Mariner 10 Credit - NASA

Mariner 10 was the first mission to use the gravitational attraction of one planet to reach another, the first mission with two planetary objectives, and (to date) the only mission ever to perform up close imaging and science at Mercury.

The vehicle's first planetary encounter was with Venus on 3 November 1973. Mariner 10 took some 4,000 photos of Venus, which revealed a nearly round planet enveloped in smooth cloud layers. The Venus flyby deflected Mariner 10's trajectory towards Mercury , which it flew past at 756 km altitude on 29 March 1974. 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's solar orbit permitted two more rendezvous with Mercury. On 21 September 1974, the second Mercury rendezvous provided another opportunity to photograph the sunlit side of the planet and the south polar region. The third and final Mercury encounter occurred on 16 March 1975, and yielded primarily fields and particles data. The vehicle was turned off on 24 March 1975 after its onboard fuel was depleted. Total mission cost was $100 million.

The spacecraft structure was an eight-sided framework of magnesium and aluminum with eight electronics compartments. It measured 1.39 m diagonally and 0.457 m in depth. Two solar panels, each 2.7 m long and 0.97 m wide, were attached at the top, supporting 5.1 sq m of solar cell area. The rocket engine was liquid-fueled, with two sets of cold gas thrusters used to stabilize the spacecraft on three axes. It carried a low-gain omnidirectional antenna, composed of a honeycomb-disk parabolic reflector, 1.37 m in diameter, with focal length 55 cm. Feeds enabled the spacecraft to transmit at S- and X-band frequencies. An experimental X-band, high-frequency transmitter was flown for the first time on this spacecraft.

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. A sunshade was deployed after launch to protect the spacecraft on the solar-oriented side. Solar panels produce 540 W maximum and recharged NiCd batteries (20 AHr). Instruments on board the spacecraft measured the atmospheric, surface, and physical characteristics of Mercury and Venus. These included cameras, a magnetometer, a plasma science experiment, a charged particle telescope, an ultraviolet spectrometer, and an infrared radiometer.

Typical orbit: Solar orbit - Venus / Mercury flyby. Mass: 526 kg (1,159 lb). Associated Launch Vehicle: Atlas Centaur SLV-3D.

• 1973 November 3 - Mariner 10 first flyby of Venus -

  The vehicle's first planetary encounter was with Venus on November 3, 1973. Mariner 10 took some 4,000 photos of Venus, which revealed a nearly round planet enveloped in smooth cloud layers.

• 1973 November 3 - Mariner 10 - Program: Mariner. Launch Site: Cape Canaveral. Launch Vehicle: Atlas. Mass: 526 kg (1,159 lb).

  Mariner 10 was the first spacecraft to reach Mercury. 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.

• 1974 February 5 - Mariner 10, Venus Flyby -

• 1974 March 29 - Mariner 10 first flyby of Mercury -

  Mariner 10 flew past Mercury at 756 km altitude. Photographs taken during the pass revealed an intensely cratered, Moon-like surface and a faint atmosphere of mostly helium.

• 1974 March 29 - Mariner 10, first Mercury Flyby -

• 1974 September 21 - Mariner 10 second flyby of Mercury -

  The second Mercury rendezvous provided another opportunity to photograph the sunlit side of the planet and the south polar region.

• 1974 September 21 - Mariner 10, second Mercury Flyby -

• 1975 March 16 - Mariner 10 third flyby of Mercury -

  The third and final Mercury encounter yielded primarily fields and particles data.

• 1975 March 16 - Mariner 10, third Mercury Flyby -

• 1975 March 24 - Mariner 10 deactivated -

  The vehicle was turned off after its onboard fuel was depleted.