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Aditya L1, India’s first mission to study the Sun, is inching closer to its destination, and would be injected into its final orbit on January 6 evening.
The spacecraft, launched on September 2, would get into what is known as a ‘halo orbit’ around the Lagrange Point 1 (L1), one of the five spots in the moving Sun-Earth system, where the gravitational effects of the two bodies roughly balance each other.
These five spots are relatively stationary to the Earth and Sun, and offer a somewhat stable location for a spacecraft to view the Sun. The L1 point is about 1.5 million kilometres from the Earth. This is just 1 per cent of the total distance between the Earth and Sun.
“Aditya L1 has already reached the L1 point and the manoeuvre (on January 6) will put it in the desired orbit. Without getting into the orbit, the spacecraft will continue to travel towards the Sun,” an ISRO official said.
Though the L1, like the other Lagrange points, is a relatively stable position, it is difficult to keep the spacecraft firmly fixed at that location. It is much better to get into an orbit around this point, called ‘halo orbit’. Moving into this three-dimensional orbit also offers the spacecraft an opportunity to view the Sun from different angles.
“Aditya L1 will make it to a halo orbit around the L1 point. As the Earth moves around the Sun, the L1 point will also move. So does the halo orbit,” Annapurni Subramaniam, director, Indian Institute of Astrophysics, Bengaluru, told The Indian Express.
Getting into this orbit is quite challenging, and it is the first time that ISRO is attempting such a manoeuvre.
“This manoeuvre is critical. It involves the firing of thrusters in order to change the speed and trajectory of the spacecraft. If the intended orbit is missed in the first attempt, there would be multiple subsequent corrections and thruster firings required,” said Dibyendu Nandi, solar physicist and Chair, Space Weather and Monitoring Committee, Aditya L1 mission.
As on Wednesday, Aditya had successfully completed 124 days in space. Since September 18, just 16 days into its journey, Aditya had started collecting scientific data and imaging the Sun. The scientists have, so far, obtained the first sneak peek into high-energy X-ray of solar flares, full solar disc images and others.
Aditya has seven scientific payloads of which the Visible Emission Line Coronograph (VELC), Solar Ultraviolet Imaging Telescope (SUIT), Solar Low Energy X-ray Spectrometer (SoLEXS), High-Energy L1 Orbiting X-ray Spectrometer (HEL1OS) are designed to directly track the Sun. There are other in-situ (on site) measuring instruments like the Aditya Solar Wind Particle Experiment (ASPEX), Plasma Analyser Package for Aditya (PAPA), and Advanced Tri-axial High Resolution Digital Magnetometers.
Four instruments, including PAPA and one component, the Solar Wind Ion Spectrometer, of ASPEX, were switched on during the spacecraft’s cruising phase and are reportedly functioning well. Aditya will be inserted into a halo orbit around L1, from where the satellite will have full access to solar storms, radiations and other emissions emerging from the Sun even before they are directed towards Earth or come under the influence of the Earth’s magnetic field. SUIT, seated on the top deck of the Aditya-L1, will be among the first to get operational once the spacecraft reaches L1.
The mission is being keenly watched across the world as its seven payloads offer a comprehensive study of the solar phenomena. The instruments can study the sun at multiple wavelengths, they can study the radiation, particles, and magnetic fields released by the Sun, and see these phenomena in different directions.
The spacecraft also has a coronagraph that will allow scientists to look much closer to the surface of the Sun and complement the data from NASA and European Space Agency’s Solar and Heliospheric Observatory (SOHO) mission — the only other satellite currently located in L1 position.
“To study the faint light coming from the corona, we need to artificially block the bright light from the photosphere or the surface of the Sun. The catch in doing that is we may not be able to block only the photosphere — the size of the occulting disk is usually bigger than the photosphere. If we assume the size of the photosphere to be 1 unit, the occulting disk has been of 2 units for previous missions. For the first time, with the Aditya L1 mission, we are trying to see as close as possible to the beginning of the corona with a smaller occulting disk that is just 1.05 times the photosphere,” Prof R Ramesh from the Indian Institute of Astrophysics had told The Indian Express recently. The coronagraph on SOHO that was lost had an occulting disc that was 1.1 times the radius of the Sun surface.
Anjali Marar works with the Raman Research Institute, Bengaluru.
