A project such as Mariner II is first a vast engineering task. Many thousands of man-hours are required to design the complex automatic equipment which must operate perfectly in the harsh environment of space. Every detail of the system must be studied and analyzed. The operations required to carry out the mission must be understood and performed with precision. A successful mission requires every member of the entire project team to do his task perfectly. Whether it be the error of a designer, mechanic, mathematician, technician, operator, or test engineer—a single mistake, or a faulty piece of workmanship, may cause the failure of the mission. Space projects abound with examples of the old saying, “For want of a nail, the shoe was lost ...,” and so on, until the kingdom is lost. Only when every member of the project team is conscious of his responsibility will space projects consistently succeed. The Mariner II Project started with the Lunar and Planetary Projects Office of the Office of Space Sciences at NASA in Washington. Jet Propulsion Laboratory, California Institute of Technology, personnel provided the main body of the team effort. They were heavily supported by industrial contractors building many of the subassemblies of the spacecraft, by scientists planning and designing the scientific experiments, and by the Air Force which supplied the launching rockets. Several thousand men and women had some direct part in the Mariner Project. It would be impossible to list all of those who made some special contribution, but each and every member of the project performed his job accurately, on time, and to the highest standards. Mariner II is only a prelude to NASA’s program of unmanned missions to the planets. Missions to Mars as well as Venus will be carried out. Spacecraft will not only fly by the planets as did Mariner II, but capsules will be landed, and spacecraft will be put into orbit about the planets. The next mission in the Mariner series will be a flyby of the planet Mars in 1965. By the end of the decade, where will we be exploring, what will new Mariners have found? Will there be life on Mars, or on any other planet of the solar system? What causes the red spot on Jupiter? What is at the heart of a comet? These and many other questions await answers obtained by our future spacecraft. Mariner II is just a beginning. W. H. Pickering _Director_ Jet Propulsion Laboratory_ California Institute of Technology_ April, 1963_ CONTENTS _FOREWORD_ _ACKNOWLEDGMENTS_ CHAPTER 1 VENUS _The Double Star of the Ancient World_ _The Consensus prior to Mariner II_ _The Cytherean Riddle: Living World or Incinerated Planet_ CHAPTER 2 PREPARING FOR SPACE _A Problem in Celestial Dynamics_ _The Organization_ _NASA: For Science_ _JPL: JATO to Mariner_ _General Dynamics: The Atlas_ _Lockheed: Agena B_