LAUNCH WILL CREATE A RADIO TELESCOPE LARGER THAN EARTH

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.