Challenges at L1 Point
AdityaL1 has travelled beyond 9.2 lakh-km, escaping Earth's influence & is heading towards L1. But reaching L1 isn’t its only challenge. Staying there’s tricky too. To ensure it's safe, Isro needs to know where it “was, is and will be”.
This tracking process, called ‘orbit determination,’ involves using mathematical formulas and specially developed software by Isro’s UR Rao Satellite Centre (URSC).
Where Aditya’s Going: When one large mass orbits another, their gravitational forces and orbital motion interact to create five equilibrium points where a spacecraft can operate for a prolonged period without having to use a lot of fuel…
These locations are known as Lagrange points. Aditya-L1’s final destination will be one of the five Lagrange points in the Sun-Earth system.
Also known as libration points, Lagrange points are unique locations in space where the gravitational force of two massive bodies (like the Sun and Earth) precisely equals the centripetal force required for a small object (like spacecraft) to move with them…
L1 is particularly significant because it's between the two primaries (Sun & Earth), making it an ideal location for spacecraft because it allows continuous observation of primary bodies, continuous communication with earth, unobstructed view of celestial bodies
These orbits are well-suited for scientific missions like Aditya which will act like a solar observatory around L1 and communicate to Earth
The Challenge: According to the European Space Agency (ESA), L1 is one of the ‘unstable’ Lagrange points, and keeping a spacecraft exactly at the L1 point is practically impossible. “Instead, spacecraft enter orbit around L1 as if Lagrange point were an ‘invisible planet
Even so, due to the instability of this orbit, small trajectory errors will grow quickly. As a result, spacecraft must perform ‘station keeping’ maneuvers roughly once a month to keep them in the correct orbit
Somanath said while L1 is an unstable point, the instability is very mild and spread over a long period making it still the best place to be for a spacecraft. “L3 and L4 are much more difficult, for instance.
That said, if we aren’t careful about orbit determination then the spacecraft can diverge. While it can be brought back, the fuel penalty will be higher,” he said
L1 & Software: Theoretically, L1 is a constant point. It is a geometrical point that one gets when one connects the Moon, Sun, and Earth
Although L1 is theoretically between two objects, when it gets influenced by other bodies, the Moon, for instance, becomes a multi-body sphere. Depending on the movement of these bodies, there are changes Isro will need to account for with time
The halo orbit Aditya-L1 will be in is a vague orbit. It’s not like rotating around a single point. It is rotating around a vast area that is a three-dimensional orbit
Therefore, the need was for a multi-body computational program to find out the trajectory of these bodies and the spacecraft. For this, Isro has designed and developed new orbit determination software for Aditya-L1.
