In the early 1990’s , the Indian Institute of Astrophysics (IIAP) and Tel Aviv University, Israel had taken up a collaborative space mission designed to study the ultraviolet sky. India’s GSAT-4 was supposed to launch this unique instrument called the Tel Aviv University Ultraviolet Explorer (TAUVEX) as a secondary payload. The orbit of the TAUVEX was expected to be 36,000 km above the Earth’s equator.
The mission was due for launch in 2009 and expected to last for three years. However after investing more than 20 years of research and millions of dollars , Israeli space officials called of the launch in early 2011. The main reason being the continued uncertainty that has enveloped the GSLV program because of launch failures.
History of a Failure
The mission was open to all Indian and Israeli scientists with equal participation by both teams. Israel had made the instrument, while IIA was responsible for mission planning, software development, processing and dissemination of data and data analysis.
The payload consisted of an optical module consisting of three identical co-aligned telescopes, and an electronics module. The structure was made of aluminum with a carbon composite for parts where thermal expansion is critical.
The 20-cm primary mirrors fitted in the telescope had a field view of 0.9 degree in diameter. Detectors have a spectral range between 140 and 300 angstroms. Each of the three telescopes observed the sky at different wavelengths.
TAUVEX operated in a different mode than most scientific missions. Normally, space telescopes scan a line of celestial latitude per day. But TAUVEX allowed coverage from the south celestial pole to the north. The exposure time was dependent on the latitude. As a result, TAUVEX was not well-suited to observe individual targets; rather it was designed as a survey instrument for observing large areas of the sky with moderate spectral resolution and high sensitivity.
With a field view of almost a degree and a resolution of 6-10 arc-second, TAUVEX was well designed to survey the sky up to a magnitude limit close to 20. Though it observed the whole sky, the total visibility available to it was limited to only 10 or 12 hours a day. The telescope is designed to avoid staring at the Sun at 90 degrees. A filter will act as a shutter when strong Sunlight falls on it. The challenge was to maximize the observation time without compromising on quality. A sky simulation software had also been developed and made available online to scientists who wished to participate in the mission.
Alas all of this has now gone to waste because of a bumbling ISRO !