khayo@sonia.math.ucla.edu (Eric Behr) (06/16/88)
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NASA ANNOUNCES CONFERENCE FOR SMALL-CLASS EXPLORERS
June 14, 1988
RELEASE: 88-79
NASA will conduct a conference to discuss space science
research opportunities in the Explorer Program at NASA's Goddard
Space Flight Center (GSFC), Greenbelt, Md., June 21, 1988.
The Explorer Program is a long-standing NASA program for
launching small and moderate-sized space science mission
payloads. Dozens of Explorers have been launched, including the
Solar Mesospheric Explorer, the Infrared Astronomical Satellite,
the Dynamics Explorer, the Active Magnetospheric Particle Tracer
Experiment and the International Ultraviolet Explorer, which has
produced scientific data for more than 1,400 articles in
scientific journals.
The new Small-class Explorer Program, to be managed by
GSFC's Special Payloads Division, will conduct scientific
research in the space science disciplines: astrophysics; space
physics; and upper atmosphere science.
The Small-class Explorer Program will consist only of the
smaller missions characterized by the scope and capability of
investigations conducted on spacecraft launched by Scout-class
launch vehicles.
Because one purpose of the Small-class Explorer Program is
to provide a rapid execution of scientific investigations, the
proposed missions should take no more than 3 years from
initiation to launch. NASA will launch up to two missions per
year allocating an average of $30 million in developmental costs
for each mission.
The development phase of the initial mission is planned to
commence in the second half of fiscal year (FY) 1989, with
tentative plans to launch in early FY 1992.
The selected investigators will have exclusive use of the
scientific data from the mission for a period of 12 months after
receipt of the data. After this period, guest observer programs
and data analysis and interpretation will be supported through
other programs.
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PIONEER 10 CONTINUES SOLAR SYSTEM EXPLORATION AND DISCOVERIES
June 13, 1988
Pioneer 10, the first spacecraft to leave the solar system,
is the most distant human-made object in existence. The Pioneer explorer
continues to make discoveries about the Sun's influence in the local
interstellar medium, called the heliosphere, and to seek the boundary between
this and the true interstellar gas. Pioneer 10 continues its search for
gravity waves and a possible 10th solar system planet.
Today, Pioneer 10 has spent 5 years beyond the orbit of the outermost
solar system planet Pluto, some 4 billion, 175 million miles from the Sun.
Radio signals, moving with the speed of light at 186,000 miles per second, now
take 12 hours and 26 minutes to travel from Earth to the explorer spacecraft
and back.
Launched in 1972, Pioneer 10 was the first spacecraft to cross the
Asteroid Belt, fly by Jupiter and return pictures, chart Jupiter's intense
radiation belts, measure the mass of its four planet-sized moons, locate the
giant planet's magnetic field and discover that Jupiter is predominantly a
liquid planet.
Its primary mission, originally scheduled for 21 months, was accomplished
by December 1973. At that point, scientists reprogrammed Pioneer for an
indefinite mission to explore the outer solar system and beyond.
Perhaps the most important finding about the outer solar system concerns
the extent and characteristics of the heliosphere. Pioneer 10 continues to
measure the "solar wind," the million-mile-per-hour flow of charged atomic
particles boiling off the sun's surface, forming the sun's tenuous
atmosphere.
Scientists had predicted in 1956 the modulation (alteration) of galactic
cosmic rays out past the orbit of Jupiter, indicating a heliosphere presence
out that far. The probe is now almost nine times that distance and has not
yet reached the boundary of the solar heliosphere. And, the sun's direct
influence continues to be strong. A number of scientists believe that this
boundary may be as far away as 9.3 billion miles.
Several scientists, including Dr. James Van Allen, one of Pioneer's
principal investigators and discoverer of the Earth's radiation belts, and Dr.
Darrell Judge, University of Southern California, also a Pioneer investigator,
suggest that the heliosphere varies in size with solar activity and is nearly
spherical in shape. Because of this, they think Pioneer 10 may break through
the boundary of the solar atmosphere and pass into interstellar space in the
next 1 to 3 years. There the spacecraft could directly measure the
interstellar gas, which so far has not been possible.
Pioneer 10 has found that the sun strongly influences the heliosphere
characteristics as far away as 4 billion miles. Scientists are finding major
variations keyed to its cycle, such as outward traveling shocks that
accelerate charged particles.
The sun changes a great deal during this cycle. The number of sunspots
-- the enormous and violent magnetic storms on the solar surface -- varies
radically, as does the shape of the sun's magnetic field and movements in the
hot gases surrounding the corona, the outer portion of the sun. The coronal
material has sparse areas called "coronal holes" located around the sun's two
magnetic poles. When the sun approaches its most active phase, solar maximum,
these coronal holes creep toward the solar equator by extending "tongues" 10
or 20 degrees wide in longitude. During the solar minimum, the holes retreat
back to the poles.
Pioneer 10 and other closer-in spacecraft are measuring the "high speed
streams" in the solar wind whose source is the movement of the coronal holes.
Pioneer 10 found that other changes are triggered by movements of a vast
electromagnetic structure called the current sheet, which bisects the sun's
field. Particles slow down as this sheet "flaps" toward them.
Pioneer also has made new findings on cosmic rays entering our portion of
the Milky Way. Cosmic rays are high velocity sub- atomic particles from our
galaxy. Normally, the number of these particles inside the heliosphere varies
with the solar cycle, and large amounts of low energy cosmic rays were found
to flow in from the galaxy during the recent low point of activity on the
sun. This may suggest that Pioneer is approaching the heliosphere boundary
where the solar influence stops.
The possible existence of a 10th planet at the outer fringes of the solar
system may be determined by measuring minute changes in Pioneer 10's flight
path. In 1978, astronomers have suggested the presence of a new planetary
body since Pluto was found to be too small to explain past irregularities in
the orbits of planets Uranus and Neptune.
Pioneer 10 and its twin, Pioneer 11, are excellent indicators of the
gravitational pull of celestial objects. Because the spacecraft are spin
stabilized, they generate almost no forces of their own that would affect
their straight-line flight path. Thus, large, nearby masses, exerting
gravitational forces, should easily be observed by changes in Pioneer 10's
flight trajectory.
Thus far, NASA scientist John Anderson has found no evidence of any
uncharted planetary bodies. Despite this lack of evidence, Anderson and
others strongly believe that the huge volume of past measurements, made by
many eminent observers, showing irregularities in the orbits of Uranus and
Neptune are too widespread and consistent to be discarded.
They suggest that whatever perturbed the outer planets between 1800 and
1900 has now "gone away." It could well be an object whose orbit is tilted at
a high angle to the plane of the solar system. These gravitational anomalies
are no longer observed because the object is currently too far away or too
high above the planets to affect either Pioneer or the outer planets.
Anderson and other researchers have suggested places to look for this
planet-sized body, and a number of groups are searching these regions of
space.
Tracking the Pioneer 10 also provides scientists with an opportunity to
detect "gravity waves," predicted by Einstein's General Theory of Relativity.
In theory, infrequent and enormously powerful cataclysmic events, such as
collisions between entire galaxies or two massive black holes, would "rattle"
the entire universe, producing gravity waves. A number of university research
groups around the world have been using elaborate equipment to search for
gravity waves for well over a decade. None so far has been found.
Gravity waves may be especially easy to detect in the extremely long
wavelengths (one to four billion miles) that both Pioneers are in position to
measure, but neither Pioneer has yet found such waves. Gravity waves would
dwarf the longest radio waves, the largest waves commonly measured on Earth,
which span only hundreds or thousands of feet.
Recent improvements in the NASA ground stations are expected to allow
communications with Pioneer 10 to continue until the range approaches 6
billion miles, more than twice the prelaunch estimates.
Project manager Richard O. Fimmel expects that NASA will be able to track
Pioneer 10 until the craft's power source limits communications toward the end
of the 1990's.
Scientists believe that both Pioneers 10 and 11 will travel among the
stars virtually forever because the vacuum of interstellar space is so empty.
Pioneer 10 and Pioneer 11 have long since passed the region of greatest
potential danger, which occurred at the Jupiter and Saturn encounters.
Both Pioneers 10 and 11 carry an easily-interpreted graphic message in
the event an intelligent life form may capture either spacecraft on its
journey. Engraved on a gold-anodized aluminum plaque, the message features a
drawing of a man and a woman, a diagram of our solar system and a map
depicting our solar system with reference to galactic "lighthouses," known as
pulsars.
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Eric