Mariner 4 Anniversary Marks 30 Years of Mars Exploration  (2024)

Three decades after Mariner 4's flyby of Mars on July 14, 1965 -- the first spacecraft ever to reach the planet and take close-up photographs of the Martian surface -- NASA is preparing a whole new decade of Mars missions that will rely on revolutionary new technologies and smaller, cheaper, faster spacecraft to continue robotic exploration of the Red Planet.

Kicking off this new decade of discovery are two missions scheduled for launch in the fall of 1996: Mars Global Surveyor, an orbiter to map the surface and atmosphere of the planet; and Mars Pathfinder, a Discovery program mission designed to deliver a lander, camera and instrumented rover to the Martian surface on July 4, 1997.

As NASA prepares for these missions, the community is also celebrating the roots of Mars exploration, which reach back 30 years to one tense day in the summer of 1965 at the Jet Propulsion Laboratory in Pasadena, Calif.

It was on July 14, 1965, that scientists and engineers waited anxiously for radio signals from NASA's Mariner 4 spacecraft, near Mars, to tell them that the spacecraft was successfully photographing the Red Planet close up for the very first time. With a round-trip communication time of 24 minutes, they could not remotely control the spacecraft. Mariner 4 was following a primitive onboard computer program and a sequence that engineers had started earlier that morning.

The signal arrived at the communication site at Goldstone, Calif., right on schedule at 5:30 p.m. Pacific Time. After 26 minutes of television recording, slightly more than 21 pictures filled the recording tape. The camera was switched off and Mariner's other instruments came on again to monitor the space environment around Mars. A few minutes later, the spacecraft flew within 10,000 kilometers (more than 6,000 miles) of Mars, then continued on its course to become one more object orbiting the Sun.

Mariner 4's flight past Mars was just the second successful interplanetary mission in history for the U.S. space program, preceded by Mariner 2's flight to Venus in 1962. The Mariner 4 mission had been developed, built and tested at the Jet Propulsion Laboratory in just two years time.

The Mariner team had to be ready for launch in November 1964 in order to reach Mars in July 1965, and the spacecraft could only weigh about 260 kilograms (575 pounds) in order to achieve the velocity needed to get to Mars.

With very little experience in interplanetary space travel, engineers did not have much of an idea about the space environment that Mariner 4 would encounter during its eight-month trip to Mars. The ability of the spacecraft and its parts to survive eight months in space was an open question -- one that only the mission itself would answer. The sheer distance alone -- nearly three times the range of the first interplanetary flight -challenged the telecommunication system. Even the precise location of Mars and the lighting conditions on its surface were unclear.

Mariner 4's sister ship, Mariner 3, was launched three weeks earlier, but was doomed when the launch rocket's nose fairing failed to jettison properly. This trapped the spacecraft and forced NASA, JPL and the contractor for the upper-stage rocket, Lockheed Corp., into a race to design and build a new fairing in time to launch the second spacecraft while the Earth and Mars were still in proper alignment with each other.

They won the race. Mariner 4 lifted off Earth on an Atlas/Agena rocket on November 27, 1964. After about a week of radio tracking on the way to Mars, the spacecraft was commanded to perform a rocket-thrust maneuver, refining its course toward Mars. Then it coasted the rest of the way.

Throughout its flight the spacecraft kept its four solar panels oriented toward the Sun to generate electric power to run its equipment and keep the battery charged. It kept up a constant two-way communication link with the Earth, providing for radar based navigation and the receipt of commands from the ground, as well as sending science data to six teams of scientists and engineering health and performance measurements to engineers.

Between February and June 1965, Mariner 4 detected the effects of five separate solar flares, significant increases in the solar wind and its spiral flow of charged particles from the Sun. These events showed up in the magnetometer, several charged particle sensors and the cosmic-ray telescope. During the flight to Mars, the cosmic dust detector indicated an irregular increase in the number of micrometeorites, counting a total of about 200 particles.

Seven and a half months after launch the spacecraft approached Mars. On command it switched from "cruise science," carried out during the flight, to "encounter science," the observations of Mars. Another command aimed the camera and seven hours later a Mars detector started the camera shutter clicking. After recording its pictures, the spacecraft passed behind Mars and its radio signal faded into silence for nearly an hour. Scientists measuring the fadeout and return of the radio signal were able to measure the ionosphere and atmospheric density of Mars, similar to the way astronomers measure planetary atmospheres through the fading of starlight.

The next day, Mariner 4 began more than a week of playback of the recorded pictures of Mars. Very slowly the cratered, cold, hostile new world crept into view. Interpreting the dim gray of the Martian images was made far easier by a new photographic tool: the computer.

Taken for granted today, digital imaging and image processing were the state of the art in the early 1960's. In fact, scientists developed image processing to help solve the anticipated difficulties in reproducing pictures of Mars taken by spacecraft, though the technique was first tested on spacecraft pictures of the Moon. Removing "noise" on the image from spacecraft circuits and the space environment, and smoothly improving the contrast of the dim Martian scenes were just the beginning of an art that now pervades medical, forensic, scientific and commercial images.

Looking at the densely packed craters in the image of the small swatch of the Martian plains, the Mariner scientists could hardly believe that almost no Earth-based astronomers had predicted that Mars might resemble Earth's Moon. But the impact craters were the dominant features of the scenery. Small craters lay on the rims of large ones and scientists judged that the topography was very old and little changed in contrast to Earth.

No mountains, valleys, ocean basins or canals were visible. The first picture revealed the edge or limb of the planet. Image processing brought out an atmospheric haze above the horizon. The last few pictures were dark, showing the night side of Mars, but just before the edge of night, what appeared to be frost glistened on crater rims.

The Mariner 4 atmospheric team estimated the Martian surface pressure to be 4 millibars to 7 millibars, compared to about 1,000 millibars on Earth. That made the air on Mars about 150 to 200 times thinner than on Earth. They concluded that it was mostly carbon dioxide. Other instruments searched in vain for indications of an Earth-like magnetic field or radiation belts.

After the Mars encounter and playback were finished, the spacecraft resumed its observations of the interplanetary environment. However, Mariner 4 and Earth soon moved in their orbits so that telemetry could no longer be detected. In 1967 the spacecraft returned to the vicinity of Earth, approaching as close as 29 million miles, and sent back data from a few months of solar wind and solar flare measurements. On December 20, 1967, after three years in flight, Mariner 4 finally ran out of the propellant used to turn and orient it, thereby ending the first mission to Mars in U.S. space exploration history.


Mariner 4 Anniversary Marks 30 Years of Mars Exploration  (2024)
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