Mercury - Mariner 10

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The American unmanned spacecraft, Mariner 10, was the only spacecraft so far to have visited Mercury. It was launched on November 3, 1973 at 12:45 A.M. (midnight, E.S.T.) or 5:45:00 U.T.C. (Universal Time). This spacecraft also studied Venus, and was the first spacecraft to study two planets. The Mariner 10 is also called the Mariner Venus, Mercury 73, Mariner-J, or 06919.

STRUCTURE:
The Mariner 10 had on board a bunch of instruments and cameras to send data back to Earth about Mercury and Venus. The instruments on board were television photography, magnetic field, plasma, and infrared radiometry, ultraviolet spectroscopy , and radio science detectors. Also for the first time, an experimental X-band high-frequency transmitter was put on the spacecraft. The spacecraft was an eight-sided framework with 2 solar panels sticking out that provided it’s energy. The frame was 1.39 m diagonally and 0.457 m in depth, with 8 electronics compartments. The 2 solar panels were each 2.7 m long and 0.97 m wide, supporting 5.1 square meters of solar cells and attached to the top of the frame. It was steered and stabilized on 3 axes with two sets of reaction jets and a liquid-fueled rocket engine pushed it along. It carried antenna that allowed it to transmit on the S- and X- band frequencies.

An artist's conception of the Mariner 10.

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GRAVITY ASSIST AND SCHEDULE:
The Mariner 10 was the first spacecraft to make use of another planet's gravitational fields to change its course. This maneuver was called a "gravity assist" which practically propelled the Voyager missions to the outer planets. The Mariner 10 was to fly by Venus and use the gravitational pull of Venus to change the probe's course by slowing it down enough to make it fall in towards the Sun and towards Mercury. A small error at the gravity assist maneuver and it could have meant missing Mercury by million miles.

Courtesy of JPL/CalTech/NASA. At first, right after launch on the Atlas Centaur launch vehicle (left), it was parked in earth orbit for about 25 minuets then sent on a spiraling heliocentric orbit towards Venus and Mercury. This motion was opposite of the motion of the Earth around the Sun. It reached Venus on February 5, 1974 at a distance of 4200 kilometer and took over 4,000 pictures of Venus. It was the only one designed to take pictures of the thick clouds. On the way to Mercury from Venus the TV and UV experiments were focused on the comet Kohoutek. Finally on March 29, 1974 the Mariner 10 reached Mercury at 20:46 UTC (3:46 PM E.S.T). The Mariner 10 flew within 460 miles (704 km) of Mercury on March 29, 1974 and took its first pictures of Mercury. It took some of the scientists by surprise. The guest-room at Jet Propulsion Labs, filled with high-ranking military personnel, commented that Mercury looked like it had been attacked by B-52 bombers.

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DATA RETURNED:
This mosaic was made out of pictures taken of Mercury as the Mariner 10 was retreating from it. Courtesy of NASA/NSSDC. At first the pictures were hazy and indistinct, but it slowly focused to be the outlines of a crater. The first feature to be recorded on Mercury was name Crater Kuiper after Gerard Kuiper, the veteran planetary scientist who died while the Mariner 10 was on the way to Mercury. During the flybys of Mercury, Mercury had the same side facing the sun, because it only turns three times in 2 Mercurial years. So the Mariner 10 only took pictures of the lighted side, which amounts to about 45% and the resolution of 1 km.

It detected the magnetic field of Mercury. The speed of Mariner 10 had made it go into orbit around the sun that took exactly 2 Mercurial years (176 days). So it would see Mercury again. The Mariner 10 had enough fuel to fly by one or two more times. On the 2nd encounter on September 21, 1974 the Mariner 10 took hundreds more as it passed only 47,000 km away. A 3rd flyby happened on March 16, 1975 at a much closer altitude of 327 km, where it detected the magnetic field of Mercury and took about 300 more pictures. Engineering tests happened up until March 24, 1975 when the craft ran out of fuel and started to tumble out of control.

The total cost of the Mariner spacecrafts (Mariner 1-10), including research, development, launch and support totaled approximately $554 million.

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