On February 24 and March 27, Mariners VI and VII were launched on flights which will carry them within about 2,000 miles of the surface of Mars to investigate the planet in late July and early August. Thes launchings marked the beginning of the final phase of the Mariner Mars '69 Program.

The spacecraft (figs. 2-9 and 2-10) are identically equipped, although they will carry out different missions at the time of the Mars encounters. Mounted on movable platforms are two television cameras, an infrared spectrometer, an infrared radiometer, and an ultraviolet spectrometer. Rotating and repositioning the platform

enables the instruments to view much more of the Martian atmosphere and surface than would be possible from a stationary position.

An equatorial pass of the planet is planned for Mariner VI, which, since its February launch, has operated as designed. It should commence encounter operations on July 28, when its long focal length TV camera will be aimed at Mars to take far-encounter or approach photographs. The pictures will be transmitted to earth over the spacecraft's radio high data rate system the next day, when the spacecraft is above the Goldstone, Calif. 210-foot tracking antenna; the transmission will be available for real-time viewing over commercial TV.

SCIENTIFIC INVESTIGATIONS IN SPACE

As Mariner VI nears the planet, the scan platform will again be repositioned, so that its remaining science instruments can view features of the Martian atmosphere and surface of interest to scientists. On July 31 (1:18 a.m., EDT) the spacecraft will be closest to the planet's surface—an estimated 2,165 miles away.

Mariner VII will approach the southern polar region of Mars. After transmitting far-encounter pictures, the spacecraft's scan platform will move into a position to obtain photographs and spectra of the Martian polar cap and regions surrounding it. Mariner VII will come within about 2,071 miles of the Red Planet at 1:00 a.m., EDT on August 5.

Mariner Mars '71

Major progress was made in the Mariner Mars '71 Program during the first six months of 1969. In February, the functional design for the spacecraft system was completed, and contractual arrangements for the Atlas-Centaur launch vehicle were begun. The mission's overall design was finished in April, and the detailed design of the spacecraft was completed in September. In addition,

SEMIANNUAL REPORT (JANUARY-JUNE 1969)

Fig. 2-10. Mariner VII being mated with its protective launch shroud.

22 major subcontractors were selected for the scientific instruments and spacecraft subsystems.

The Martian-orbiting spacecraft of Mariner Mars '71 will make maximum use of Mariner Mars '69 hardware (20th Semiannual Report, p. 64.) For example, the proof test model of the spacecraft for the 1969 flybys was being disassembled, inspected, and modified to become the proof test model for the 1971 mission.

Viking

In addition to the Mariner flybys of Mars in 1971, NASA plans to send two instrumented spacecraft to the planet in 1973* to collect additional scientific data, particularly emphasizing extraterrestrial life-related experiments. Each of the Viking program spacecraft will be made up of a soft lander of the Surveyor class and an orbiter of the Mariner type. The lander will photograph its landing site, search for organic compounds and living organisms, investigate the environment's capacity to support life, and make measurements to determine the composition and structure of the Martian atmosphere. The orbiter will carry out comprehensive surveys of the landing sites and study the planet's dynamic characteristics and atmosphere.

A contract was negotiated for building the lander, and scientists were asked to help plan the Viking project and develop instruments for it. Over 150 proposals were submitted, and 38 scientists were selected and organized into eight teams, to assure the maximum return of scientific data from the mission.

Langley Research Center was assigned overall Viking project management and responsibility for the lander. The Jet Propulsion Laboratory will manage the orbiter portion of the program and be responsible for tracking and data acquisition. Lewis Research Center will manage the Titan III-Centaur launch vehicle.

Pioneer Spacecraft

Pioneers VI through IX, from widely separated orbits about the sun, continued transmitting data on solar activity and related interplanetary phenomena. Launched in 1965, 1966, 1967, and 1968, they detected significant solar activity in March and April of this year and made is possible to forecast disruptions of communications on earth, such as occurred in the arctic where redio communications were almost impossible for about a week due to the solar storm.

Pioneer E (or X), the last of this series, was being prepared for launching in August. Also, procurement contracts were under negotiation for Pioneers F and G-to be orbited in 1972 and 1973. These will pass through the asteroid belt and fly close to Jupiter. Their experiments (whose selection was completed in June) will measure the properties of energetic particles, magnetic fields, and cosmic dust throughout the mission. In addition, instruments on board will be able to make direct measurements in the infrared, visual, and ultraviolet wavelengths of the electromagnetic spectrum in the immediate vicinity of the planet and its atmosphere.

The Viking missions were rescheduled to 1975, after this report was completed.