India's first solar observation mission
Aditya-L1 (Sanskrit: 'Sun', L1 'Lagrange Point 1') is a coronagraphy spacecraft for studying the solar atmosphere, designed and developed by the Indian Space Research Organisation (ISRO) and various other Indian Space Research Institutes. It is orbiting at about 1.5 million km from Earth in a halo orbit around the Lagrange point 1 (L1) between the Earth and the Sun, where it will study the solar atmosphere, solar magnetic storms, and their impact on the environment around the Earth.
It is the first Indian mission dedicated to observe the Sun. Nigar Shaji is the project's director. Aditya-L1 was launched aboard the PSLV C57 at 11:50 IST on 2 September 2023. It successfully achieved its intended orbit nearly an hour later, and separated from its fourth stage at 12:57 IST. It was inserted at the L1 point on 6 January 2024, at 4:17 pm IST.
Mission objectives.
The main objectives of Aditya-L1 are:
History.
The mission was conceptualised in January 2008 by the Advisory Committee for Space Sciences (ADCOS). It was initially envisaged as a small, satellite in a Low Earth Orbit (800 km) with a coronagraph to study the solar corona. An experimental budget of ₹ was allocated for the financial year 2016–2017. The scope of the mission has since been expanded and it became a comprehensive solar and space environment observatory to be placed at Lagrange point 1 (L1), hence the mission was renamed as "Aditya-L1." As of  2019[ [update]], the mission has an allocated cost of ₹, excluding launch costs.
The European Space Operations Centre (ESOC), operated by the European Space Agency (ESA) is supporting the mission.
On 11 January 2024, ISRO successfully deployed a 6-meter magnetometer boom aboard the Aditya-L1 in the Halo orbit at the Lagrange Point L1. After the liftoff, the boom had been stowed for 132 days. The in-orbit deployment period that was measured was roughly 9 seconds, which is well within the 8–12 second prediction range. The magnetometer boom will measure the low-intensity interplanetary magnetic field in space using two high-accuracy fluxgate magnetometer sensors that are carried aboard. In order to reduce the impact of the spacecraft's magnetic field on measurements, the sensors are placed 3 and 6 meters away from the craft. Using a dual sensor system also helps to cancel out the spacecraft's magnetic influence and facilitates accurate estimation. The carbon-fiber-reinforced polymers (CFRP) was used in the construction of the boom segments. Through the use of spring-driven hinge mechanisms, the five pieces are joined to enable folding in close proximity to the craft throughout the journey and opening up upon reaching the desired orbit. The hinges lock into place as the mechanism fans out. In the stowed position, two hold-downs firmly secure the boom in place. Information obtained via the telemetry switches validates the release of the hold-down, the initial motion, and the locking of every hinge.
Overview.
The mission took 126 Earth days after launch to reach the halo orbit around the L1 point, which is about from Earth. The spacecraft is planned to remain in the halo orbit for its mission duration while being maintained at a stationkeeping Δv of 0.2–4 m/s per year. The satellite carries seven science payloads with various objectives, including instruments to measure coronal heating, solar wind acceleration, coronal magnetometry, origin and monitoring of near-UV solar radiation (which drives Earth's upper atmospheric dynamics and global climate), coupling of the solar photosphere to the chromosphere and corona, and in-situ characterisations of the space environment around Earth by measuring energetic particle fluxes and magnetic fields of the solar wind, and solar magnetic storms.
Aditya-L1 will provide observations of the Sun's photosphere, chromosphere and corona. Its scientific payloads must be placed outside the interference from the Earth's magnetic field, and hence, could not have been useful in the low Earth orbit, as proposed in the original mission concept back in 2008.
One of the major unsolved problems in the field of solar physics is coronal heating. The upper atmosphere of the Sun has a temperature of , whereas the lower atmosphere is just . In addition, it is not understood exactly how the Sun's radiation affects the dynamics of the Earth's atmosphere on a shorter as well as a longer time scale. The mission will obtain near-simultaneous images of the different layers of the Sun's atmosphere, which will reveal the ways in which energy is channeled and transferred from one layer to another. Thus, the mission will enable a comprehensive understanding of the dynamical processes of the Sun and address some of the outstanding problems in solar physics and heliophysics.
Payloads.
The instruments of Aditya-L1 are tuned to observe the solar atmosphere, mainly the chromosphere and corona. In-situ instruments will observe the local environment at the L1 point. There are seven payloads on board, with four for remote sensing of the Sun and three for in-situ observation. The payloads have been developed by different laboratories in the country with close collaborations of various ISRO centres.
Visible Emission Line Coronagraph (VELC).
The Visible Emission Line Coronagraph (VELC) is a key instrument on the Aditya spacecraft. The VELC is an internally occulted reflective coronagraph designed to fulfil specific observation needs. The instrument allows for high spatial resolution imaging 1.25-2.5 arcseconds of the Sun's corona, simultaneous observations in three modes (Imaging, Spectroscopy and Spectro-polarimetry), and even utilizes artificial intelligence to aid in the detection of coronal mass ejections (CMEs). The instrument was developed by Indian Institute of Astrophysics, Bangalore.
Solar Ultraviolet Imaging Telescope (SUIT).
The SUIT is an ultraviolet imaging telescope designed to study the solar spectral radiation in the ultraviolet range, using narrowband and broadband spectral filters in the range of 200-400 nm with the hope of developing a better understanding between solar activity and the atmospheric dynamics of Earth. The SUIT provides near-simultaneous coverage of the solar atmosphere, from lower photosphere to the upper chromosphere. The instrument was developed by Inter University Centre for Astronomy &amp; Astrophysics, Pune, in collaboration with ISRO.
Solar Low Energy X-ray Spectrometer (SoLEXS).
The SoLEXS is an X-ray spectrometer designed to continuously measure the solar soft X-ray flux (1 keV-22 keV) from the Sun-Earth Lagrangian point L1. These measurements can be used to better understand the properties of the Sun's corona, in particular, why the temperature of the corona is so high. The SoLEXS will observe solar flares, and in conjunction with data provided by the VELC, will help study the complex thermal properties of the Sun's outer layers. The instrument was developed by U R Rao Satellite Centre, Bangalore.
High Energy L-1 Orbiting X-ray Spectrometer (HEL1OS).
Developed by the Space Astronomy Group, URSC, the HEL1OS (pronounced "helios)" is an x-ray spectrometer designed to study solar flares in the x-ray spectrum, in particular, energy bands of 10-150 Kev (kilo-electron volts). Using a twin-pair of Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CZT) detectors, the instrument aims to study the acceleration and movement of electrons in the Sun's corona, as well as to study the cut-off energy between thermal and non-thermal solar emissions.
Aditya Solar Wind Particle Experiment (ASPEX).
The ASPEX is an instrument composed of low and high energy particle spectrometers, designed to conduct measurements of the Sun's solar wind particles. Solar Wind Ion Spectrometer (SWIS), the low energy spectrometer, contains two analysers, each designed to study particles entering the device in different planes. Supra Thermal Energetic Particle Spectrometer (STEPS), the high energy spectrometer, also consists of two parts, STEPS 1 and STEPS 2, both designed to separate protons and alpha particles and measure the integrated flux. The instrument was developed by the Physical Research Laboratory, Ahmedabad.
Plasma Analyser Package for Aditya (PAPA).
The PAPA is an instrument on board the Aditya-L1 designed to study the temperature, distribution and velocity of the solar winds. The instrument contains two sensors; the Solar Wind Electron Energy Probe (SWEEP) and the Solar Wind lon Composition Analyser (SWICAR). The detectors are used in conjunction to analyse the energy levels of electrons and ions within the solar wind. The instrument was developed by the Space Physics Laboratory of the Vikram Sarabhai Space Centre, Thiruvananthapuram.
Digital Magnetometers.
On board the Aditya-L1 spacecraft are a pair of magnetic sensors on a deployable boom, one positioned in the middle and the other at the tip. The purpose of these sensors is to gather information about the magnitude and direction of the Interplanetary Magnetic Fields (IMF), as well as to study other events such as Coronal Mass Ejections (CME). Data from the magnetic sensors will be used to supplement that of the PAPA and ASPEX sensors.
Mission profile.
Launch.
On 2 September 2023, at 11:50 IST, the Polar Satellite Launch Vehicle (PSLV-C57) accomplished a successful launch of the "Aditya-L1" from the Second Launch Pad of the Satish Dhawan Space Centre (SDSC) located in Sriharikota.
"Aditya-L1", following a flight duration of 63 minutes and 20 seconds, achieved a successful injection into an elliptical orbit around the Earth at 12:54 IST.
"Aditya-L1" underwent a series of four Earth-bound orbital maneuvres prior to its injection to a transfer orbit towards the Lagrange point (L1). It reached its designated orbit at the L1 point 126 days after its launch on 6 January 2024 at 4:17 IST.
Orbit raising burns.
On 3 September 2023, the "Aditya-L1" performed its first Earth-bound maneuvre, raising its orbit to a into orbit.
On 5 September 2023, "Aditya-L1" performed its second Earth-bound maneuvre, raising its orbit to a into orbit.
On 10 September 2023, "Aditya-L1" performed its third Earth-bound maneuvre, raising its orbit to a into orbit.
On 15 September 2023, "Aditya-L1" performed its fourth Earth-bound maneuvre, raising its original orbit to a into orbit. This was the last of such maneuvers, being directly followed by the Trans-Lagrangian 1 Injection, which took place on 19 September.
On 19 September 2023, "Aditya-L1" performed its last maneuvre around Earth to escape its orbit and headed towards the Lagrange 1 point, taking at least four months to further reach its destination, 1.5 million kilometers away.
On 30 September 2023, "Aditya-L1" had escaped the Earth's sphere of influence and was on the way to the Lagrange point 1.
On 6 October 2023, "Aditya-L1" performed a Trajectory Correction maneuvre (TCM1). It was needed to correct the trajectory evaluated after tracking the Trans-Lagrangian Point 1 Insertion (TL1I) maneuvre performed on 19 September 2023.
On 6 January 2024, "Aditya-L1" was successfully injected on the Halo orbit of Lagrange point 1 (HOI), at 4:17 pm IST.
Orbit.
Aditya-L1 completed its first halo orbit around L1 point on July 2, 2024. It takes it approximately 178 days to complete each orbit. It underwent two station-keeping maneuvers on February 22 and June 7, and later one on July 2.
Science Phase.
Following commissioning and checkout, Adiya L1 began Science observations about three months into the mission. The PAPA instrument on the spacecraft was operationalised on December 12, 2023 and made its first observation on February 10 and 11, 2024.
In conjunction with the Udaipur Solar Observatory and research stations at Thumba, ISRO mobilised all its observation platforms and systems to record the signatures of a Massive Solar Flare in May 2024. Aditya-L1, Chandrayaan-2's orbiter and XPoSat have made observations and observed signatures have been analysed. Aditya-L1 used ASPEX, SOLEX, HEL1OS an its magnetometer instruments to record data. On July 16, 2024, the VELC instrument was used to measure a large Coronal Mass ejection from the Sun. It also studied an accompanying solar flare and the motion of solar particles within the Sun.
Marking its first year of science observation, ISRO released the maiden set of the scientific data from the Aditya L1 to the global scientific community on January 6, 2025 at the ISRO Headquarters in Bengaluru.
Gallery.
Images of the sun taken from SUIT( Solar Ultraviolet Imaging Telescope) instrument of Aditya-L1 in different wavelengths.
References.
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