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Mariner 3 & 4
Readied for launch in 1964, Mariner 3 and 4 were NASA’s first attempt to send a spacecraft to Mars. Their mission would be to “flyby” Mars, measure the atmosphere, and take some historic pictures. The Soviet Union had already attempted several flybys, but all had failed. Not wanting to surrender any ground in the space race by letting America succeed, the Russians readied their own probe in 1964 which they called Zond 2.

Mariner 3 was launched on November 5, 1964 on an Atlas/Agena rocket. Shortly after liftoff, problems began. The probe was shielded from the friction of the Earth’s atmosphere during launch by a protective covering. It was supposed to be jettisoned when the probe reached space. But soon after takeoff, the covering collapsed, destroying the probe. Before the launch window for Mariner 4 closed (which would delay the next attempt for almost 2 years), NASA spent three frantic weeks designing, building, and testing a new covering for the second Mariner attempt.

On November 38, Mariner 4 lifted off from Cape Canaveral and was catapulted successfully to Mars. The rocket, the probe, and the new shield worked perfectly. Just two days later, the CIA informed NASA that the Soviets had launched Zond 2. The first race to Mars was underway.

But Zond 2 failed halfway to Mars, just like a previous Soviet flyby attempt called Mars 1. NASA engineers joked about a “great galactic ghoul” that gobbled up the spacecraft, and didn’t wanting them to reach Mars. But they stopped joking when Mariner 4 began to behave strangely during its pass through the same region where Zond 2 failed. In the end, the glitches turned out to be nothing, and Mariner 4 continued on its journey.

Once it arrived at Mars, Mariner 4 would not enter orbit, but would sweep past Mars in a gentle arc, snapping pictures and taking measurements, and relaying them back to Earth. There would only be one chance; the probe could not return to Mars if something went wrong. Even more dangerous, it would pass behind Mars, losing contact with the Earth and losing its solar power from the Sun. If there was a problem with the probe’s battery, it may not be able to acquire data or send it back to the Earth.

On July 15, 1965 after seven months in space, Mariner 4 flew behind the planet as planned, becoming the first traveler from Earth to ever reach Mars. The probe discovered that Mars had no magnetic field, had an atmosphere that was only one-half of one percent as dense as the Earth’s, and that the ice in the polar caps was actually frozen carbon dioxide & dry ice.

All of this was a shock to those who expected Mars to be a sister planet of Earth, with abundant and possibly intelligent life. The first pictures that came back from Mariner 4 showed that the surface of Mars was marred by craters, looking a lot like the Moon.

Mariner 6 & 7
Four years later, NASA readied two identical spacecraft, Mariners 6 and 7, which would further study Mars by flying past the planet three times closer than Mariner 4. The probes benefited from the advancements in technology, and carried reprogrammable computers for the first time on a robotic space mission. They could also transmit data back to Earth at a rate almost 2000 times that of Mariner 4.

Mariner 6 launched on February 24, 1969, and Mariner 7 on March 27, 1969 on twin Atlas-Centaur rockets. Mariner 6 had an uneventful cruise to Mars, and successfully flew past the planet on July 30, 1969, only 10 days after Neil Armstrong became the first man to set foot on the moon.

Mariner 7, taking a more direct path to Mars, caught up to Mariner 6 and was only 5 days behind once it flew past the Red Planet. On July 30th, contact was lost with Mariner 7 for about seven hours. Once telemetry was returned, it was discovered that the camera-pointing instrument had failed. Fortunately, ground controllers were able to manually orient the spacecraft to take images during the flyby, demonstrating the benefit of the reprogrammable computer onboard.

Mariners 6 and 7 each acquired a series of “far encounter” images as they approached the planet, and a series of near encounter images. In total, 143 far encounter images and 58 near encounter images were transmitted. The two spacecraft concentrated their views on different areas of the planet; Mariner 6 imaged near the equator, and Mariner 7 imaged the edge of the polar cap and other northern regions. The images still disappointed scientists, as they showed mostly flat, cratered terrain instead of the expected variations that were hoped for. But future missions would later reveal the truth about the surface.

The probes also acquired measurements of Mars’ atmosphere and a radio-occultation experiment that originally flew on the Mariner 4 mission once again returned results. It detected that Mars’ ionosphere was present only on the sunlit side of the planet.

Mariner 9
The next opportunity to launch a spacecraft to Mars occurred in 1971, and was to be the best yet. No less than five probes were being prepared, and NASA was readying Mariner 8 and 9 which would orbit the planet for the first time. Mariner 8 would go into a polar orbit and map 70% of the surface and Mariner 9 would try to explain why some regions of Mars are dark and some are light. The Soviets had a more ambitious goal: they would try to land on Mars. Their three probes were comprised of orbiter-lander pairs, and were designed to land their payloads on the Martian soil in order to send back the first pictures from the surface. Each of the Russian probes weighed 10,000 pounds, over four times the weight of each U.S. Mariner probe.

Mariner 8 launched on May 8, 1971, but the rocket’s second stage failed and it tumbled helplessly into the Atlantic. The first Soviet probe had a similar fate, as its upper stage was mistakenly set to fire in 1.5 years instead of 1.5 hours.

However, the remaining three probes had much better luck. The Soviets launched Mars 2 on May 19 and Mars 3 on May 28. Back in the U.S., Mariner 9 successfully launched on May 30. As the three probes from Earth cruised toward Mars, astronomers reported a yellow cloud enveloping the red planet. It was a Martian dust storm, and it turned out to be the largest and fiercest ever observed. For the first time, three explorers were on their way to Mars and the planet was completely hidden behind a shroud of dust. Nobody could be sure what would happen when the probes reached Mars.

Mariner 9, on a faster trajectory than the Soviet probes, reached the planet first and became the first probe to ever orbit Mars succesfully. The first pictures sent back were totally black, since Mariner’s camera could not penetrate the global dust storm. Fortunately, NASA engineers had designed Mariner 9 to carry a reprogrammable spacecraft, so that it was able to alter its mission while in space. It would be able to wait out the storm in Mars orbit.

But unfortunately for the Soviets, their technology was not as advanced and their probes could not have this capability. Mars 2 arrived 2 weeks after Mariner and dispatched its lander automatically, right into the swirling dust storm. The lander was pelted by dust, unable to navigate, and crashed into the surface. Although it was unsuccessful, it still made Mars 2 the first object from Earth to reach the surface of Mars. The Soviets reported that Mars 2 had carried a small hammer-and-sickle pin. Soviet power had spread to Mars!

Mars 3 followed Mars 2 into a successful orbit, and also automatically dispatched its lander. This lander seemed to have more luck, and apparently landed successfully on the surface, sending back a faint signal. But soon, the signal disappeared. Perhaps the dust storm had blown the lander over.

The Mars 2 and 3 orbiters, like the landers, could not be reprogrammed to wait out the storm, and began taking pictures of the dust-covered planet. They used up all their battery power taking useless black images, although they did return some science data from their other instruments. All in all, Mars 2 and 3 were major disappointments for the Russian exploration of Mars.

Mariner 9 waited out the storm for a month, turning off its instruments to save power. When the storm subsided, the camera was turned on, and took pictures of four huge craters, as much as 50 miles wide. They turned out to be volcanoes! The largest, Olympus Mons, is the tallest mountain in the solar system, at 17 miles high & three times as high as Mt. Everest. It’s base is 400 miles across, as big as the state of Arizona. Mariner also discovered a vast canyon system, six miles deep and as long as the entire United States. It was named Valles Marineris, in honor of its discoverer Mariner 9. The probe discovered vast networks of what looked like channels carved by rivers and floods. Had water once flowed on the surface of Mars?

Mariner 9 showed that Mars was neither a lifeless, barren world like the Moon, nor an Earthlike world with abundant life and flowing water. But it could once have been the latter, and the search for the evidence of life on Mars, past or present, really began with this knowledge. Mariner 9 was designed to operate for 90 days, but in fact continued to send back data for a year. It sent back over 7,000 pictures of Mars and its moons, and more data than had been received by all previous explorations missions in the solar system put together.