On this page
Crop estimates, forest maps, flood damage and city planning in India all lean on images taken from orbit. The programme that produces them began with two experimental satellites in the late 1970s and early 1980s, and the scientist who led them was K. Kasturirangan. This post covers his path, the satellites, a worked example on IRS-1A's orbit and camera, and what students can learn from how he worked.
Who was K. Kasturirangan?
According to his obituary in Nature India, Krishnaswamy Kasturirangan was born in Ernakulam, Kerala, on 24 October 1940 and died in Bengaluru on 25 April 2025, aged 84. ISRO's page on him as a former chairman says he took BSc (Honours) and MSc degrees in physics from Bombay University and a doctorate in experimental high-energy astronomy in 1971 at the Physical Research Laboratory, Ahmedabad.
He began as an astrophysicist. ISRO's page describes his research on cosmic X-ray sources, celestial gamma rays and the effect of cosmic X-rays on the lower atmosphere. Nature India adds that his early work involved high-altitude balloon experiments to detect X-ray and gamma-ray sources.
What were Bhaskara-I and Bhaskara-II?
ISRO's page says he was project director for India's first two experimental Earth observation satellites, Bhaskara-I and II.
Bhaskara-I was launched on 7 June 1979 on a Soviet launcher. It weighed 442 kg and carried TV cameras and a three-band microwave radiometer called SAMIR. ISRO says the camera images were used in hydrology and forestry, and the radiometer data in ocean studies.
Bhaskara-II, launched on 20 November 1981, carried a two-band TV camera, one band in visible light (0.54 to 0.66 micrometres) and one in near-infrared (0.75 to 0.85 micrometres). Despite a problem with one camera, ISRO says it sent more than two thousand images.
These were learning satellites: they showed what Indian-built instruments could see and what users could do with the data.
How did IRS-1A make remote sensing routine?
As director of the ISRO Satellite Centre, ISRO's page says, Kasturirangan oversaw the development of INSAT-2 and the Indian Remote Sensing satellites IRS-1A and 1B, and was responsible for the overall direction of IRS-1A, the first operational one.
ISRO's IRS-1A page gives the details. It was launched on 17 March 1988 into a polar sun-synchronous orbit at 904 km, inclined at 99.08 degrees. It carried push-broom cameras with resolutions of 72.5 m (LISS-1) and 36.25 m (LISS-2), each covering a strip about 140 km wide. It repeated its ground track every 22 days, which is 307 orbits, and served until July 1996.
He chaired ISRO from 1994 until 27 August 2003. ISRO's page credits that period with the PSLV becoming operational, the first successful flight test of the GSLV, and the IRS-1C and 1D satellites. Nature India adds that he later chaired the committee that drafted the National Education Policy 2020.
Worked example: IRS-1A's orbit and camera
You can check ISRO's numbers with Class 11 gravitation. Use Earth's radius R = 6371 km and GM = 3.986 × 10¹⁴ m³/s².
Orbit radius: r = 6371 + 904 = 7275 km = 7.275 × 10⁶ m.
Period: T = 2π √(r³/GM). r³ = 3.850 × 10²⁰ m³. Divide by GM: 9.66 × 10⁵ s². Square root: 982.9 s. So T = 2π × 982.9 ≈ 6176 s ≈ 102.9 minutes.
Check with ISRO's repeat cycle: 22 days = 31,680 minutes. Divided by 307 orbits: 31,680 / 307 ≈ 103.2 minutes. The two agree to within about 0.3%.
Orbital speed: v = 2πr / T = (2π × 7.275 × 10⁶) / 6176 ≈ 7.4 km/s.
Camera: a 140 km strip at 36.25 m per pixel is 140,000 / 36.25 ≈ 3,860 pixels across.
Common mistakes: using the height (904 km) instead of the radius from Earth's centre, and forgetting to convert kilometres to metres before using GM. Our post on gravitation and satellite problems has more practice.
What can a student take from how Kasturirangan worked?
Start with experiments. Bhaskara-I and II were tests that taught the team what an operational satellite needed.
Think about the user. The value of an Earth observation satellite is measured in maps and crop estimates, not only in launches.
Keep learning outside your field. An X-ray astronomer became a satellite builder and later shaped education policy.
Orbits are easier to grasp when you can move the satellite and watch the period change. The Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read. For the satellite that came before Bhaskara, read about U. R. Rao and Aryabhata.
Next step: redo step 2 for a satellite at 500 km and see how much shorter its period is.
