LAUNCH WILL CREATE A RADIO TELESCOPE LARGER THAN EARTH
Donald Savage, Mary Hardin, David Finley
NASA and the National Radio Astronomy
Observatory are joining with an international
consortium of space agencies to support the launch of
a Japanese satellite next week that will create the
largest astronomical “instrument” ever built — a
radio telescope more than two-and-a-half times the
diameter of the Earth that will give astronomers their
sharpest view yet of the universe.
The launch of the Very Long Baseline
Interferometry (VLBI) Space Observatory Program (VSOP)
satellite by Japan’s Institute of Space and
Astronautical Science (ISAS) is scheduled for Feb. 10
at 11:50 p.m. EST (1:50 p.m. Feb. 11, Japan time.)
The satellite is part of an international
collaboration led by ISAS and backed by Japan’s
National Astronomical Observatory; NASA’s Jet
Propulsion Laboratory (JPL), Pasadena, CA; the
National Science Foundation’s National Radio Astronomy
Observatory (NRAO), Socorro, NM; the Canadian Space
Agency; the Australia Telescope National Facility; the
European VLBI Network and the Joint Institute for Very
Long Baseline Interferometry in Europe.
Very long baseline interferometry is a technique
used by radio astronomers to electronically link
widely separated radio telescopes together so they
work as if they were a single instrument with
extraordinarily sharp “vision,” or resolving power.
The wider the distance between telescopes, the greater
the resolving power. By taking this technique into
space for the first time, astronomers will
approximately triple the resolving power previously
available with only ground-based telescopes. The
satellite system will have resolving power almost
1,000 times greater than the Hubble Space Telescope at
optical wavelengths. The satellite’s resolving power
is equivalent to being able to see a grain of rice in
Tokyo from Los Angeles.
“Using space VLBI, we can probe the cores of
quasars and active galaxies, believed to be powered by
super massive black holes,” said Dr. Robert Preston,
project scientist for the U.S. Space Very Long
Baseline Interferometry project at JPL. “Observations
of cosmic masers — naturally-occurring microwave
radio amplifiers — will tell us new things about the
process of star formation and activity in the heart of
other galaxies.”
“By the 1980s, radio astronomers were observing
the universe with assemblages of radio telescopes
whose resolving power was limited only by the size of
the Earth. Now, through a magnificent international
effort, we will be able to break this barrier and see
fine details of celestial objects that are beyond the
reach of a purely ground-based telescope array. We
anticipate a rich harvest of new scientific knowledge
from VSOP,” said Dr. Paul Vanden Bout, Director of
NRAO.
In the first weeks after launch, scientists and
engineers will “test the deployment of the reflecting
mesh telescope in orbit, the wide-band data link from
the satellite to the ground, the performance of the
low noise amplifiers in orbit, and the high-precision
orbit determination and attitude control necessary for
VLBI observations with an orbiting telescope,”
according to Dr. Joel Smith, manager of the U.S. Space
VLBI project at JPL. Scientific observations are
expected to begin in May.
The 26-foot diameter orbiting radio telescope
will observe celestial radio sources in concert with a
number of the world’s ground-based radio telescopes.
The 1,830-pound satellite will be launched from ISAS’
Kagoshima Space Center, at the southern tip of Kyushu,
one of Japan’s main islands, and will be the first
launch with ISAS’ new M-5 series rocket.
The satellite will go into an elliptical orbit,
varying between 620 to 12,400 miles above the Earth’s
surface. This orbit provides a wide range of
distances between the satellite and ground-based
telescopes, which is important for producing a high-
quality image of the radio source being observed. One
orbit of the Earth will take about six hours.
The satellite’s observations will concentrate on
some of the most distant and intriguing objects in the
universe, where the extremely sharp radio “vision” of
the new system can provide much-needed information
about a number of astronomical mysteries.
For years, astronomers have known that powerful
“engines” in the hearts of quasars and many galaxies
are pouring out tremendous amounts of energy. They
suspect that supermassive black holes, with
gravitational fields so strong that not even light can
escape them, lie in the centers of these “engines.”
The mechanism at work in the centers of quasars and
active galaxies, however, remains a mystery. Ground-
based radio telescopes, notably NRAO’s Very Long
Baseline Array (VLBA), have revealed fascinating new
details in recent years, and VSOP is expected to add a
wealth of new information on these objects, millions
or billions of light-years distant from Earth.
Many of these same objects act as super-powerful
particle accelerators to eject “jets” of subatomic
particles at nearly the speed of light. Scientists
plan to use VSOP to monitor the changes and motions in
these jets to learn more about how they originate and
interact with their surroundings.
The satellite also will aim at regions in the
sky where giant collections of water and other
molecules act as natural amplifiers of radio emission
much as lasers amplify light. These regions, called
cosmic masers, are found in areas where new stars are
forming and near the centers of galaxies.
Observations can provide the detail needed to measure
motions of individual maser “spots” within these
regions, and provide exciting new information about
the star-forming regions and the galaxies where the
masers reside. In addition, high-resolution studies
of cosmic masers can allow astronomers to calculate
distances to them with unprecedented accuracy, and
thus help resolve continuing questions about the size
and age of the universe.
The project is a major international
undertaking, with about 40 radio telescopes from more
than 15 countries having committed time to co-observe
with the satellite. This includes the National
Science Foundation’s Very Long Baseline Array (VLBA),
an array of 10 telescopes spanning the United States
from Hawaii to Saint Croix; NASA’s Deep Space Network
(DSN) sites in California, Spain, and Australia; the
European VLBI Network, more than a dozen telescopes
ranging from the United Kingdom to China; a Southern
Hemisphere array of telescopes stretching from eastern
Australia to South Africa; and Japan’s network of
domestic radio telescopes.
In the United States, NASA is funding critical
roles in the VSOP mission at both JPL and NRAO. JPL
has built an array of three new tracking stations at
its DSN sites in Goldstone, CA; Madrid, Spain; and
near Canberra, Australia. A large existing tracking
station at each of these sites has also been converted
to an extremely sensitive radio telescope for
simultaneous observations with the satellite. JPL
also is providing precision orbit determination,
scientific and operational planning support to the
Japanese, and advice to U.S. astronomers who wish to
observe with the satellite. NRAO is building a new
tracking station at Green Bank, WV; contributing
observing time on the VLBA array of telescopes;
modifying existing data analysis hardware and
software, and aiding astronomers with the analysis of
the VSOP data. Much of the observational data will be
processed at NRAO’s facility in Socorro, NM, using the
VLBA Correlator, a special purpose high-performance
computer designed to process VLBI data.
VSOP is the culmination of many years of
planning and work by scientists and engineers around
the world. Tests using NASA’s Tracking and Data Relay
Satellite System (TDRSS) proved the feasibility of
space VLBI in 1986. Just last year, those old data
were used again to test successfully the data-
reduction facilities for VSOP.
JPL manages the U.S. Space Very Long Baseline
Interferometry project for NASA’s Office of Space
Science, Washington, DC. The VLBA, headquartered in
Socorro, NM, is part of the National Radio Astronomy
Observatory, a facility of the National Science
Foundation, operated under cooperative agreement by
Associated Universities, Inc.