archive: SETI [ASTRO] Pioneer 10 Update - December 1, 1998

SETI [ASTRO] Pioneer 10 Update - December 1, 1998

Larry Klaes ( )
Mon, 21 Dec 1998 15:03:01 -0500

>X-Authentication-Warning: majordom set sender
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>Date: Mon, 21 Dec 1998 18:55:23 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] Pioneer 10 Update - December 1, 1998
>Reply-To: Ron Baalke <>
>Pioneer 10 Mission Status
>December 1, 1998
>Dr. Lawrence Lasher, Pioneer Project Manager
> Pioneer 10
>(Launched 2 March 1972)
>Distance from Sun (1 December 1998): 71.44 AU Speed relative to the Sun:
>12.24 km/sec (27,380 mph) Distance from Earth: 10.56 billion kilometers
>(6.563 billion miles) Round-trip Light Time: 19 hours 34 minutes
>The mission formally ended on 31 March 1997 when funding ended in favor of
>more scientifically productive Heliospheric missions. However, a waiver was
>given to operate Pioneer 10 as part of the Lunar Prospector controller
>training program as long as other NASA missions were not interfered with.
>Pioneer 10 has continued at a much reduced activity level under those
>guidelines. We are deeply grateful for the gracious way that the Lunar
>Prospector staff and the DSN have managed this extra burden on their time.
>The spacecraft is at a distance of 6.6 Billion miles (71 AU's) and is the
>farthest out in the opposite direction to which the Sun moves. Voyager 1
>passed Pioneer 10 in mileage out of the Solar System earlier this year but
>is travelling in the opposite direction.
>The low-power Geiger-Tube-Telescope (GTT) instrument still yields valuable
>scientific data. We also receive data from the Charged Particle Instrument
>but only for a few hours each week to conserve battery power on Pioneer 10.
>Continuing GTT data from Pioneer 10 during the next few months will be of
>special importance in determining whether or not Pioneer 10 is still
>interior the heliopause.
>Neutron monitors on Earth (e.g., 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
>early 1999. The approximate 9 month delay from Earth to Pioneer 10
>corresponds to the distance of 71 AU covered by the solar wind assuming a
>speed of 450 km/s. If Pioneer10 has passed outside the heliopause into
>interstellar space, then the decrease in cosmic intensity will not be
>observed at Pioneer 10.
>Tracking of Pioneer is expected to continue for several more months under
>the current pointing arrangements, at which time another repositioning
>maneuver would be due. The battery reading is very low - perhaps at a
>minimum. Pioneer 10 persists longer than ever conceived or expected. Stay
>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.
>SUNWARD PULL!?(See the December 1998 issue of Scientific American)
>A team of planetary scientists and physicists led by John Anderson (Pioneer
>10 Principal Investigator for Celestial Mechanics) has identified a tiny
>unexplained acceleration towards the sun in the motion of the Pioneer 10,
>Pioneer 11 and Ulysses spacecraft. The anomalous acceleration - about 10
>billion times smaller than the acceleration we feel from Earth's
>gravitational pull - was identified after detailed analyses of radio data
>from the spacecraft. A variety of possible causes were considered including:
>perturbations from the gravitational attraction of planets and smaller
>bodies in the solar system; radiation pressure, the tiny transfer of
>momentum when photons impact the spacecraft; general relativity;
>interactions between the solar wind and the spacecraft; possible corruption
>to the radio Doppler data; wobbles and other changes in Earth's rotation;
>outgassing or thermal radiation from the spacecraft; and the possible
>influence of non-ordinary or dark matter. After exhausting the list of
>explanations deemed most plausible, the researchers examined possible
>modification to the force of gravity as explained by Newton's law with the
>sun being the dominant gravitational force. "Clearly, more analysis,
>observation, and theoretical work are called for," the researchers
>concluded. The scientists expect the explanation when found will involve
>conventional physics.
>Pioneer 11
>(Launched 5 April 1973)
>The Mission of Pioneer 11 has ended. Its RTG power source is exhausted.
>The last communication from Pioneer 11 was received in November 1995,
>shortly before the Earth's motion carried it out of view of the spacecraft
>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.