India’s first space-based observatory to study the Sun, Aditya-L1, is headed to the Lagrangian 1 (L1) point as ISRO carried out the Trans-Lagrangian 1 Insertion (TL1I) manoeuvre in the early hours of September 19.

The TL1I manoeuvre marks the beginning of Aditya-L1’s 110-day journey towards the L1 point which lies between the Sun-Earth line. L1 is about 1.5 million km from the Earth and the distance of L1 from Earth is approximately 1% of the Earth-Sun distance.

“Off to Sun-Earth L1 point! The Trans-Lagrangean Point 1 Insertion (TL1I) maneuvre is performed successfully. The spacecraft is now on a trajectory that will take it to the Sun-Earth L1 point. It will be injected into an orbit around L1 through a maneuver after about 110 days. This is the fifth consecutive time ISRO has successfully transferred an object on a trajectory toward another celestial body or location in space,” ISRO posted on X.

Aditya-L1 was launched on September 2 by the Polar Satellite Launch Vehicle (PSLV) from the Satish Dhawan Space Centre in Sriharikota.

Following the launch, Aditya-L1 carried out four earth-bound manoeuvres between September 3 and September 15.

Aditya-L1, which is dedicated to the comprehensive study of the Sun, has seven payloads. Five payloads were developed by ISRO and two by Indian academic institutes in collaboration with the space agency.

Upon arrival at the L1 point in January 2024, another manoeuvre will be performed which will bind Aditya-L1 to an orbit around L1. The satellite will spend its mission life orbiting around L1 in an irregularly shaped orbit in a plane roughly perpendicular to the line joining the Earth and the Sun.

Aditya-L1 has a mission life of five years during which its payloads are expected to provide the most crucial information to understand the problem of coronal heating; coronal mass ejection; pre-flare and flare activities and their characteristics; dynamics of space weather; and propagation of particles and fields.

Scientific data collection has started: ISRO

ISRO on September 18 announced that the Supra Thermal and Energetic Particle Spectrometer (STEPS) instrument, a part of the Aditya Solar Wind Particle EXperiment (ASPEX) payload, has begun the collection of scientific data.

STEPS comprises six sensors, each observing in different directions and measuring supra-thermal and energetic ions ranging from 20 keV/nucleon to 5 MeV/nucleon, in addition to electrons exceeding 1 MeV. These measurements are conducted using low and high-energy particle spectrometers. The data collected during Earth’s orbits helps scientists to analyse the behaviour of particles surrounding the Earth, especially in the presence of the magnetic field of Earth.

“STEPS was activated on September 10, 2023, at a distance greater than 50,000 km from Earth. This distance is equivalent to more than 8 times the Earth’s radius, placing it well beyond Earth’s radiation belt region. After completing the necessary instrument health checks, data collection continued until the spacecraft had moved farther than 50,000 km from Earth,” the space agency said.

It added that each unit of STEPS is operating within normal parameters.

“A figure displays measurements depicting variations in the energetic particle environment within Earth’s magnetosphere, collected by one of the units. These STEPS measurements will persist during the cruise phase of the Aditya-L1 mission as it progresses toward the Sun-Earth L1 point. They will continue once the spacecraft is positioned in its intended orbit. Data collected around L1 would provide insights into the origin, acceleration, and anisotropy of solar wind and space weather phenomena,” ISRO said.

STEPS was developed by the Physical Research Laboratory (PRL) with support from the Space Application Centre (SAC) in Ahmedabad.

Aditya-L1, the first space-based Indian mission to study the Sun underwent the second earth-bound manoeuvre successfully, during the early hours on Tuesday, ISRO said.

ISRO’s Telemetry, Tracking and Command Network (ISTRAC) carried out the operation.

“The second Earth-bound manoeuvre (EBN#2) is performed successfully from ISTRAC, Bengaluru. ISTRAC/ISRO’s ground stations at Mauritius, Bengaluru and Port Blair tracked the satellite during this operation. The new orbit attained is 282 km x 40225 km,” ISRO said in a post on X (formerly Twitter).

The next manoeuvre (EBN#3) is scheduled for September 10, 2023, around 02:30 Hrs. IST, it said.

Aditya-L1 is the first Indian space based observatory to study the Sun from a halo orbit around first sun-earth Lagrangian point (L1), which is located roughly 1.5 million km from earth.

The first earth-bound manoeuvre was successfully performed on September 3.

The spacecraft will undergo two more earth-bound orbital manoeuvres before placing in the transfer orbit towards the Lagrange point L1. Aditya-L1 is expected to arrive at the intended orbit at the L1 point after about 127 days.

ISRO’s Polar Satellite Launch Vehicle (PSLV-C57) on September 2 had successfully launched the Aditya-L1 spacecraft, from the Second Launch Pad of Satish Dhawan Space Centre (SDSC), Sriharikota.

After a flight duration of 63 minutes and 20 seconds, Aditya-L1 spacecraft was successfully injected into an elliptical orbit of 235×19500 km around the earth.

According to ISRO, a satellite placed in the halo orbit around the L1 point has the major advantage of continuously viewing the Sun without any occultation /eclipses. This will provide a greater advantage of observing the solar activities and its effect on space weather in real time.

Aditya-L1 carries seven scientific payloads indigenously developed by ISRO and national research laboratories including Indian Institute of Astrophysics (IIA), Bengaluru, and Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune.

The payloads are to observe the photosphere, chromosphere and the outermost layers of the Sun (the corona) using electromagnetic and particle and magnetic field detectors.

Using the special vantage point L1, four payloads directly view the Sun and the remaining three payloads carry out in-situ studies of particles and fields at the Lagrange point L1, thus providing important scientific studies of the propagatory effect of solar dynamics in the interplanetary medium.

The suits of Aditya L1 payloads are expected to provide the most crucial information to understand the problem of coronal heating, coronal mass ejection, pre-flare and flare activities and their characteristics, dynamics of space weather, propagation of particles and fields.

According to scientists, there are five Lagrangian points (or parking areas) between the Earth and the Sun where a small object tends to stay if put there. The Lagrange Points are named after Italian-French mathematician Joseph-Louis Lagrange for his prize-winning paper — “Essai sur le Problème des Trois Corps, 1772.”

These points in space can be used by spacecraft to remain there with reduced fuel consumption.

At a Lagrange point, the gravitational pull of the two large bodies (the Sun and the Earth) equals the necessary centripetal force required for a small object to move with them.

For launching its Aditya-L1 mission on September 2, the Indian Space Research Organisation (ISRO) will be using a variant of the Polar Satellite Launch Vehicle (PSLV) which also launched India’s first missions to the moon and Mars.

With the PSLV-C57/Aditya-L1 mission, India’s first solar mission, the PSLV-XL variant will mark its 25th flight.

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