Overview

VSOP (VLBI Space Observatory Programme) is a large-scale international joint observation program that includes the radio-astronomy satellite HALCA (Highly Advanced Laboratory for Communications and Astronomy)(MUSES-B), Very Long Baseline Interferometry (VLBI) with more than 25 ground-based radio telescope arrays, five tracking stations, and three correlators.

HALCA was launched on February 12, 1997 by an M-V rocket from Kagoshima Space Center (now Uchinoura Space Center). Its weight was approximately 830 kg, size was 1.5 m x 1.5 m x 1.0 m, equipped with a large deployable antenna with a maximum diameter of 10 m (effective diameter of 8 m) at the top, and orbited a long elliptical orbit with a perigee altitude of 560 km, apogee altitude of 21,400 km, and orbital inclination of 31 degrees at a speed of about 6 hours 20 minutes per revolution. Simultaneous observations by HALCA on orbit and the ground-based radio telescope array enabled space VLBI (Very Long Baseline Interferometry) observations with a baseline about three times longer than the diameter of the Earth, and realized imaging observations with the highest resolution far exceeding those on Earth.

Until the operation was terminated on November 30, 2005, more than 700 observations were made which was decided on by the Science Review Committee and the VSOP International Science Council (VISC) or adopted observation proposals submitted by the public.

Observation Instruments

Radio Telescope

The main instrument of HALCA is a radio telescope with a main reflector of 8 m effective diameter. This reflector consists of a mesh of gold-plated molybdenum wire and is supported by six telescopic masts. The telescope uses Cassegrain optics and has a hexagonal subreflector inscribed in a circle 1.1 m in diameter. The subreflector is positioned 3.4 m above the surface of the main reflector.

The planned frequencies for observations were 1.60 - 1.73 GHz, 4.7 - 5.0 GHz, and 22.0 - 22.3 GHz, but shortly after launch it was found that the 22 GHz band had very low sensitivity, so observations were concentrated at 1.6 GHz and 5.0 GHz.

Achievements

HALCA was the first spacecraft in the world to successfully deploy a giant 8-meter antenna in space, and was also the world's first engineering demonstration of a space VLBI intereference system in combination with ground-based instruments.

Through VSOP observations, we succeeded in obtaining the highest resolution images of the jets and other objects in active galactic nuclei, and revealed that the inner structure of the jets, which were thought to be straight and elongated, is more complex. Through the shadow of the jets in active galactic nuclei, the existence and state of plasma disks around active galactic nuclei were also revealed. In addition, many high-luminosity temperature sources were identified through survey observations.

Mission overview paper

• Hirabayashi, H. et al. (1998) Science - Overview and Initial Results of the Very Long Baseline Interferometry Space Observatory Programme
• Hirabayashi, H. et al. (2000) Publications of the Astronomical Society of Japan - The VLBI Space Observatory Programme and the Radio-Astronomical Satellite HALCA
• Inoue, M. et al. (1993) Sub-Arcsecond Radio Astronomy - Space VLBI Project VSOP
• Hirosawa, H. et al. (1994) Proceedings of the 19th International Symposium on Space Technology and Science - Design of the Space-VLBI Satellite MUSES-B