Scientists and engineers were now faced with an arduous task. Within an 11-month period, on a schedule that could tolerate no delays, two spacecraft had to be designed, developed, assembled, tested, and launched. In order to meet the schedule, tested flight assemblies and instruments would have to be in the Pasadena assembly facility by mid-January, 1962, just four months after the start of the project. Probably no other major space project of similar scope had ever been planned on such a demanding schedule. [Illustration: _Mariner II travelled across 180 million miles of space within our solar system as it spanned the gap between Earth and Venus (shown here as the third and second planets, respectively, from the Sun)._] With the shipment of equipment to Atlantic Missile Range (AMR) scheduled for 9½ months after inception of the project, management and design teams went all-out on a true “crash” effort. Quick decisions had to be made, a workable design had to be agreed upon very early, and, once established, the major schedule objectives could not be changed. Certain design modifications and manufacturing changes in the Atlas-Agena launch vehicle were also necessary. Wherever possible, Ranger design technology had to be used in the new spacecraft and adapted to the requirements of a planetary probe. Other necessary tasks included trajectory calculation; arrangements for launch, space flight, and tracking operations; and coordination of AMR Range support. Following NASA’s September, 1961 decision to go ahead with the Mariner R Project, JPL’s Director, Dr. William H. Pickering, called on his seasoned team of scientists and engineers. Under Robert J. Parks, Planetary Program Director, Jack N. James was appointed as Project Manager for Mariner R, assisted by W. A. Collier. Dan Schneiderman was appointed Spacecraft System Manager, and Dr. Eberhardt Rechtin headed the space tracking program, with supervision of the Deep Space Instrumentation Facility (DSIF) operations under Dr. Nicholas Renzetti. The Mariner space flight operations were directed by Marshall S. Johnson. A PROBLEM IN CELESTIAL DYNAMICS In order to send Mariner close enough to Venus for its instruments to gather significant data, scientists had to solve aiming and guidance problems of unprecedented magnitude and complexity. The 447-pound spacecraft had to be catapulted from a launching platform moving around the Sun at 66,600 miles per hour, and aimed so precisely that it would intercept a planet moving 78,300 miles per hour (or 11,700 miles per hour faster than the Earth) at a point in space and time some 180.2 million miles away and 109 days later, with only one chance to correct the trajectory by a planned midcourse maneuver.