[iii] The Mariner 10 mission to Venus and Mercury scored many firsts. It was the first multiple-planet mission, borrowing energy from the gravity of Venus to make possible a flight to Mercury otherwise unachievable. This required navigation of a precision never before attempted equivalent to shooting a rifle bullet through a 2-inch knothole more than 100 miles away. During its Venus swingby, Mariner 10 took the first close-up photographs of Venus. revealing the intricate spiral structure in its cloud layers that confirmed the classic circulation theory hypothesized by the astronomer Hadley more than 200 years ago and believed to be the basic driving mechanism behind weather on Earth. On the way from Venus to Mercury, Mariner 10 also made the first practical use of solar sailing, a novel technique that I predict will be used increasingly in the future to replace more expensive space propulsion systems. And as it flew by Mercury, Mariner 10 entered an orbit that, for the first time, provided two subsequent flyby revisits.
The hard-working Mariner 10 team also scored a number of management firsts. It was the first space project team to ever receive a NASA performance award prior to launch-a tribute to their determination and skill in pioneering daring techniques to cut the cost of space missions at the same time they were actually upgrading the quality of the science return.
Of all the firsts, undoubtedly the outstanding achievement of the Mariner 10 mission was the spectacular unveiling of the planet Mercury. Mercury's closeness to the Sun makes it an almost impossible object for astronomical study, and the total knowledge of Mercury prior to Mariner 10 was miniscule. Even its rate of rotation was not determined until 1965. Mercury's surface was almost totally unknown, with considerable conjecture that total surface melting could have left Mercury as smooth as a billiard ball.
Then came the tiny Mariner 10 spacecraft, a bright sunlit speck of a solar sailing craft speeding in from the blackness of space. Aboard was an imaging system born of the ingenuity and close cooperation between space systems engineers and the scientists of the imaging experiment team. Using a narrow-angle television camera, it could take only postage-stamp-size pictures of the surface. But it could flash them back to Earth with such rapidity that it was possible to map the entire lighted portion of the planet with excellent resolution.
This Atlas is a tribute to the accomplishments of that highly productive team effort. As you turn its pages you will see the face of Mercury as it was unveiled to mankind for the very first time. If it is not a beautiful face, it is nevertheless a most fascinating one, marked with a character all its own, including "wrinkles" over 2000 km long. Even its noticeable similarities to the Moon are fascinating why should both the Moon and Mercury have the smooth mare areas located predominantly on one face with rough highlands on the other? Why should Mercury, so far from the asteroid belt, have a surface just as pocked by bombardment as the Moon'? Clearly, adding the portrait of Mercury to our gallery of terrestrial planets will contribute greatly to our knowledge of the violent accretion process that formed the planets.
Even with the two revisits of Mariner 10 to Mercury, we have seen only one side of the planet-a limitation imposed by Mercury's harmonic rotational lock to the Sun. I wait with eager anticipation for the day when we return to see the other face of Mercury.