Pioneer 10 was launched on 2 March 1972 (!) on a trajectory which
encountered Jupiter on 5 December 1973. Because of its intententional
close approach to Jupiter, Pioneer 10 was accelerated to a speed in
excess of solar escape velocity.
Distant Pioneer Needs New Home
by Simon Mansfield
Wayout - August 4, 1999 - The first interstellar explorer Pioneer 10,
is alive and well as it's plutonium battery continues to feed a
trickle of energy from its decaying core. On July 10 Pioneer 10 was
commanded to make a precession maneuver that will keep it's antenna
aligned towards Earth until at least September, when it will start to
drift aimlessly unless funding is found.
With the Lunar Prospector operations team winding down, the
opportunity to continue some basic station keeping of Pioneer 10 will
soon lapse. Since 1997, the Lunar Prospector mission team has used
Pioneer 10 as a training operation, enabling ongoing precession
maneuvers to keep the spacecraft aligned for NASA's Deep Space
However, if control is lost, Pioneer 10 will drift into eternity
carrying only its etched gold card that may one day point someone to
Sol. The spacecraft as of August 1, was 73.16 AUs relative to the Sun
or some 11 billion kilometers from Earth while moving at 12.24 km/sec
or 27,380 mph. The current round trip light time is now over 20 hours
While Pioneer 10's antenna continues to point towards Earth and the
telemetry quality remains okay it will be possible to operate Pioneer
10 into September. Tracking is on the 70 meter antennas only. The
signal level is between -177 to -179 dbm, with SNR from 0.8 to 1.5 dB.
The other issue is of course the RTG pack, which currently has a bus
voltage of around 27.5 volts (nominal value = 28 volts). But this
power is still sufficient for limited science with Pioneer 10
returning data a few hours each week from the low-power
Geiger-Tube-Telescope and the Charged Particle Instrument.
Continuing GTT data from Pioneer 10 during the first part of 1999 has
been of of special importance in determining whether or not Pioneer 10
is still interior to the heliopause.
Neutron monitors on Earth at Climax and Goose Bay recorded a marked
and rapid decrease in cosmic ray intensity of about 4 % during April
and early May of 1998. If Pioneer 10 is still inside the heliopause,
we can expect a decrease in cosmic-ray intensity at Pioneer 10 to
occur during 1999.
The approximate 9 month delay from Earth to Pioneer 10 corresponds to
the distance of ~72 AU covered by the solar wind assuming a speed of
450 km/s. If Pioneer 10 has passed outside the heliopause into
interstellar space, then the decrease in cosmic intensity will not be
observed at Pioneer 10.
Pioneer 10 will continue into interstellar space, heading generally
for the red star Aldebaran, which forms the eye of Taurus (The Bull).
Aldebaran is about 68 light years away and it will take Pioneer over 2
million years to reach it.