Pioneer 11
Pioneer 11 is a NASA robotic space probe launched on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, the solar wind, and cosmic rays. It was the first probe to encounter Saturn, the second to fly through the asteroid belt, and the second to fly by Jupiter. Later, Pioneer 11 became the second of five artificial objects to achieve an escape velocity allowing it to leave the Solar System. Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on September 30, 1995, and the last good engineering data was received on November 24, 1995.
Mission background
History
Approved in February 1969, Pioneer 11 and its twin probe, Pioneer 10, were the first to be designed for exploring the outer Solar System. Yielding to multiple proposals throughout the 1960s, early mission objectives were defined as:- Explore the interplanetary medium beyond the orbit of Mars
- Investigate the nature of the asteroid belt from the scientific standpoint and assess the belt's possible hazard to missions to the outer planets.
- Explore the environment of Jupiter.
- Map the magnetic field of Saturn and determine its intensity, direction, and structure.
- Determine how many electrons and protons of various energies are distributed along the trajectory of the spacecraft through the Saturn system.
- Map the interaction of the Saturn system with the solar wind.
- Measure the temperature of Saturn's atmosphere and that of Titan, the largest satellite of Saturn.
- Determine the structure of the upper atmosphere of Saturn where molecules are expected to be electrically charged and form an ionosphere.
- Map the thermal structure of Saturn's atmosphere by infrared observations coupled with radio occultation data.
- Obtain spin-scan images of the Saturnian system in two colors during the encounter sequence and polarimetry measurements of the planet.
- Probe the ring system and the atmosphere of Saturn with S-band radio occultation.
- Determine more precisely the masses of Saturn and its larger satellites by accurate observations of the effects of their gravitational fields on the motion of the spacecraft.
- As a precursor to the Mariner Jupiter/Saturn mission, verify the environment of the ring plane to find out where it may be safely crossed by the Mariner spacecraft without serious damage.
Spacecraft design
The Pioneer 11 bus measures deep and with six panels forming the hexagonal structure. The bus houses propellant to control the orientation of the probe and eight of the twelve scientific instruments. The spacecraft has a mass of 259 kilograms.Scientific instruments
Pioneer 11 has one additional instrument more than Pioneer 10, a flux-gate magnetometer.Mission profile
Launch and trajectory
The Pioneer 11 probe was launched on April 6, 1973, at 02:11:00 UTC, by the National Aeronautics and Space Administration from Space Launch Complex 36A at Cape Canaveral, Florida aboard an Atlas-Centaur launch vehicle, with a Star-37E propulsion module. Its twin probe, Pioneer 10, had been launched on March 3, 1972.Pioneer 11 was launched on a trajectory directly aimed at Jupiter without any prior gravitational assists. In May 1974, Pioneer was retargeted to fly past Jupiter on a north–south trajectory, enabling a Saturn flyby in 1979. The maneuver used of propellant, lasted 42 minutes and 36 seconds, and increased Pioneer 11
Encounter with Jupiter
Pioneer 11 flew past Jupiter in November and December 1974. During its closest approach, on December 2, it passed above the cloud tops. The probe obtained detailed images of the Great Red Spot, transmitted the first images of the immense polar regions, and determined the mass of Jupiter's moon Callisto. Using the gravitational pull of Jupiter, a gravity assist was used to alter the trajectory of the probe towards Saturn and gain velocity. On April 16, 1975, following the Jupiter encounter, the micrometeoroid detector was turned off.Encounter with Saturn
Pioneer 11 passed by Saturn on September 1, 1979, at a distance of from Saturn's cloud tops.By this time, Voyager 1 and Voyager 2 had already passed Jupiter and were en route to Saturn, so it was decided Pioneer 11 would pass through the Saturn ring plane at the same position Voyager 2 would later have to fly through in order to reach Uranus and Neptune. If there were faint ring particles capable of damaging a probe in that area, mission planners felt it was better to learn about it via Pioneer. Thus, Pioneer 11 was acting as a "pioneer" in a true sense of the word; if danger were detected, then Voyager 2 could be redirected further away from the rings but miss the opportunity to visit the ice giants in the process.
Pioneer 11 imaged—and nearly collided with—one of Saturn's small moons, passing at a distance of no more than. The object was tentatively identified as Epimetheus, a moon discovered the previous day from Pioneers imaging, and suspected from earlier observations by Earth-based telescopes. After the Voyager flybys, it became known that there are two similarly sized moons in the same orbit, so there is some uncertainty about which one was the object of Pioneer's near-miss. Pioneer 11 encountered Janus on September 1, 1979, at 14:52 UTC, at a distance of. At 16:20 UTC the same day, Pioneer 11 encountered Mimas at a distance of.
Besides Epimetheus, instruments located another previously undiscovered small moon and an additional ring, charted Saturn's magnetosphere and magnetic field, and found its planet-sized moon, Titan, to be too cold for life. Hurtling underneath the ring plane, the probe sent back 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.
Interstellar mission
On February 25, 1990, Pioneer 11 became the fourth human-made object to pass beyond the orbit of the planets.By 1995, Pioneer 11 could no longer power any of its detectors, so the decision was made to shut it down. On September 29, 1995, NASA's Ames Research Center, responsible for managing the project, issued a press release that began, "After nearly 22 years of exploration out to the farthest reaches of the Solar System, one of the most durable and productive space missions in history will come to a close." It indicated NASA would use its Deep Space Network antennas to listen "once or twice a month" for the spacecraft's signal, until "some time in late 1996" when "its transmitter will fall silent altogether." NASA Administrator Daniel Goldin characterized Pioneer 11 as "the little spacecraft that could, a venerable explorer that has taught us a great deal about the Solar System and, in the end, about our own innate drive to learn. Pioneer 11 is what NASA is all about – exploration beyond the frontier." Besides announcing the end of operations, the dispatch provided a historical list of Pioneer 11 mission achievements.
NASA terminated routine contact with the spacecraft on September 30, 1995, but continued to make contact for about two hours every two to four weeks. Scientists received a few minutes of good engineering data on November 24, 1995, but then lost final contact once Earth moved out of view of the spacecraft's antenna.
Current status
Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on September 30, 1995, and the last good engineering data was received on November 24, 1995.As of June 24, 2024, Pioneer 11 is estimated to be from the Earth and from the Sun. It was traveling at relative to the Sun and traveling outward at about 2.35 AU per year. The spacecraft is heading in the direction of the constellation Scutum near the current position RA 18h 54m dec -8° 46', close to Messier 26. In 928,000 years, it will pass within of the K dwarf TYC 992-192-1 and will pass near the star Lambda Aquilae in about four million years.
Pioneer 11 has been overtaken by the two Voyager probes launched in 1977. Voyager 1 has become the most distant object built by humans and will remain so for the foreseeable future, as no probe launched since Voyager has the speed to overtake it.