After a successful landing on the Moon, the Indian Space Research Organisation is ready to launch its Aditya-L1 mission to study the Sun at 11.50 am on Saturday from the second launch pad at Sriharikota.
The 1,480 kg spacecraft will be carried by India’s workhorse Polar Satellite Launch Vehicle (PSLV) and put in a highly elliptical orbit of 235 km x 19,500 km around the Earth. The PSLV in its XL configuration, which has six solid fuel-based boosters, will take just over an hour to place the satellite in orbit.
The orbit as well as the velocity of the spacecraft will then be increased till it is slingshot towards the Sun. The distance of 1.5 million km to L1 point will be covered in nearly four months (125 days). The spacecraft will then be inserted in a halo orbit around the L1 point. The seven science experiments onboard will continue collecting data for the next five years.
The 23-hour 40-minute countdown started just after noon on Friday. The range the spacecraft will travel is just 1% of the 150 million km distance to the Sun. “The Sun is a giant sphere of gas and Aditya-L1 would study the outer atmosphere of the Sun. Aditya-L1 will neither land on the Sun nor approach the Sun any closer,” the space agency said on Friday.
Why L1 point?
The L1 point lies much beyond the orbit of the Moon and it does not have any other planet crossing by so the view from the spacecraft will remain free of an eclipse even when it is experienced on the Earth. Studying the sun from space also ensures that there are no distortions to the measurements that would be experienced on Earth due to the atmosphere, magnetic field and dust particles.
ISRO lists the payloads and their capabilities as below:
Remote Sensing Payloads
|Visible Emission Line Coronagraph(VELC)
|Corona/Imaging & Spectroscopy
|Solar Ultraviolet Imaging Telescope (SUIT)
|Photosphere and Chromosphere Imaging- Narrow & Broadband
|Solar Low Energy X-ray Spectrometer (SoLEXS)
|Soft X-ray spectrometer: Sun-as-a-star observation
|High Energy L1 Orbiting X-ray Spectrometer(HEL1OS)
|Hard X-ray spectrometer: Sun-as-a-star observation
|Aditya Solar wind Particle Experiment(ASPEX)
|Solar wind/Particle Analyzer Protons & Heavier Ions with directions
|Plasma Analyser Package For Aditya (PAPA)
Solar wind/Particle Analyzer Electrons & Heavier Ions with directions
|Advanced Tri-axial High Resolution Digital Magnetometers
|In-situ magnetic field (Bx, By and Bz).
The Sun mission, which comes soon after the historic Chandrayaan-3 mission that put India in an elite club of four countries that have soft landed on the Moon, has been planned to allow the best observation window to study the Sun.
“For a mission to L1 point, the ideal launch window is between January and September, considering the fuel requirements and planetary positions. The good thing is that the spacecraft will reach its designated orbit in early 2024, allowing it a good few months of observation of the ascending solar cycle and then the descending cycle in 2025,” said Prof R Ramesh from Indian Institute of Astrophysics, whose team was involved in developing the scientific experiments that will be carried by the mission. The solar cycle usually follows an 11-year pattern.
The mission had initially been conceptualised as just an experiment to study a layer of the Sun’s atmosphere called the Corona from a low earth orbit in 2006. The mission was later switched to one with more complex instruments belonging to the observatory class of satellites that could study the Sun from the L1 point without any obstruction caused by events such as eclipse.
There are five Lagrange points between any two 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.
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 affect us. The advanced scientific experiment will also allow the researchers to look into the lower layers of the solar corona, hopefully offering clues to why the corona is a million degrees Celsius when the surface of the Sun is just 5,500 degrees Celsius.