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Pioneers (1958-2003)

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Almost everyone has heard of Pioneer 10 and 11, the two spacecraft that were the first to visit the Outer Solar System. But very few people have ever known that there were earlier and later Pioneer craft that visited the Inner Solar System. There were over a dozen Pioneer missions, and they helped scientists to learn more about spacecraft operations, and the environments in interplanetary space.

The Terran and Lunar Pioneers

Pioneer 1 was the first spacecraft launched by NASA and provided data on the extent of the Earth's radiation belts.

Pioneer 2 suffered a launch vehicle failure.

Pioneer 3 discovered a second radiation belt around Earth.

Pioneer 4 was the first American spacecraft to escape Earth's gravitational pull as it passed within 58,983 km (36,650 miles) of the moon. The spacecraft returned data on the moon's radiation environment, although the desire to be the first man-made vehicle to fly past the moon was lost when the Soviet Union's Luna 1 passed by the moon several weeks before Pioneer 4.

Pioneer 5 was designed to provide the first map of the interplanetary magnetic field. The vehicle functioned for a record of 106 days and communicated with Earth from a record distance of 36.2 million km (22.5 million miles).

The early Pioneers were exploratory missions that led to intriguing new questions that required more advanced types of spacecraft capable of exploring space to considerable distances within and beyond Earth's orbit. This led to the Pioneer 6 through 9 series that made the first detailed comprehensive measurements of the solar wind, solar magnetic field, and cosmic rays.

The Inner Pioneers

Pioneers 6 through 9 were of all of the same construction, as they were all designed as tests for spacecraft operation in space. They all weighed about 68 kg (150 lbs), and were 94x88.9 cm (37x35 in.). The spacecraft were stabilized by spinning (at about once per second) and designed to last at least six months. Pioneers 6-9 demonstrated that spacecraft could be stabilized by rotation. They supplied much information about interplanetary conditions, solar activity on Earth, the solar wind, cosmic rays, the sun's plasma and magnetic fields, physics of particles in space, and the nature of sun storms which produce solar flares.

Pioneer 6 was launched on December 16, 1965, and circled the sun at an average distance of 0.8 A.U. (1 A.U. is the distance from the Earth to the sun, about 93,000,000 miles (149,668,992 km)). It was commanded through its backup transmitter tube (TWT) in July of 1996, for its prime TWT failed in December 1995. Pioneer 6 became the oldest operating spacecraft (its cosmic ray detector and plasma analyzers were still operational) ever when it was tracked last on October 6, 1997.

Pioneer 7 was launched on August 17, 1966, and circled the sun at 1.1 A.U. It was last tracked successfully in March of 1995.

Pioneer 8 was launched on December 13, 1967, and circled the sun at 1.1 A.U. It was last tracked successfully on August 22, 1996, and was commanded to its backup TWT.Pioneer 10 and 11

Pioneer 9 was launched on November 8, 1968 and circled the sun at 0.8 A.U., and failed in 1983.

The Outer Pioneers

Pioneer 10 and 11 were designed to test the environment in the Outer Solar System, see if the asteroid belt was navigable, and to discover if the magnetic and radiation fields around Jupiter could be withstood by spacecraft. Pioneer 10 was launched on March 2, 1972, and Pioneer 11 was launched on April 5, 1973.

The Pioneer craft survived the asteroid belt easily. However, the ions trapped in Jupiter's magnetic field nearly fried the crafts. This was no surprise to scientists, for the radiation around Jupiter is about 1000 times the lethal dose for humans.

Jupiter from PioneerPioneer 10 became the first craft to flyby Jupiter December 3, 1973. In 1983, Pioneer 10 became the first spacecraft to travel beyond the orbit of Pluto. Pioneer 11 passed Jupiter on December 2, 1974, and then on September 1, 1979 it became the first probe to study Saturn. Pioneer 11, in its quick survey of Saturn, found a very narrow "F" ring, and two more small moons. This was the first narrow ring to be found around a planet.

Before their power supplies died (or nearly died), the Pioneers made valuable contributions to science. Some were proving that spacecraft could actually go this far. Others were in studying Jupiter and Saturn. Also, while they could, they studied parts of the heliopause (border of the sun's influence).Saturn from Pioneer

Pioneer 11's power supply died as of September 30, 1995, and the last communication from it was in November, 1995. Pioneer 10 is barely functioning at 82.04 A.U. away. It is not tracked regularly due to budget cuts, and the last data received by it was on December 5, 2002. The craft is still functioning normally.

They will become the first craft to head into interstellar (between stars) space (besides Voyager 1, which recently passed Pioneer 1). Pioneer 10 and 11 carry six by nine inch gold plaques which hold a graphic message on them (below). The plaques are bolted to the spacecrafts' main frame.

Pioneer Plaque

Pioneer 10 is headed towards the constellation of Taurus (The Bull) at a speed of 12.24 km/sec (7.6 miles/sec). It will take Pioneer 10 over 2 million years to pass by Aldebran, the red star that forms the eye of the Bull. Pioneer 11 is headed toward the constellation of Aquila (The Eagle), northwest of the constellation of Sagittarius. It may pass near one of the stars in the constellation in about 4 million years.

The Venus Pioneers

Another Pioneer craft was the Pioneer Venus Orbiter, officially called Pioneer 12. The Orbiter was launched on May 20, 1978, and reached Venus on December 4, 1978. The Orbiter was placed into a very elliptical orbit, for the closest it came to Venus was about 150 km (93 miles), and the farthest point of its orbit was 66,000 km (41,000 miles). It orbited Venus once every 23 hours and 11 minutes.

Pioneer Venus 12This particular orbit allowed global mapping of the clouds, atmosphere and ionosphere, measurement of upper atmosphere, ionosphere, and solar wind-ionosphere interaction, and mapping of the planet's surface by radar. For the first 19 months (until July 1980), the Orbiter maintained its closest point to Venus (the periapsis) by periodic maneuvers. As propellant began to run low, the maneuvers were discontinued, and solar gravitational effects caused the periapsis to rise to about 2,300 km (1,430 miles). By 1986, the gravitational effects caused the periapsis to start falling again, and the Orbiter's instruments could again make direct measurement within the main ionosphere.

During the Orbiter's mission, opportunities arose to make systematic observations of several comets with its Ultraviolet Spectrometer (OUVS). The comets and their date of observation were: Encke April 13 through April 16, 1984; Giacobini-Zinner, September 8 through 15, 1985; Halley, December 27, 1985 to March 9, 1986; Wilson, March 13 to May 2, 1987; NTT, April 8, 1987; and McNaught, November 19 through 24, 1987. The Orbiter's observation of Halley showed that when the comet comes closest to the sun, it releases 40 tons of water vapor per second.

Starting in September 1992, controllers used the remaining fuel in a series of maneuvers to keep raising periapsis altitude for as long as possible. On October 8, 1992, its fuel supply exhausted, the Orbiter ended its mission as a meteor flaming through the dense atmosphere of Venus.

Pioneer 13 was commonly called the Pioneer Venus Multiprobe Mission. On August 8, 1978, slightly less than three months after Pioneer 12 left Earth, the Multiprobe spacecraft was launched from the Kennedy Space Center. Its mission was to deploy four probes into the Venusian atmosphere.

On November 16, 1978, the Large Probe was released from the Bus toward an entry near the equator on the day side of Venus. Four days later, on November 20, 1978, the three Small Probes were released from the Bus. Two of the probes were targeted to enter on the night side and one was targeted to enter on the Venus day side. On December 9, 1978 the Bus with its instruments was re-targeted to enter Venus' day side.

When the probes separated from the Multiprobe Bus, they went "off the air" because they did not have sufficient on-board power or solar cells to replenish their batteries. Preprogrammed instructions were wired into them and their timers had been set before they separated from the Bus. The on-board countdown timers were scheduled to bring each probe into operation again three hours before the probes began their descent through the Venusian atmosphere. On December 9, 1978, just 22 minutes before entry, the Large Probe began to transmit radio signals to Earth. Only 17 minutes before hurtling into the Venusian atmosphere at almost 42,000 km/hr (26,099 miles/hr) did all of the Small Probes started transmitting.

All four probes were designed for a descent time of approximately 55 minutes before impacting the surface. None were designed to withstand the impact. However one Small Probe (the Day Probe) did survive and sent data from the surface for 67 minutes. Engineering data radioed back from the Day Probe showed that its internal temperature climbed steadily to a high of 126 °C (260 °F). Then its batteries were depleted, and its radio became silent.

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