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15th December 2023
Greetings astrophiles!
In today’s instalment, we will learn about the different payloads on Aditya-L1 and try to understand how they will make observations.
An overview:
Aditya L1 is India's first space-based mission to study the sun. L1 here stands for ‘Lagrange point 1’. A Lagrange point is where a small object would remain stable because the centrifugal force due to its motion is balanced out by the gravitational force due to 2 large bodies. In this case, the small object is Aditya L1 and the two large bodies are the Sun and Earth. There are five Lagrange points as shown in the figure below.
An interesting point to note is that the L1 point is 1% closer to the sun compared to Earth (about 1.5 million km) but is farther away than the moon!
Aditya L1 It will be launched by a PSLV XL (Polar Satellite Launch Vehicle, XL denotes that it is a version of PSLV) rocket from SDSC-SHAR, Sriharikota (if you remember, this is the same place Chandrayaan-3 was launched from!). The total time for it to reach L1 would be about 4 months from launch (September 2, 2023). It stayed Earth-bound for 16 days, during which it underwent 5 manoeuvres to gain the necessary velocity to complete its journey.
Why is it important to be in the L1 position?
Well, the main reason is to observe solar radiation and magnetic storms without Earth’s magnetic field and atmosphere interrupting them. Another reason is that the L1 position is a stable point therefore constant manoeuvring to maintain its orbit won’t be necessary.
Objectives:
To study the solar upper atmospheric dynamics, chromosphere, and corona
To analyse the chromospheric and coronal heating, physics of the partially ionised plasma, initiation of the coronal mass ejections, and solar flares (an intense burst of radiation coming from the release of magnetic energy associated with sunspots, for more information visit https://www.nasa.gov/image-article/what-solar-flare/#:~:text=A%20solar%20flare%20is%20an,last%20from%20minutes%20to%20hours )
To observe the in-situ particle and plasma environment providing data for studying particle dynamics from the sun.
To study the physics of solar corona and its heating mechanism.
To diagnose the coronal and coronal loops plasma – temperature, velocity, and density.
To study the development, dynamics, and origin of Coronal Mass Ejections (CMEs)
To identify the sequence of processes that occur at multiple layers – chromosphere, base, and extended corona– which eventually lead to solar eruptive events.
To observe the magnetic field topology and magnetic field measurements in the solar corona.
To determine the drivers for space weather– origin, composition, and solar wind dynamics.
Scientific Payloads:
Aditya L1 had a total of seven scientific payloads on board. Four will carry out remote sensing of the sun while the other 3 will carry out in-situ observations.
Remote sensing payloads include
Visible Emission Line Coronagraph (VELC):
It's designed as an internally occulted reflective coronagraph. It will conduct simultaneous observations of the solar corona by imaging, spectroscopy, and spectro-polarimetry. It will take measurements of the coronal magnetic field. It also has AI on board for detecting Coronal Mass Ejections (CMEs). This payload will help us diagnose the temperature, velocity and density of the coronal and coronal loops plasma. It will also help us understand the process that heats the solar corona and the origin of CMEs along with how they develop and their dynamics. It will also help us gain insights into what drives the space weather.
Extra Facts: it has a multi-split spectrograph that works in Littrow configuration. It will enable us to collect many spectroscopic observations simultaneously. For more information on Littrow configuration, visit https://en.wikipedia.org/wiki/Blazed_grating
VELC was developed by Indian Institute of Astrophysics (IIA), Bangalore
Solar Ultraviolet Imaging Telescope (SUIT):
It is a UV telescope to image the solar disk. It uses Narrow-Band (NB) and Broad-Band (BB) spectral filters in the range of 200-400nm, with low stray light and high contrast. The observations made by SUIT will help us to determine how energy is channelised and transferred from the photosphere (the visible surface of the sun) to the chromosphere (an irregular layer just above the photosphere and below the corona where the temperature rises from 6000°C to 20,000°C). It will also help us determine how the sun’s activity affects the Earth’s atmosphere. Additionally, we will also be able to collect data about how the different phases of a solar flare look in the lower solar atmosphere and at what wavelength flares radiate most of their energy. We will also be able to try to understand the mechanisms responsible for the stability, dynamics, and eruption of solar prominences (When viewed against the solar disc, a filament is a large, bright feature extending outward from the sun’s surface. They are anchored to the sun’s surface in the photosphere and extend outwards into the sun’s corona. For more information visit https://www.nasa.gov/image-article/what-solar-prominence/#:~:text=A%20solar%20prominence%20 )
SUIT was developed by Inter University for Astronomy and Astrophysics (IUCAA), Pune.
Solar Low Energy X-ray Spectrometer (SoLEXS):
It’s a soft X-ray spectrometer which will continuously measure the solar soft energy flux. Soft X-rays are of the magnitude of 1 to 22 keV. The data collected by this payload will allow us to understand the source of the corona’s high temperatures by observing the solar flares and with data collected by VELC. it will also help us observe the change in abundance of low first-ionization potential (FIP) elements (elements such as Silicon, Calcium, and Iron with FIP less than 10eV). It also independently measures the coronal temperature and Differential Emission Measure (DEM, the amount of emission from plasma at a specific temperature) along with the abundance of coronal plasma.
It also deduces the physical characteristics of solar flares ranging from the X-class to sub-A-class and its association with CMEs observed with the coronograph VELC.
A Small Detour: Classes of Solar Flares
Solar flares are classified according to the peak flux in watts per square meter of soft X-rays, in the wavelength range of 1 to 8 Angstroms. There are 5 classes — A, B, C, M, and X — where A has the smallest peak flux and X has the highest. Each of these classes can be divided into 9 subclasses, starting from 1 to 9 (e.g. A1-A9, B1-B9, C1-C9 and so on).
SoLEXS was developed by the Space Astronomy Group, U R Rao Satellite Centre (URSC), Bangalore.
High Energy L1 Orbiting X-ray Spectrometer (HEL1OS):
HEL1OS is a hard X-ray spectrometer which can observe solar flares in the X-ray energy range of 10-150 keV with a field of View (FoV) of 6°✕6°. It has 2 different types of detectors— Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CZT). To capture the targeted spectral sensitivity, two CdTe detectors are operated to capture the 10-40 keV band and two CZT detectors to capture the 20-150 keV band. The major scientific aims include studying the explosive energy release, acceleration, and transport of electrons using fast-timing measurements and high-resolution spectra. It will also allow us to study the evolution of the cut-off energy between thermal and non-thermal emission (here, non-thermal radiation means electromagnetic radiation released by the de-excitation of electrons from a higher energy state to a lower one in an atom.) as a function of flare evolution and its relation with the spectral parameters of the accelerated electron distribution. Additionally, we will be able to observe Quasi-Periodic Pulsations (QPPs of the electromagnetic radiation emitted in solar flares are detected in all bands of radiation, from microwaves to gamma rays).
HEL1OS was developed by the Space Astronomy Group, U R Rao Satellite Centre (URSC), Bangalore.
In-situ Payloads include
Aditya Solar wind Particle Experiment (ASPEX):
It comprises low and high-energy particle spectrometers to carry out in-situ measurements of solar wind particles. It has two sub-systems— SWIS (Solar Wind Ion Spectrometer) and STEPS (Suprathermal and Energetic Particle Spectrometer). Both SWIS and STEPS consist of two parts, THA1 & THA2 and STEPS1 & STEPS2 respectively. SWIS is a low-energy ion spectrometer that measures ion flux in the energy range of 100eV to 20keV—primarily protons and alpha particles. STEP is a high-energy ion spectrometer that measures ion flux in the energy range of 20 keV to 5 MeV, primarily protons and alpha particles. The various units of these spectrometers are arranged in such a way that they can simultaneously conduct measurements in multiple directions.
ASPEX was developed by Physical Research Laboratory (PRL), Ahmedabad.
Plasma Analyser Package For Aditya (PAPA):
It aims to study the composition of solar wind and its energy distributions. It is made up of two sensors, SWEEP (Solar Wind Electron Energy Probe) and SWICAR (Solar Wind Ion Composition Analyser). They are mounted perpendicular to each other with a common PAPA Processing Unit (PPU). SWEEP consists of two guiding plates, for direction sweep, and an electrostatic analyser section that contains the deflection plates, for energy analysis. The electrons after energy analysis are detected using a Channel Electron Multiplier detector (CEM, for more information visit https://www.sjuts.com/Introduction_Principles.html#:~:text=Channel%20electron%20multipliers%20(CEMs)%20are,has%20a%20high%20surface%20resistance) and the signal is smoothed and conditioned by a Front-end Electronics card (FEE) and then fed into the PPU for further processing. SWICAR can be used for energy analysis of electrons and ions and is equipped with a linear Time of Flight (ToF) section with CEM detectors to facilitate mass analysis of ions in SWICAR ion mode operation.
PAPA was developed by the Space Physics Laboratory, Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram.
Fluxgate Magnetometer (MAG):
It is a dual triaxial magnetic sensor which is installed on a 6m, 5-segment deployable boom, mounted on the sun-facing deck of the Aditya-L1 spacecraft. It is constructed by initially winding an excitation coil on a Supermalloy ring core in a toroidal fashion and placing it in a MACOR bobbin (in human terms, the excitation coil along with the sense coil— mentioned later— will essentially detect a magnetic field, supermalloy is an alloy of nickel, iron and molybdenum, Macor is a thermal insulator and a bobbin is a permanent container for a wire to retain shape and rigidity, and to ease assembly of the windings into or onto a magnetic core.). Subsequently, a sense coil is wound on top of the bobbin, completely enclosing the excitation winding (winding and coil both mean the same thing here). Both triaxial fluxgate sensors have three orthogonally mounted fluxgate sensors. A common electronics package processes output signals from the two sensors.
(for more information about fluxgate sensors visit https://www.imperial.ac.uk/space-and-atmospheric-physics/research/areas/space-magnetometer-laboratory/space-instrumentation-research/magnetometers/fluxgate-magnetometers/how-a-fluxgate-works/ )
MAG was developed by the Laboratory for Electro Optics Systems (LEOS), Bangalore.
Picture Credits: ISRO
Picture Credits: ISRO
Picture Credits: ISRO
Written by Charvi Joshi
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