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EARTH STRAINS TO HEAR PIONEER 10 SOME 7 BILLION MILES AWAY

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March 3rd, 2000 - Issue #189



28 YEAR-OLD PIONEER 10 SPACECRAFT GETS A REVIVAL

Originally launched in 1972, Pioneer 10 is still providing valuable
scientific data.  The program nearly died a few years ago due to
lack of funding, but was revived when scientists studying chaos theory
took an interest. Also, in 2 million years, it should the red star
Aldebaran, carrying a message from humanity for any sentient life
it encounters en route.


http://cnn.com/2000/TECH/space/03/02/venerable.probes/index.html





Space Science News for March 2, 2000



Six billion miles and counting....

Last month NASA received a weak signal from Pioneer 10, twice as far from
the Sun as Pluto and speeding toward the constellation Taurus. The hardy
spacecraft, which is so low on power that it can't transmit and maneuver at
the same time, is still returning data from the outer solar system. This is
also a good time of year to see where Pioneer 10 is heading from your own
back yard.






Pioneer status


March 2, 1999




PIONEER 10 MISSION STATUS

STATUS UPDATED: 2 March 1999


(Launched 2 March 1972)

Distance from Sun (1 March 1999): 72.08 AU 

Speed relative to the Sun: 12.24 km/sec (27,380 mph) 

Distance from Earth: 10.81 billion kilometers (6.716 billion miles) 

Round-trip Light Time: 20 hours 01 minutes


CONGRATULATIONS PIONEER 10! Happy 27th Birthday. Two years into retirement,
Pioneer 10 is flying high and still calling home.


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 >6.7 Billion miles (>72 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 on 17 February 1998 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.


POSSIBLE HELIOPAUSE DATA

Continuing GTT data from Pioneer 10 during the first part of 1999 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 ~72 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.


The battery reading is very low - perhaps at a minimum. Pioneer 10 persists
longer than ever conceived or expected. Stay tuned!


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.


Project Manager: Dr. Lawrence Lasher






Pioneer 10

(Launched 2 March 1972)


STATUS UPDATED: 8 February 1999


Distance from Sun (1 February 1999): 71.88 AU Speed relative to the Sun:
12.24 km/sec (27,380 mph) Distance from Earth: 10.70 billion kilometers
(6.646 billion miles) Round-trip Light Time: 19 hours 49 minutes


PIONEER 10 CARRIES ON! One more successful precession maneuver to point the
spacecraft to Earth was accomplished on 6-8 February 1999.


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 > 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 on 17 February 1998
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.


POSSIBLE HELIOPAUSE DATA

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
tuned!


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.


Dr. Larry Lasher

Pioneer Project Manager

NASA Ames Research Center




NASA Ames Research Center, Mountain View, CA


March 27, 1997



PIONEER 10 SPACECRAFT BRIEFING SCHEDULED MONDAY AT NASA AMES

Media are invited to a briefing and photo opportunity March 31 at 10:30 a.m.
at NASA Ames Research Center to observe the final signal acquisition from
the Pioneer 10 spacecraft. Brief statements will be made in Bldg. N-244,
Room 103 at 10:30 a.m. A photo opportunity will take place at 11:15 a.m. in
the Pioneer Mission Control Center, 3rd floor, Bldg. N-244.


Pioneer 10's last support is being conducted from NASA's Deep Space Station
63, located near Madrid, Spain. The final downlink of the signal begins at
5:25 a.m. PST March 31. Signal acquisition will end at 11:45 a.m PST March
31.


The Geiger Tube Telescope Instrument data from this support will be the last
data samples processed for the Principal Investigator Dr. James Van Allen
under the Pioneer 10 project. The Pioneer 10 signal, transmitted 6.2 billion
miles from Earth, is equal to 2.5 billionth of a trillionth of a watt. The
signal strength measurement of Pioneer 10 on the computer screen will
visibly drop at 11:45 a.m. and the lights will be symbolically turned off in
the control room.


Future support of the Pioneer 10 spacecraft will be on a non-interference
basis to other NASA projects and will be used for the purpose of training
Lunar Prospector controllers in Deep Space Network coordination of tracking
activities.


Intermittant tracking for Pioneers 6, 7 and 8, in Earth-like solar orbits,
will also cease on Mar. 31. The briefing will include a brief summary of the
entire Pioneer program, United State's longest running spacecraft program,
which began in 1958. Speakers are: Dr. Larry Lasher, Pioneer Project
Manager, "Overview of Pioneer Program"; Charles Hall, Pioneer Project
Manager (1969-80) "Interplanetary, Planetary, Outer Solar System Pioneer
Missions"; Dr. David Morrison, Director of Space, NASA Ames, "Pioneer's
Relevance to the Future of Space Exploration"; Scott Hubbard, Assoc.
Director of Space, Lunar Prospector Mission Manager, NASA Ames, "Transition
to Lunar Prospector".




Ames Research Center, Mountain View, CA

Feb. 27, 1997


WORLDWIDE VIRTUAL CONFERENCE CELEBRATES PIONEER 10 ANNIVERSARY

People located in at least 11 countries will be virtual attendees at a March
3 conference honoring the silver anniversary of the launch of Pioneer 10,
the oldest working spacecraft that is still speeding away from the solar
system.


Those wishing to participate will be able to attend the conference by
Internet hookup. Through the medium of their computers, they will be able to
hear eight talks about planets and astronomy by experts, including Dr. James
Van Allen, Pioneer 10 Principal Investigator for whom Earth's Van Allen Belt
is named. Remote conference attendees also will be able to see graphics on
their computer screens illustrating the audio presentations.


The day-long educational conference, co-sponsored by NASA's Ames Research
Center, Mountain View, CA, and The Planetary Society, will take place at
NASA Headquarters, Washington, DC. "It's going to be attended by as many as
200 DC-area educators and Planetary Society members," said Dr. Larry Lasher,
NASA event organizer and Pioneer project manager. The conference is
scheduled to begin at 9:30 a.m. and conclude at 4:30 p.m. EST.


"People from all over the world have been following Pioneer 10 developments
for decades. This virtual conference will allow them to learn more about the
mission," said Andrea McCurdy, one of the NASA Ames K-12 Internet Initiative
team members. McCurdy was instrumental in helping to establish the 
silver anniversary Pioneer 
web stite.


Internet participants will not only be able to view the conference
proceedings, they will also be able to use the world wide web to send typed
questions to experts and to receive audio answers.


"We are using an additional technology that will allow the user to receive
audio, to send questions via their keyboards and to receive text answers.
With this technology, they can also view computer pictures that will
automatically change during the talks," McCurdy said.


More than 150 Internet attendees from Australia, Belgium, Canada, Denmark,
Italy, Japan, Kenya, the Netherlands, the United Kingdom and the United
States have registered to attend the conference. More people are expected to
enroll before the virtual conference begins. They will be to participate in
advance in practice sessions to learn how to use audio, "chat" and other web
tools, according to McCurdy. However, Internet attendees are not required to
register in advance, she said.


"We can accommodate up to 200 people during the virtual conference. If the
system becomes congested, we have the capability to double that number," she
said. Potentially, thousands of people could drop in to the virtual
conference and not cause any problems, according to McCurdy.


If attendees miss the live sessions, they will be able to look at a complete
Internet archive of the Pioneer event at a later time. "All the audio files,
text, transcriptions and graphics will be there. We don't plan to remove
them from the Internet," McCurdy said.


Presenters will include Pioneer 10 project manager Dr. Larry Lasher; former
Pioneer 10 project managers Richard Fimmel, speaking on "Pioneer Firsts" and
Fred Wirth talking on "Operating and Controlling Pioneer;" Planetary Society
executive director Dr. Louis Friedman, presenting "Pioneer: Segue to the
Future;" and the Jet Propulsion Laboratory's Pioneer 10 principal
investigator (PI) Ed Smith talking about "Outer Planets and Magnetospheres."


Other Pioneer 10 PIs scheduled to speak will include Dr. John Simpson from
the University of Chicago on "The Heliosphere: Our Laboratory in Space," and
the University of Maryland's Dr. Frank McDonald presenting "The Heliosphere:
The Barrier to Interstellar Space." In addition, Ames Research Center
Director Dr. Henry McDonald will offer remarks and Director of the Space
Directorate at Ames, Dr. David Morrison, will speak on "Future Exploration
of Outer Space." Dr. Wesley Huntress, NASA Associate Administrator, Space
Sciences, will also address participants.


Pioneer 10 was the first artifact to leave the solar system on June 13,
1983, when the spacecraft passed beyond the system's farthest known planet.
The spacecraft is now approaching a point 7 billion miles from the Sun.
Sunday, March 2, is the official 25th anniversary of the beginning of
Pioneer 10's flight.




NASA Headquarters, Washington, DC

Ames Research Center, Mountain View, CA


Feb. 27, 1997


PIONEER 10 SPACECRAFT NEARS 25TH ANNIVERSARY, END OF MISSION

A major milestone for humanity's most distant and longest-lived
interplanetary explorer will occur on March 2, 1997, when NASA's hardy
Pioneer 10 spacecraft reaches its 25th anniversary in space.


"Pioneer 10 exemplifies the American pioneering spirit of exploration far
beyond the frontier," said Dr. Wesley T. Huntress, Jr., Associate
Administrator for Space Science at NASA Headquarters, Washington, DC. "Not
only has it made many major scientific discoveries in the far reaches of
space, we're proud that it has managed to stay alive almost ten times longer
than the original mission called for, a tribute to the designers and
builders at TRW, and the operators at NASA's Ames Research Center.


"NASA operated the Pioneer 10 mission as long as it had enough power to
return science data about the conditions in space as far from Earth as
possible. We will end the science mission at the end of March because the
power has finally become too weak to do significant science," Huntress said.


Launched from Cape Kennedy on March 2, 1972, aboard an Atlas Centaur rocket
for what had been planned as a two-year mission to Jupiter, Pioneer 10 is
now so far away that its radio signal, traveling at the speed of light
(186,000 miles per second), takes nine hours and ten minutes to reach the
Earth. Currently twice as far from the Sun as Pluto, Pioneer is returning
data about the farthest reaches of the Sun's atmosphere.


Now 6.2 billion miles from Earth, Pioneer 10, built by TRW Space and
Electronics Group, Redondo Beach, CA, was the first spacecraft to travel
through the asteroid belt and explore the outer solar system, the first
spacecraft to visit Jupiter, the first to use a planet's gravity to change
its course and to reach solar-system-escape velocity, and the first
spacecraft to pass beyond the known planets.


Now traveling at 28,000 miles per hour, Pioneer 10 is recording the
intensity of galactic cosmic rays in the outer heliosphere (the region of
solar wind influence) and searching for the heliopause, the true outer
boundary of the solar system where the flow of hot gas from the Sun (the
solar wind) bumps into the interstellar medium. The spacecraft is heading in
the direction of the long "tail" of the teardrop-shaped heliosphere.


Many scientists rank the first crossing of the asteroid belt between Mars
and Jupiter as one of Pioneer 10's major achievements. Before the crossing,
no one knew how many rocks, as well as grains of sand, speeding through
space at thousands of miles per hour would impact and possibly disable the
spacecraft. Pioneer 10 made the crossing nearly unscathed, thus opening the
way for other spacecraft to explore beyond Mars, including its sister
Pioneer 11, the twin Voyager spacecraft, the Galileo mission to Jupiter and,
later this year, the Cassini mission to Saturn.


The spacecraft also survived Jupiter's intense radiation belts when it flew
safely by the giant planet in December 1973. Providing the best information
of the planet obtained to that date, Pioneer 10's instruments studied
ultraviolet and infrared radiation and charged particles, and provided the
first "close-ups" of Jupiter and its moons. It also was the first to measure
the planet's giant radiation belts, magnetic field and magnetosphere, as
well as its atmosphere and interior. The spacecraft measured the exact
masses of Jupiter and its four planet-sized moons, Io, Europa, Ganymede and
Callisto.


After its Jupiter flyby, the spacecraft continued its mission of exploration
for over two decades, and in 1983 became the first spacecraft to travel
beyond the outermost planets, Neptune and Pluto. Pioneer 10 will have its
first "near-star-encounter" in about 30,000 years when it will pass within
approximately three light years of the red dwarf star Ross 248 in the
constellation Taurus. In the next million years, Pioneer 10 will pass ten
stars at distances ranging from three to nine light years, and will probably
still be traveling through the Milky Way galaxy when the Sun becomes a red
giant and destroys the Earth five billion years from now.


Pioneer carries a message for any intelligent life forms that it might
encounter on its trek across the galaxy. A gold-anodized aluminum plaque
designed by Dr. Frank Drake and the late Dr. Carl Sagan is bolted to the
spacecraft. The plaque's engraving depicts a man and a woman, a map of
Earth's solar system, and other symbols which may help intelligent beings
interpret the message and understand something about the spacecraft's
creators, and where they lived.


The 570-lb. spacecraft carries 11 instruments that have been used to measure
magnetic fields, solar wind, high energy cosmic rays, cosmic and asteroidal
dust, and Jupiter's ultraviolet and infrared radiation. Pioneer 10 obtains
power from four radioisotope thermoelectric generators that originally
supplied 160 watts, but are now two-thirds degraded. The spacecraft is
spin-stabilized and has a nine-foot dish antenna. Pioneer's 8-watt signal,
equal to the power of a night light, now reaches the 70-meter antennae and
sensitive receivers at NASA's Deep Space Network with the strength of .3
billionths of a trillionth of a watt. More information on Pioneer 10
(including an image of the plaque) is available via the Internet at URL:



http://pyroeis.arc.nasa.gov/pioneer/PN10&11.html


The 25th Anniversary of Pioneer 10's launch will be celebrated March 3 in
Washington, DC. The events include a day-long Educator's Conference at NASA
Headquarters, co-sponsored by the Ames Research Center and The Planetary
Society, which will be linked worldwide by the Internet, with a virtual
conference featuring RealAudio, WebChat, and E-mail questions for those not
attending onsite. Visit the 
Pioneer 10 web site.


The Pioneer 10 mission is managed by the Ames Research Center, Mountain
View, CA, for the Office of Space Science, NASA Headquarters, Washington,
DC.




SKY & TELESCOPE NEWS BULLETIN

FEBRUARY 28, 1997


PIONEER 10's ANNIVERSARY

March 2nd marks the 25th anniversary of the launch in 1972 of Pioneer
10.  The "Energizer Bunny" of interplanetary spacecraft, Pioneer 10 is
almost exactly 10 billion kilometers from Earth, more than 9 light-hours
away.  The spacecraft made history with its close flyby of Jupiter in
December 1973.  Together with Pioneer 11, which arrived the following
year, these 570-pound spacecraft took many pictures of Jupiter and its
major moons. But the twin spacecraft will be most remembered for their
measurements of the fields and charged particles in Jupiter's immense
magnetosphere.


Incredibly, Pioneer 10 maintains contact with Earth using just an 8-
watt transmitter, but the electricity supplied by the plutonium-fueled
generators on board is weakening. Even so, the spacecraft is still
returning data on the intensity of galactic cosmic rays, using the
instrument developed by space pioneer James Van Allen. Some 30,000
years from now the spacecraft will pass in the general vicinity of
Ross 248, a 15th-magnitude star in the constellation Taurus.




PIONEER 10 TURNS 25 ON MARCH 2

A TRW news release

February 27, 1997


REDONDO BEACH, Calif. - 1972 was a good year for launching careers: Hewlett
Packard introduced the world's first hand-held scientific calculator; Jimmy
Connors and Chris Evert became professional tennis players; and NASA
launched the TRW-built Pioneer 10 spacecraft.


The venerable HP-35 electronic calculator, priced at $395 per copy, replaced
the faithful slide rule, transforming complete industries almost overnight.
The Connors/Evert duo brought celebrity and a new, innovative style of play
to center court, helping to transform professional tennis into one of the
world's richest-paying spectator sports.


And Pioneer 10, the first man-made object to leave the solar system, proved
that travel to the outer solar system was possible, paving the way for a
generation of successful NASA interplanetary space missions including
Pioneer 11, Voyagers 1 and 2 and Galileo.


On Sunday, March 2, Pioneer 10 will celebrate its 25th birthday in space.
Still operating, it is now more than 6.1 billion miles from the Earth,
making it NASA's most distant spacecraft. Like Connors, Evert and the
hand-held calculator, it owes its success to innovation -- and rugged,
well-designed packaging.


And like those other pioneers, its career has produced new ways of thinking
about the world that have fundamentally altered the course of history.


"Pioneer 10 is a wonderful example of the engineering excellence and
superior mission performance that TRW has delivered to its space customers
since 1958," said Tim Hannemann, executive vice president and general
manager of TRW Space & Electronics Group.


"The spacecraft's innovative, low-risk design allowed it to remain in
service 15 times longer than its intended mission life, giving NASA and
scientists worldwide an unprecedented look at Jupiter and the outer reaches
of our solar system."


Rendezvous with Jupiter

Designed and built by TRW Space & Electronics Group, the Pioneer 10
spacecraft was originally "hired" by NASA Ames Research Center, Mountain
View, Calif., as an interplanetary scout. Its mission, intended to last just
21 months, was to explore the giant planet Jupiter using its payload of 11
science instruments.


To succeed in the job, Pioneer 10 would have to overcome two significant
hurdles: an asteroid belt of rock and space debris between the orbits of
Mars and Jupiter considered to be a barrier to interplanetary space travel;
and several belts of radiation near Jupiter feared strong enough to render
the spacecraft inoperable.


Just in case their "new hire" didn't reach Jupiter safely on the first try,
NASA asked TRW to build an identical back-up spacecraft, Pioneer 11.


TRW's Ed Wheeler, a member of Pioneer 10's original design team, recalled,
"Since no other spacecraft had ever made this trip, we knew we had to make
it extremely reliable and ensure, as best we could, that it could survive a
harsh radiation environment." Wheeler and his colleagues completed design,
production and integration of the 570-pound spacecraft in about
two-and-a-half years.


Pioneer 10 was launched on March 2, 1972 from Cape Kennedy aboard an
Atlas/Centaur launch vehicle. A year later, it began its trek across the
uncharted asteroid belt. To the amazement of NASA scientists, it emerged
seven months later, virtually unscathed.


In December 1973, Pioneer 10 became the first spacecraft to fly by Jupiter,
snapping the world's first close-up photos of the giant planet. That's when
TRW's foresight in designing a simple, rugged spacecraft began to pay off.


"We designed many of Pioneer 10's components with proven, radiation-hardened
medium-scale integrated circuits, instead of the newer, but riskier very
large-scale integrated circuits available in the late '60s," explained
Wheeler.


"When the spacecraft flew by Jupiter, it was exposed to radiation levels
100,000 times stronger than a lethal dose for a human being. The glass on
its star tracker, a navigation instrument, turned black, but the spacecraft
suffered only minor damage."


Before it left Jupiter's neighborhood, Pioneer gathered the first definitive
set of data about the solar system's largest planet. Among its findings:


 Discovery that Jupiter is a liquid planet with little or no solid core;

 First model of Jupiter's pulsating magnetosphere and huge radiation
     belts;

 Discovery of helium in the Jovian atmosphere;

 First close-up photos of Jupiter's Great Red Spot; and

 First accurate measurements of the mass and densities of Jupiter's
     planet-sized moons.


On to Other Worlds

Having achieved NASA's original mission goals, Pioneer 10 was directed to
help the world's scientists explore and characterize the next frontier,
interstellar space. This new mission would take it to the outer reaches of
the solar system, where sunlight becomes too faint to power solar arrays.


Fortunately, Pioneer 10's design team had planned for this situation by
equipping it with a self-contained nuclear power system. Its four
radioactive isotope thermoelectric generators (RTGs), which produce energy
from the radioactive decay of plutonium, each provided 40 watts of power at
4 volts.


As Pioneer 10 passed by Jupiter, its career received the first
"interplanetary jump start." A TRW engineer calculated that if the
spacecraft were targeted for a "near miss" with Jupiter (fly within 80,000
miles), the immense gravitational attraction of the planet would boost the
satellite's velocity to more than 82,000 miles per hour, the escape velocity
of the solar system.


The successful "slingshot" maneuver around Jupiter, which allowed NASA to
retarget Pioneer 10 for a spot outside the solar system, is now standard
operating practice for interplanetary space travel.


On June 13, 1983, more than 11 years after launch, Pioneer 10 became the
first man-made object to leave the solar system. With seven of its
instruments still sending back data about interstellar space, though, its
career was far from over.


A Unique Brand of Spacecraft

Pioneer 10 was the first spacecraft designed with the ability to
automatically point itself at the Earth. Until 1983, it used the Sun as a
reference point to determine which direction to point its 9-foot-wide
antenna to provide scientists on Earth with the strongest possible signal.


By the time Pioneer 10 crossed Pluto's orbit for the last time, however, the
Sun had become too distant a star to provide useful navigational clues.


Today, Pioneer 10 orients itself with the aid of a strong beacon-like signal
sent out about twice a year from NASA's Deep Space Network. Using the beacon
as a reference point, Pioneer 10's programmable processor - one of the first
ever flown in space - commands the spacecraft's attitude control thrusters
to turn the spacecraft toward the Earth.


The single most important factor behind the success of these on-orbit
"steering" maneuvers - NASA successfully performed the latest one just last
month - is Pioneer 10's hydrazine-based propulsion system. In 25 years, the
spacecraft's four tiny one-pound attitude control thrusters - the "oars"
that turn the spacecraft during the pointing maneuvers - have never missed a
day of work.


TRW credits this performance, in part, to the tiny electric heaters that
insulate the thrusters and their liquid propellant lines against the extreme
cold of space. Design variations on these units have been the standard for
TRW spacecraft attitude control systems since the early '70s.


As the world's ambassador to the universe, Pioneer 10 also carries with it
the world's first "interstellar postcard," a 6-inch by 9-inch anodized gold
plaque bolted to the spacecraft's main frame.


Designed by the late Dr. Carl Sagan, the plaque is inscribed with symbols,
binary numbers and drawings meant to communicate the nature and the location
in the universe of the civilization that launched the Pioneer 10 spacecraft.


The Final Road

Now in the twilight of its career, Pioneer 10 continues its outward trek
through the universe, still hurtling along at nearly 28,000 miles per hour.
Even at that speed, it will probably not encounter another star system for
at least 32,600 years, most likely the star Ross 248.


Six of its original 11 instruments are still functional, but its power
generators are running out of fuel. The energy produced by the satellite's
RTGs is now barely sufficient to operate just two instruments: a Geiger tube
telescope and an ultraviolet photometer.


Still, Pioneer 10's durable 8-watt transmitter, the power equivalent of a
home night light, continues to transmit its findings about the outer reaches
of the heliosphere, that portion of space affected by the solar wind.


By the time the signals reach the football-field-sized antennas of NASA's
Deep Space Network - a one-way trip takes more than 9 hours, 10 minutes at
the speed of light - they measure less than one-billionth of a trillionth of
a watt (.2 x 10-21 watts).


Like the power in Pioneer 10's generators, though, the scientific value of
Pioneer 10 data - and the availability of NASA resources to continue
tracking the spacecraft - is rapidly dwindling. On March 31, 1997, the
funding needed to continue mission operations will cease. But Pioneer 10's
faint signal will continue to serve the cause of space exploration.


Its real-time tracks will still be used to train spacecraft controllers and
data archivists at NASA's Deep Space Network and other NASA tracking
facilities as they prepare for upcoming NASA Discovery missions such as
Lunar Prospector.


As it sails into eternity, Pioneer 10 will be remembered not only as "NASA's
trailblazer to the stars," but also, in Wheeler's words, as an "innovative
little spacecraft that found a cheap, simple way to perform an extraordinary
mission."


And who knows, maybe one day someone in a distant universe will discover
Pioneer 10's interstellar post card, figure it out -- and send it back.


The TRW-built Pioneer 11 spacecraft, twin sister to Pioneer 10, was launched
on April 5, 1973 following Pioneer 10's successful trek across the feared
Mars-Jupiter asteroid belt. It followed Pioneer 10's same trajectory to
Jupiter, then headed for Saturn, where it made the first direct observations
of the ringed planet in 1979.


After continuing its studies of energetic particles, it too exited the solar
system. Pioneer 11's mission ended in September 1995. Its electrical power
source exhausted, the spacecraft could no longer operate any of its
scientific instruments, nor point its antenna toward Earth. The spacecraft
is now headed toward the constellation of Aquila, northwest of the
constellation of Sagittarius. It may pass near one of the stars in the
constellation in about 4 million years.



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