out. Through their frugality, mission planners stayed sufficiently under budget to divert some funding to constructing a backup spacecraft. Still, in the event that Mariner 10 failed, NASA would only allow the backup to be launched if the fatal error was diagnosed and fixed—this would have to be completed in the two-and-a-half weeks between the planned launch and launch window closing.
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Mariner 10 conducted seven experiments at Venus and Mercury. Six of these experiments had a dedicated scientific instrument to collect data.
The imaging system, the Television Photography Experiment, consisted of two 15 cm (5.9″) Cassegrain telescopes feeding vidicon tubes. The entire imaging system was imperiled when electric heaters attached to the cameras failed to turn on immediately after launch. To avoid the Sun's damaging heat, the cameras were deliberately placed on the spacecraft side facing away from the Sun. Consequently, the heaters were needed to prevent the extremely cold environment from harming the cameras. JPL engineers found that the vidicons could generate enough heat through normal operation to stay just above the critical temperature of -40 °C; therefore they advised against turning off the cameras during the flight. Fortunately, test photos of the Earth and Moon showed that image quality had not been significantly affected. The camera heaters started working for the first time on January 17, two months after launch. Later investigation concluded that a short circuit in a different location on the probe had prevented the heater from turning on. This allowed the vidicons to be turned off as needed. The main telescope could be bypassed to a smaller wide angle optic, but using the same tube. It had an 8-position filter wheel, with one position occupied by a mirror for the wide-angle bypass. The system returned about 7000 photographs of Mercury and Venus during Mariner 10's flybys.
The infrared radiometer detected infrared radiation given off by Mercury's surface and Venus' atmosphere, from which the temperature could be calculated. How quickly the surface lost heat as it rotated into the planet's dark side revealed aspects about the surface's composition, such as whether it was made out of rocks, or out of finer particles. The infrared radiometer contained a pair of Cassegrain telescopes fixed at an angle of 120 degrees to each other, and a pair of detectors made from antimony-bismuth thermopiles. The instrument was designed to measure temperatures as cold as -193 °C and as hot as 427 °C. Stillman C. Chase, Jr. of the Santa Barbara Research Center headed the infrared radiometer experiment.
Two ultraviolet spectrometers were involved in this experiment. The occultation spectrometer scanned Mercury's edge as it passed in front of the Sun, and detected whether solar ultraviolet radiation was absorbed at certain wavelengths, which would indicate the presence of gas particles, and therefore an atmosphere. The airglow spectrometer detected extreme ultraviolet radiation emanating from atoms of gaseous hydrogen, helium, carbon, oxygen, neon, and argon. Unlike the occultation spectrometer, it did not require backlighting from the Sun, and could move along with the rotatable scan platform on the spacecraft. The experiment's most important goal was to ascertain whether Mercury had an atmosphere, but would also gather data at Earth and Venus and study the interstellar background radiation.
The plasma experiment's goal was to study the ionized gases (plasma) of the solar wind, the temperature and density of its electrons, and how the planets affected the velocity of the plasma stream. The experiment contained two components, facing in opposite directions. The Scanning Electrostatic Analyzer was aimed toward the Sun, and could detect positive ions and electrons, which were separated by a set of three concentric hemispherical plates. The Scanning Electron Spectrometer was aimed away from the Sun, and detected only electrons, using just one hemispherical plate. The instruments could be rotated about 60 degrees to either side. By gathering data on the solar wind's movement around Mercury, the plasma experiment could be used to verify the magnetometer's observations of Mercury's magnetic field. Using the plasma detectors, Mariner 10 gathered the first in situ solar wind data from inside Venus' orbit.
Shortly after launch, scientists found that the Scanning Electrostatic Analyzer had failed because a door shielding the analyzer did not open. An unsuccessful attempt was made to forcibly unfasten the door with the first course correction maneuver. The experiment was still able to collect some data using the properly functioning Scanning Electron Spectrometer.
Charged particle telescopes
Celestial Mechanics and Radio Science experiment
Departing the Earth–Moon system
Boeing finished building the spacecraft at the end of June 1973, and Mariner 10 was delivered from Seattle to JPL's headquarters in California, where JPL comprehensively tested the integrity of the spacecraft and its instruments. After the tests were finished, the probe was transported to the Eastern Test Range in Florida, the launch site. Technicians filled a tank on the spacecraft with 29 kilograms (64 lb) of hydrazine fuel so that the probe could make course corrections, and attached squibs, whose detonation would signal Mariner 10 to exit the launch rocket and deploy its instruments. The planned gravity assist at Venus made it feasible to use an Atlas-Centaur rocket instead of a more powerful but more expensive Titan IIIC. The probe and the Atlas-Centaur were attached together ten days prior to liftoff. Launch posed one of the largest risks of failure for the Mariner 10 mission—Mariner 3 and Mariner 8 both failed due to different malfunctions of the Atlas-Centaur rocket. The mission had a launch window of about a month in length, from October 16, 1973, to November 21. NASA chose November 3 as the launch date because it would optimize imaging conditions when the spacecraft arrived at Mercury.
On November 3 at 12:45 am Eastern Time, the Atlas-Centaur carrying Mariner 10 lifted off from pad SLC-36B. The Atlas stage burned for around four minutes, after which it was jettisoned, and the Centaur stage took over for an additional five minutes, propelling Mariner 10 to a parking orbit. The temporary orbit took the spacecraft one-third of the distance around Earth: this maneuver was needed to reach the correct spot for a second burn by the Centaur engines, which set Mariner 10 on a path towards Venus. The probe then separated from the rocket; subsequently, the Centaur stage diverted away to avoid the possibility of future collision. Never before had a planetary mission depended upon two separate rocket burns during the launch, and even with Mariner 10, scientists initially viewed the maneuver as too risky.
During its first week of flight, the Mariner 10 camera system was tested by taking five photographic mosaics of the Earth and six of the Moon. It also obtained photographs of the north polar region of the Moon where prior coverage was poor. These photographs provided a basis for cartographers to update lunar maps and improve the lunar control net.
Cruise to Venus
A trajectory correction maneuver was made on November 13, 1973. Immediately afterwards, the star-tracker locked onto a bright flake of paint which had come off the spacecraft and lost tracking 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 necessitated reconfiguring the clock sequence and subsystems. Periodic problems with the high-gain antenna also occurred during the cruise. In January 1974, Mariner 10 made ultraviolet observations of Comet Kohoutek. Another mid-course correction was made on January 21, 1974.
The spacecraft passed Venus on February 5, 1974, the closest approach being 5,768 km at 17:01 UT. Using a near-ultraviolet filter, it photographed Venus's chevron clouds and performed other atmospheric studies. It was discovered that extensive cloud detail could be seen through Mariner's ultraviolet camera filters. Venus's cloud cover is nearly featureless in visible light. Earth-based ultra-violet observation did reveal some indistinct blotching even before Mariner 10, but the detail seen by Mariner was a surprise to most researchers.
Mariner photograph of Venus in ultraviolet light
First Mercury flyby
Second Mercury flyby
After looping once around the Sun while Mercury completed two orbits, Mariner 10 flew by Mercury again on September 21, 1974, at a more distant range of 48,069 km (29,869 mi) below the southern hemisphere.
Third Mercury flyby
After losing roll control in October 1974, a third and final encounter, the closest to Mercury, took place on March 16, 1975, at a range of 327 km (203 mi), passing almost over the north pole.
Mercury in false-color
A prominent scarp, Discovery Rupes, photographed during first flyby
Old basin, 190 km in diameter, filled by smooth plains. The basin's hummocky rim is partly degraded and cratered by later events
End of mission
With its maneuvering gas just about exhausted, Mariner 10 started another orbit of the Sun. Engineering tests were continued until March 24, 1975, when final depletion of the nitrogen supply was signaled by the onset of an un-programmed pitch turn. Commands were sent immediately to the spacecraft to turn off its transmitter, and radio signals to Earth ceased. Mariner 10 is still orbiting the Sun, although its electronics have probably been damaged by the Sun's radiation.
During its flyby of Venus, Mariner 10 discovered evidence of rotating clouds and a very weak magnetic field.
The spacecraft flew past Mercury three times. Owing to the geometry of its orbit – its orbital period was almost exactly twice Mercury's – the same side of Mercury was sunlit each time, so it was only able to map 40–45% of Mercury’s surface, taking over 2,800 photos. It revealed a more or less Moon-like surface. It thus contributed enormously to our understanding of Mercury, whose surface had not been successfully resolved through telescopic observation. The regions mapped included most or all of the Shakespeare, Beethoven, Kuiper, Michelangelo, Tolstoj, and Discovery quadrangles, half of Bach and Victoria quadrangles, and small portions of Solitudo Persephones (later Neruda), Liguria (later Raditladi), and Borealis quadrangles.
Mariner 10 also discovered that Mercury has a tenuous atmosphere consisting primarily of helium, as well as a magnetic field and a large iron-rich core. Its radiometer readings suggested that Mercury has a night time temperature of −183 °C (−297 °F) and maximum daytime temperatures of 187 °C (369 °F).
Planning for MESSENGER, a spacecraft that surveyed Mercury until 2015, relied extensively on data and information collected by Mariner 10.
Mariner 10 Commemoration
On February 10, 1975, the US Post Office issued a commemorative stamp featuring the Mariner 10 space probe. The 10-cent Mariner 10 commemorative stamp was issued on April 4, 1975, at Pasadena, California.
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|Wikimedia Commons has media related to Mariner 10.|
- The Voyage of Mariner 10: Mission to Venus and Mercury (NASA SP-424) 1978 This is an entire book about Mariner 10, with all pictures and diagrams, on-line! Scroll down to click on the "Table of Contents" link. PDF version
- 'Mariner 10', NASA's 1973–75 Venus/Mercury Mission
- Mariner 10 image archive
- Mariner 10 mission bulletins
- Mariner 10 Mission Profile by NASA's Solar System Exploration
- Calibrated images from the Mariner 10 mission to Mercury and Venus
- Master Catalog entry for Mariner 10 at the National Space Science Data Center
- Boeing: History – Products – Boeing Mariner 10 Spacecraft