GAGAN, the satellite based augmentation system, is a joint project of ISRO and which organisation?

The correct answer is B, Aryabhata in 1975. It was launched on 19 April 1975 by a Soviet launch vehicle, since India had no vehicle of its own at the time, and it carried experiments in X-ray astronomy, solar physics and the ionosphere. It was named after the ancient Indian mathematician and astronomer.

Option A, Rohini of 1980, holds a different record: it was the first satellite placed in orbit by an Indian launch vehicle, SLV-3, on 18 July 1980, and candidates who mix the two records choose it. Option C, Bhaskara-1 of 1979, was the first experimental earth observation satellite. Option D, APPLE of 1981, was the first experimental communication satellite and went up on the European Ariane rocket. The clean chain to memorise is 1975 first satellite, 1979 first earth observation, 1980 first Indian launch, 1981 first communication satellite.

The correct answer is A, Navigation with Indian Constellation. The name was given in 2016 to the Indian Regional Navigation Satellite System, IRNSS, when the seventh satellite of the constellation was placed in orbit, and the word navik also carries the sense of a sailor or navigator, which is why it was chosen.

Options B, C and D are invented expansions of the kind an examiner adds to see whether the candidate has read the term or only heard it. The two facts that go with the full form are that NavIC is the Indian system built so that the country does not depend on another nation's signals, and that it is a regional system covering India and a belt of about 1,500 km beyond its boundary rather than the whole earth. Keep IRNSS and NavIC as the old and new names of one system.

The correct answer is B, seven. The system was designed as a constellation of seven satellites, three of them in geostationary orbit and four in geosynchronous orbits inclined to the equatorial plane, a small number being enough because the service area is regional and not global. IRNSS-1G, launched in April 2016, completed the seven.

Option A, four, is the number of inclined satellites alone and is the trap for a candidate who remembers the split but not the total. Option D, twenty-four, is roughly the size of a global constellation such as GPS, which needs satellites spread over the whole earth. Option C, nine, matches no system. Remember the split as three plus four, and remember that the second-generation NVS satellites are replacing the first-generation ones as they age.

The correct answer is B, Kalpana-1. Launched in 2002 as METSAT, it was the first Indian satellite built only for weather work, and it was renamed Kalpana-1 in memory of Kalpana Chawla, the India-born astronaut who died in the Columbia accident of 2003. Its instruments watched cloud cover, water vapour and sea surface temperature for cyclone warning.

Option A, INSAT-1B of 1983, carried meteorological instruments but was primarily a communication satellite, which is the distinction the word exclusively tests. Option C, Bhaskara-2, belonged to the early experimental earth observation series of 1979 and 1981. Option D, Oceansat-1 of 1999, studied the sea, its colour and winds over it, so it is an ocean rather than a weather satellite. The later dedicated weather satellites in this line are the INSAT-3D series.

The correct answer is B, a dedicated multi-wavelength space observatory. Astrosat was launched on 28 September 2015 by a PSLV and carries instruments that observe the same cosmic source in the ultraviolet, the visible and the X-ray bands at the same time, which is what multi-wavelength means and what makes the mission unusual among space telescopes of its size.

Option A describes the RISAT series, which images the ground through cloud and at night using radar. Option C describes the IRNSS and NVS satellites of the NavIC constellation. Option D describes EDUSAT of 2004, the first Indian satellite meant only for education and classroom broadcasting. Two other science missions belong in the same list of firsts: Aditya-L1 of 2023, the first solar observatory, and XPoSat of 2024, which studies the polarisation of cosmic X-rays.