Aditya-L1, first Indian space mission to study the Sun spacecraft, made its fourth maneuver towards Earth on Friday. The next maneuver for sending from Earth is scheduled for September 19 around 02:00 IST, ISRO said in its latest update. The third maneuver was completed on September 10.
India successfully launched its first space satellite observatory to study the Sun from space Satish Dhawan Sriharikota center on September 2. Aditya-L1 on its 1.5 million kilometer journey will be placed in a halo orbits around the Lagrange point (L1) of the Sun-Earth system, which has the advantage of seeing the Sun without any eclipses. This will provide greater benefit to observation solar activities permanently.
In total, five maneuvers will be carried out throughout the 16-day journey around the Earth of the spacecraft, during which it will build up the speed required for its onward journey to L1.
These maneuvers are crucial during the 16-day trajectory around the Earth, facilitating the spacecraft to gain the speed necessary for its movement towards the Lagrange point L1.
What is an orbital maneuver
In spaceflight, an orbital maneuver (otherwise known like a burn) is the use of propulsion systems to change the orbit of a spacecraft. For spaceships far from Earth (those orbiting the Sun), an orbital maneuver is called deep space maneuver.
A maneuver is required to raise the orbit and increase the speed of the spacecraft so that it can move towards its destination. Interplanetary missions like Chandrayaan, Mangalyaan or Aditya L1 require taking the spacecraft outside Earth’s sphere of influence.
This requires the spacecraft to have extra speed which can be provided directly by the launcher or can be obtained by successive shots from the spaceship Propulsion system. Direct insertion by launching the vehicle can result in much faster transfer trajectories, but requires powerful rockets.
Raise the orbit
The maneuvers are mainly done to optimize the mission achieve its goals. These are planned well in advance as part of of the mission,” says Anil Bhardwaj, Director Physics Research Laboratory (PRL), which developed and designed one of the most important instruments – ASPEX on board.
Bhardwaj said that if the speed increases when the the spacecraft gets closer to Earth, the orbit becomes more elliptical. “The Earth Burn or the maneuvers as we know them better are made to put the spacecraft into the correct orbit and win speed. This is a new method that saves a lot of propellant.
Santosh Vadawale, astrophysicist at PRL involved in the ASPEX payload stated that the multiple Earth-bound orbits also offer the possibility of making possible corrections necessary, which allows better control of the final trajectory.
The final orbital maneuvers came after calculations and simulations to optimize the final mass and the duration.
Mylswamy Annadurai, director of India’s First Moon mission, said PSLV is a cost-effective and proven way launcher but it is not possible to place Aditya L1 spacecraft of mass 1475 kg by PSLV-C beyond 235×19500 km around the Earth.
“From this orbit to go to the Sun-Earth-L1 point of 1.5 millions of kilometers from Earth the optimal fuel mission plan requires little earthbound maneuvering by the spacecraft propulsion system as was done in Chandrayaan 1, Chandrayaan 2, Chandrayaan 3 and Mangalyaan.
Ditto Ajay Lele, space expert and consultant, Manohar Parrikar Institute for Defense Studies and Analysis. “To reach its destination point L1, it must travel a distance of 15 lakh km. To reach such a long distance, the first step consists of reaching an orbit from which the craft would be shifted to transfer the orbit to L1 and to objective, four orbital maneuvers towards Earth are necessary to gradually raise the orbit of the spaceship,” he said.
increase the speed
On the surface of the Earth, if you throw something else greater than 11.2 km/sec, it will escape Earth’s gravity and will not come back. At an altitude of 235 km, where the PSLV Aditya-L1 injected, it is around 10.8 km/s., says an ISRO scientist.
“Some space centers have powerful rockets that can push directly with this speed. But in our case, the the spacecraft was injected at 9.4 km/sec. In order to win speed, we have to perform maneuvers, which means burn the propellants using the propulsion systems inside the satellite,” he said.
Each time the maneuver occurs, there is a gain in the speed and increase in the height of the apogee (point farthest from Earth) When the speed reaches 10.8 km/sec, it is injected into the orbit linked to the Sun. Generally, the number maneuvers depend on the weight of the spacecraft and a balance between a speed deficit and the quantity of propellant transported. There are also other reasons for making these ‘burns’
MS Pannirselvam, former director of shooting range operations Mas Mission and former general director of the Satish Dhawan Space Center, Sriharikota says that Aditya L1 while traveling to point L1 must exceed the orbit of the Moon around the Earth.
“If the Moon is anywhere nearby it will affect Aditya’s path. We we must make sure that the Moon is far away. Like the new the moon occurred on September 14 (the day the The Moon is located between the Earth and the Sun), the maneuver was necessary to ensure that when Aditya crosses the orbit of the Moon, the Moon will be behind the Earth,” he explained.
The spacecraft was initially kept in Earth’s orbit and the orbit was raised step by step to the designated place time for L1 insertion.
Pannirselvam maintains that when Aditya L1 leaves Ethe sphere of influence of Art and enters the sphere of influence of the Sun. influence, the plane of the earth’s equator and its orbital plane around the Sun must be aligned.
“This happens twice a year, on March 21 and September 21. Therefore, the Lagrangian insertion date and time are corrected on this basis. Otherwise, it will take a lot of fuel to take it towards point L1,” he adds.
Former ISRO scientist TN Suresh Kumar argues that when the spacecraft is lifted off the rocket, it is launched in an elliptical orbit. The closest point to Earth is called perigee and the farthest point is called apogee.
“We need to fire up the spaceship’s engines so that the orbit gradually rises. The initial climax is 19,500 km and we have to increase it gradually in four steps through these shots and maneuvers. The last maneuver that occurred on September 15 at 2:15 a.m. hours brought the peak to 1.21 lakh km. There will be a final maneuver on September 19, after which Aditya will come out of the influence of earth’s gravitation, he said.
Essentially, Earthbound maneuvers are necessary to increase the height of the orbit so that it does not return to Earth PJ Bhat, former deputy satellite director UR Rao Center, ISRO claims that the PSLV launcher put the spacecraft in an elliptical orbit around the earth with perigee 235 km and Apogee 19500 Km.
“But the ultimate goal is to put the spacecraft in a halo orbit around the Earth-Sun Lagrange point L1 which is about 1.5 million kilometers from Earth. The maneuvers are necessary to change the orbit in several stages in such way the apogee reaches near L1, so that a a maneuver can be carried out to establish it in the halo orbits around L1,” he says.
In L1, the spacecraft would remain fairly stable with a minimum propulsion energy requirements for sound corrections orbit, such that one side of Aditya always faces the Sun and the collected data can be transmitted to Earth from Earth-opposite side.
(Edited by : CH Unnikrishnan)
First publication: September 17, 2023 6:08 p.m. STI