Mariner 10

Launch data: Designation 06919 / 73085A Launch date 03 Nov 1973 - 05:45 UT Launch site CC, LC-36B Launch vehicle Atlas-SLV3D Centaur-D1A (AC-34/5014D) Satellite type Mission Venus Flyby, Mercury Flyby Heliocentric orbit Perihelion x Aphelion 0.70 x 1.11 A.U. Eccentricity  0.23 Inclination 2.6 deg Period 317 days Venus orbit on 1974 Mar 30: Perihelion x Aphelion 0.387 x 0.839 A.U. Eccentricity  0.369 Inclination 2.6 deg Period 176 days

Specifications: Prime contractor   Operator   Platform   Mass at launch kg Dry Mass  526 kg Dimension 2.90? long - 1.27 dia Basic shape Octagon cylinder Solar array   Stabilization   Lifetime  Indefinite - Sun orbit

Mission details:

• Mariner 10 was a robotic space probe launched on November 3, 1973 to fly by the planets Mercury and Venus. It was launched approximately 2 years after Mariner 9 and was the last spacecraft in the Mariner program (Mariner 11 and 12 were purposed to the Voyager program and redesignated Voyager 1 and Voyager 2).
  
  

• 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.

  
  
• Departing the Earth/Moon system:
  During its first week of flight, Mariner 10 tested its camera system by returning 5 mosaics of Earth and 6 of the Moon. It also obtained photographs of the north polar region of the moon where prior coverage was poor. These 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 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. In January 1974 Mariner 10 made ultraviolet observations of Comet Kohoutek. Another mid-course correction was made on January 21, 1974.
  
  
• Venus flyby:
  

  The spacecraft passed Venus on February 5, 1974, at a closest range of 5768 km at 17:01 UT. Using a near-ultraviolet filter, it photographed the Cytherean chevron clouds and performed other atmospheric studies. It was discovered that extensive cloud detail could be seen via Mariner's ultra-violet 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.

  
  
• Mercury flyby:
  The first Mercury encounter took place at 20:47 UT on March 29, 1974 at a range of 703 kilometres (437 miles).
  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 (29,870 mi).
  
  

  First Mercury encouter

  Second Mercury encounter

  
  
  

  Images from the second encounter, covering the equator to the south pole

  Discovery rupes photographed during first flyby

  
  
  A third and final encounter, the closest to Mercury, took place on March 16, 1975 at a range of 327 km (203 mi).
  
  

• 6 hours before closest approach

  Third Mercury encounter

  
  
  

  6 hours after closest approach

  Old bassin, 190 km in diameter, filled by smooth plains

  
  
• 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 the final depletion of the nitrogen supply was signaled by the onset of an un-programmed pitch turn. Commands were immediately sent to the spacecraft to turn off its transmitter, and radio signals to Earth ceased.
  Presently, Mariner 10 is still orbiting the sun, although its on-board electronics have probably been damaged by the sun's radiation.
• Discoveries:
  

  During its flyby of Venus, Mariner 10 discovered evidence of rotating clouds and a very weak magnetic field. Mariner 10 flew past Mercury three times in total. 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 the planet, 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, and small portions of Solitudo Persephones, Liguria, and Borealis. 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).

  Mercury image. The smooth band is an area of which no images were taken.

  
  

Mission resume:

• Mariner 10 was the seventh successful launch in the Mariner series and the first spacecraft to visit Mercury. It was also the first spacecraft to use the gravitational pull of one planet (Venus) to reach another (Mercury), and the first spacecraft mission to visit two planets. The spacecraft flew by Mercury three times in a retrograde heliocentric orbit and returned images and data on the planet. Mariner 10 returned the first-ever close-up images of Venus and Mercury. 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.
• Mariner 10 was placed in a parking orbit for 25 minutes after launch, then accelerated to a trans-Venus escape trajectory. The television and ultraviolet experiments were trained on the comet Kohoutek while the spacecraft was en route to its destination. The vehicle's first planetary encounter was with Venus on February 5, 1974, at a distance of 4200 km. Mariner 10 took 4,000 photos of Venus, which revealed a nearly round planet enveloped in smooth cloud layers. The gravity of Venus bent the orbit of the spacecraft and sent it towards Mercury. It crossed the orbit of Mercury on March 29, 1974, at 20:46 GMT, at a distance of 704 km from the surface. Photographs taken during the pass revealed an intensely cratered, Moon-like surface and a faint atmosphere of mostly helium. After the first flyby, Mariner 10 entered solar orbit, which permitted two more rendezvous with Mercury. On September 21, 1974, the second Mercury rendezvous, at an altitude of about 47,000 km, provided another opportunity to photograph the sunlit side of the planet and the south polar region. The third and final Mercury encounter on March 16, 1975, at an altitude of 327 km, yielded 300 photographs and magnetic field measurements. The vehicle was turned off March 24, 1975 when the supply of attitude-control gas was depleted.