spase://SMWG/Observatory/Pioneer10

This mission was the first to be sent to the outer solar system and the first to investigate the planet Jupiter, after which it followed an escape trajectory from the solar system. The spacecraft achieved its closest approach to Jupiter on December 3, 1973, when it reached approximately 2.8 Jovian radii (about 200,000 km). As of Jan. 1, 1997 Pioneer 10 was at about 67 AU from the Sun near the ecliptic plane and heading outward from the Sun at 2.6 AU/year and downstream through the heliomagnetosphere towards the tail region and interstellar space. This solar system escape direction is unique because the Voyager 1 and 2 spacecraft (and the now terminated Pioneer 11 spacecraft mission) are heading in the opposite direction towards the nose of the heliosphere in the upstream direction relative to the inflowing interstellar gas. The spacecraft is heading generally towards the red star Aldebaran, which forms the eye of Taurus (The Bull). The journey over a distance of 68 light years to Aldebaran will require about two million years to complete. Routine tracking and project data processing operatations were terminated on March 31, 1997 for budget reasons. Occasional tracking continued later under support of the Lunar Prospector project at NASA Ames Research Center with retrieval of energetic particle and radio science data. The last successful data acquisitions through NASA's Deep Space Network (DSN) occurred on March 3, 2002, the 30th anniversary of Pioneer 10's launch date, and on April 27, 2002. The spacecraft signal was last detected on Jan. 23, 2003 after an uplink was transmitted to turn off the last operational experiment, the Geiger Tube Telescope (GTT), but lock-on to the sub-carrier signal for data downlink was not achieved. No signal at all was detected during a final attempt on Feb. 6-7, 2003. Pioneer Project staff at NASA Ames then concluded that the spacecraft power level had fallen below that needed to power the onboard transmitter, so no further attempts would be made.

The history of the Pioneer 10 tracking status is available from the web site of the former Pioneer Project at the following location:

http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNhome.html

Fifteen experiments were carried to study the interplanetary and planetary magnetic fields; solar wind parameters; cosmic rays; transition region of the heliosphere; neutral hydrogen abundance; distribution, size, mass, flux, and velocity of dust particles; Jovian aurorae; Jovian radio waves; atmosphere of Jupiter and some of its satellites, particularly Io; and to photograph Jupiter and its satellites. Instruments carried for these experiments were magnetometer, plasma analyzer, charged particle detector, ionizing detector, non-imaging telescopes with overlapping fields of view to detect sunlight reflected from passing meteoroids, sealed pressurized cells of argon and nitrogen gas for measuring the penetration of meteoroids, UV photometer, IR radiometer, and an imaging photopolarimeter, which produced photographs and measured polarization. Further scientific information was obtained from the tracking and occultation data.

The spacecraft body was mounted behind a 2.74-m-diameter parabolic dish antenna that was 46 cm deep. The spacecraft structure was a 36-cm-deep flat equipment compartment, the top and bottom being regular hexagons. Its sides were 71 cm long. One side joined a smaller compartment that carried the scientific experiments. The high-gain antenna feed was situated on three struts, which projected forward about 1.2 m. This feed was topped with a medium-gain antenna. A low-gain omnidirectional antenna extended about 0.76 m behind the equipment compartment and was mounted below the high-gain antenna. Power for the spacecraft was obtained by four SNAP-19 radioisotope thermonuclear generators (RTG), which were held about 3 m from the center of the spacecraft by two three-rod trusses 120 deg apart. A third boom extended 6.6 m from the experiment compartment to hold the magnetometer away from the spacecraft. The four RTG's generated about 155 W at launch and decayed to approximately 140 W by the time the spacecraft reached Jupiter, 21 months after launch. There were three reference sensors: a star sensor for Canopus which failed shortly after Jupiter encounter and two sun sensors. Attitude position could be calculated from the reference directions to the earth and the sun, with the known direction to Canopus as a backup. Three pairs of rocket thrusters provided spin-rate control and changed the velocity of the spacecraft, the spin period near the end of the mission being 14.1 seconds. These thrusters could be pulsed or fired steadily by command. The spacecraft was temperature-controlled between minus 23 deg C and plus 38 deg C. A plaque was mounted on the spacecraft body with drawings depicting a man, a woman, and the location of the sun and the earth in our galaxy.

Communications were maintained via (1) the omnidirectional and medium-gain antennas which operated together while connected to one receiver and (2) the high-gain antenna which was connected to another receiver. These receivers could be interchanged by command to provide some redundancy. Two radio transmitters, coupled to two traveling-wave tube amplifiers, produced 8 W at 2292 MHz each. Uplink was accomplished at 2110 MHz, while data transmission downlink was at 2292 MHz. The data were received by NASA's Deep Space Network (DSN) at bit rates up to 2048 bps enroute to Jupiter and at 16 bps near end of the mission.

Space experiments mostly continued to operate for planetary or interplanetary measurements until failure or until insufficient spacecraft power from the RTG's was available for operation of all instruments, such that some were turned off permanently and others were cycled on and off in accordance with a power sharing plan implemented in September 1989. The Asteroid/Meteroid Detector failed in December 1973, followed by the Helium Vector Magnetometer (HVM) in November 1975 and the Infrared Radiometer in January 1974. The Meteroid Detector was turned off in October 1980 due to inactive sensors at low temperatures. The spacecraft sun sensors became inoperative in May 1986, and the Imaging Photopolarimeter (IPP) instrument was used to obtain roll phase and spin period information until being turned off in October 1993 to conserve power. The Trapped Radiation Detector (TRD) and Plasma Analyzer (PA) were respectively turned off in November 1993 and September 1995 for the same reason. As of January 1996 the final power cycling plan included part-time operations of the Charged Particle Instrument (CPI), the Cosmic Ray Telescope (CRT), the Geiger Tube Telescope (GTT), and the Ultraviolet Photometer (UV). As of August 2000, only the GTT instrument was still returning data.

Various other spacecraft subsystems also either failed or were turned off for power or other reasons, and an account of these may be of interest for engineering design of long duration deep space missions. The primary antenna feed offset bellows failed sometime in 1976 but a redundant unit was available for use thereafter. The Program Storage and Execution (PSE) subsystem was turned off in September 1989 for power conservation, after which spacecraft maneuvers were performed by ground command sequences. A receiver problem in mid-1992 prevented uplink to the high gain antenna, after which uplink commands could only be sent with 70-meter DSN antennas which also supported the 16 bps downlink. The Backup Line Heater experienced a sticking thermostat operation in March 1993 for 30 days but the problem did not reoccur. Undervoltage Protection Logic was turned off in December 1993 to prevent loss of critical spacecraft systems in the event of a transient undervoltage condition. Duration and Steering Logic (DSL) was turned off in February 1995 to conserve power, after which it was turned on again only for spacecraft maneuvers. RTG power levels are low enough that the spacecraft occasionally relies in part on battery power (accumulated during inactive periods) to run experiments and other systems.

The total mission cost for Pioneer 10 through the 1997 end of official science operations was about 350 million in FY 2001 U.S. dollars. This included about 200 million dollars for pre-launch design and development, and another 150 million for launch, telemetry tracking, mission operations and data analysis. These estimates were provided by the former Pioneer Project at NASA Ames Research Center.