The successful accomplishment of the Halo-Orbit Insertion (HOI) for the Aditya-L1 solar observatory spacecraft marks a significant milestone in India’s space exploration endeavors. Executed at approximately 16:00 Hrs on January 6, 2024 (IST), the final phase of this complex maneuver involved a brief firing of control engines.
Aditya-L1’s Unique Halo Orbit:
The Aditya-L1 spacecraft is now positioned in a periodic Halo orbit, situated approximately 1.5 million km from Earth along the continuously moving Sun–Earth line. This three-dimensional orbit involves the Sun, Earth, and the spacecraft, with an orbital period of approximately 177.86 Earth days.
The selection of this specific Halo orbit is strategic, aiming for a mission lifetime of 5 years while minimizing fuel consumption and ensuring an uninterrupted view of the Sun.
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Advantages of the Halo Orbit:
Placing Aditya-L1 in a Halo orbit around Lagrangian point L1 offers several advantages over a Low Earth Orbit (LEO):
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- Smooth Sun-Spacecraft Velocity Change: The orbit provides a smooth change in Sun-Spacecraft velocity throughout the orbit, ideal for helioseismology.
- Outside Earth’s Magnetosphere: Being outside the Earth’s magnetosphere allows for “in situ” sampling of the solar wind and particles.
- Unobstructed Continuous Observation: The orbit enables continuous, clear observation of the Sun and provides a constant view of Earth for seamless communication with ground stations.
Halo Orbit Insertion Process:
The insertion process was initiated as the spacecraft crossed the XZ plane in the Sun-Earth-L1 rotating system, necessitating precise orbital state conditions. The maneuver aimed to nullify X and Z velocity components and achieve the required Y-velocity in the L1 rotating frame for the Halo orbit. The targeted Halo orbit for Aditya-L1 had specific dimensions (Ax: 209200 km, Ay: 663200 km, Az: 120000 km).
The insertion phase demanded meticulous navigation and control, involving constant monitoring and adjustment of the spacecraft’s speed and position using onboard thrusters. The success of this insertion not only showcases ISRO’s prowess in complex orbital maneuvers but also instills confidence in handling future interplanetary missions.
Journey to the Halo Orbit:
Aditya-L1, designed and realized at UR Rao Satellite Centre (URSC), commenced its journey on September 2, 2023, when PSLV-C57 launched it into an elliptical parking orbit (EPO). The spacecraft gradually increased its orbital size through five liquid engine burns during the Earth orbit phase, culminating in the trans-L1 injection (TL1I) maneuver.
To minimize incremental velocity addition (ΔV) and reduce exposure to high radiation Van Allen belts, two trajectory correction maneuvers (TCM-1 and TCM-2) were conducted. A cruise phase of approximately 110 days preceded the Halo-Orbit Insertion targeted for January 6, 2024.
Payload Testing and Confirmation:
All payloads onboard Aditya-L1, developed by Indian scientific laboratories (IIA, IUCAA, and ISRO), underwent rigorous testing during the pre-commissioning phase. The performance of these payloads has been confirmed as satisfactory, ensuring the spacecraft’s capability to fulfill its mission objectives.
The graphical representation of the Halo orbit insertion process vividly depicts the spacecraft’s trajectory from Earth towards the L1 point in the direction of the Sun. The strategic firings, particularly TCM1 and TCM2, oriented the spacecraft towards the Halo Orbit, culminating in the minimum fuel consumption condition achieved during the HOI on January 6, 2024 (indicated by the red dot).
The final firing at this point aligned the spacecraft precisely with the Halo Orbit, highlighting the criticality of the HOI maneuver for mission success. If not executed as planned, the spacecraft would have followed an alternate trajectory, as depicted in the illustration.
Source: ISRO
