ISRO is India’s premier space agency that undertakes numerous missions aimed to explore the space, different planets and the moon. ISRO’s vision is to “harness space technology for national development while pursuing space science research & planetary exploration.” Recently, a new dedicated mission has been planned by ISRO to study the sun. This mission commonly referred to as Aditya-L1 will be India’s first solar mission and it aims to study sun’s outer most layers i.e the corona (aura of plasma that envelopes the sun), photosphere (the visible surface of the Sun) and the chromosphere (a transparent layer between the corona and the photosphere) besides collecting data about coronal mass ejection and other relevant information related to sun’s effect on space and on the earth. The mission was conceptualised in 2008 and since then it has modified and grown and is expected to be launched in early 2021.
The mission was known as Aditya-1 in 2008 and was supposed to be a 400kg class satellite carrying a single payload i.e the Visible Emission Line Coronagraph (VELC) which was to be launched in an 800km low earth orbit. However, after considering certain additional advantages of placing the satellite in the halo orbit around the Lagrangian point, its launch point was changed to Lagrangian point (L1) at an approximate distance of 1.5 million km from the earth and 6 additional payloads were added apart from the VELC taking the total payload count to 7. Thereafter the project was renamed as Aditya-L1 based on its final orbit around Lagrangian point L1. The project will cost approximately Rs 400 crores and will be carried out as a joint venture lead by ISRO and involving various Indian Research Institutes like the Indian Institute of Astrophysics- Bangalore, Inter-University Centre for Astronomy and Astrophysics- Pune, Indian Institute of Science, Education and Research- Kolkata, Tata Institute of Fundamental Research- Mumbai etc.
Details of The Mission
The mission is concerned with three bodies namely the sun, the earth and a satellite which is almost of negligible mass compared to the other two bodies. In such a scenario, the term Lagrangian point comes to the fore. Lagrangian points are points in space found in the orbits of two large bodies where a third body of very small mass can be placed so that it is able to maintain its position relative to the two larger bodies because of balanced gravitational pull from both the bodies at such points. Such points are important in space exploration and provide advantage to the orbiting satellites due to reduced effect of gravitational forces on the satellites. There are 5 different Lagrangian points in the space that can be found in systems like the earth-moon system, earth-sun system etc. The path around the Lagrangian points that is used by the satellite for orbiting is known as halo orbit. Out of these 5 points, ISRO has planned to launch Aditya-L1 into the Lagrangian point L1 which is at an approximate distance of 1.5 million km from the earth. The point L1 provides the satellite an advantage of viewing the sun continuously without any obstructions from eclipses. Also due to balanced play of gravitational forces of sun and earth as discussed earlier, Aditya-L1 will require little energy to keep itself in place.
Aditya L1 will be launched using the Polar Satellite Launch Vehicle (PSLV)-XL and will be a 1500 kg class satellite. As has been decided by ISRO, the Aditya-L1 will have 7 payloads namely- ‘First, the Visible Emission Line Coronagraph (VELC) for studying the solar corona, its dynamics, origin of Coronal Mass Ejections, magnetic field of solar corona etc and study will be conducted by Indian Institute of Astrophysics. Second, the Solar Ultraviolet Imaging Telescope (SUIT) that will be used to takes images of solar photosphere and chromosphere and study will be conducted by Inter-University Centre for Astronomy and Astrophysics. Third, the Aditya Solar wind Particle Experiment (ASPEX) that will be used to study the variation of solar wind properties and its distribution and study will be conducted by Physics Research Laboratory. Fourth, the Plasma Analyser Package for Aditya (PAPA) which will be used to study the composition of solar wind and its energy distribution and study will be conducted by Space Physics Laboratory. Fifth, Solar Low Energy X-ray Spectrometer (SoLEXS) which will be used to monitor the X-ray flares in order to understand the heating mechanism of solar corona and study will be done by ISRO Satellite Centre. Sixth, High energy L1 Orbiting X-ray Spectrometer (HEL1OS) that will be used for observing the dynamic events in the corona and will subsequently provide an estimate of the energy used to accelerate the particles during eruptive events and study will be done by ISRO Satellite Centre (ISAC) and Udaipur Solar Observatory (USO). Seventh, will be the Magnetometer which will be used to measure the magnitude and nature of interplanetary magnetic field and study will be conducted by Laboratory for Electro-Optic Systems (LEOS) and ISAC.’
The mission is expected to address certain problems in solar physics and will be helpful in completing a comprehensive study of the dynamic processes of the sun. This will help in understanding the crucial role that sun plays on the environment in space (known as space weather) which is affected to a great extent due to the sun, its solar storms or flare and it will also help to understand the effect of dynamics of sun which affect the earth. The solar coronagraph will provide images of corona and chromospheres of the sun which will help in better understanding of the properties of sun’s corona and its role in space weather. The forecast of solar storms originating from the sun and path taken by them through the interplanetary space to reach the earth is currently done using forecast models and calculations made by NASA. However, the successful completion of solar mission will give rise to the possibility of Indians developing their own models for predicting space weather. The space weather has significant effect on functioning of satellites and interferes in electronic circuitry of satellites and also has an effect on lifetime of satellite. Further, the positional accuracy, GPS navigational network, telecommunications and satellite TV broadcast also gets affected by space weather which is affected by the solar storms. Aditya-L1 will provide a deep and clarified insight to these issues affecting the space missions. The mission will also provide information about a long unsolved mystery in solar physics i.e how is the corona at such high temperature of around 1 million degree Kelvin (that is referred to as coronal heating problem) despite a deeper layer of sun i.e the photosphere being at much lower temperature of around 6000 Kelvin.
Accomplishments by Other Countries in This Area
Few other countries have launched their own successful solar missions in the past to study different aspects of sun and space weather. As early as 1960, USA had launched its Pioneer series satellites that studied different aspects like the magnetic field phenomena, solar flare particles, solar wind, cosmic rays, magnetic fields etc. In 1974 and 1976, USA and Germany worked in collaboration and launched Helios-A and B satellites to study cosmic rays and cosmic dust between Earth and Sun, observations of solar wind etc. Later in 1994, NASA launched WIND to study the solar winds and their measurements. In 1995, NASA-ESA (Europe) launched mission SOHO for investigation of sun’s core, corona and solar winds. However, the coronagraph of SOHO broke down shortly after commencement of the mission and therefore at present there are no satellites capturing images of sun from the space.
USA has also launched other solar missions like the Stereo A and B in 2006 that was used for stereoscopic imaging of coronal mass ejections, DSCOVR in 2015 for monitoring solar wind and coronal mass ejection. In 2018, NASA launched its 1.5 billion dollar Parker Solar Probe mission with the aim of conducting close-range solar coronal study. The satellite will reach the closest to the centre of Solar system than any object in the human-history as it will enter right into the atmosphere of the sun. Similarly, in 2020, ESA launched its Solar orbiter satellite to study solar and heliospheric physics.
Challenges to The Mission
The planned solar mission is one of the rare ones and launch to such orbits have not been attempted too often so it leaves ISRO with less information about the challenges the satellite will have to face. Also the satellite has to utilise its own energy to remain in the orbit and the space conditions may affect it adversely thereby hindering its smooth functioning. The mission is planned to be 100% indigenous and all its components along with the entire operation is to be conducted by India independently. This will be a challenging situation to deal with. Another tricky part is the humongous distance between earth and sun which is about 149 million km. Ultra hot radiations, temperatures etc increase exponentially as the satellite closes towards the sun. Even though Aditya-L1 satellite will only explore the L1 region between earth and sun and the ultra hot radiations are not expected to cause much problem but it still will have some effect on the satellite. Besides these challenges, there will be design challenges that have to be overcome by ISRO due to the complexity of the mission. The cost of the mission due to involvement of various complex structures and parts will also be a problem that will need to be addressed. In this matter it can be said that it will not prove to be much of a challenge as ISRO has proved in the past that it is capable of successfully completing complex projects at low costs.
Aditya-L1 is an ambitious project planned by ISRO. It will help to address some of the unanswered questions till now in the field of solar physics like the excessive coronal heating and will also be crucial in decoding the effect of sun on space weather and also on the earth. The effect of sun on satellites will also be deciphered to some extent which will prove to be beneficial for upcoming space missions. Aditya-L1 will be the next complex feat to be achieved by ISRO that will allow UV imaging of the sun for the first time and the halo orbit of L1 will keep it free from the interference of eclipses thereby giving the satellite a continuous view of the sun. The satellite is expected to be in its orbit for a minimum of 5 years and it may extend further for much longer period. Aditya-L1 will enable comprehensive understanding of the dynamical processes of the sun. Further it will help India to develop its own space weather prediction models and hence become independent in the matter of forecasting models. Aditya-L1 will negotiate a challenging orbit and it will prove to be beneficial not only for India but for the entire global scientific community in understanding the complex dynamical processes of the sun.
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