New Delhi: Just a week after Indian Space Research Organisation (ISRO) successfully landed its Chandrayaan-3 on the Moon’s south pole, it is all set to begin its tryst with the Sun.
On 2 September, ISRO will launch Aditya-L1, the first space-based Indian observatory to study the Sun.
Placed at about 1.5 million km from the Earth, the satellite will be in a position to continuously view the Sun without any obstructions or eclipses.
The main science objective of Aditya-L1 mission is to observe the solar atmosphere, mainly the corona and chromosphere, the first and second layer making up the Sun’s outer layer. It has a third layer called the photosphere.
The spacecraft’s payloads will study the solar upper atmospheric dynamics, chromospheric and coronal heating, physics of the partially ionised plasma, initiation of the coronal mass ejections, and flares. It will also observe the in-situ particle and plasma environment, providing data for the study of particle dynamics from the Sun, physics of solar corona and its heating mechanism, as well as drivers for space weather, among other things.
The spacecraft will be launched aboard ISRO’s PSLV XL — a 44.4-metre-tall satellite capable of launching multiple satellites and in multiple orbits. With a lift off mass of 320 tonnes, the rocket made its first successful launch in 1993.
The Aditya-L1 will carry seven payloads to observe the photosphere, chromosphere and the outermost layers of the Sun using electromagnetic and particle and magnetic field detectors.
Of these, four — namely, Visible Emission Line Coronagraph (VELC), Solar Ultraviolet Imaging Telescope (SUIT), Solar Low Energy X-ray Spectrometer (SoLEXS) and High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) — are the remote sensing payloads that will be directly looking at the Sun.
The remaining three — the Aditya Solar wind Particle Experiment (ASPEX), Plasma Analyser Package for Aditya (PAPA) and Advanced Tri-axial High Resolution Digital Magnetometers — will carry out studies of the effect of changes in the solar atmosphere on the interplanetary medium.
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Where Aditya-L1 will be placed
The satellite will be placed in an orbit around what is known as the Lagrange Point 1 (L1) of the Sun-Earth system.
Named in honour of Italian-French mathematician Joseph-Louis Lagrange, Lagrange points are positions in space where objects sent there tend to stay put. At Lagrange points, the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them. These points in space can be used by spacecraft to reduce fuel consumption needed to remain in position.
An analogy for this would be holding a thread with a bead at the centre with two hands and spinning it. At some point, the bead, moving in a two-dimensional orbit around an invisible point, will be exerting a centripetal force that equals the force holding the thread in place.
That invisible point, would be a Lagrange point. The position of the two hands would be the sun and the Earth, the thread would be the gravitational pull of the two bodies, and the bead is where Aditya L1 will be.
There are five special points where a small mass can orbit in a constant pattern with two larger masses.
Lagrange points — labeled L1, L2 and L3 — lie along the line connecting the two large masses, while L4 and L5 form the apex of two equilateral triangles that have the large masses at their vertices.
Being at L1 would give the spacecraft an uninterrupted view of the Sun.
Remote sensing payloads
The Visible Emission Line Coronagraph (VELC) — one of its payloads — will take images of the Sun’s corona, capturing images of the solar corona. This instrument is designed to capture sudden solar flares, as well as piece together an overall image of the Sun’s corona by taking a few pictures at a time.
The Solar Ultraviolet Imaging Telescope (SUIT) onboard Aditya-L1 will measure and monitor the solar radiation emitted in the near-ultraviolet wavelength range (200-400 nanometres). It will simultaneously map the photosphere and the chromosphere of the Sun using 11 filters sensitive to different wavelengths, and covering different heights in the solar atmosphere to help us understand the processes involved in the transfer of mass and energy from one layer to the other.
SUIT will also allow us to measure and monitor spatially resolved solar spectral irradiance that governs the chemistry of oxygen and ozone in the stratosphere of Earth’s atmosphere. This is central to our understanding of the relationship between the Sun and the Earth’s climate.
The Solar Low Energy X-ray Spectrometer (SoLEXS) instrument will detect soft X-ray energy. The instrument is meant to complement VELC by making independent and accurate estimates of temperature and emission measure at flaring sites.
This instrument also provides an alert of sorts that can detect an oncoming flare for the main payload — which would help optimise the on-board memory storage.
The High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) will observe the hard X-ray (HXR) emission from the Sun in the energy range of 10-150 kilo-electron-volt (keV). This will provide direct information of electrons accelerated in flares.
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In-situ payloads
To study the solar winds, the Aditya-L1 will make use of its two payloads—the Aditya Solar wind Particle Experiment (ASPEX) and Plasma Analyser Package for Aditya (PAPA).
ASPEX’s primary objective is to understand the solar and interplanetary processes (like shock effects, wave-particle interactions etc.) in the acceleration and energisation of the solar wind particles from L1 point. To achieve these objectives, ASPEX measures low as well as high energy particles associated with slow and fast components of solar wind.
The PAPA, on the other hand, aims to study the composition of solar winds and its energy distributions.
Solar wind is a magnetised plasma consisting of charged particles — protons, alpha particles, electrons, and heavier ionised atoms with a magnetic field embedded in it — flowing out of the Sun in all directions at very high speeds. On average, its speed is about 400 km/second. It is responsible for the anti-sunward tails of comets and the shape of the magnetic fields around the planets. The exact mechanism of solar wind formation is not known.
PAPA will contain two sensors — Solar Wind Electron Energy Probe (SWEEP) and Solar Wind Ion Composition Analyser (SWICAR) — to measure, respectively, the solar wind electron and ion fluxes and composition as a function of direction and energy.
Advanced Tri-axial High Resolution Digital Magnetometers will also be used for sensing the magnetic field at the L1 point to help ISRO keep track of the orientation of the Aditya L1 spacecraft.
(Edited by Zinnia Ray Chaudhuri)
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