Orbiting Radio Telescopes: New Tool for Astronomers

An international team of radio astronomers, using an orbiting communications satellite, has demonstrated the feasibility of placing radio telescopes in orbit around Earth, in effect creating giant antennas thousands of miles in diameter.

Radio astronomers have long dreamed of creating a network of orbiting and ground-based antennas that would be linked to form a giant antenna, and the experiments announced today in Science magazine show that it can be done, according to Gerald S. Levy of the Jet Propulsion Laboratory, one of the participanting scientists.

“This is a validation of our contention that the technology is at hand,” Levy said.

Orbiting radio telescopes could reveal much about areas of the universe, such as the center of the Milky Way galaxy, that are obscured by interstellar dust and thus hidden from optical telescopes.

Radio telescopes use radio waves emitted by distant celestial objects to produce images, sometimes called “radio maps,” just as a camera uses light to produce photographs. Since the sharpness of the image depends on the size of the antenna, radio telescopes have grown in size, in some cases covering areas the size of football fields.

In recent years, radio astronomers have linked radio telescopes together in what is called very long baseline interferometry. By blending the data together from each telescope, the system acts as a single antenna.

Radio telescopes on different continents have been linked through interferometry, in effect turning the entire Earth into an antenna, and that has yielded some extremely sharp images of radio sources, including pictures of distant stars as they are born and die.

“The problem is that you are limited by the physical dimensions of the Earth,” Levy said.

That has led scientists in the United States, Europe, Japan and the Soviet Union to consider launching radio antennas into space.

“There was some question about the feasibility of that,” Levy said. “We showed it is feasible.”

Levy’s group, which included nine other scientists at the Jet Propulsion Laboratory, as well as scientists in the United States, Australia and Japan, used the National Aeronautics and Space Administration’s tracking and data relay satellite system to prove the concept.

The system includes a satellite that is in a fixed orbit off the coast of South America. The satellite is used by NASA to transmit data and live television pictures from space shuttles.

In July and August, the team linked the satellite to ground stations in Australia and Japan, and all three points added up to a giant antenna. Several observations were made of a quasar, a star-like object that emits radio waves.

Levy said the system produced several images, although not of great quality because the satellite system turned out to be inadequate for serious astronomical observations. It nevertheless proved that an antenna properly designed for radio astronomy and placed in a suitable orbit will give astronomers a powerful new tool, he said.

“We will do some more experiments in January,” he said.

He said NASA and the European Space Agency are considering a joint effort to launch a radio observatory with a 15-meter antenna into an elliptical orbit ranging from about 2,500 miles above Earth to nearly 10,000 miles.

That kind of orbit would allow scientists to collect data from various distances, in effect altering the size of the antenna as the observatory moved through its orbit.

“That gives you better coverage,” Levy said. “You want to have as many distances as possible.”

The Soviets are also considering placing a radio telescope in orbit, and some American scientists have suggested that U.S. and Soviet antennas in space could be linked together, forming a giant, international observatory.