PIONEER 10 &11
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PIONEER 10
PIONEER 11
POWER LIMITATIONS MANEUVERS
SPACECRAFT
PIONEER 6-9
LINKS		 JUPITER

View the Pioneer history

PIONEER 10
ROCKET

On 2 March 1972 Pioneer 10 was launched on top of an Atlas/Centaur/TE364-4 launch vehicle. This was the first time the Atlas-Centaur launch vehicle had three-stages . The third stage was required to rocket Pioneer 10 to the speed of 51,810 kilometers per hour (32,400 mph) needed for the flight to Jupiter. This made Pioneer the fastest manmade object to leave the Earth, fast enough to pass the Moon in 11 hours and to cross the Mars orbit, about 80 million kilometers (50 million miles) away, in just 12 weeks.


On 15 July 1972 Pioneer 10 entered the Asteroid Belt, a doughnut shaped area which measures some 280 million kilometers wide and 80 million kilometers thick. The material in the belts travels at speed about 20 km/sec. and ranges in size from dust particles to rock chunks as big as Alaska.

After safely traversing the Asteroid Belt, Pioneer 10 headed toward Jupiter. Accelerated by the massive giant to a speed of 132,000 km/hr (82,000 mph), Pioneer 10 passed by Jupiter within 130,354 km (81,000 miles) of the cloud tops on December 3, 1973. During the passage by Jupiter, Pioneer 10 obtained the first close-up images of the planet, charted Jupiter's intense radiation belts, located the planet's magnetic field, and discovered that Jupiter is predominantly a liquid planet.

Following its encounter with Jupiter, Pioneer 10 is exploring the outer regions of our Solar system, studying energetic particles from our Sun (Solar Wind), and cosmic rays entering our portion of the Milky Way. As of March 2, 1998, Pioneer 10 was at a distance of 10.43 billion km from Earth. At that distance, it took over 9 hours and 19 minutes for the radio signal (which is traveling at the speed of light) to reach Earth.


PIONEER 11
On 5 April 1973 Pioneer 11 was launched , like Pioneer 10, on top of an Atlas/Centaur/TE364-4 launch vehicle. After safe passage through the Asteroid belt on 19 April 1974, the thrusters were fired to add another 63.7 m/sec (210 ft/sec) to the spacecraft's velocity. This adjusted the aiming point at Jupiter to 43,000 km (26,725 miles) above the cloud tops. The close approach also allowed the spacecraft to be accelerated by Jupiter to a velocity 55 times that of the muzzle velocity of a high speed rifle bullet - 173,000 km/hr (108,000 mph) - so that it would be carried across the Solar System some 2.4 billion kilometers (1.5 billion miles) to Saturn.

Pioneer 11 obtained dramatic images of the Great Red Spot, it made the first observation of the immense polar regions, and determined the mass of Jupiter's moon, Callisto during its flyby of Jupiter on 2 December 1974.

Looping high above the ecliptic plane and across the Solar System, Pioneer 11 raced toward its appointment with Saturn on 1 September 1979. Pioneer 11 flew to within 13,000 miles of Saturn and took the first close-up pictures of the planet. Pioneers instruments located two previously undiscovered small moons and an additional ring, it also charted Saturn's magnetosphere and magnetic field and found its planet-size moon, Titan, to be too cold for life. Hurtling underneath the ring plane, Pioneer 11 sent back amazing pictures of Saturn's rings. The rings, which normally seem bright when observed from Earth, appeared dark in the Pioneer pictures, and the dark gaps in the rings seen from Earth appeared as bright rings.

Following its encounter with Saturn, Pioneer 11 explored the outer regions of our Solar system, studying energetic particles from our Sun (Solar Wind), and cosmic rays entering our portion of the Milky Way. In September 1995, Pioneer 11 was at a distance of 6.5 billion km (4 billion miles) from Earth. At that distance, it takes over 6 hours for the radio signal (which is traveling at the speed of light) to reach Earth.
By September 1995, its power source was nearly exhausted, Pioneer 11 could no longer make any scientific observations, and routine mission operations were terminated. There have been no communications with Pioneer 11 since November 1995 when the last transmission was received right before the Earth's motion carried it out of view of the spacecraft antenna. The Earth's motion has carried it out of the view of the spacecraft antenna. The spacecraft cannot be maneuvered to point back at the Earth because of the lack of power. It is not known whether the spacecraft is still transmitting a signal. No further tracks of Pioneer 11 are scheduled. The spacecraft is headed toward the constellation of Aquila (The Eagle), Northwest of the constellation of Sagittarius. Pioneer 11 may pass near one of the stars in the constellation in about 4 million years.

POWER SOURCE, RTGs
RTGs As you may have read in my page about the Voyager spacecraft the Voyager´s uses RTGs (Radioisotope Thermoelectric Generators) for a power source, Pioneer also uses this. These RTGs contain plutonium 238 isotope, as the plutonium decays it produces heat. Thermoelectric couples inside the RTGs converts this heat into electrical current which then is used by the spacecraft.
The electrical output depends on how hot the junction temperature is, as time passes by the thermoelectric junction degrades, resulting in a lower output. The Pioneer 10 spacecraft has been in space since 1972, at launch the spacecraft produced 155 Watts, but as time passed by the Watt output decreased, I am not sure how much it decreases in a year, but on the Voyager spacecraft it lies at approximately 5 Watts a year. As less power is available systems/instruments has to be turned off. As of March 1998 there was approximately an output of 12 Watts from the RTGs on Pioneer 10 (that is extremely little). This is barely enough power to keep the Iowa Geiger Tube telescope and the Charged particle instrument alive a couple hours a week. The Charged particle instrument is turned on for 4 hours every 2 weeks. Current operation of the instruments dips into the batteries, sometimes resulting in a low value of 0.94 volts during a track. This indicates further degradation of the RTGs. It was anticipated that the transmitter would keep working to sometime in 1998 but it is now 1999 and the spacecraft is still working. If it keeps working the Geiger-Tube-Telescope will yield important information over the next few months, telling us if the probe is still in the heliopause. No one knows how long it will survive, the Watt output of the RTG's is very low and the battery reading is at it's minimum and any use of the two still functioning instruments dips into the little battery power available. The spacecraft is currently 71 AU's from the sun (January 1999)

PRECESSION MANEUVER
For the spacecraft to have contact with Earth, the Earth has to be within 0,8 degrees of the boresight of the spacecraft antenna. Since the Earth moves by almost 2 degrees from the spacecraft's point of view it has to be re-aimed at Earth about twice a year to stay in communication with us down here on the Earth, if this is not done the spacecraft signal gets weaker until it is not heard at all. This re-aiming is done by a "CONSCAN (conical scan) precession maneuver" executed by the spacecraft.

According to Lawrence Lasher, Pioneer Project Manager, Pioneer 10 has 34 Kg of the original 124 Kg hydrazine left in its tanks (February 1998). Enough to last long after the power source is exhausted.
When the command to the spacecraft is given to do the CONSCAN precession maneuver it is done with the radio on. This maneuver requires power like the rest of the systems on Pioneer 10, and because of the decreasing amount of power available there was not enough power to do this maneuver, but it had to be done, so to get enough power to do the maneuver on January 26 1997, the radio had to be switched off. This does not sound to serious but the radio had never been switched off before during a precession maneuver. The people at NASA Ames Research Center were concerned that turning the transmitter's traveling wave tube off in the deep cold of space for 90 minutes to do the maneuver and then back on again would cause a thermal shock that might shatter the helix in the tube.

The spacecraft, 6.6 billion miles from the Earth, has a round-trip light time of 18 hours 20 minutes. The command-off signal to the spacecraft transmitter was sent at 3:00 am PST, Jan. 26; the command-on signal at 4:30 am PST. Confirmation of the transmitter's turn-off was received at 9:20 pm Jan. 26 Notice of the transmitter's restoration and the maneuver's success was received in the jubilant Pioneer Control Room at 10:50 pm that evening. This maneuver has been done succesfully 2 times more now, on 9 August 1997 2 and February 1998.


DESCRIPTION OF THE SPACECRAFT
Measured from its farthest ends, from the horn of the medium-gain antenna to the tip of the omnidirectional antenna, The Pioneer spacecraft is 2.9 meters long measured from the horn of the medium-gain antenna to the tip of the omnidirectional antenna. Pioneer weighs 270 kilograms. The spacecraft is spin-stabilized, spinning about the axis of the high gain dish antenna at approximately 5 rpm. Six Hydrazine thrusters provide velocity, attitude and spin-rate control.

Four radioisotope thermoelectric generators (RTGs) provide electrical power, each providing 40 watts of power at launch. Two three-rod trusses, 120 degrees apart, project from the equipment compartment to deploy the RTG power sources about 10 feet from the center of the spacecraft. A third boom, 120 degrees from the others, projects from the experiments compartment and positions the helium vector magnetometer sensor 20 feet from the spacecraft center.

plaque
As the first two spacecraft to leave our solar system, Pioneer 10 & 11 carry a graphic message in the form of a 6- by 9-inch gold anodized plaque bolted to the spacecraft's main frame.



Pioneer Instruments

Module Mass
(Kg)		 Usable propellant mass Propulsion Height
(in flight)		 Instrument payload Electric
power
Pioneer 10 270 Kg 124 Kg 6 Hydrazine
thrusters		 2.9 m 11 instruments 4 RTGs,
155 W
Pioneer 11 270 Kg 124 Kg 6 Hydrazine
thrusters		 2.9 m 12 instruments 4 RTGs,
155 W

Pioneer Project History
PIONEER 6-9
Pioneers 6-9 were launched into Solar orbit between 1965 and 1968. Their prime mission completed years ago, the spacecraft are being tracked only occasionally.

Pioneer 6 was launched on 16 December 1965. Some time after 15 December 1995 (almost 30 years after it was launched) the primary transmitter (TWT) failed. During a track on 11 July 1996 the spacecraft was commanded to switch to the backup TWT, and the downlink signal was re-acquired. The spacecraft, and two of the science instruments were again functioning. Pioneer 6 was recently tracked on 6 October 1997 as part of a training program for flight controllers of the Lunar Prospector (now in orbit around the Moon).

Pioneer 7 was launched on 17 August 1966. It was last tracked successfully on 31 March 1995. The spacecraft and one of its science instruments were still functioning.

Pioneer 8 was launched on 13 December 1967. Its primary TWT failed several years ago, but on 22 August 1996 the spacecraft was commanded to switch to the backup TWT, and the downlink signal was re-acquired. The spacecraft and one of its science instruments were again functioning.

Pioneer 9 was launched on 8 November 1968. The spacecraft failed in 1983.

Pioneer Venus
The Pioneer Venus Orbiter spacecraft was launched on 20 May 1978. It orbited the planet Venus for 14 years until it entered the Venus atmosphere on 8 October 1992 and was destroyed.

The Pioneer Venus Multiprobe spacecraft was launched on 8 August 1978. Three small probes, one large probe, and the spacecraft bus entered the Venus atmosphere on 9 December 1978.

To find out more go to http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNhome.html
and
http://quest.arc.nasa.gov/pioneer10