ISRO to work with NASA and manage traffic around Aditya-L1's destination 

Chennai, India

Before heading on out a long drive, don't we assess the traffic situation and look at the possible bottlenecks on an app? Likewise, space agencies constantly monitor what is known as 'Space Situational Awareness' (SSA). Simply put, SSA is like the traffic data for a particular region in space - it mentions the number of spacecraft or crewed crafts operating in orbit and also helps predict the risk of them coming within the vicinity of each other and even colliding.

Based on such data and resultant calculations, each space agency draws its own conclusion and decides to manoeuvre its spacecraft and prevent danger, while also sharing information with the other concerned parties (nations or private firms) who operate spacecraft in the region. 

Launched into Earth's orbit on Sep 2, India's Aditya-L1 craft had been circling the Earth and gradually pushing itself further away from Earth for a little more than two weeks. On Sep 18, the craft slingshot itself totally out of Earth's orbit and commenced a journey that would take it to its destination- the Earth-Sun Lagrangian Point 1, which is 1.5 million kilometres away from Earth. 

Also read: Aditya-L1: What You Should Know about India's Sun Mission

L1 is a significant vantage point because it is situated between the Sun and Earth, making it an ideal location for spacecraft, as this spot allows continuous observation of the Sun. From the L1 point, spacecraft can continuously communicate with the ground stations on Earth and have an unobstructed view of celestial bodies. These orbits are well-suited for scientific missions like Aditya which will act like a solar observatory around L1. 

In the past, various missions have stayed put at the Sun-Earth L1 point, including the International Sun-Earth Explorer (ISEE-3), the Genesis mission, ESA's LISA Pathfinder, China's Chang'e 5 lunar orbiter, and NASA's Gravity Recovery and Interior Recovery (GRAIL) mission. These missions have contributed to mankind's understanding of space and the ability to monitor space weather events.

Watch: India sun mission Aditya-L1 begins collecting data from distance of 50,000 km 

At present, four operational spacecraft are stationed at the Sun-Earth L1 point. They provide vital early warnings on adverse space weather events that help protect orbiting space assets and ground-based infrastructure. The four crafts are- NASA WIND(to observe the unperturbed solar wind before reaching the magnetosphere of Earth), NASA-ESA SOHO(Solar and Heliospheric Observatory- to study the sun and Heliosphere) NASA ACE(Advanced Composition Explorer - observe particles of the solar wind, and of galactic origins) and NASA DSCOVER (Deep Space Climate Observatory to Monitor space weather and climate, deep space Earth observation). 

While there are only four crafts that are far apart circling the L1 point, and India's Aditya expected to join them as the fifth in January 2024, it is still necessary to assess the traffic and possible collision risk. "Despite the extremely sparse population in L1 point and the vast separation between them, close approach assessment for an operational spacecraft at Lagrange Point Orbit (LPO) is desirable because of the large positional uncertainty and sensitivity to other perturbative forces," ISRO said. 

Generally, to determine the orbit of crafts circling Lagrangian Point 1, tracking data collected over a few days is required. The accuracy of the orbit so calculated might not be very accurate. Therefore, ISRO said that they plan to carry out such analysis periodically to ensure safety and avoid any possibility of close approaches with other neighbouring spacecraft, with the support from NASA-JPL. 

It is common for space agencies to predict the path and orbit of their satellites. In case a close approach or risk of collision with another nation's satellite is predicted, then both involved parties take a decision to manoeuvre one or both of their crafts. For example, India's Chandrayaan 2 orbiter which circles the moon, had to avoid collision with foreign satellites on many instances, over the last four years.