Aditya-L1 and Space Science Missions: Notes and MCQs

Space missions are the part of Science and Technology that examiners can turn into one line questions without any physics: a mission, its rocket, its date and what it went to do. Aditya-L1 is the natural centre of this topic, because it is the first Indian mission built to watch the Sun, and because the idea behind it, a spacecraft parked at a Lagrange point, explains half the space questions in modern papers. These notes place Aditya-L1 among the Indian missions that came before and beside it.

Aditya-L1, the Indian solar mission

Aditya-L1 was launched on 2 September 2023 by PSLV-C57 from Satish Dhawan Space Centre at Sriharikota. It is India first space based observatory to study the Sun. After raising its orbit around the Earth in stages, it was inserted in January 2024 into a halo orbit around Lagrange point L1 of the Sun and the Earth, about 1.5 million kilometres from the Earth, which is roughly one hundredth of the distance to the Sun.

A Lagrange point is a place where the pull of the Sun and the pull of the Earth, together with the motion of the spacecraft, balance so that the craft keeps pace with the Earth without using much fuel. There are five such points for any pair of bodies. L1 lies between the Sun and the Earth, which gives a spacecraft there an unbroken view of the Sun, never blocked by an eclipse or by the night side of the Earth. That unbroken view is the whole reason for choosing L1.

The mission carries seven payloads. Four of them look at the Sun from a distance and three sample the particles and fields that arrive at the spacecraft itself. The chief instrument is the Visible Emission Line Coronagraph, known as VELC, which blocks the bright disc of the Sun so that the faint outer atmosphere, the corona, can be studied. Beside it are the Solar Ultraviolet Imaging Telescope, a soft and a hard X-ray spectrometer, a particle experiment, a plasma analyser and a magnetometer. Together they study the corona, the flares and the coronal mass ejections that drive space weather and can disturb satellites and power grids on the Earth.

The Indian missions before it

Chandrayaan-3 is asked more often than any other mission. It was launched by the LVM3-M4 vehicle, its landing site was named Shiv Shakti Point, and 23 August is now observed as National Space Day. Its lander carried ChaSTE, which measured how temperature changes with depth in the lunar soil, an instrument to record moonquakes and one to study the plasma near the surface, while the rover carried two instruments to find out what the soil is made of.

Terms and milestones worth memorising

• ISRO was formed on 15 August 1969, and Vikram Sarabhai is called the father of the Indian space programme. Its headquarters is at Bengaluru.
• India first rocket was launched from Thumba near Thiruvananthapuram on 21 November 1963.
• Gaganyaan is the Indian human spaceflight programme, and its first uncrewed test of the crew escape system, TV-D1, flew in October 2023.
• Rakesh Sharma became the first Indian in space in 1984, aboard a Soviet Soyuz spacecraft.
• A geostationary satellite sits about 36,000 kilometres above the equator and appears fixed in the sky, which is why communication satellites use that orbit; remote sensing satellites use low polar orbits instead.
• NavIC is the Indian regional navigation system, and the INSAT and GSAT families carry communication, while the IRS and Cartosat families carry remote sensing.

Solar missions of the world

Aditya-L1 is not alone at L1. The SOHO observatory of NASA and the European Space Agency has watched the Sun from there since the nineteen nineties. The Parker Solar Probe, launched in 2018, flies far closer and passes through the outer corona itself, and the Solar Orbiter, launched in 2020, studies the poles of the Sun. The James Webb Space Telescope, launched in 2021, sits instead at L2, on the far side of the Earth from the Sun, where it can keep its mirrors cold and in shadow. Knowing which instrument sits at which Lagrange point is a favourite one line question.