NASA’s international Space Station (ISS) completes 17 years of existence on 20 November 2015 since its first component was launched into space in 1998. It reflects the stepping stone and desire of mankind for sustainable habitation of space by humans. Built at a cost of some US$ 100 billion, the construction of ISS required contributions from the US, Russia, Canada, the European Space Agency and Japan, the construction also requiring over 100 rocket and shuttle launches and 160 spacewalks. It is a laboratory with an international crew of six people at a time that travels at the speed of eight kilometers per second, orbiting earth every 90 minutes. Crew members spend about 35 hours each week conducting research in many disciplines to advance scientific knowledge in earth, space, physical, and biological sciences for the benefit of people living on earth. Occupied since November 2000, the ISS has been visited by over 200 people from 15 countries. The US is using it as a platform for developing commercial cargo, commercial crew space transportation capabilities, and as springboard for the next great leap in exploration, enabling research and technology developments that will benefit human and robotic exploration of destinations beyond low-Earth orbit, including asteroids and Mars. But while the ISS besides demonstrating America’s prowess in space is all about global cooperation enabling multinational partnership and advances shared goals in space exploration,
India’s ISRO has been making singular advances in space exploration at the individual level. ISRO’s ASTROSAT launched on 28 September 2015 has been a singular achievement; the first attempt at setting up a space observatory from way study of the cosmological phenomenon can be undertaken by India.
ASTROSAT is a multi-wavelength astronomy mission on an IRS-class satellite into a near-Earth, equatorial orbit. The scientific payload with a mass of 1513 kg contains six instruments: one, the Ultra Violet Imaging Telescope (UVIT; two, the Soft X-ray imaging Telescope (SXT); three, the LAXPC Instrument; four, the Cadmium Zinc Telluride Imager (CZTI); five, the Scanning Sky Monitor (SSM), and; six, the Charged Particle Monitor (CPM) – all covering the visible (320–530 nm), near UV (180–300 nm), far UV (130–180 nm), soft X-ray (0.3–8 keV and 2–10 keV) and hard X-ray (3–80 keV and 10–150 keV) regions of the electromagnetic spectrum. Being the first observatory in space, ASTROSAT will have main scientific focus on: simultaneous multi-wavelength monitoring of intensity variations in a broad range of cosmic sources; monitoring the X-ray sky for new transients; sky surveys in the hard X-ray and UV bands; broadband spectroscopic studies of X-ray binaries, AGN, SNRs, clusters of galaxies, and stellar coronae; and, studies of periodic and non-periodic variability of X-ray sources. While radio, optical, and IR observations would be coordinated through ground-based telescopes, the high energy regions, i.e., UV, X-ray and visible wavelength, would be covered by the dedicated satellite-borne instrumentation onboard ASTROSAT. The mission would also study near simultaneous multi-wavelength data from different variable sources.
In addition, ASTROSAT’s observatory will also undertake: low- to moderate resolution spectroscopy over a wide energy band with the primary emphasis on studies of X-ray-emitting objects; timing studies of periodic and aperiodic phenomena in X-ray binaries; studies of pulsations in X-ray pulsars; quasi-periodic oscillations, flickering, flaring, and other variations in X-ray binaries; short- and long-term intensity variations in active galactic nuclei; time-lag studies in low/hard X-rays and UV/optical radiation; and, detection and study of X-ray transients. More specifically, ASTROSAT will train its instruments at active galactic nuclei like core of the Milky Way, which are believed to contain super-massive black holes. The Ground Command and Control Centre for ASTROSAT is the ISRO Telemetry, Tracking and Command Network (ISTRAC) at Bangalore. Directing ASTROSAT and data download will be done during every visible pass over ISTRAC; 10 out of 14 orbits per day will be visible to the ground station.
ASTROSAT adds new dimension to ISRO’s capabilities after Chandrayaan and Mangalyaan. Chandrayaan confirmed presence of water on the moon. But these missions were essentially building the foundation for India’s deeper exploration into space. Other satellites that ISRO placed in space over past three decades were mainly geared at applications like remote sensing, communications, mapping, navigation etc essential to our space program but ASTROSAT is to study of astronomical phenomena. Earth based telescopes only receive modified signals, which have to be adjusted for accuracy. In contrast, a space observatory like ASTROSAT receives pure signals because of which the readings are more accurate. Though mission life of ASTROSAT is five years, ISRO has put India in the exclusive club of nations with space-based observatories, others being the US, Russia, European Space Agency and Japan.