Revision as of 18:49, 10 January 2024

Aditya L-1

As on the eve of its launch/ 2023 Aug

Sep 2, 2023: The Indian Express

The Indian Space Research Organisation (ISRO) launched Aditya L-1, its first space-based mission to study the Sun, from the Satish Dhawan Space Centre in Sriharikota today at 11:50 am. The lift-off took place barely 10 days after ISRO became the first space agency to soft-land a spacecraft near the Moon’s south pole.

How did the Aditya L-1 mission reach space? Where will it be placed in space? What are its objectives? What payloads it is carrying? And, why does ISRO need to examine the Sun anyway? Here is everything you need to know about ISRO’s Aditya-L1 mission.

How did the Aditya L-1 go into space?

The solar probe was carried into space by the Polar Satellite Launch Vehicle (PSLV) in ‘XL’ configuration. PSLV is one of the most reliable and versatile workhorse rockets of ISRO. Previous missions like Chandrayaan-1 in 2008 and Mangalyaan in 2013 were also launched using PSLV. The rocket is most powerful in the ‘XL’ configuration as it is equipped with six extended strap-on boosters — they are larger than the boosters of other configurations and, therefore, can carry heavier payloads.

PSLV-XL can lift 1,750 kg of payloads to the sun-synchronous polar orbit (spacecraft here are synchronised to always be in the same ‘fixed’ position relative to the Sun), and much more — 3,800 kg — to a lower Earth orbit (normally located at an altitude of less than 1,000 km but could be as low as 160 km above the planet). As Aditya L-1 weighs 1,472 kg, it was launched aboard PSLV.

Notably, Chandrayaan-3 took off aboard LVM3, the most powerful rocket of ISRO, because it was more than two times heavier than the solar probe.

What is the Aditya L-1 mission?

The PSLV will initially place the Aditya L-1 in a lower Earth orbit. Subsequently, the spacecraft’s orbit around the Earth will be raised multiple times before it is put on a path to a halo orbit around the L1 Lagrange point.

The spacecraft will finally be stationed in a halo orbit around the Lagrange point 1 (L1) of the Sun-Earth system (more on this later), which is about 1.5 million km from the Earth. Named after the rising Sun, the Aditya L-1 will cover its journey to the L1 point in about four months. The spacecraft will carry seven payloads to observe solar activities for five years.

What are the objectives of the Aditya L-1?

The mission’s main objective is to expand our knowledge of the Sun, and how its radiation, heat, flow of particles, and magnetic fields affect us. Below is the list of other objectives that the mission will embark upon:

To study the upper atmospheric layers of the Sun called chromosphere and corona. While the corona is the outermost layer, the chromosphere is just below it.

To examine coronal mass ejections (CMEs), which are large expulsions of plasma and magnetic fields from the Sun’s corona.

To analyse the corona’s magnetic field and the driver of the space weather.

To understand why the Sun’s not-so-bright corona is a million degree Celsius hot when the temperature on the surface of the Sun is just about 5,500 degree Celsius.

To help scientists know the reasons behind the acceleration of particles on the Sun, which leads to the solar wind — the constant flow of particles from the Sun.

What is space weather?

Space weather refers to changing environmental conditions in space. It is mainly influenced by activity on the Sun’s surface. In other words, the solar wind, magnetic field, as well as solar events like CME affect the nature of space.

“During such events, the nature of the magnetic field and charged particle environment near to the planet change. In the case of the Earth, the interaction of the Earth’s magnetic field with the field carried by CME can trigger a magnetic disturbance near the Earth. Such events can affect the functioning of space assets,” ISRO says.

What are the payloads?

There are essentially seven payloads on the Aditya L-1. The main one is the Visible Emission Line Coronagraph (VLEC) to study the solar corona from the lowermost part upwards. The Solar Ultraviolet Imaging Telescope (SUIT) will capture the UV image of the solar photosphere and chromosphere. It will examine the variation in light energy emitted.

Meanwhile, the Solar Low Energy X-ray Spectrometer (SoLEXS) and High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) will analyse X-ray flares. The Aditya Solar wind Particle Experiment (ASPEX) and Plasma Analyser Package for Aditya (PAPA) have been built to study the solar wind and energetic ions. Read this explainer for more details.

What are the Lagrange points?

There are five Lagrange points, L1 to L5, between any two-celestial body system. At these positions, the gravitational pull of the celestial bodies equals the centripetal force required to keep a smaller third body in orbit. In simpler words, the forces acting on the third body cancel each other out.

The points can be used as ‘parking spots’ for spacecraft in space to remain in a fixed position with minimal fuel consumption, according to NASA. They have been named after Italian-French mathematician Joseph-Louis Lagrange (1736-1813), who was the first one to find the positions.

So, between the Earth and the Sun, a satellite can occupy any of five Lagrangian points. “Of the five Lagrange points, three are unstable and two are stable. The unstable Lagrange points – labelled L1, L2, and L3 – lie along the line connecting the two large masses. The stable Lagrange points – labelled L4 and L5 – form the apex of two equilateral triangles,” NASA explains. The L4 and L5 are also called Trojan points and celestial bodies like asteroids are found here.

What is a halo orbit?

NASA says a spacecraft can “orbit” about an unstable Lagrange point with a minimum use of thrusters for stationkeeping. Such an orbit is known as a halo orbit as “it appears as an ellipse floating over the planet”. A halo orbit, however, isn’t the usual orbit because the unstable Lagrange point doesn’t exert any attractive force on its own.

“In the Sun-Earth case for example, the spacecraft’s true orbit is around the Sun, with a period equal to Earth’s (the year). Picture a halo orbit as a controlled drift back and forth in the vicinity of the L point while orbiting the Sun,” the space agency adds.

Why will the probe go around L1?

It’s because L1 gets a continuous and unhindered view of the Sun. L2 is located behind the Earth, and thus obstructs the view of the Sun, while L3 is behind the Sun which is not a great position to communicate with Earth. L4 and L5 are good and stable locations but are much farther from Earth compared to L1, which is directly between the Sun and the Earth.

The European Space Agency’s (ESA) Solar and Heliospheric Observatory spacecraft (SOHO) is also stationed at a halo orbit around the L1 point of the Earth-Sun system. The spacecraft has been operational since 1996 and has discovered more than 400 comets, studied the outer layers of the Sun and examined solar winds.

Why study the Sun from space?

According to ISRO, the Sun “emits radiation/light in nearly all wavelengths along with various energetic particles and magnetic fields. The atmosphere of the Earth as well as its magnetic field acts as a protective shield and blocks a number of harmful wavelength radiations including particles and fields.”

This means studying the Sun from Earth can’t provide a complete picture and it becomes crucial to observations from outside the planet’s atmosphere i.e., from space.

Scientists shunned perfumes

Vindhya Pabolu, Sep 3, 2023: The Times of India

Bengaluru : Smelling nice is not an option when you are aiming for the Sun. For the scientists and engineers working on the main payload of Aditya L-1, at least, it was a strict no-no. The Indian Institute of Astrophysics (IIA) team that built Aditya’s main payload — Visible Emission Line Coronagraph (VELC) — to understand the efforts that could lead to unravelling the mysteries of the Sun, stayed away from all kinds of perfumes and sprays.


At the heart of VELC operations was the cutting-edge vibration and thermotech facility in Hoskote near Bengaluru, where component-level vibrations — a crucial step in integrating detectors and optical elements — were conducted. After this integration, a delicate calibration dance unfolded in the pristine cleanroom, where the team, in full-suits resembling futuristic explorers, warded off electrostatic discharge and contamination. Perfumes were taboo there and every single screw had to undergo ultrasonic cleaning.


These suits were shields guarding the sensors and optics, while the cleanroom was a “sanctuary”. “It (cleanroom) had to be kept 1-lakh times cleaner than a hospital ICU,” Nagabushana S, VELC tech nical team head, told STOI.


“We used HEPA (high efficiency particulate air) filters, isopropyl alcohol (99% concentrated) and rigorous protocols to ensure no foreign particles caused disruptions. A single particle discharge could have undone days of hard work,” Sanal Krishna from IIA, a member of the VELC technical team, said. Scientists worked six-hour shifts and refrained from using even medicinal sprays.
STOI spoke to at least three Isro scientists who have spent hours in the cleanroom for various satellite projects. While all of them agreed that cleanrooms need to be pristine, none of them had given up on perfumes. “Maybe the IIA scientists were taking extra precaution,” one of them said.

High throughput X- band

Sep 3, 2023: The Times of India

Bengaluru : Isro has achieved a new milestone, graduating from the S-band telemetry and command regime used for communication with its space modules to a high throughput X-band frequency for Aditya-L1, India’s first Sun mission that completed the first of five Earthbound manoeuvres at 11.40am Sunday, reports Chethan Kumar. So far, Isro had used X-band only for payload data downloads. Compared to S-band (2-2.5GHz), X band functions with 8-8.5GHz.

2024 Jan: reaches L1vantage point

Chethan Kumar, January 6, 2024: The Times of India

Solar Mission, Aditya- L1
From: Chethan Kumar, January 6, 2024: The Times of India

BENGALURU: In just a few hours, Isro will perform the final manoeuvre to put India’s Aditya-L1 space probe into a halo orbit, the solar space observatory’s final destination some 1.5 million-km from Earth, from where it will study the Sun for an expected period of five years.

The space agency launched Aditya-L1 on September 2 on its workhorse, the PSLV and the spacecraft commenced its journey to its final destination, the Sun-Earth Lagrange’s Point 1 (L1), on September 19. The L1 is a region of stability between Earth and Sun where the gravity of the two bodies and the centrifugal force balance out. Aditya-L1 carries 7 instruments to study the Sun and solar storms, and L1 offers an unobstructed view of the Sun (read more below).

If reaching L1 is a challenging journey, staying there is also tricky. To ensure it gets to its destination and stays safely in orbit, Isro needs to know exactly where their spacecraft “was, is and will be”. This tracking process, called ‘orbit determination,’ involves using mathematical formulae and specially developed software by Isro’s URSC.

“...Once it reaches there, we will perform periodic manoeuvres to keep the spacecraft in the intended orbit,” Isro chairman S Somanath had told TOI.

The spacecraft will carry seven payloads to observe the photosphere, chromosphere, and the outermost layers of the Sun (the corona) using electromagnetic and particle detectors. Using the special vantage point of L1, four payloads will directly view the Sun and the remaining three payloads will carry out in-situ studies of particles and fields at the Lagrange point L1.

The suit of Aditya L1 payloads are expected to provide most crucial information to understand the problems of coronal heating, Coronal Mass Ejection, pre-flare and flare activities, and their characteristics, dynamics of space weather, study of the propagation of particles, fields in the interplanetary medium, etc. Now, let’s get into different aspects of the mission, beginning with the final destination, its subject of study, the Sun, the instruments that will enable this, and more:

Lagrange Points

For a two-body gravitational system, the Lagrange Points are positions in space where a small object tends to stay, if put there. These points in space for two-body systems such as Sun and Earth can be used by spacecraft to remain at these positions with reduced fuel consumption.

“Technically at Lagrange point, the gravitational pull of the two large bodies equals the necessary centripetal force required for a small object to move with them. For two body gravitational systems, there are a total five Lagrange points denoted as L1, L2, L3, L4 and L5,” Isro said.

The Lagrange point L1 lies between the Sun-Earth line. The distance of L1 from Earth is approximately 1% of the Earth-Sun distance.

The Sun

Sun, a hot glowing ball of hydrogen and helium gases, is the nearest star and the largest object in the solar system, whose estimated age is 4.5 billion years. It is about 150 million-km from Earth, and is the source of energy for the entire solar system. Without solar energy, life on Earth, as we know, can not exist. The gravity of the sun holds all the objects of the solar system together. At the central region of the Sun, known as ‘core’, the temperature can reach as high as 15 million degree Celsius. At this temperature, a process called nuclear fusion takes place in the core which powers the Sun. The visible surface of the sun known as photosphere is relatively cool and has temperature of about 5,500°C.

Given that it is the nearest star and therefore can be studied in much more detail as compared to other stars, studying Sun can teach much more about stars in the Milky Way and those from other galaxies.

Space Weather

The Sun constantly influences the Earth with radiation, heat and constant flow of particles and magnetic fields. The constant flow of particles from the sun is known as solar wind and are mostly composed of high energy protons. The solar wind fills nearly all the space of the known solar system. Along with the solar wind, the solar magnetic field also fills the solar system.

“The solar wind along with other explosive/eruptive solar events like Coronal Mass Ejection (CME) affects the nature of space. During such events, the nature of the magnetic field and charge particle environment near to the planet change. In the case of the Earth, the interaction of Earth's magnetic field with the field carried by CME can trigger a magnetic disturbance near the Earth. Such events can affect the functioning of space assets,” Isro has said. “Space weather refers to changing environmental conditions in space in the vicinity of Earth and other planets. We use more and more technology in space, as understanding space weather is very important. Also, understanding near Earth space weather sheds light on the behaviour of space weather of other planets,” it added.

Protecting Spacecraft & More

“The Sun is a very dynamic star that extends much beyond what we see. It shows several eruptive phenomena and releases immense amounts of energy in the solar system. If such explosive solar phenomena is directed towards the earth, it could cause various types of disturbances in the near earth space environment,” Isro says.

Various spacecraft and communication systems are prone to such disturbances and therefore an early warning of such events is important for taking corrective measures beforehand. India has satellites worth crores of rupees in Space and this can be critical. In addition to these, if an astronaut is directly exposed to such explosive phenomena, he/she would be in danger.

Payloads Aditya-L1 Carries

■ VELC | Visible Emission Line Coronagraph is designed to study solar corona and dynamics of coronal mass ejections. The payload is developed by Indian Institute of Astrophysics, Bengaluru in close collaboration with ISRO.

■ SUIT | Solar Ultra-violet Imaging Telescope to image the Solar Photosphere and Chromosphere in near Ultra-violet (UV) and, to measure the solar irradiance variations in near UV. The payload is developed by Inter University Centre for Astronomy and Astrophysics, Pune in close collaboration with ISRO.

■ SoLEXS & HEL1OS | Solar Low Energy X-ray Spectrometer and High Energy L1 Orbiting X-ray Spectrometer are designed to study the X-ray flares from the Sun over a wide X-ray energy range. Both these payloads are developed at U R Rao Satellite Centre, Bengaluru.

■ ASPEX & PAPA | Aditya Solar wind Particle EXperiment and Plasma Analyser Package for Aditya payloads are designed to study the solar wind and energetic ions, as well as their energy distribution. ASPEX is developed at Physical Research Laboratory, Ahmedabad. PAPA is developed at Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram.

■ MAG | Magnetometer payload is capable of measuring interplanetary magnetic fields at the L1 point. The payload is developed at Laboratory for Electro Optics Systems, Bengaluru.

Major Science Objectives

■ Understanding Coronal Heating and Solar Wind Acceleration.

■ Understanding initiation of Coronal Mass Ejection (CME), flares and near-earth space weather.

■ To understand coupling and dynamics of the solar atmosphere.

■ To understand solar wind distribution and temperature anisotropy

Uniqueness Of Aditya-L1

■ First-time spatially resolved solar disk in the near UV band

■ CME dynamics close to the solar disk (~from1.05 solar radius) thereby providing information in the acceleration regime of CME, which is not observed consistently

■ Onboard intelligence to detect CMEs and solar flares for optimised observations and data volume

■ Directional and energy anisotropy of solar wind using multi-direction observations

See also

Indian Space Research Organisation (ISRO)

The ISRO Spy case: 1994

Moon mission, India/ Chandrayaan

Satellites: India

Space technology: India

Sun mission, India/ Aditya