SETI bioastro: Pioneer 10 article from Sky & Telescope

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From: Larry Klaes (larry.klaes@incent.com)
Date: Wed May 09 2001 - 13:30:10 PDT


PIONEER 10 LIVES ON

After 8.5 months of silence, Pioneer 10 is once again in touch with
its handlers here on Earth. Ground controllers heard from the
spacecraft for about 90 minutes on April 28th while tracking it with
NASA's 70-meter receiving dish in Spain. The long-distance call came
down "sweet as could be -- a nice, strong signal," says Lawrence
Lasher, Pioneer project manager at the Ames Research Center in
California.

The breakthrough came after weeks of failing to pick up Pioneer's
feeble signal by merely listening for it. Lasher now believes that the
spacecraft can no longer maintain a stable transmission frequency. To
sidestep this malfunction, the Spanish station beamed a
single-frequency carrier signal to the spacecraft, which then echoed
it back to Earth (after a round-trip travel time of 21.8 hours).
Ground controllers used this same two-way communication scheme when
they last heard from Pioneer 10 on August 6, 2000. Keeping in touch
with the 29-year-old craft has become very difficult because it is now
11.7 billion kilometers from Earth and because onboard power is barely
adequate to run the 8-watt transmitter. Although its mission
officially ended in 1997, Pioneer 10 has avoided a complete shutdown
because Ames engineers are using the weakening radio beacon to test a
new tracking method based on chaos theory.

Lasher plans other communication sessions in the coming weeks to
assess Pioneer 10's condition and to beam up some housekeeping
instructions. Commanding the spacecraft came a halt last year when the
last of the project's decades-old PDP computers failed, complicating
efforts to keep Pioneer's antenna pointed toward Earth. But since then
critical command sequences have been transferred to a modern desktop
system. "We're in business again," Lasher says. According to James A.
Van Allen, whose Geiger-tube telescope is the sole experiment still
sending back data, Pioneer 10 could reach the boundary marking true
interstellar space within a few years. Even though the odds are long,
he and Lasher hope the spacecraft will still be functioning well
enough to announce its arrival there.


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