In DepthAstronomy

India to put observatory in orbit

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Science  18 Sep 2015:
Vol. 349, Issue 6254, pp. 1271-1272
DOI: 10.1126/science.349.6254.1271

On 28 September, India plans to launch a major space-based observatory that will set a milestone for a developing country—and also mark a first for space science. The $45 million Astrosat mission will put India in an elite group of science powers—the United States, the European Union, and Japan—doing astronomy from orbit. The spacecraft also has a unique design. Instead of focusing on a single region of the spectrum, it carries a suite of five instruments, including two telescopes, which will observe cosmic objects simultaneously in several wavebands: visible, ultraviolet, and soft and hard x-rays.

Astrosat's capabilities are “unique and very powerful,” especially for active galactic nuclei and certain x-ray sources, which vary on fast timescales and radiate over many wavelengths, says mission collaborator John Hutchings, an astrophysicist at the Herzberg Institute of Astrophysics in Victoria, Canada. The spectral symphony should allow Astrosat “to unveil a few mysteries of the universe,” adds Sujan Sengupta, an astrophysicist at the Indian Institute of Astrophysics in Bengaluru, who is not affiliated with the project.

The launch, from Sriharikota spaceport in Andhra Pradesh, culminates a 2-decade odyssey. A team led by former Indian Space Research Organisation (ISRO) Chairman K. Kasturirangan conceived the mission in 1996; the space agency aimed to put the satellite in orbit in 2007. But funds were slow in coming, and ISRO and its partner institutes encountered hardware-related glitches. The soft x-ray imaging telescope, manufactured at the Tata Institute of Fundamental Research in Mumbai, was especially tricky; hundreds of gold-coated mirrors for reflecting the x-rays onto a charge-coupled device imager had to be positioned to an accuracy of less than the width of a human hair.

Astrosat is jam-packed with telescopes and imagers.


Astrosat's multiwavelength capability could pay special dividends with sources that flare up rapidly, such as x-ray binaries. These pairs, which harbor a dense object such as a black hole and an ordinary star, are undetectable—except when they suddenly flare, or outburst. Observing in wavelengths longer than x-rays can help researchers get a handle on the size and shape of the accretion disks responsible for emissions. In the past, astronomers have marshaled multiple ground- and space-based telescopes to observe outbursts across the spectrum, but doing so entails “a lot of coordination and difficulty,” says K. Suryanarayana Sarma, Astrosat's project director at ISRO in Bengaluru. It's hard to free up telescopes on short notice, meaning observations often lag the initial burst.

“To study these sources, it is necessary to detect them as early as possible in the outbursting phase,” which lasts only a few months, says Somasundaram Seetha, program director in ISRO's space science program office. The new spacecraft should make that possible by lying in wait, tracking x-ray emissions across the sky. When it catches an outburst, she says, Astrosat's instruments will swing into action, and ISRO will also send out a worldwide alert.

In another first, a U.S. firm will hitch a ride on an Indian launch. Piggybacking on Astrosat's heavy lift rocket are four LEMUR CubeSats, designed for Earth observation and as a technology demonstration by Spire Global, Inc., based in San Francisco, California.

Astrosat's anticipated mission life is 5 years. Observing time will be opened to the global community 1 year after launch, says Kiran Kumar, chairman of ISRO. Kasturirangan is confident that the long delay has not dimmed the observatory's prospects. “There is no doubt,” he says, “that Astrosat is still very relevant for the world.”

  • * in New Delhi; Pallava Bagla is a science journalist in New Delhi.


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