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Thirty-seven years ago this month, the Mariner 10 interplanetary space probe successfully conducted a flyby encounter with the planet Venus.  The Venusian flyby served as a necessary prelude to a subsequent first-ever flyby of the planet Mercury.

The Mariner Program concentrated on the scientific exploration of the inner planets of the solar system.  Namely, Mars, Venus and Mercury.  A total of ten (10) Mariner missions were attempted; seven (7) of which were successful.  These missions were flown between 1962 and 1974.  As outlined below, the Mariner Program recorded a number of important spaceflight firsts.  

Mariner spacecraft were the first to successfully conduct a flyby of Venus (Mariner 2), Mars (Mariner 4) and Mercury (Mariner 10).  Additionally, the first close-up photos of Mars and Venus were taken by Mariner 4 and Mariner 10, respectively.  Mariner 9 was the first spacecraft to orbit Mars.  Finally, Mariner 10 was the first space probe to fly a gravity assist trajectory and perform a flyby of two (2) planets (Venus and Mercury) during a single mission.

Mariner spacecraft weighed between 450 and 950 lbs for flyby missions and 2,200 lbs for an orbital mission.  Each carried a variety of mission-specific sensors including radiometers, spectrometers and television cameras.  Atlas-Agena (Mariners 1 to 5) and Atlas-Centaur (Mariners 6 to 10) launch vehicles provided the energy required for Earth-escape.

Mariner 10 was the last mission of the Mariner Program.  The primary objectives were to make measurements of the space, atmospheric and surface environments of Venus and Mercury.  This dual-planet mission required the first-ever use of a gravity assist maneuver to get to Mercury.  In particular, the gravity of Venus would be used to deflect the Mariner 10 trajectory such that it would be able to encounter Mercury.

Mariner 10 was launched from Cape Canaveral’s LC-36B at 05:45 UTC on Saturday, 03 November 1973.  It took 94 days for Mariner 10 to arrive at Venus.  As a bonus, the space probe trained its complement of sensors on the Comet Kohoutek along the way.  On Tuesday, 05 February 1974, Mariner 10 passed within 3,100 nm of the Venusian surface at 17:01 UTC.  The spacecraft then sailed on toward its future flyby encounters with Mercury.

Mariner 10 learned many things about Venus.  Venus was found to have an atmospheric circulation pattern somewhat like that of Earth.  Although its strength is very much less than that of Earth, Venus was found to have a magnetic field.  The planet’s ionosphere also interacted with the solar wind to produce a huge bow shock flowfield in the exoatmospheric region surrounding the planet.

Between March of 1974 and March of 1975, Mariner 10 performed three (3) flybys of the planet Mercury.  The closest approach to the planet’s surface was  a mere 177 nm.  Mercury’s surface was found to be very Moon-like in that it is heavily-cratered.  Spacecraft measurements also confirmed that Mercury does not have an atmosphere.  Further, Mercury was found to have a predominatly iron-laden core as well as a small magnetic field.

Following the last of the trio of flyby encounters with Mercury, Mariner 10 systems were put through a number of engineering tests.  The mission was officially brought to an end on Monday, 24 March 1975 when the spacecraft attitude control system propellant supply went to zero.  Today, the Mariner 10  hulk continues in an eternal orbit about the Sun.

Posted in Aerospace, History

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