CHENNAI: From capturing strange celestial objects to uncovering the nature of neutron stars, black holes and hot star, Astrosat, India’s dedicated space observatory, has done it all by circling the Earth nearly 18,000 times in over three years. 

But do you know how the satellite functions and astronomers receive data? In its Astrosat Photo of the Month, Indian Space Research Organisation reveals it all.

Astrosat takes about 97 minutes to orbit the Earth once. The observatory, launched on September 28, 2015 onboard a PSLV, is at an altitude of about 650 km above the Earth.

The orbit is not exactly over the equator but is inclined at an angle of about 6 degrees to it. Why was this orbit chosen?

The post put up on ISRO’s website explained that the Earth has a magnetic field, which behaves like a bar magnet with its poles a few degrees from the poles defined by the planet’s rotation. These magnetic fields trap charged particles within them, which form the Van Allen Belts. These radiation belts are much closer to the Earth over the southern Atlantic Ocean. An equatorial orbit reduces the effect of this radiation belt on Astrosat, which carries very sensitive instruments.

“Making the inclination exactly zero requires more resources and hence a 6 degree inclination was chosen,” read the post.

But as Astrosat circles the Earth, it does not pass directly overhead the same point in successive orbits. Each orbit, therefore, will be slightly shifted with respect to the previous one.

Data is beamed from an antenna in the satellite when it passes over India. The data is received by ISRO’s dedicated Indian Deep Space Network antenna in Byalalu near Bangalore. All orbits of Astrosat fall within the visibility of this antenna. ISRO can also use an antenna in Indonesia to monitor the satellite when needed. All the command, control and tracking of Astrosat are done by ISTRAC in Bangalore.