The VSOP (VLBI Space Observatory Programme) mission is led by the Institute of Space and Astronautical Science, in collaboration with the National Astronomical Observatory of Japan.

The technique of Very Long Baseline Interferometry (VLBI) uses widely spaced telescopes to synthesize a telescope as large as the greatest distance between the telescopes. The reason for doing this is to study celestial radio sources in more detail, i.e. at higher resolution.

The first VSOP satellite was successfully launched 12 February 1997 on the new ISAS M-V rocket from the Kagoshima Space Center. The satellite, renamed HALCA after its successful launch, sucessfully deployed an 8 meter diameter radio telescope in orbit on 27 & 28 February 1997.

HALCA is in an elliptical Earth orbit, with an apogee height of 21,000km and a perigee height of 560km, which enables VLBI (Very Long Baseline Interferometry) observations on baselines up to three times longer than those acheivable on Earth.
An upper illustration expresses the image of a composed telescope.

Observations will be made at 1.6GHz (18cm), 5GHz (6cm) and 22GHz (1.3cm). First fringes between the satellite and ground radio telescopes were found at the Mitaka correlator in May, and at the Penticton and Socorro correlators in June. First images made with data from the satellite and ground radio telescopes have been made at 1.6GHz and 5GHz.

On November 30, 2005, after long operation of 8 years and 9 months, HALCA performed its last operation and retired.
HALCA breathes its last