ISRO’s Aditya-L1 to be launched on September 2: With feet on the Moon, the space agency eyes the Sun

What is the Aditya-L1 mission?

The Aditya-L1 mission will see the Polar Satellite Launch Vehicle (PSLV) carry the 1,475-kg spacecraft to an elliptical orbit around the Earth. The spacecraft, which will carry seven scientific payloads, is more than two times lighter than the one to the Moon.

Like the Chandrayaan-3 mission, the orbit as well as the velocity of the spacecraft around the Earth will be increased till it is slingshot towards the Sun. The distance to L1 point will be covered in nearly four months. The spacecraft will then be inserted into a halo orbit around the L1 point. It will collect data for five years.

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What is the L1 point?

There are five Lagrange points, L1 to L5, between any two orbiting celestial bodies. These points can act as parking spots in space where the gravitational pull of the celestial objects equals the centripetal force required to keep a satellite in orbit. This means satellites placed at Lagrange points do not need to expend a lot of fuel to remain in position.

First, going to Lagrange 1 places the spacecraft at a point beyond the Moon between the Earth and the Sun. This offers the spacecraft an unobstructed view of the Sun even during phenomena like an eclipse.

Second, with the mission covering only 1% of the distance between the Earth and Sun, the payloads will be able to look directly at the Sun. “This position will allow the main payload, VLEC, to look directly into the source of coronal mass ejection. Once at L1, it will be the best instrument observing the solar corona,” said Prof Dipankar Banerjee, director of Aryabhatta Research Institute of Observational Sciences (ARIES), which will host the support cell for the Aditya-L1 mission. Third, the L1 point makes the mission fuel-efficient.

What are the science objectives of Aditya-L1?

The main objective of the mission is to get a deeper understanding of the star closest to us, and how its radiation, heat, flow of particles, and magnetic fields affects us. The payloads on the mission will study the upper atmospheric layers of the Sun called chromosphere and corona. They will study the expulsion of plasma and magnetic fields called coronal mass ejection (CME). The magnetic field of the corona and the drivers of the space weather will also be studied.

Importantly, it might provide clues to scientists about a long-standing mystery: why the not-so-bright corona of the Sun is a million degree C hot, when the temperature on the surface of the Sun is just about 5,500 degree C. It will also help scientists understand the reasons behind acceleration of particles on the Sun, which leads to solar winds.

“The VLEC has mechanisms by which the bright visible light is occluded and only the light coming from the corona is detected. It will use very short exposures of about 5 milliseconds to study the corona,” said Banerjee.

The spacecraft will be placed in a halo orbit around the L1, which is about 1.5 million km from the Earth. (Photo courtesy: ISRO)

What are the payloads?

The main payload is the Visible Emission Line Coronagraph (VLEC), designed by the Indian Institute of Astrophysics, which will help study the solar corona from the lowermost part upwards. The VELC can image the solar corona down to 1.05 times the solar radius, the closest any such payload has imaged.

The Solar Ultraviolet Imaging Telescope (SUIT) designed by the Inter University Centre for Astronomy and Astrophysics (IUCAA) will capture the UV image of the solar photosphere and chromosphere. It will help study the variation in light energy emitted.

The Solar Low Energy X-ray Spectrometer (SoLEXS) and High Energy L1 Orbiting X-ray Spectrometer (HEL1OS), developed by the UR Rao Satellite Centre, will study X-ray flares.

The Aditya Solar wind Particle EXperiment (ASPEX) and Plasma Analyser Package for Aditya (PAPA) are designed to study the solar wind and energetic ions. The first payload has been developed by ISRO’s Physical Research Laboratory and the latter by the Space Physics Laboratory of ISRO’s Vikram Sarabhai Space Centre.

Why study the Sun from space?

The Sun is the nearest star to us and therefore can be studied in much greater detail than others. Studying the Sun can also help us understand more about other stars. While the Sun supports all life on Earth, it also has various explosive phenomena. These can damage our satellites and communication systems. Studying the Sun may help in providing early warnings for such events.

“The various thermal and magnetic phenomena on the Sun are of extreme nature. Thus, the Sun provides a good natural laboratory to understand them, which cannot be directly studied in the lab,” ISRO said.

It is important to study the Sun from space because the Earth’s atmosphere and the magnetic field act as protective shields that block out harmful radiations, such as UV light. This means studying the Sun from the Earth can’t provide a complete picture.