First Satellites To Reach Outer Planets

The Pioneer Spacecraft Missions are a series of eight spacecraft missions managed by NASA's Ames Research Center's Pioneer Project Office.

Satellites have been an integral part of man’s quest to learn more about our world, and beyond what we can see. Between 1965 and 1968, Pioneers 6-9, managed by NASA’s Ames Research Center’s Pioneer Project Office, were launched into solar orbit. Pioneer 6, the oldest NASA spacecraft still in operation, made a successful contact for about two hours on December 8, 2000, to commemorate its 35th anniversary.  These satellites, now past their primary mission, are only occasionally tracked. 

Pioneer 10 launched on March 2, 1972, and became the first spacecraft to make direct observations and capture close-up images of Jupiter. The data obtained was crucial in realizing the fatal nature of Jupiter’s radiation belts to humans. Pioneer 10 is now more than 8 billion miles away.

Its successor, Pioneer 11, the first spacecraft to study Saturn, has a more curious tale. The motion of the Earth pushed it out of range of the spacecraft’s antenna, rendering it unable to turn to face Earth. In about 4 million years, the spacecraft will pass close to one of the stars in the constellation Aquila (the Eagle).

In the 1970s and ‘80s, Voyager 1 and 2 conducted a “grand tour” of the outer planets, discovering new moons and rings, compiling movies of the atmospheres of planets, and other observations. While Voyager 1 focused on Jupiter and Saturn, Voyager 2 was tasked to fly past Uranus and Neptune- a remarkable feat that has not been replicated since.

With these successful missions in its belt, NASA launched the Galileo spacecraft that arrived at Jupiter in December 1995. The spacecraft would then spend seven years studying Jupiter, its moons, and its turbulent atmosphere until it met its end by crashing into Jupiter. Galileo’s success was limited by a malfunctioning radio antenna, reducing the amount of data transmitted to a trickle.

Our knowledge about Saturn can be credited to Cassini, launched into orbit around Saturn in the summer of 2004. It has captured the true wonders of Saturn, its rings and moons, and has sent back tens of thousands of images. Cassini has also carried the Huygens probe, which parachuted to a soft landing on Titan in January 2005. Their findings reveal the possibility of liquid pools and a volcano on the planet’s surface. Cassini remained a great source of data till its end when it was sent on a final mission that would exhaust its fuel supply.