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Aditya-L1, India’s first solar space observatory mission, will be launched in PSLV’s 59th flight, after several years of development. So far, only the US and the European Space Agency (ESA) have independently (also jointly) launched solar missions while Germany has sent probes with US’s Nasa.
Aditya-L1 mission launch: Live updates
The PSLV, in its XL configuration, will place the spacecraft in a highly eccentric Earth-bound orbit, an elliptical orbit whose Perigee (closest point to Earth) is expected to be around 235km while the Apogee (farthest point from Earth) would be more than 19,000km.
From there, the spacecraft will perform multiple orbital manoeuvres by using its liquid apogee motors (LAM) — powerful engines that will play a critical role in taking it to its destination — to reach the Lagrange Point-1 (L1) about 1.5-million-km away. That is 1/100th of the distance between Earth and Sun.
Why 63-mins for separation
Unlike a regular PSLV launch profile, which places the spacecraft into an orbit roughly under 25 minutes from lift-off, Aditya’s separation is projected to happen 63 minutes after the rocket blasts off from the second launch pad in Sriharikota.
This will be one of the longest PSLV missions ever undertaken. The February 2021 mission that put Brazil’s Amazonia satellite and 18 others into orbits took more than 1-hour-55-minutes, while the February 2016 mission that put eight satellites into orbits took 2-hours-and-15 minutes. Both involved multiple satellites and orbits, unlike Aditya-L1.
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ISRO: India’s first solar mission Aditya-L1, all set to launch
On why such a long time for separation, VSSC director S Unnikrishnan Nair told TOI: “Spacecraft demands a specific AOP (argument of Perigee). To meet the AOP, we’re not firing PSLV’s final stage (PS4) in a single go. PS4 is fired for 30 seconds when we reach a normal orbit and stay there until we get the required AOP naturally. Then, PS4 is fired again before separation. The separation occurs at 63 minutes because PS4 only separates after the AOP is achieved.”
AOP & path to reach L1
Stating that an AOP defines the path of the spacecraft to the final destination, Nair said in Aditya’s case, AOP is “when the ascending trajectory of the spacecraft cuts the (Earth’s) equator”. This angle has been defined and needs to be achieved to make it to L1 as desired.
“If we wanted a launch profile without this specific AOP, we needed to use the window available next January. To launch now, we need to ensure this AOP to account for the celestial movements,” Nair explained.
Lagrange Point-1 or L1 is a vantage point. Any satellite placed in the halo orbit around L1 has the major advantage of continuously viewing the Sun without any occultation/eclipses. This will provide a greater advantage of observing the solar activities and its effect on space weather in real-time.
“Post launch, Aditya-L1 stays in Earth-bound orbits for 16 days, during which it undergoes 5 manoeuvres to gain the necessary velocity for its journey. Subsequently, it undergoes a Trans-Lagrangian1 Insertion (TLI) manoeuvre, marking the beginning of its 110-day trajectory to the destination around the L1 Lagrange point. Upon arrival at L1, another manoeuvre binds Aditya-L1 to an orbit around L1,” Isro said.
Space weather & more
Close on the heels of its successful lunar endeavour, Isro, with Aditya-L1, will venture into the study of solar activities and its effect on space weather. The scientific objectives of Aditya-L1 include the study of coronal heating, solar wind acceleration, coronal mass ejections (CMEs), dynamics of solar atmosphere and temperature anisotropy. To achieve this, the spacecraft is packed with seven scientific instruments, which TOI has reported in detail earlier.
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