After Beating US, China & Russia To Moon’s South Pole, India Puts Aditya-L1 In Halo Orbit To Study Sun

On January 6, India achieved a significant space exploration milestone when its solar mission vehicle was put in the halo orbit through a critical maneuver to study the Sun. This comes just months after India became the first nation to land a probe mission at the Moon’s South Pole in August.

“Halo-Orbit Insertion (HOI) of its solar observatory spacecraft, Aditya-L1, was accomplished at 16.00 Hrs (approx) on January 6, 2024 (IST). The final phase of the maneuver involved the firing of control engines for a short duration,” the Indian Space Research Organization (ISRO) said in a statement on its website.

The orbit of the Aditya-L1 spacecraft is a periodic Halo orbit located roughly 1.5 million km (932,000 miles or just 1% of the distance between Earth and Sun) on the continuously moving Sun–Earth line with an orbital period of about 177.86 Earth days. The maneuver on January 6 provided the Indian Solar Observatory spacecraft the capability to monitor the Sun without worrying about interruptions.

“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, minimizing station-keeping maneuvers and thus (saving) fuel consumption and providing a continuous, unobstructed view of the Sun,” ISRO said.

The Aditya-L1 mission, named after the Hindu Sun God ‘Surya,’ also known as Aditya, is an Indian solar observatory at Lagrangian point ‘L1’ for “Observing and understanding the chromospheric (outer atmosphere) and coronal dynamics of the Sun” continuously.

Placing the Aditya-L1 in a halo orbit around the L1 point has advantages compared to putting it in a Low Earth Orbit (LEO). According to the European Space Agency, a Lagrange point is a spot where the gravitational forces of two large objects – such as the Sun and the Earth – cancel each other out, allowing a spacecraft to “hover,” the BBC said in a report at the time of Aditya-L1’s launch by India.

This provides a smooth Sun-spacecraft velocity change throughout the orbit, appropriate for helioseismology, which studies the Sun’s structure and dynamics through its oscillations. The L1 is outside Earth’s magnetosphere, thus suitable for the “in situ” solar wind and particle sampling.

It allows unobstructed, continuous observation of the Sun and view of Earth, enabling constant communication to ground stations. The studies will help scientists understand solar activity, such as solar wind and solar flares, and their real-time effect on Earth and near-space weather.

Halo Orbit Insertion

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 constantly monitoring and adjusting the spacecraft’s speed and position using onboard thrusters. The success of this insertion signifies ISRO’s capabilities in such complex orbital maneuvers and gives the confidence to handle future interplanetary missions, ISRO said.

Aditya-L1 was designed and realized at UR Rao Satellite Centre (URSC) with participation from various ISRO centers. The payloads onboard Aditya-L1 were developed by Indian scientific laboratories, IIA, IUCAA, and ISRO.

The Aditya-L1 spacecraft was launched by PLSV-C57 on September 2, 2023, from Satish Dhawan Space Center at Sriharikota into an elliptical parking orbit (EPO). From here, Aditya-L1 embarked on an extraordinary journey towards the Sun-Earth-L1 Lagrange point; with the onboard propulsion system’s help, it progressively increased its orbital size and moved toward the L1 point.

Five liquid engine burns (LEB) were executed during the Earth orbit phase, gradually raising the apogee of the EPO to attain the desired trajectory with the fifth burn, known as the trans-L1 injection (TL1I) maneuver. The maneuver strategy is carefully devised to minimize incremental velocity addition (ΔV) for reaching the target L1 halo orbit while restricting the number of perigee passes to reduce the spacecraft’s exposure to the high Van Allen radiation belts.

To address errors during the TL1I phase, a short burn of the engines, called TCM-1, was conducted on October 5, 2023, and another TCM-2 on December 14, 2023, to ensure compliance with Halo orbit insertion condition parameters. The spacecraft underwent a cruise phase lasting approximately 110 days to achieve the present condition before HOI was carried out on January 6, 2024.

The Aditya-L1 spacecraft moved from Earth towards the L1 point in the direction of the Sun. The TCM 1 & 2 firing oriented the spacecraft toward the Halo Orbit, making it reach the HOI condition (a minimum fuel consumption condition) as of January 6, 2024.

The final firing was done, aligning the spacecraft with the Halo Orbit. If the HOI maneuver had not been conducted, the spaceship would have moved in a different direction and would have been useless for its intended mission.

India Beat US, China, Israel, And Russia To Moon’s South Pole

On August 23, 2023, India won the cosmic competition, setting Chandrayaan-3 down gently in the polar dust on the Moon’s South Pole, becoming the first nation globally to do so. “We have achieved a soft landing on the moon,” ISRO Chairman S. Somanath announced, then to a packed mission control. “India is on the moon!”

On July 14, the Indian spacecraft Chandrayaan-3 blasted off from the Satish Dhawan Space Center in Sriharikota in southern India, carrying the 1,726-kg lander, which contained a little 26-kg rover. Then, on August 9, 2023, Russia followed in hot pursuit, launching its 1,750-kg Luna 25 lander from the newly built Vostochny Cosmodrome in the country’s far eastern Amur Oblast region.

However, to the world’s surprise, India achieved the feat ahead of any other nation, while Russia failed after its Luna 25 lander crashed. This Russian attempt failed after it plunged into the Moon’s surface on August 20, 2023, after an engine firing intended to maneuver its descent went haywire.

Before this race between India and Russia to the Moon’s South Pole, three other nations — the US, China, and the former Soviet Union — had also achieved soft lunar landings. Still, none of them were ever about to reach the south lunar pole. But that’s not due to a lack of attempts.

In 2019, Israel privately built and funded the Beresheet spacecraft to make the Lunar South Pole landing. But it crashed after ground controllers lost touch with it when it was only 149 meters above the polar soil. In late April, a Japanese probe carrying a rover built by the United Arab Emirates failed in the same region when it, too, lost contact with Earth and went into a 4.8 km death plunge before making impact with the surface.

According to a report in Time magazine, the Moon’s South Pole is one of the more challenging places on the lunar surface to land because it is heavily boulder-strewn, without the vast, flat expanses that the Apollo astronauts and early uncrewed landers targeted in the equatorial regions of the Moon’s Earth-facing hemisphere.

“Of the spacecraft that crashed in the South Pole, none got close enough to negotiate the boulder fields. That ISRO was able to do so—briefly placing Chandrayaan-3 in hover mode when it was 850 meters above the surface while it looked for a clear parking spot is a testament to the skill of the ship and the deft touch of the engineers in mission control,” it said.

• NC Bipindra is a 30-year veteran in journalism specializing in strategic affairs, geopolitics, aerospace, defense, and diplomacy. He has written extensively for the Times of India, New Indian Express, Press Trust of India, and Bloomberg News. He can be reached at ncbipindra (at) gmail.com
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