Isro’s Aditya L1 spacecraftwhich was put into a trajectory to reach the Sun-Earth Lagrangian (L1) point Tuesday, is likely to require a Trajectory Correction Manoeuvre (TCM) in the coming days because of anomalies that may have crept into the early trajectory, scientists have indicated.
Indian Space Research Organisation scientists are waiting for data to arrive at ground stations Thursday morning, 48 hours after the Trans-Lagrangian Point 1 Insertion (TL1I) manoeuvre was carried out at 2.30 am on September 19, to assess the trajectory that has been achieved by Aditya L1 and to determine the timing and amount of trajectory correction that will be required.
“A trajectory correction manoeuvre will be done. We have to decide when it will be done after the assessment of information after 48 hours,” said M Sankaran, Director, U R Rao Satellite Centre..
Trajectory correction manoeuvres or trim manoeuvre is part of the planning of all deep space missions where spacecraft have to travel long distances after insertion into trajectories that carry the spacecraft to a desired orbit around the moon, Mars and the L1 point, which is 1.5 lakh km en route to the sun in the case of the Aditya L1 mission.
Aditya L1 is to be injected into an orbit around L1 after about 110 days. For this to be achieved, the spacecraft has to travel on a planned trajectory.
Isro sources said there were some anomalies in the data for orbit determination and the orienting of antennas at ground stations that have resulted in the need for a trajectory correction manoeuvre in the coming days for the Aditya L1 mission. Scientists in the mission are keeping their fingers crossed on the need for the TCM, the sources added.
On Tuesday, Isro had stated that the Aditya-L1 Mission is “off to Sun-Earth L1 point!”
“The Trans-Lagrangian Point 1 Insertion (TL1I) maneuver was performed successfully. The spacecraft is now on a trajectory that will take it to the Sun-Earth L1 point. It will be injected into an orbit around L1 through a manoeuvre after about 110 days. This is the fifth consecutive time ISRO has successfully transferred an object on a trajectory toward another celestial body or location in space,” the space agency had said.
Isro’s ground stations at Mauritius, Bengaluru, and Port Blair reportedly tracked the satellite during the manoeuvre.
After the Trans Lagrangian Point 1 Insertion manoeuvre, scientists have found there could be trajectory errors which would need correction after the exact determination of the current trajectory and the required trajectory for the injection into an orbit around the L1 point after 110 days of journeying towards the point.
Sources said that anomalies in the orientation of antennas at ground stations in India and the absence of support from ground stations of Nasa’s Jet Propulsion Laboratory (JPL), which provide highly accurate data on spacecraft orientation, could have caused errors in orbit-raising manoeuvres carried out on the Aditya L1 spacecraft.
“This has been part of the mission plans since Chandrayaan 1. For every orbit-raising manoeuvre, we look at what orbit was realised. If there is something to be done then we have to do it at the earliest and we cannot wait for much later,” a former senior Isro scientist said.
“When you are going for a long period of coasting (for the spacecraft) we have to make sure that we are not making any mistakes. After an orbit manoeuvre, we wait for one or two days for the orbit determination. Here it is a long duration coasting and if small deviations are there then over the month or three months there will be implications and so we have to correct it now itself,” the former Isro scientist said.
“We have to assess how much correction is needed. When we do small manoeuvres we know the quantification and as long as we do for that amount then it is okay. Some shortfall would have happened and that will have to be covered so that it will not be a problem. It is usually a very small manoeuvre,” the senior scientist added.
“It is possible that there are issues with the ground antenna. When we talk about an orbit prediction it is the anticipation of the orbit in which the movement is happening and that will be taken by the angles from the antenna as it keeps shifting to follow the satellite. The second is the range which is measured by sending out signals and receiving them back at the ground station – this is the distance,” he said.
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“The distance and the angle will provide you with the data of how the orbit is going – if there is an error in any one of them then that will reflect in the wrong information. For that there is some sort of calibration done for the antenna nominally,” he added.
According to the former scientist, it is important to collect orbit determination point data from more than one ground system for a good outcome in a deep space mission – including foreign ground stations like JPL.
“Trim manoeuvre is usually a small manoeuvre – if you delay it then it will be a big manoeuvre because if you want to do it after a month or more then the penalty is more and that is why we have to be 100 per cent sure that what we are doing is correct. Small manoeuvres can create a problem if we are not 100 per cent sure of what we are doing,” the former scientist said.
First published on: 21-09-2023 at 09:12 IST
