When humans finally set foot on Mars, it will be the culmination of a journey that has taken decades. As in any voyage, the most important step is the first. That occurred with humanity’s first up-close encounter with the Red Planet on July 14, 1965, when the pioneering Mariner 4 spacecraft took the first detailed photographs of the Martian surface, paving the way for future missions to successfully land a probe on the ground.
One of a series of 10 space probes designed to gather information about the solar system’s planets, Mariner 4 weighed 260.8 kg and measured 2.89 metres high by 6.88 metres wide. Its four solar panels contained a total of 28,224 solar cells, able to generate 310 watts of power at the distance of Mars from the Sun. Its octagonal central frame housed electronic equipment, a propulsion system and gas tanks for attitude control. Technical instruments, most of which were mounted on the frame’s exterior, included a magnetometer, dust detector, cosmic ray telescope, trapped radiation detector, solar plasma probe, Geiger counter and, most importantly, a television camera.
The Mariner 4 mission was the seventh attempt to send a spacecraft to Mars. Between 1960 and 1964 the Soviet Union tried and failed five times. NASA launched Mariner 3, also intended for Mars, four weeks before Mariner 4 but it failed to separate from the Atlas-Agena rocket that boosted it into space. Mariner 4 was launched from Cape Canaveral, Florida, on November 28, 1964. The above photo captures the dedication of NASA staff to the success of the mission. It was taken in the computer room of the “Echo” antenna at the Goldstone Tracking Station in the Mojave Desert, California.
After traveling for 228 days Mariner 4 flew within 10,000 km of Mars, capturing the first images of another planet ever taken in space. This is an enhanced contrast version of the first Mars photograph, released on July 15, 1965. It was radioed back to Earth as digital data. Mariner 4 could transmit information through its high-gain antenna at a speed of 33.3 bits per second and its low-gain antenna at 8.3 bps. Sending a whole image (200 by 200 pixels) took about 10 hours.
Digital image data transmitted by Mariner was converted by a “real-time data translator” into numbers printed on thin strips of paper. Too impatient to wait for the official processed image, members of the telecommunications section at NASA’s Jet Propulsion Laboratory manually arranged the strips and hand-coloured the numbers to produce the above picture. The completed image was subsequently framed and presented to JPL’s director, William Pickering.
Over a few hours Mariner 4 took a grand total of 21 complete pictures of Mars (plus part of a 22nd). This was dictated by the limits of the four-track magnetic tape recorder on which the images were initially stored for later transmission; its 100 metres of tape had a storage capacity of 5.24 million bits, or 655 kilobytes – cutting-edge for its time. With each photo covering an area of about 200 square kilometres, the fuzzy black-and-white images collectively captured just 1% of the Martian surface; but it was enough.
Mariner 4’s mission put an end to centuries of fantasies about Mars. It showed the Red Planet to be a battered, crater-pocked world, more like the Moon than Earth, with no signs of water or other necessary conditions for life. It also collected data about the planet crucial to the success of subsequent exploration missions. One of the most important observations was the unexpected finding that Mars has very low atmospheric pressure – a fraction of what is found on Earth. Scientists thus knew that successfully landing a module on the surface would require retro rockets as well as parachutes.
Mariner 4 continues to be regarded as one of NASA’s most successful missions – well worth its estimated $US 83 million cost. After its Mars flyby, the spacecraft coasted into solar orbit, continuing to return data to Earth for another three years. Final contact was lost on December 21, 1967.