Pic: ASTROSAT before it’s launch at ISAC Bengaluru
India’s first multi-wavelength observatory ASTROSAT was launched on Sept 28, 2015 from the first launch pad of Satish Dhawan Space Centre at Shriharikota, Andhra Pradesh at 10 am by Polar Satellite launch vehicle (PSLV- C30). The satellite weighed 1513kg is launched into a 650km (around 404miles) orbit inclined at an angle of 6° to the equator. It is launched with a life-time of five years. Total cost of the project was approximately 180 crores. Prior to this mission, India was mainly focusing on communication, navigation, education, earth observations but this was the first time when Indian scientists worked for a dedicated astronomy mission.
Conceptualization of India’s astronomy mission was started in the year 1996 and a project report outlining the mission was submitted in 2000. In 2002 the project got approved by Indian Space Research Organization (ISRO) with the grant of seed fund. Later, in 2004 the mission gained approval and full funding from Gov. of India. The mission was aimed to be launched in the year 2011 but due to some technical issue it has suffered a long delay. Resolution of technical issues and prelaunch testing of instruments was complete by Aug 10, 2015. The satellite was assembled at ISRO Satellite Centre (ISAC), Bengaluru and finally placed into orbit on Sept 28, 2015.
Why ASTROSAT was needed:-
The universe has always been a fascinating subject. Ever since the dawn of human civilization the mysteries of universe has been drawing the curious minds of the societies to study the universe. It was this thirst of curiosity which first led to assumption about outer space, different stars, and distance between them, followed by dedicated study in this field. The space science started booming after the development of telescopes that was further led to new height with the development of ground based astronomical observatories. The ground based observatories provided the scientists a peep through the Earth’s atmosphere into outer space. With the advent of time and technology scientists felt a need to develop a space observatory as ground based observatories suffered many limitations, prime being the atmospheric distortion. A space observatory is any instrument (such as telescope) in outer space that is used for observing distant planet, galaxies and other outer space objects. India already had ground based telescopes like Giant Metrewave Radio Telescope near Pune and Indian Astronomical Observatory in Ladakh. Ground based telescopes have limitations of detecting radio-waves and infrared radiations only, as these penetrate the Earth’s atmosphere. Moreover ground based observatories had to contend with atmospheric turbulences and suffer light pollution and daylight problem. Indian scientists had to depend on international resources for the study of entire radiation bands. If India wants to be at the forefront of worldwide scenario of space technology it cannot afford to rely on foreign data resources for longer period of time. The time had come when India felt the need for development of its own indigenous space observatory and Indian scientist came up with the idea of India’s first astronomy mission “ASTROSAT”. ASTROSAT is targeted to observe distant celestial object in full electromagnetic spectrum range in order to have better understanding of our Universe. It is for the first time any space observatory would be observing the universe in such a broad range of wavelength. Multi-wavelength observations of ASTROSAT can be further extended with co-ordinated observations using other space crafts and ground based observations.
Uniqueness of ASTROSAT:
Pic: Payloads of ASTROSAT
ASTROSAT has five payloads which have been developed by ISRO in collaboration with four Indian Institutions and two foreign organizations. The payloads of ASTROSAT will facilitate a deeper insight into our universe. It will help in monitoring the various astrophysical processes occurring in the various types of astronomical objects in space. These payloads relay on the visible,UV and X-rays coming from distant celestial sources. The payloads of carried by ASTROSAT are as follow:
1. Ultra-violet Imaging Telescope( UVIT) :– UVIT was developed by the Indian Institute of Astrophysics, Bengaluru, and the Inter- University Centre for Astronomy and Astrophysics, Pune. It consist of two telescope and three independent detector system. The detector in each channel is a photon counting image device which is capable of observing the sky in visible(320-530nm), near UV( 180-300nm) and far UV(130-180nm) regions of the electromagnetic spectrum. Multiple choices of filters are available in each channel.
2. Large Area X-ray Proportional Counter( LAXPC):– LAXPC was developed by the Raman Research Institute, Bengaluru, and the TATA Institute of Fundamental Research, Mumbai. It is a non imaging instrument. The main objective of this instrument is to record and study the variation of total intensity of sources within 1degree field of view with high time resolution and moderate spectral resolution of X-rays from sources like X-ray binaries, Active Galactic Nuclei and other cosmic sources.
3.Soft X-ray Telescope(SXT):– It was developed by TIFR, the University of Leicester, U.K., and ISRO. It has a focusing X-ray telescope fitted with a CCD imaging camera. It is designed for studying how the X-ray spectrum of 0.3-8kev and 2-10kev range coming from distant celestial bodies varies with time. It will work primarily in photon counting mode, recording the position, time and energy of every detected photon.
Pic: ASTROSAT instrument details
4.Cadmium Zinc Telluride Imager( CZTI):– It was provided by TIFR, IUCAA, ISRO. It has a hard X-ray coded mask camera which has a coarse imaging capability. It function in the X-ray region extending the capability of the satellite to sense X-rays of high energy in 10-100kev range.
5.Scanning Sky Monitor(SSM):– developed by ISRO satellite centre, Bengaluru, and IUCAA. It will monitor the highly variable X-ray sources in the sky. It is intended to scan the sky for long term monitoring of bright X-ray sources in binary stars, and for the detection and location of sources that became bright in X-rays for a short duration of time. The main purpose of SSM is to quickly detect suddenly appearing interesting sources.
6.Charged Particle Monitor( CPM):– a separate CPM is included as a part of payload to control operation of LAXPC and SSM instruments through zones of high fluxes of charged particles. A Scintillator Photodiode Detector( SPD) with a built in preamplifier is used for CPM.
The satellite was assembled at ISRO’s satellite centre, Bengaluru. Generally the payload mass is less than 10% of the mass of the satellite but because of the lower orbit ASTROSAT could afford to have heavier payloads. The combined mass of the payloads is more than the mass of the satellite.
The satellite during its mission life will be managed by the spacecraft control centre at Mission Operations Complex (MOX) of ISRO Telemetry, Tracking and Command Network (ISTRAC) at Bengaluru. The satellite will gather data of various astrophysical processes occurring in universe and will send it to ground station at MOX. This data will then be processed and distributed by Indian Space Science Data Centre( ISSDC). All major astronomy institutions and some universities in India will also participate in these observations. The archival data will be accessible to any scientist in the world from data centre.
Scientific Objectives of ASTROSAT:
ASTROSAT versus Hubble:-
The successful launch of ASTROSAT has marked several successes for India. Now India has joined the elite group of nations like US, Japan, Europe and Russia marking a fifth rank in the world when a space program has succeed in sending a space observatory. It is being considered as India’s Hubble with the uniquely of covering multi-wavelength bands. ASTROSAT mission has provided opportunity to Indian scientists to work in the frontier areas of high energy Astrophysics. Such missions inspire and motivate young minds and open new arena of research.
ASTROSAT had marked strong imprint on the success road of Indian space research following the step of its first successful mission Manglayan launched a year ago. The two consecutive successes were not only a morale booster but showed India’s capability in space research, drawing world’s attentions at India’s fast growing astronomy credentials.
Author:- Aastha Saxena