Pioneer program

The Pioneer programs were two distinct series of space probes launched by the United States. These robotic spacecraft were designed to explore the Moon, the planets, and the space between them. The first series operated from 1958 to 1960. It focused on early attempts to reach the Moon and interplanetary space. The second series ran from 1965 to 1992. This later period involved much more complex missions to the inner and outer Solar System.

The first program was a time of difficult testing and learning. NASA, which formed from the old NACA, worked with the Army and the Air Force Ballistic Missile Division. Many early missions faced technical failures during launch or flight. For example, Pioneer 0 was destroyed only 77 seconds after launch on August 17, 1958. Pioneer 1 and Pioneer 2 also failed to reach their goals due to third-stage failures. However, the program achieved success with Pioneer 4. Launched on March 3, 1959, it successfully achieved Earth escape velocity. This is the speed required to break free from Earth's gravity.

The second program used the Pioneer name for a wide variety of scientific goals. One major goal was creating an interplanetary space weather network. This was accomplished using four spacecraft: Pioneer 6, 7, 8, and 9. These probes were launched between 1965 and 1968. They were placed in solar orbits to monitor the Sun. Pioneer 6 and 9 orbit at 0.8 AU from the Sun. This distance is closer than Earth is to the Sun. Because of this, their orbital periods are slightly shorter than Earth's. Pioneer 7 and 8 orbit at 1.1 AU. This makes their orbital periods slightly longer than Earth's.

Because these probes have different orbital periods, they see the Sun from unique angles. They can sometimes sense parts of the Sun before Earth-based observatories can. This happens because the probes can see sides of the Sun that are hidden from Earth. This network provided a constant way to watch the weather of our solar system. The program also moved toward the outer planets. Pioneer 10 launched in March 1972 to study Jupiter and the interstellar medium. Pioneer 11 followed in April 1973 to explore both Jupiter and Saturn.

These outer planet missions were historic achievements. Pioneer 10 and Pioneer 11 were the first two of five artificial objects to reach escape velocity. This speed allows them to leave our entire Solar System behind. To share a message with the universe, they each carry a golden plaque. The plaque depicts a man and a woman. It also contains information about the origin of the probes and their creators. This was intended as a message for any extraterrestrials that might find them.

The name "Pioneer" has an interesting history involving the Air Force. Stephen A. Saliga, a chief designer of Air Force exhibits, is credited with the name. He was assigned to the Air Force Orientation Group at Wright-Patterson Air Force Base. When a new lunar-orbiting vehicle was described to him, he found the technical description too long. He wanted a name that had a theme for exhibit designs. He suggested "Pioneer" because the Army was already calling themselves "Pioneers in Space." Saliga believed this name would help the Air Force make a "quantum jump" in its identity.

In the later years of the program, scientists focused on the planet Venus. In 1978, the program moved from flyby missions to orbital insertion. Orbital insertion means the spacecraft enters a stable path around a planet. The Pioneer Venus project included the Pioneer Venus Orbiter and the Pioneer Venus Multiprobe. The Multiprobe mission used several different types of probes. It included a 300 kg large probe that used a parachute. It also used three 75 kg impactor probes named the North, Night, and Day probes. These missions allowed for a much closer look at the atmosphere of Venus.