A rich sequence of space missions that paints a vivid picture of India’s journey in space exploration, from the early days of Aryabhata to the Chandrayaan-3’s Vikram lander on the Moon

India’s space odyssey began with the launch of its first satellite, Aryabhata, in April 1975. Hitching a ride aboard a Soviet Kosmos-3M launch vehicle, Aryabhata was equipped with two low-energy X-ray detectors. These detectors had a specific purpose – to measure X-rays in the energy range of 2.5 keV to 155.0 keV. Remarkably, Aryabhata’s detectors made pioneering observations of celestial phenomena, including the X-ray spectrum of Cygnus X-1 and X-ray sources at the center of our Milky Way galaxy.

1984 USSR stamp featuring Bhaskara-I, Bhaskara-II and Aryabhata satellites. Image scanned by Andrew Butko.

In the years that followed, India continued to make its mark in space research with contributions like the low-energy cosmic-ray detector Anuradha, which flew aboard the NASA Challenger Space Shuttle. Anuradha recorded solar and galactic cosmic ray events, providing crucial insights into the properties of cosmic rays and interstellar atoms.

The 1990’s

The year 1994 marked another significant milestone when India launched the SROSS-C2 satellite, featuring the Gamma Ray Burst Experiment (GRBE). This gamma-ray detector was highly sensitive, capable of detecting gamma rays within a wide band ranging from 20 keV to 3 MeV. In the course of its mission, GRBE detected more than 50 gamma ray bursts, enhancing our understanding of these enigmatic cosmic phenomena.

Fast forward to 1996, and India’s space endeavors continued to expand with the launch of the IRS-P3 satellite, carrying the Indian X-ray Astronomy Experiment (IXAE). This experiment, comprising four detectors with capabilities in the 2 keV to 20 keV range, conducted observations of neutron stars, black hole binaries, X-ray transients, and X-ray pulsars. These observations yielded more than 31 publications and supported four doctoral theses, including detailed studies of X-ray sources such as GRS 1915+105 and XTE J1748-288. IXAE even provided evidence suggesting the disappearance of stellar matter into the event horizon of the black hole candidate GRS 1915+105.

The 2000’s

In the pursuit of understanding our own star, the Sun, India launched the Solar X-ray Spectrometer (SOXS) aboard the ISRO GSAT-2 satellite. SOXS featured two X-ray detectors, one operating in the low-energy range and the other in the high-energy range. This duo enabled comprehensive observations of the Sun’s X-ray activity, shedding light on the complex processes occurring within our nearest star, both temporally and in terms of X-ray energy spectra.

The culmination of India’s space science efforts came with the launch of the Roentgen Telescope 2 (RT-2) in January 2009 aboard the Roscosmos CORONAS-Photon solar research satellite. RT-2 was a high-energy X-ray and gamma-ray telescope operating in the 15 keV to 1 MeV range. During its mission, RT-2 observed a multitude of gamma-ray bursts, solar flares, and X-ray pulsars, expanding our understanding of high-energy astrophysical phenomena.

Image of Vikram lander on lunar surface taken by Pragyan rover at 1104 IST, 30 August 2023 from 15 meters away. Credits: Indian Space Research Organisation

The last decade witnessed two the most remarkable achievements of India’s, and perhaps of the world’s, space exploration: AstroSat and the the Chandrayaan-3’s Vikram lander on the Moon. Launched on September 28 2015, into an orbit 650 kilometers above our planet, AstroSat carries with it a suite of five telescopes capable of observing the universe across a broad spectrum, from visible light to X-rays. This unique capability sets AstroSat apart as the only space observatory in the world that can simultaneously study the cosmos in such a diverse range of wavelengths. Over the past seven years, AstroSat has been diligently at work, contributing to more than 254 research publications during its first six years of operation. A great success followed by another great achievement on the 23rd of August 2023, at 12:33 UTC, when the Chandrayaan-3’s Vikram lander – carrying a rover in its belly – touched down on the lunar soil. With this mission, India set down a robotic probe on the Moon, becoming the first country to land near the lunar south pole.

References:

Ritesh Singh Astronomy & Geophysics, Volume 63, Issue 4, August 2022, Pages 4.27–4.29, https://doi.org/10.1093/astrogeo/atac051

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