Halo-Orbit Insertion of Aditya-L1 Successfully Accomplished

The Indian Space Research Organisation (ISRO) has placed the Aditya-L1 spacecraft in a halo orbit around the Lagrangian point (L1).

India’s maiden solar mission Aditya-L1 reached the L1 point on January 6, 127 days after it was launched on September 2, 2023.

After a 1.5-million km journey, the spacecraft was placed in a halo orbit around L1 following a firing maneuver carried out by ISRO scientists and engineers at the ISRO Telemetry Tracking and Command Network (ISTRAC) in Bengaluru.

ISRO Chairman S Somnath said that the halo orbit insertion process was carried out as intended. “Today’s event was to place the Aditya L-1 in the precise halo orbit. The spacecraft was moving towards the halo orbit but we had to make some corrections to put it in the right place. If we do not do the correction today there could have been a possibility that it could escape from this point (L-1 point). But we would not have allowed that to happen as there are some contingencies in place, but I am only saying mathematically it can escape.”

“So that has been very precisely done [placing the spacecraft in the halo orbit]. What we have achieved today is exact placement based on our measurement and a very correct prediction of the velocity requirement. Right now, in our calculation the spacecraft is in the right place,” he added.

Prime Minister Narendra Modi announced that the Aditya-L1 has reached its destination.

“India creates yet another landmark. India’s first solar observatory Aditya-L1 reaches its destination. It is a testament to the relentless dedication of our scientists in realising the most complex and intricate space missions. I join the nation in applauding this extraordinary feat. We will continue to pursue new frontiers of science for the benefit of humanity,” Mr. Modi said in a post on X (formerly Twitter).

The ISRO said that the halo orbit insertion of Aditya-L1 was accomplished at 4 p.m. and that the final phase of the maneuver involved the firing of control engines for a short duration.

“The orbit of Aditya-L1 spacecraft is a periodic halo orbit which is located roughly 1.5 million km from earth on the continuously moving Sun–Earth line with an orbital period of about 177.86 earth days. This halo orbit is a periodic, three-dimensional orbit at L1 involving the Sun, Earth, and a spacecraft.

This specific halo orbit is selected to ensure a mission lifetime of 5 years, minimising station-keeping maneuvers and thus fuel consumption and ensuring a continuous, unobstructed view of the Sun,” the ISRO said after the orbit Insertion was accomplished.

It further said that the insertion of Aditya-L1 into this halo orbit presents a critical mission phase, which demands precise navigation and control.

“A successful insertion further involved constant monitoring along with the adjustment of the spacecraft’s speed and position by using onboard thrusters. The success of this insertion not only signifies ISRO’s capabilities in such complex orbital maneuvers, but it gives the confidence to handle future interplanetary missions,” the space agency added.

Aditya-L1, the first Indian space-based observatory to study the sun, was launched on September 2, 2023, from the Satish Dhawan Space Centre in Sriharikota.

Subsequently, ISTRAC carried out four earth-bound maneuvers between September 3 and September 15.

Aditya-L1 on September 19 underwent the Trans-Lagrangian 1 insertion maneuver, marking the beginning of its 110-day trajectory to the destination around the L1 point.

The distance of L1 from the Earth is approximately 1% of the Earth-sun distance.

The Aditya-L1 satellite will be continuously viewing the sun without any occultation or eclipse and provides a greater advantage of observing solar activities without obstruction. Aditya-L1 carries seven payloads to observe the photosphere, chromosphere, and the outermost layer of the sun (corona) using electromagnetic and particle detectors.

Using the special vantage point of L1, four payloads will directly view the sun and the remaining three payloads will carry out in-situ studies of particles and fields at the L1.

According to the ISRO, the satellite will spend 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.

Aditya-L1 has a mission life of five years during which its payloads are expected to provide the most crucial information to understand the problem of coronal heating; coronal mass ejection; pre-flare and flare activities and their characteristics; dynamics of space weather; and propagation of particles and fields.

What are Lagrange points?

According to the ISRO, for a two-body gravitational system, the Lagrange Points are the positions in space where a small object tends to stay if put there.

These points in space for a two-body system such as the sun and earth can be used by the spacecraft to remain at these positions with reduced fuel consumption. For two-body gravitational systems, there are a total of five Lagrange points, denoted as L1, L2, L3, L4, and L5.

What is the L1 point?

The L1 lies between the sun-earth line which is about 1.5 million km from the earth. The distance of L1 from Earth is approximately 1% of the Earth-sun distance. A satellite placed in the halo orbit around the L1 point has the major advantage of continuously viewing the sun without any occultation/eclipse. This will provide a greater advantage of observing solar activities continuously.

There are currently four operational spacecraft at L1 which are WIND, Solar and Heliospheric Observatory (SOHO), Advanced Composition Explorer (ACE), and Deep Space Climate Observatory (DSCOVER).

Time line: Aditya-L1’s journey to Lagrangian point (L1)

SEPTEMBER 2

The Aditya-L1 spacecraft launched by the PSLV from Sriharikota was placed into an elliptical orbit of 235x19500 km around the Earth.

Subsequently, ISTRC in Bengaluru carried out four earth-bound maneuvers between September 3 and September 15.

SEPTEMBER 3

The first maneuver placed the spacecraft in the 245 km x 22459 km orbit.

SEPTEMBER 5

The second manoeuvre placed the spacecraft in the 282 km x 40225 km orbit.

SEPTEMBER 10

The third maneuver placed the spacecraft in the 296 km x 71767 km orbit.

SEPTEMBER 15

The fourth maneuver placed the spacecraft in the 256 km x 121973 km orbit.

SEPTEMBER 19

Aditya-L1 underwent the Trans-Lagrangian1 insertion maneuver, marking the beginning of its 110-day trajectory to the destination around the L1 point.

• The Indian Space Research Organisation (ISRO) has placed the Aditya-L1 spacecraft in a halo orbit around the Lagrangian point (L1).
• The Aditya-L1 satellite will be continuously viewing the sun without any occultation or eclipse and provides a greater advantage of observing the solar activities without obstruction. Aditya-L1 carries seven payloads to observe the photosphere, chromosphere, and the outermost layer of the sun (corona) using electromagnetic and particle detectors.
• Aditya-L1 has a mission life of five years during which its payloads are expected to provide the most crucial information to understand the problem of coronal heating; coronal mass ejection; pre-flare and flare activities and their characteristics; dynamics of space weather; and propagation of particles and fields.