Satellite Technology for Astronomy: The ASTROSAT of ISRO

Recently, I was exploring a different domain of science, something about which I was fascinated since a very long time. This is a brief article on ASTROSAT and the basic understanding of its complexity.

Ever heard of this magnum opus space project of ISRO, the ASTROSAT? The origin of this interesting project dates to the year 1996. During that time, about 50 astronomers from various parts of the country came together and envisioned something that the world would witness as ASTROSAT, several years later. ASTROSAT is basically a small 1600-watt solar powered satellite weighing about 1515 kg. It is also equipped with two lithium-ion batteries to power it up when sunlight is not falling on it.

ASTROSAT was launched into space using the polar satellite launch vehicle, PSLV. The satellite was put to a 650 KM near equatorial altitude orbit on 28th September 2015. It would take the satellite a duration of 97 minutes to complete one orbit. This technological marvel is a true data miner that would help astronomers to unravel the mysteries of the universe in years to come. The mission life is expected to be a minimum of 5 years.

ASTROSAT has a total of 6 amazing payload experiments on board which is used for measuring various parameters and observing the universe. These are as follows;

1. Ultraviolet Imaging Telescope (UVIT)

It is an amazing 230 Kg 3 in 1 telescope that can simultaneously observe in near ultra-violet, visible, and far ultra-violet. The hybrid telescope in-fact is made of two telescopes. UVIT has a spatial resolution of 1.8 arc microseconds with a field of view of 0.5 degrees. UVIT was a sensitive instrument to build, The CMOS detector converts incoming photons to electric charges. This means that there is a chance that the equipment can be permanently damaged on exposure to bright light.

2. Soft X-ray Telescope (SXT)

This instrument operates at 0.3 to 8 KeV. The SXT uses a special geometry called Walter type 1 geometry where rays are reflected twice, once by a parabolic mirror followed by a hyperbolic mirror before they are focussed. SXT is nearly 2.5 meters in length and has 320 nested mirror foils to increase the collecting area of X-rays. The focussed X-ray photons are finally collected by a charged coupled device. This CCD is maintained at a temperature lower than -80 degrees centigrade to avoid generation of unwanted photons.

3. Large Area X-ray Proportional Counter (LAXPC)

This instrument is basically used for broadband spectroscopy for various astrophysical sources. This instrument can measure X-ray spectra at very short time scales over a large range of energies. This unique instrument is even capable of measuring changes in brightness of celestial sources in microsecond range giving it a great precision and setting it up as an exceptional tool for observing various cosmic bodies. At a weight of about 415 Kg, this instrument was developed entirely indigenously by Tata Institute of Fundamental Research.

4. Cadmium-Zinc Telluride Imager (CZTI)

This is basically a solid-state detector that can detect and differentiate events that are due to X-ray photons and those due to charged particles. Basically, a Caesium-Thallium-Iodide crystal is placed under the detector. As the high energy particles pass through the detector, they deposit their energy both on the CZT detector as well as the iodide crystal while the X-ray photons deposit their entire energy only in the CZT. This instrument is known to perform at its best at around 0 to 15 centigrade.

5. Scanning Sky Monitor (SSM)

This is a standard instrument on board most observatory satellites. It has a large field of few and observes for any special transient events in space. If it detects anything, the other instruments on board the satellite as well as the ground observatories can be used to focus on the anomaly and investigate further. As the name suggests, it basically scans the sky and monitors it.

6. Charged Particle Monitor (CPM)

The final payload to discuss is a small 2 Kg weighed instrument, also developed by TIFR. Its main function is to detect charged particles.

This satellite can cover a large range of energy allowing it to perform simultaneous observations on various classes of objects that puzzle humans till date. UVIT is specially designed making it a subtle instrument for observing the White Dwarfs, which is essentially a stage of the star after all the fuel in it for a nuclear fusion is over. Such hot objects emit radiations in the ultraviolet region. Globular clusters of Stars are another cosmic object that can be detected and observed by UVIT. One of the main features of ASTROSAT is its ability to study the same objects variation in UV emissions and X-ray emissions simultaneously which helps in understanding the behavior of peculiar double star systems.

What are the main mission objectives?

A satellite of such complexity and specialization was built, keeping in mind a few important objectives. Its main function was to study celestial sources simultaneously in X-ray, UV and visible spectrum. Study of these rays from outer space helps us to understand some high energy processes in binary star systems, search for black holes within the galaxy, measure the magnetic field of neutron stars and many more extragalactic events as well.

Also, it is not just about ASTROSAT but how it can collectively contribute to our scientific understanding of the universe. It is expected that by collectively using data generated by ASTROSAT along with data generated from other space and ground-based observatories, even greater insights can be derived and analyzed.

Space is an endless infinitely complex spectacle defining existence. Exploring all of it is an eternal continual effort nearly impossible with current potential. Understanding it all is another humongous feat even for a supercomputer integrated with the intelligence of a human brain. No words can accurately describe the marvels that the universe holds within itself and yet, isn’t it amazing how a tiny human-made object like the ASTROSAT floating in an abyss of emptiness out there can be the key to deciphering the secrets of everything. More than often, what we discover is limited by our own imagination. The Universe is truly a beautiful place and the study of it, equally enthralling. No wonder, it made humans look up to the sky and beyond from time and again to find answers that remain unknown to this day.

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