Orbiting VLBI First Images

A new radio telescope over twice the size of the Earth is now producing its first pictures. This mega-telescope is made by combining the signals from HALCA, an orbiting spacecraft with a radio telescope, with those from many radio telescopes on the ground. HALCA's elliptical orbit takes it as far as 21000 kilometers from the Earth, making it possible to produce such an enormous telescope.

The HALCA satellite was launched on the 12th of February 1997 by Japan's Institute of Space and Astronautical Science. The 8-meter radio telescope, designed especially for this mission, was folded up like an umbrella inside the spacecraft before the launch and then successfully opened on the 26th of February using telemetry commands from the Kagoshima Space Center on Kyushu Island, Japan.

Project Scientist for the VLBI Space Observatory Programme, Prof. Hisashi Hirabayashi of ISAS, said "We are very pleased with HALCA's first pictures. The clarity of the images made with HALCA confirms that the chain from the satellite to the tracking stations, to the orbit determination and the combining of the signals is all working well. The success of this Japanese-led project is due to the hard work of many engineers and scientists and the strong support of many international partners."

The international character of this project is unique. Forty telescopes from 14 countries around the world are being used with HALCA; Tracking stations in four continents transmit data to, and receive data from, the satellite; The signals from each telescope are sent to one of three locations in Japan, Canada and the US, where a special purpose computer called a correlator is used to combine the signals from each telescope and where images are then made. Finally, scientists from all part of the world have submitted proposals to use this unique radio telescope over its expected five year life time.

HALCA's first image was made on June 15th of the quasar PKS1519-273, and it showed only a point because of its very compact nature. This was an important step in verifying the whole system since the image was not blurred.

HALCA has also observed a distant quasar, called 1156+295, with ten telescopes spread across the USA. The image of this quasar made from the ground telescopes only is shown on the left. The strongest radio signals are produced near the center of the quasar where astronomers believe that hot gas and stars are interacting with a super-massive black hole. On the right is another image of the quasar but with the radio signals from HALCA added. The material which is being blown out from the quasar can be seen more clearly. This unprecedented angular resolution at the observing wavelength of 18 cm allows radio astronomers to probe closer to the black hole in order to understand the nature of such a mysterious objects.

Earth-based radio telescopes contributing to VLBI Space Observatory Programme belong to the National Radio Astronomy Observatory (USA) (which were used for the quasar images), the Australia Telescope National Facility, the European VLBI Network, NASA's Deep Space Network and a number of other institutions. The five tracking stations are located at Usuda (Japan), operated by the Institute of Space and Astronautical Science; Green Bank (West Virginia, USA), operated by the National Radio Astronomy Observatory; and sites near Goldstone (California, USA), Canberra (Australia) and Madrid (Spain), operated as part of NASA's Deep Space Network. The signals from the satellite and ground telescopes are combined at one of three correlators operated by Japan's National Astronomical Observatory, the Canadian Space Agency and the USA's National Radio Astronomy Observatory. Orbit determination teams at the Institute of Space and Astronautical Science and NASA's Jet Propulsion Laboratory have provided the detailed predictions of the satellite's location and velocity needed for tracking the satellite and correlating the data from it.

Hundreds of quasars, radio galaxies and pulsars will be imaged with this mega-telescope over the satellite's lifetime. These pictures will have the sharpest view of the Universe ever achieved at these wavelengths, up to 100 times the resolution of the Hubble Space Telescope.

HALCA, in Japanese, means `far away' which accurately describes the location of the satellite at the farthest point of its 6-hour orbit. The name HALCA is also an acronym for the Highly Advanced Laboratory for Communications and Astronomy. The two way communications between the satellite and tracking stations has been one of the technological triumphs of the mission.

The first high resolution image from HALCA is shown below right. The image on the left is the ground-only image of the radio source. Notice the much improved angular resolution image made using HALCA data.
The two images above are of an extreamly high energy jet of particles ejected from the center of the distant blazar 1156+295. The bright white component in the center of the image is due to material falling onto a giant black hole at the center of the object. Magnetic fields surrounding the black hole accellerate the particles into a narrow jet.

Return to the tracking station home page. The National Radio Astronomy Observatory (NRAO) is a facillity of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Last update: 97 July 4