Other than Earth, the three inner planets of the solar system are: Mercury, Venus, and Mars. While the outer gas planets have fascinating colors and textures, the inner planets have their own unique traits. The Mariners were a series of ten spacecraft that were launched between 1962 and 1973 to explore the inner planets.
An Atlas-Agena rocket, which was actually a military intercontinental ballistic missile, launched all the Mariner spacecraft. Since the spacecraft were going toward the Sun, solar power was the most effective choice to power the spacecraft. Each of them were equipped with four solar panels.
Mariner 1, 2, 5: Missions to Venus
Compared to the Soviet Venera program, the United States showed little interest in Venus. Still, the few missions towards the planet were all successful… except the first one. Mariner 1, set off on July 22, 1962, veered off course shortly after the launch. The Range Safety officer had no choice but to press the destruct button and the launcher and payload fell in pieces into the Atlantic.
However, the back-up Mariner 2 was soon ready to be launched and this time it was successful. On December 14, 1962, it flew pass Venus. Instruments detected temperatures of more than 427*C (800*F) and an atmospheric pressure 100 times greater than on Earth.
By the time Mariner 5 was launched, the design of the Mariner spacecraft had been slightly modified. It was slightly heavier and larger than the earlier probes, weighing about 245 kg (540 lb). The probe was also equipped with a collection of new instruments, including a central computer [always a good thing]. Mariner 5 flew within 3990 km (2478 mi) of Venus and provided additional information about the planet's atmosphere.
Mariner 3, 4, 6-9: Missions to Mars
Mariner 3 was launched toward Mars in November 1964. However, the mission ended much quicker than planned when the probe's protective shroud failed to open after being launched. Later that month, after a quick redesign of the shroud, Mariner 4 was launched. It flew past Mars at a distance of 9846 km (6115 mi) and returned the first close-up pictures of the red planet. Mariner 4 detected that Mars had no radiation belts and no magnetic field, indicating that Mars does not have a metallic core.
Mariner 6 and Mariner 7 were identical spacecraft. These 412 kg (910 lb) probes were fully automatic but could be reprogrammed remotely from Earth. Launched in 1969, the probes transmitted television images of Mars and analyzed the planet's surface and atmosphere with radio ultraviolet and infrared signals.
On May 30, 1971, 22 days after Mariner 8 failed to launch, Mariner 9 was launched toward Mars. Weighing 998 kg (1.1 tons), it was the largest of the Mariner probes. Mariner 9 entered the obit of Mars and became the first artificial satellite of another planet. The probe sent more than 7000 photos of Mar's surface.
Mariner 10: The Distinguished Finale
When Mariner 10 launched in November 1973, the design and capabilities of the Mariner spacecraft had improved greatly. Mariner 10 was able to perform more extensive scientific research while being relatively smaller, only half the weight of Mariner 9. Mariner 10 passed Venus at 4200 km (2609 mi) and used the planet's gravity to slingshot the probe toward Mercury (a technique used widely later). Mariner 10 revealed Mercury to be heavily cratered like the moon. Using solar orbit, Mariner 10 was able to circle back and visit Mercury 2 more times.
Throughout the Mariner program, we have gained information about the inner solar system as well as experience and technology with building robotic spacecraft. The knowledge gained was directly applied to the Voyager program, where 2 spacecraft were sent to explore the outer planets of the solar system.
