Aditya-L1 Spacecraft’s Separation Time: ISRO’s First Solar Satellite to Revolutionize Solar Science
India’s space agency, ISRO (Indian Space Research Organisation), is gearing up for the launch of Aditya-L1, its first solar space observatory mission. This landmark mission will kick off at 11:50 AM on a Saturday, following years of development. It’s worth noting that until now, only the United States and the European Space Agency (ESA) have independently or jointly launched solar missions, while Germany has collaborated with NASA on solar probes.
The launch vehicle for Aditya-L1 is the PSLV (Polar Satellite Launch Vehicle) in its XL configuration. The spacecraft will be placed in a highly eccentric Earth-bound orbit, with a Perigee (closest point to Earth) of approximately 235 kilometers and an Apogee (farthest point from Earth) exceeding 19,000 kilometers.
Afterward, the spacecraft will perform multiple orbital maneuvers using its powerful Liquid Apogee Motors (LAM) to reach its destination: Lagrange Point-1 (L1), which is about 1.5 million kilometers away, representing just 1/100th of the distance between Earth and the Sun.
Unlike a typical PSLV launch, where the spacecraft is placed in orbit in under 25 minutes, Aditya-L1’s separation is expected to occur 63 minutes after liftoff. This makes it one of the longest PSLV missions ever undertaken. The extended separation time is due to the spacecraft’s specific orbital requirements. According to S Unnikrishnan Nair, Director of VSSC (Vikram Sarabhai Space Centre), the spacecraft demands a specific Argument of Perigee (AOP) for its trajectory. To achieve this AOP, the final stage of the PSLV (PS4) is not fired in a single go. Instead, it is fired for 30 seconds initially to reach a normal orbit and remains in that orbit until the required AOP is naturally achieved. PS4 is then fired again before separation occurs, which happens after 63 minutes.
The AOP essentially defines the spacecraft’s path to its final destination. In the case of Aditya, it’s the point where the spacecraft’s ascending trajectory intersects the Earth’s equator. This precise angle must be achieved to reach Lagrange Point-1 as planned. Nair explained that without this specific AOP, the mission would have had to wait until the next available launch window in January. The current launch timing is dictated by the need to account for celestial movements.
Lagrange Point-1 (L1) is a strategically important vantage point. Satellites positioned in a halo orbit around L1 enjoy uninterrupted views of the Sun without eclipses or occultations. This unique perspective allows for continuous observation of solar activities and their impact on space weather in real-time.
Following the launch, Aditya-L1 will spend 16 days in Earth-bound orbits, during which it will execute five maneuvers to gain the necessary velocity for its journey. Subsequently, it will perform a Trans-Lagrangian1 Insertion (TLI) maneuver, marking the start of its 110-day trajectory toward its destination around L1. Upon arrival at L1, another maneuver will bind Aditya-L1 to an orbit around the Lagrange point.
With Aditya-L1, ISRO aims to study solar activities and their effects on space weather. The scientific objectives of the mission include investigating coronal heating, solar wind acceleration, coronal mass ejections (CMEs), dynamics of the solar atmosphere, and temperature anisotropy. To achieve these goals, the spacecraft is equipped with seven scientific instruments.
In conclusion, Aditya-L1 represents a significant milestone for ISRO as it expands its scientific exploration beyond the Moon and into the realm of solar studies and space weather analysis.