Illustration of the Mariner 2 spacecraft

Thirty years ago, Dec. 14, 1962, the first successful interplanetary traveler reached Venus after a 108-day journey from Earth. Named Mariner 2, it was a 200-kilogram (450-pound) machine carrying six scientific instruments, a two-way radio, a solar power system and assorted electronic and mechanical devices. Its crew, numbering roughly 75, stayed behind at NASA's Jet Propulsion Laboratory.

The Mariner planetary spacecraft series began in 1960 as a group of mission studies at JPL; by 1975 there had been 10 Mariner flights, seven of them successful explorations of the inner Solar System. Mariner 2 became the model for planetary space flights, one that emphasized good and copious scientific data collection, utilizing remote sensing of planets and in-situ measurement of the space environment; all of is this supported by high-quality engineering.

The resulting program eventually led to close observation of all the planets but Pluto, planetary orbiters and landers, international cooperative missions and flights right out of the Solar System. What became the Mariner 2 mission was authorized by NASA in August 1961, less than a year before the first launch window. The limited capacity of Atlas/Agena, the largest available launch vehicle, severely restricted launch opportunities and spacecraft size. The first launch, Mariner 1, was aborted when its launch vehicle strayed from the safe flight corridor and was destroyed by the Range Safety Officer.

Mariner 2 was successful, however; since that trailblazer mission, there have been about four dozen U.S., Soviet and other flights -- the majority successful -- reaching every planet from Mercury to Neptune, plus comets and an asteroid, and one joint U.S.-European mission (still underway) to the poles of the Sun. These are in addition to dozens of lunar spacecraft and the manned lunar flights of Project Apollo. Liftoff

A few minutes before 2 a.m. on Aug. 27, 1962, Mariner 2 lifted off the pad at Cape Canaveral aboard its Atlas-Agena rocket. It was nearly as much an experiment for the rocket and spacecraft engineers as for the space scientists intent on observing interplanetary space and the planet Venus.

During its three-and-a-half-month odyssey of some 290 million kilometers (180 million miles), reaching a third of the way around the Sun to Venus, Mariner 2 transmitted coded signals continuously to the Earth, mixing scientific measurements of interplanetary dust, magnetism, cosmic rays and solar plasma with engineering data on the health and performance of the spacecraft.

As Earth turned beneath the feeble radio transmissions, three great steerable antennas (now the Deep Space Network) captured Mariner's signals in turn, first in California, then Australia, Africa and California again.

Mariner 2 suffered and survived a number of unanticipated events during the flight. It lost its attitude orientation; one of the solar panels failed; many temperature readings rose ominously as Mariner approached Venus; and, just before the Venus encounter, the computer/sequencer became erratic. But Mariner automatically recovered its orientation, survived solar heating, and, as sunlight grew more intense, one solar panel did the work of two. When the flight engineers saw the sequencer faltering, they started the encounter sequence by radio commands from Earth.

On Dec. 14, 1962, Mariner's infrared and microwave radiometers scanned back and forth across the planet, capturing data that would prove Venus's surface to be fire-hot -- about 425 degrees Celsius or 800 Fahrenheit -- warmed in part by a runaway greenhouse effect in the thick carbon dioxide atmosphere. About three weeks after its historic Venus flyby, Mariner 2 went off the air. Its signal was last received on Jan. 3, 1963.

The ability of Mariner's crew and equipment to overcome in-flight problems, and simply to complete the flight to the planet Venus, constituted major technical advances in addition to the scientists' discoveries about Venus and the Solar System. The spacecraft design proved robust, and the attitude-stabilized spacecraft concept feasible for long-term exploration. To Mars

Two years later -- Nov. 28, 1964 -- a second-generation Mariner set forth -- this time on an eight-month journey to Mars. Mariner 4, like its predecessor, survived the loss of a twin and the rigors of an alien environment. Also like the earlier Mariner it was extremely light in weight, solar-powered, fully stabilized, automated, in constant contact with a team of engineers and scientists back on Earth and bristling with instruments.

Unlike Mariner 2, this machine could see: a TV camera and tape recorder caught the first close-up pictures of the surface of Mars, revealing moon-like craters, some of them topped with frost. The navigators sent Mariner 4 behind Mars, letting the radio link with Earth serve as a probe of the atmospheric density and revealing a surface pressure less than 1 percent of Earth's.

Following the pattern set by Mariner 2 and Mariner 4, NASA/JPL sent spacecraft back to Venus and Mars, into Mars orbit and to Mercury. The latter flight, made by Mariner 10 in 197374, used the gravitational field of Venus to boost it inward to the orbit of Mercury. In the 1970s, various USSR spacecraft orbited Venus, entered its thick atmosphere, even landed.

In 1976, two NASA scientific stations landed on Mars, remaining in operation for several years. This Viking mission, encompassing two large Mars-orbiting spacecraft as well as the two landers, conducted a comprehensive, long-term mapping survey of the entire planet, spot investigations of special areas (including the moons Phobos and Deimos), and atmospheric studies. Viking also produced biological, chemical, meteorological, physical and image data collected at the landing sites. A Grand Tour

A year later two spacecraft were launched on what became the grand tour of the outer planets: the Voyager mission to Jupiter, Saturn, Uranus, Neptune and -- still going -- beyond the Solar System to interstellar space. Voyager 1 used Jupiter's gravitational field to speed it on to Saturn and then, after tens of thousands of images of the two planets and their many satellites, it left the plane of the ecliptic. Voyager 2 also flew past Jupiter (1979) and Saturn (1981), but its path was designed to use additional gravity assists to sling it onward to Uranus (1986) and Neptune (1989).

The two Voyagers took a total of well over 100,000 images of the outer planets, rings and satellites, as well as millions of chemical spectra, magnetic and radiation measurements. They discovered rings around Jupiter, volcanoes on Io, shepherding satellites in Saturn's rings, new moons around Uranus and Neptune, geysers on Triton. The last imaging sequence was Voyager 1's portrait of the Solar System, showing Earth and six other planets as sparks in a dark sky lit by a single bright star, the Sun.

Two spin-stabilized Pioneer spacecraft had preceded the Voyagers to Jupiter, and one of them went on to Saturn, before heading out of the System. Thus, four NASA spacecraft are now actively searching, in different directions, for the frontier between solar and interstellar space; at least one is expected to detect it in the next quarter-century. New Era

Shortly before Voyager 2's Neptune encounter, a new generation of planetary exploration began. Magellan set out for Venus in 1989 to map the surface from orbit using imaging radar. A Pioneer spinning spacecraft had been orbiting Venus for more than a decade, completing a low-resolution radar topographic map and many other planetary and solar studies; the Soviets compiled radar images of the northern part of Venus, landed more cameras and deployed balloons into the atmosphere. Magellan mapped 99 percent of the surface at high resolution, parts of it in stereo, and is presently mapping the gravitational field.

In October 1989, NASA/JPL's Galileo spacecraft began a gravity-assisted journey to Jupiter, where it will place a probe in the atmosphere and observe planet and satellites from orbit for two years. On the way, Galileo performed gravity-assist encounters with Venus and the Earth and made the first close flyby of asteroid Gaspra in 1991.

In a joint mission with the European Space Agency, NASA launched the Ulysses spacecraft in 1990 on a flight over the poles of the Sun. To achieve high orbital inclination, the spacecraft did a gravity-assist flyby of Jupiter, measuring the magnetosphere as it did so.

In September 1992, Mars Observer was launched to Mars. It is scheduled to go into orbit around the planet in August 1993 and make many observations during a period of one Martian year.

As 1992 rounded out three decades of scientific growth and achievement in observing and understanding the Solar System and the development of highly sophisticated spacecraft and missions, NASA began to look anew to the small, purposeful, higher-risk kind of mission represented by Mariner 2 thirty years ago.

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