The Pioneer 10 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 3 December 1973,
when it reached approximately 2.8 Jovian radii (about 200,000 km).
Pioneer 11 was the second mission to investigate Jupiter and the outer solar system and
the first to explore the planet Saturn and its main rings. Pioneer 11, like Pioneer 10,
used Jupiter's gravitational field to alter its trajectory radically. It passed close to
Saturn and then it followed an escape trajectory from the solar system.
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:
- Asteroid/Meteroid Detector (non-imaging telescopes with overlapping fields of view to
detect sunlight reflected from passing meteoroids)
- Meteroid Detector (sealed pressurized cells of argon and nitrogen gas for measuring the
penetration of meteoroids)
- Helium Vector Magnetometer (HVM)
- Infrared Radiometer
- Imaging Photopolarimeter (IPP)
- Trapped Radiation Detector (TRD)
- Plasma Analyzer (PA)
- Charged Particle Instrument (CPI)
- Cosmic Ray Telescope (CRT)
- Geiger Tube Telescope (GTT)
- Ultraviolet Photometer (UV)
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
- the omnidirectional and medium-gain antennas which operated together while connected to
one receiver and
- 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.
A third set of parts has been assembled as a third probe, Pioneer H, as potential a back-up and was considered later for a Jupiter fly-by with a subsequent out-off-ecliptic mission. This mission was never approved and the probe is now on diplay at the National Air and Space Museum in Washington, D.C.
