Aditya-L1 begins its long solar voyage

At 11.45am on Sunday, Isro will perform the first Earth-bound firing to raise the orbit of the Aditya-L1 craft.

India’s first solar mission took off successfully on Saturday, embarking on a 125-day journey before it is placed in a halo orbit around Lagrange Point 1 (L1), a spot between the Sun and the Earth about 1.5 million kilometres from us.

The Aditya-L1 spacecraft takes off from the Satish Dhawan Space Centre in Sriharikota. (AFP)

Insertion in L1 will enable the solar observatory Aditya-L1 to monitor the Sun with a “constant, uninterrupted view”.

But the process for its final placement is long, and requires a series of intricate manoeuvres, the first of which will be performed on Sunday, as the craft uses Earth’s gravity to gather momentum.

At 11.45am on Sunday, the Indian Space Research Organisation will perform the first Earth-bound firing to raise the orbit of the Aditya-L1 craft and ensure that the craft gains the necessary velocity for its journey.

“Aditya-L1 will stay Earth-bound for 16 days, during which it will undergo five manoeuvres to gain the necessary velocity for its journey,” a senior Isro scientist explained.

The Earth-bound manoeuvres will involve the rockets firing and some adjustments to angles, as required. How this will work can perhaps be understood by taking the example of when a person is on a swing — to make the swing go higher, a pressure (by shifting body weight) is applied when in the phase when the swing is coming down towards the ground. In Aditya-L1’s case, once it gains enough velocity, it will slingshot around to its intended path towards L1.

“This will mark the beginning of its 110-day trajectory to the destination around the L1 Lagrange point,” the scientist said, requesting anonymity.

Once the spacecraft arrives at the L1 point — the position in space where the gravitational forces of a two-body system (the Earth-Sun system here) produce enhanced regions of attraction and repulsion — another manoeuvre will be performed to bind the Aditya-L1 craft to the orbit, the space agency said.

“The satellite spends its whole mission life orbiting around L1 in an irregularly shaped orbit in a plane roughly perpendicular to the line joining the Earth and the Sun,” an Isro document read.

The strategic placement will ensure that Aditya-L1 can continuously monitor the Sun.

“The strategic placement at the L1 Lagrange point ensures that Aditya-L1 can maintain a constant, uninterrupted view of the Sun. This location also allows the satellite to access solar radiation and magnetic storms before they are influenced by Earth’s magnetic field and atmosphere,” the document said.

The gravitational stability at this point will also minimize the need for frequent orbital maintenance, it said. “Additionally, the L1 point’s gravitational stability minimises the need for frequent orbital maintenance efforts, optimizing the satellite’s operational efficiency.”

Explaining the similarity between Chandrayaan-3’s route and the route that Aditya-L1 will take, Annapurni Subramaniam, director, Indian Institute of Astrophysics (IIA), said, “It will go on a circular orbit first, then it will slingshot and make it into an elliptical orbit and after four such orbit enhancements, it will go on a cruise phase. It will take over 120 days to reach the L1 point.”

The IIA has designed the primary payload of the mission — Visible Emission Line Coronagraph (VELC).

On Saturday, after a successful lift off from the Satish Dhawan Space Centre in Sriharikota, the spacecraft was placed in an elliptical orbit of 235X19,500kms. This means that the Perigee (the point in a satellite’s orbit at which it is nearest to the Earth) was 235kms, and the Apogee (the point in the orbit at which the satellite is farthest from the Earth) was 19500kms.

With Aditya-L1, which was launched on Isro’s most-trusted PSLV-XL, scientists performed a unique flight sequence, where the upper stage of the rocket took two burn sequences for injecting the primary satellite.

Explaining the reason for this, a second Isro official said that a specific angle of Perigee (AOP) — the angle between the ascending node and perigee directions, measured along the orbital plane — was required for the mission.

“The final stage of PSLV was fired for about 30 seconds and then we waited for the AOP to reach the required range, and then it was fired again. The separation took place after that. The entire process took over an hour, which in a lighter mission would take around 25 minutes,” a senior Isro official said.

Following the successful launch, project director for Aditya-L1 Nigar Shaji said that it was a “dream come true” for the scientist.

“Aditya (L1) has started its 125-day journey. The mission has been planned to study all the major solar events. We have seven payloads that will be studying aspects including coronal mass ejections (CME), solar flares, solar winds etc. We will try to understand these major events and its impacts on space weather,” she said.

Scientists from IIA said that after 125 days, a few tests will be conducted, and the first set of data from the instruments on board is expected from February or March next year.

While the mission is designed to provide data for the next five years, experts said that there is a possibility of it going on till 10 or even 15 years.