[iv] THE MISSION OF MARINER 10 was unique in several ways. It was the first American spacecraft to take photographs of Venus. It was the first to use the gravity and motion of one planet to alter the flight path of a spacecraft and send it to another planet. It was the first to explore the planet Mercury, which was previously but a hazy image in the best Earth-based telescope pictures.
The success of Mariner 10 in attaining&emdash;and exceeding&emdash;its goals is attributable to the dedicated effort of the relatively small but exceedingly competent and highly motivated group of men and women from universities, industry, and government who made up the Mariner Venus/ Mercury 1973 project team.
Mariner 10 visited Venus once and Mercury three times in a period of a little over 500 days on a voyage of more than a billion kilometers. Shortly after the spacecraft left Earth it was oriented to the Earth and the Moon and returned the first of over 8000 pictures that were taken throughout its trip. These pictures of the Earth and Moon provided a calibration for later pictures of Venus and Mercury.
During the cruise from Earth to Venus, Mariner 10 acquired data about the environment of interplanetary space and obtained information about the comet Kohoutek, which passed by the Sun shortly after the launch.
On February 5, 1974, after traveling 236 million kilometers, Mariner 10 skimmed past Venus within 12 kilometers of the preplanned aim point. Over 3500 pictures were obtained as the spacecraft first saw a thin crescent and then the full face of Venus. These photos revealed a global distribution of ultraviolet clouds which rotate about the planet some 50 times faster than the planet rotates on its axis.
On March 29, 1974, following several additional course corrections which were made after leaving Venus, the spacecraft reached its primary goal: Mercury. Man obtained for the first time brilliantly clear pictures of this planet.
Mercury looks a great deal like the Moon. However, it has a dense interior and unexpectedly possesses a weak magnetic field. Mariner's cameras also revealed surface features not previously seen on other planets.
The surface of Mercury records the early history of the cataclysmic events that occurred during the formation of our solar system. The primordial state of the planet's surface, when studied in combination with similar data obtained from the Moon and Mars, should provide a great step forward in our understanding of the origin and evolution of the solar system and thus of our planet Earth.
[v] Even though the spacecraft experienced several serious problems during its trip to Mercury, and its gas supply nearly ran out, it performed its basic job flawlessly, and plans were laid for a return visit to Mercury about 6 months later.
Through the efforts of an ingenious and dedicated operations team the art of "solar sailing" was perfected and the spacecraft's gas usage was greatly reduced, thus permitting not one but two returns to Mercury. These bonus revisits provided additional pictures of Mercury's surface, including a spectacular view of the planet's south pole. The third encounter unequivocally confirmed the existence of Mercury's magnetic field.
This book records the historical details of the Mariner 10 mission from its original concept to its ultimate success. It provides a selection of some of the images obtained by the spacecraft at both Venus and Mercury. A detailed Atlas of the Mercury images is being published separately by NASA.
Mariner 10 reaped a bountiful harvest of new information about the inner planets of the solar system, information which combined with that from the exploration of other planets may provide us with an increasingly clear view of the origin of our solar system and possibly a clue to its destiny.
John E. Naugle