Aditya-L1 Flew 1.5 Million Kilometres to Watch the Sun, Then Logged the Eruptions Behind the Strongest Geomagnetic Storm Since 2003

A PSLV rocket left the Second Launch Pad at Sriharikota at 11.50 on the morning of 2 September 2023. ISRO’s launch release says that after a flight of 63 minutes and 20 seconds the spacecraft was in an elliptical orbit of 235 by 19,500 kilometres around the Earth, and that it would take about 127 days to reach its destination.

The spacecraft was Aditya-L1, India’s first space observatory built to study the Sun. In the mission control room, Jitendra Singh, the Union minister who holds the space portfolio, called the launch “a sunshine moment for India.” He added that 2 September 2023 was “a day of reckoning.”

A parking place 1.5 million kilometres out

Aditya-L1 circles an empty point in space called L1, the first Lagrange point of the Sun-Earth system. NASA describes Lagrange points as positions where objects sent there tend to stay put, because the gravitational pull of two large masses equals the force needed for a small object to move with them. NASA’s page adds that L1 gives an uninterrupted view of the Sun and that it is home to the Solar and Heliospheric Observatory, SOHO. It also says L1 is unstable on a timescale of roughly 23 days, so satellites there need regular course corrections.

L1 is about 1.5 million kilometres from Earth, which the Tribune puts at about 1 per cent of the distance between the Earth and the Sun. ISRO did not park Aditya-L1 exactly on the point. It put the spacecraft into a halo orbit, a large looping path around it. That orbit gives a mission life of five years while keeping station-keeping manoeuvres, and so fuel use, to a minimum, ISRO says. One loop takes about 177.86 Earth days. Targeted halo amplitudes, in ISRO’s figures, are 209,200 km, 663,200 km and 120,000 km along three axes.

A satellite in a halo orbit around L1 sees the Sun without eclipses or occultations, PIB’s launch-day release says, so solar activity can be watched, and its effect on space weather followed, in real time.

One hundred and twenty-six days to get there

Aditya-L1 climbed away from Earth in steps. According to the timeline the Tribune published, burns on 3, 5, 10 and 15 September lifted its Earth orbit to 245 by 22,459 km, then 282 by 40,225 km, then 296 by 71,767 km, then 256 by 121,973 km. On 30 September it left the Earth’s sphere of influence, the region where Earth’s gravity dominates, and headed for L1. By ISRO’s account the cruise lasted approximately 110 days and included two trajectory correction manoeuvres, on 5 October and 14 December 2023.

On 6 January 2024, at about 4 pm Indian time, Aditya-L1 fired its control engines for a short burst and entered its halo orbit. ISRO had said before launch that the trip would take about 127 days. Insertion came 126 days after lift-off. PIB’s release that evening said the insertion “demanded precise navigation and control.” ISRO’s Bengaluru-based tracking network, ISTRAC, handled the final approach by monitoring the spacecraft and adjusting its speed and position with on-board thrusters, according to the Tribune.

ISRO chairman S. Somanath told reporters: “It was a complex mission, I won’t say challenging mission. Challenges are something which we love, complexities are something which we have to overcome. Today, we have overcome the complexity, and we were able to achieve that precisely.” Prime Minister Narendra Modi wrote on X that he joined the nation “in applauding this extraordinary feat.” President Droupadi Murmu noted the large number of women engineers and scientists in the team, and the Tribune reported that the project director, Nigar Shaji, is a woman.

Four instruments that look at the Sun

Aditya-L1 carries seven payloads. Four are remote sensing instruments pointed at the Sun, and three measure what reaches the spacecraft. The most complete description from before launch is a paper by the instrument teams, led by Durgesh Tripathi of the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune. Most figures in this section and the next come from it.

VELC, the Visible Emission Line Coronagraph, blocks the Sun’s bright disc inside the telescope so that the corona, the Sun’s thin outer atmosphere, becomes visible. Its entrance aperture is 148 millimetres. It images the corona in white light from 1.05 to 3.0 solar radii and runs a spectrograph on three emission lines. Its authors say the line at 1074.7 nanometres is meant to give the topology of the coronal magnetic field “for the first time from space.” They also explain why the inner corona matters. Earlier coronagraphs on SOHO could only follow a coronal mass ejection, a cloud of solar plasma thrown into space, beyond 2.5 solar radii. It cites a study finding that 90 per cent of a CME’s acceleration happens below 2 solar radii.

SUIT, the Solar Ultraviolet Imaging Telescope, is a Ritchey-Chretien reflector with a 140 millimetre primary mirror and 11 science filters between 200 and 400 nanometres. Its pixels are 0.7 arcseconds wide, and it can take an image every 4 to 40 seconds depending on its mode. It tracks regions of interest by itself and adjusts exposure automatically for flare observations. This band is absorbed by Earth’s atmosphere, so only a telescope in space can see it. IUCAA says the payload was conceived in 2013 and delivered to ISRO on 6 June 2023.

Two X-ray instruments watch the Sun as a single point of light. SoLEXS, the Solar Low Energy X-ray Spectrometer, covers 1 to 30 keV, the soft X-rays that carry the heat of a flare. It has two identical detectors with different aperture sizes, one sensitive to small flares and one to large ones, and it can produce a spectrum every second during a flare. It also detects the start of a flare on board and passes that signal to SUIT. HEL1OS, the High Energy L1 Orbiting X-ray Spectrometer, covers 10 to 150 keV with cadmium zinc telluride and cadmium telluride detectors, aimed at the impulsive phase of a flare, when most of the emission is non-thermal, meaning it comes from accelerated particles rather than heated gas. Together the pair covers 1 to 150 keV.

Three that sample what arrives

Three instruments do not look at the Sun at all. They sit in the stream of particles and magnetic field that reaches L1.

ASPEX, the Aditya Solar Wind Particle Experiment, has two ion spectrometers. One, SWIS, covers 0.1 to 20 keV. The other, STEPS, covers 20 keV per nucleon to 5 MeV per nucleon and looks in six directions, including straight at the Sun and along the Parker spiral, the curved path of the solar wind. PAPA, the Plasma Analyser Package for Aditya, measures solar wind electrons between 0.01 and 3 keV and ions between 0.01 and 25 keV, and its ion sensor identifies elements with masses from 1 to 60 atomic mass units.

MAG, the magnetometer, uses two fluxgate sensors on a boom, because the spacecraft itself is not magnetically clean. According to ISRO, the 6 metre carbon-fibre boom was deployed on 11 January 2024, after 132 days folded up since launch. Sensors sit 3 and 6 metres from the body, and comparing the two lets scientists cancel out the spacecraft’s own field. The boom has five segments, a Kevlar control loop and thermal cutters that release it on command. Deployment took approximately 9 seconds by ISRO’s measure, inside the predicted 8 to 12.

The first pictures

SUIT was powered on 20 November 2023. It took its first science images on 6 December, and its principal investigator, Durgesh Tripathi, was quoted by IUCAA: “It is a lifetime opportunity for a scientist to conceive the idea of such a complex space telescope payload and then to get to see the first light observations. Full disk images in this combination of wavelengths are being taken for the first time ever by a space telescope.”

In its release of 8 December 2023, ISRO said the images, taken through eleven filters, were the first full-disc images of the Sun in wavelengths from 200 to 400 nanometres, apart from one calcium line that other observatories had already covered. Sunspots, plages (bright patches around active regions) and quiet Sun regions are marked on the Mg II h image. IUCAA says the first runs used three filters and that the rest were then tested and gave good images.

The storm of May 2024

In early May 2024 an active region labelled AR13664 threw a series of X-class flares and coronal mass ejections toward Earth. In its account of 14 May, ISRO calls the resulting geomagnetic storm the most intense since 2003, with a Dst index of minus 412 nanotesla, a planetary Kp index of 9, which is the maximum, and a flare of class X5.8.

Aditya-L1 saw it from L1. ASPEX’s SWIS recorded an increase in the flux of alpha particles and protons in the solar wind, and STEPS recorded a steady rise in energetic ions through the event. SoLEXS and HEL1OS logged multiple X and M class flares in soft and hard X-rays, and MAG recorded disturbances in the interplanetary magnetic field. Chandrayaan-2’s X-ray monitor, in lunar orbit, picked up the same events from the Moon.

What happened on and above India is in the same account. Total electron content, a measure of the ionosphere, dropped by more than 50 per cent over Gadanki from midnight on 10 May to the morning of 11 May, and over Thumba it reached about 80 TECu against a typical 10 to 20 at that hour. According to the release, none of ISRO’s 30 geostationary spacecraft had a major upset, that none of its Earth observation satellites visible from its ground stations had upsets or latch-ups, and that the NavIC navigation service saw no or negligible impact. In low Earth orbit the extra drag was measurable: EOS-07, at about 430 km, lost 600 metres of orbit on 11 May against a nominal 300 metres.

From flare kernels to iron glow

Papers followed. On 22 February 2024 SUIT watched an X6.3 flare. In its release of 28 February 2025, ISRO says SUIT recorded the first-ever image of a solar flare “kernel” in the photosphere and chromosphere, the Sun’s lower atmosphere, in near ultraviolet. Two bright kernels showed up in filters that see the photosphere, which means the flare reached layers below the chromosphere. Brightening in the lower atmosphere matched a rise in the temperature of plasma in the corona. The result appeared in The Astrophysical Journal Letters.

On 16 July 2024 VELC watched the onset of a coronal mass ejection through the 5303 angstrom green line, light given off by iron atoms at coronal temperatures. Researchers from the Indian Institute of Astrophysics reported in The Astrophysical Journal Letters that the corona near the source region dimmed by about 50 per cent for about six hours, that the line broadened by about 15 per cent, and that the plasma showed a redshifted Doppler velocity of about 10 kilometres per second. The Government’s Parliament reply of 23 July 2026 lists among the mission’s major achievements “the first-ever spectroscopic signatures of the onset phase of a Coronal Mass Ejection,” without naming the instrument.

ISRO opened the data to everyone. On 6 January 2025, a year after orbit insertion, Somanath released the first datasets from all seven instruments at ISRO Headquarters in Bengaluru, in front of 40 scientists, academics and students from 15 institutions. Data sit on ISRO’s PRADAN portal. In July 2026 a third-cycle announcement of opportunity invited Indian researchers to propose observations with VELC and SUIT.

Results kept coming in 2026. On 3 July ISRO reported that SoLEXS had seen photospheric iron fluorescence, a glow at 6.40 keV produced when flare X-rays strike neutral iron atoms on the Sun’s surface, across 47 X-class flares in 2024. The paper appeared in Solar Physics. Fluorescence is strong for flares near the middle of the disc and suppressed near the edge, which matches theory. The Parliament reply of 23 July adds that scientists combined ground measurements with Aditya-L1 particle and field observations to gain insights into the intense geomagnetic storms of May and October 2024. The reply is careful on one point: Aditya-L1 is “a solar physics mission, and does not fall under the category of a space weather mission.”

What the mission cost

No ISRO page used for this article gives a cost. On the day of orbit insertion, PIB reported the Union minister as saying the mission was “not only indigenous but also a very cost effective mission” with “a budget of only Rs. 600 Crore.” At launch, Outlook Business reported that ISRO had not given a figure and that reports in the Indian media put it at Rs 3.78 billion, which is Rs 378 crore. Those numbers differ, and tuput did not find a published explanation of the gap.

Where it sits after Chandrayaan-3

Ten days before the launch, Chandrayaan-3 landed on the Moon. ISRO’s mission log for 23 August 2023 reads “Chandrayaan-3 has successfully soft-landed on the moon.” A Parliament reply of July 2026 says Chandrayaan-3 is, so far, the only successful mission to the polar region of the Moon. Its longer record is told in an earlier tuput piece on ISRO, and the private companies now entering the sector are covered in another.

On the evening of 6 January 2024, PIB quoted the minister’s post on X, “From Moon walk to Sun Dance!”, and described Aditya-L1 as the third of ISRO’s three successes in quick succession, after Chandrayaan-3 and XPoSat. The 2026 Parliament reply says the halo orbit maintenance and autonomous payload operations learned on Aditya-L1 feed into planning for the Venus Orbiter Mission. ISRO’s call for the third round of observation proposals, issued in July 2026, schedules approved VELC and SUIT observations for October to December 2026.