MUFONET-BBS GROUP - MUFONET-BBS NETWORK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SPACE NEWS - WIRE
~~~~~~~~~~~~~~~~~~~
3/17/93: 3 SPACECRAFT TO CONDUCT 3-WEEK
GRAVITATIONAL WAVE SEARCH

Donald L. Savage
Headquarters, Washington, D.C. March 17, 1993

Franklin O'Donnell
Jet Propulsion Laboratory, Pasadena, Calif.

RELEASE: 93-48

Three interplanetary spacecraft, now headed quietly toward
Mars, Jupiter and over the poles of the sun, soon may prove
the existence of elusive waves in the universe's
gravitational field by bobbing on ripples in space like
corks bobbing on ripples in a pond.

Such waves of gravity have never been directly detected,
although their existence was predicted decades ago in
Einstein's theory of relativity and there is indirect
evidence that they exist. The waves are believed to be
produced by supernova explosions, collapsing black holes and
other catastrophic events. Past searches with ground-based
equipment and single spacecraft have failed to discover
them.

Astrophysicists are hoping to make this major discovery by
spending the next few weeks "listening" for passing
gravitational waves with three "borrowed" spacecraft at the
same time in the most sensitive detection system yet
assembled to search for very low frequency gravitational
waves.

The spacecraft, now on their way to separate destinations in
the solar system, are NASA's Mars Observer, Galileo and the
European Space Agency (ESA) Ulysses spacecraft.

The joint NASA-ESA experiment will run from March 21 to
April 11, marking the first time three spacecraft will make
observations simultaneously, greatly increasing the
reliability of any detection.

"If this experiment succeeds in detecting gravitational
waves it may answer fundamental questions about the nature
of gravity as well as give further support for Einstein's
theory of general relativity," said Dr. Robert Stachnik,
Gravitational Wave Program Scientist in NASA's Astrophysics
Div., Office of Space Science, Washington, D.C.

"We're also very excited about the possibility of making a
major discovery with such a cost-effective experiment. We
were able to take advantage of three spacecraft already in
space which soon will be in the correct relative positions
and distances we need to do this experiment. We can just
borrow them for a few weeks, without any added cost for
equipment and no change to their missions. It's big science
on a small budget," Stachnik said.

"Einstein predicted the existence of gravitational waves in
his theory of general relativity, and radio astronomy
observations of pulsars have suggested they indeed exist --
but no one has ever detected a gravitational wave directly,"
said Dr. John W. Armstrong of NASA's Jet Propulsion
Laboratory, Pasadena, Calif., who will work with the Mars
Observer and Galileo spacecraft.

The experiment is built around a simple concept. During the
3-week experiment, the antennas of NASA's Deep Space
Network (DSN) on Earth will beam radio signals to the three
spacecraft at precisely known frequencies. Each spacecraft
will send signals back to Earth at the same frequency it
receives. If no gravitational waves are passing through the
Solar System, the signals returned to Earth should have
exactly the same frequencies as the original signals sent
from the DSN, shifted only by the Doppler effect of
spacecraft motion.
However, if a strong enough gravitational wave passes --
produced perhaps from collapsing masses of stars in the
hearts of galaxies or from the spiraling together and
collision of two black holes -- both the Earth and the
spacecraft will experience a slight "bobbing" from the
ripple-like passage of the gravitational wave. This
interaction cannot be directly detected at either the Earth
or the spacecraft alone, but would show up as a slight
change in the frequency of the radio signal finally received
back at Earth.

The hydrogen maser clocks that control the DSN transmitters
and receivers are so accurate that scientists will be able
to detect a change in radio frequency of as little as a few
parts in a quadrillion (a quadrillion is 1 followed by 15
zeroes).

"This should allow us to detect gravitational waves from
objects such as massive pairs of black holes hidden in the
hearts of other galaxies," said Hugo D. Wahlquist of JPL,
who will work on the Ulysses spacecraft with Sami W. Asmar
of JPL, Prof. Bruno Bertotti of the University of Pavia,
Italy, and Prof. Luciano Iess of the University of Rome La
Sapienza.

Scientists emphasize, however, that snaring a gravitational
wave during the 3-week experiment will depend on a good bit
of luck -- whether a suitable astronomical event happens to
occur during the relatively brief opportunity when data can
be taken. All three spacecraft will be in the Earth's night
sky at that time, so interference with their radio signals
due to charged particles in the solar wind will be at a
minimum.

Successful detection of gravitational waves could open up an
entirely new kind of astronomy. Because the gravitational
waves do not readily interact with matter, detecting them
may open a window to the interiors of powerful -- and
sometimes catastrophic -- events such as supernova
explosions and collapsing black holes.

"Gravitational wave research is now in the hands of
physicists. Once signals are detected, the astronomers will
be beating down the doors," said Stachnik.

Sensitive ground-based interferometer antennas now are being
built in both the United States and Europe to search for
gravitational waves with wavelengths of thousands of
kilometers.

"In addition to searching for the shorter waves that can
affect antennas here on Earth, we now will be using radio
signals sent to spacecraft hundreds of millions of
kilometers away to search for waves of much longer
wavelength," said Dr. Frank B. Estabrook of JPL, who will
work with the Galileo spacecraft.

Detection of the gravitational waves, even if they occur,
will still take at least several months of patient data
analysis. "The spacecraft systems can detect large enough
gravitational waves, if they exist," said Dr. Bevan M.
French, Program Scientist for the Mars Observer. "But it
won't be one of those sudden 'Eureka!' situations. We'll be
looking for a few small wiggles in a huge amount of radio
data. It will take time."

To identify the unique signals of gravitational waves, the
scientists also will have to eliminate such mundane effects
as planned changes in the orientation of the spacecraft,
interference from charged particles (plasmas) in space and
even atmospheric changes, rain and snow on Earth.

Mars Observer, launched in September 1992, will reach the
Red Planet Aug. 24 of this year. Launched in 1989, NASA's
Galileo spacecraft will arrive at Jupiter in 1995. The ESA
Ulysses spacecraft was launched in 1990, and it will fly
over the sun's poles in 1994 and 1995.

Gravitational wave research is supported by the Astrophysics
Division of NASA's Office of Space Science and by each of
the three spacecraft projects, which scheduled the radio
searches during their interplanetary cruise periods.


-END OF FILE-

Robert,
ricksbbs.synchro.net
http://ricksbbs.synchro.net:8080
irc www.irccloud.com/irc/ricksbbs/channel/ricksbbs
---
þ Synchronet þ Rick's BBS telnet://ricksbbs.synchro.net:23