Aditya-L1 and further Indian missions to the Sun

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Halo-Orbit Insertion (HOI) of its solar observatory spacecraft, Aditya-L1 was accomplished at 16.00 Hrs (approx) on January 6, 2024 (IST). The final phase of the maneuver involved firing of control engines for a short duration.

The orbit of Aditya-L1 spacecraft is a periodic Halo orbit which is located roughly 1.5 million km from earth on the continuously moving Sun – Earth line with an orbital period of about 177.86 earth days. This Halo orbit is a periodic, three-dimensional orbit at L1 involving Sun, Earth and a spacecraft. This specific halo orbit is selected to ensure a mission lifetime of 5 years, minimising station-keeping manoeuvres and thus fuel consumption and ensuring a continuous, unobstructed view of sun.

The picture below shows the Halo orbit insertion process graphically in a two dimension picture. The Aditya-L1 spacecraft was moving from Earth towards the L1 point in the direction of Sun. The TCM1 &2 firing oriented the spacecraft toward the Halo Orbit, making it reach the HOI condition (which is a minimum fuel consumption condition) as on 6th January 2024 (Marked by the red dot). The final firing was done at this point, making the spacecraft align with the Halo Orbit. If the HOI manoeuvre was not conducted as done today, the spacecraft would have moved in the direction marked (Without HOI).
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Quoted tweet below.
The 6 meter long Magnetometer Boom on the #AdityaL1 spacecraft has finally been extended! #ISRO In the 1st and 2nd pictures, you can see an illustration and an actual image of the Magnetometer Boom in stowed condition during testing, and in the 3rd and 4th pictures, you can see another illustration and a real image of the boom in deployed condition. The boom remained in stowed condition until 132 days after launch and was finally deployed on January 11. It consists of two magnetometer sensors located in the middle and at the very end of the boom to measure the low intensity interplanetary magnetic field in space.
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PAPA payload aboard Aditya-L1 detects solar wind impact of Coronal Mass Ejections
February 22, 2024
The Plasma Analyser Package for Aditya (PAPA) payload onboard the Aditya-L1 has been operational and performing nominally. Its advanced sensors have successfully detected the impact of coronal mass ejections (CMEs) including those that occurred during February 10-11, 2024.
PAPA is an energy and mass analyzer designed for in-situ measurements of solar wind electrons and ions in the low energy range. It has two sensors: the Solar Wind Electron Energy Probe (SWEEP, measuring electrons in the energy range of 10 eV to 3 keV) and the Solar Wind Ion Composition Analyser (SWICAR, measuring ions in the energy range of 10 eV to 25 keV and mass range of 1-60 amu). The sensors are also equipped to measure the direction of arrival of solar wind particles.
The payload has been operational since December 12, 2023. Its observations during the Halo Orbit Insertion (HOI) phase are shown in Figure 1. The figure illustrates the time series of SWEEP electron energy spectra and total count observed during the HOI phase and the period preceding and succeeding it. It reveals about three-order magnitude change in electron counts from 10 eV to 3000 eV. The majority of electrons have energy below 40 eV. It displays an excellent signal-to-noise ratio and energy resolution. Drastic reduction in the electron energy spectra and the total count occurs during the HOI phase due to the change in payload orientation away from the sun direction during this orbit maneuvering period. This is also evident in the ion energy spectra observed using SWICAR (Figure 2).
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Figure 1: Time series of SWEEP electron energy spectra taken from 04:00:30 UTC to 17:59:58 UTC on January 6, 2024, covering Pre-HOI, HOI and Post-HOI phases. The dip seen in the spectra is due to spacecraft rotation (HOI phase) when the sensor direction is away from the Sun. The time series of the integrated counts are shown in the upper panel.
Figure 2 shows the time series of SWICAR ion energy spectra and integrated counts during the specified timeframe. It exhibits the expected patterns of ion energy spectra under normal space weather conditions. The ion energy spectrum indicates the dominance of protons (H+ @ 1 amu at around 800 eV) and alpha particles (He++ @ 2 amu at around 1600 eV). The ability of SWICAR to identify individual ion masses aligns with its design.
The electron (SWEEP) and ion (SWICAR) energy spectra observed before and after the HOI phase are comparable.
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Figure 2: Time series of SWICAR ion energy spectra and the integrated counts from 04:01:36UTC to 17:58:53 UTC on January 6, 2024 (Top two panels) showing the variations during Pre-HOI, HOI and Post-HOI phases. The observed energy-direction spectrogram (bottom panel) shows two dominant species (H+ and He++) in the solar wind and their angular variations.
The data collected by PAPA revealed the occurrence of Coronal Mass Ejection (CME) events, notably on December 15, 2023, and during February 10-11, 2024, as shown in Figures 3 and 4. The CME on December 15, 2023, was a single event. PAPA observations during this period (Figure 3) showed an abrupt increase in total electron and ion counts and the time variations align with the solar wind parameters and magnetic field measurements obtained from the Deep Space Climate Observatory (DSCOVR) and Advanced Composition Explorer (ACE) satellites at the L1 point. In contrast, the observed variations in electron and ion counts during February 10-11, 2024 are the result of multiple minor events, with differences in the time variations of electrons and ions.
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Figure 3: Time series of the integrated raw counts for (a) solar wind electrons measured by PAPA-SWEEP sensor, and (b) solar wind ions measured by PAPA-SWICAR sensor, from 05:45:00 UT on 15 December to 23:55:00 UT on 16 December 2023. (c) The corresponding time series of the total magnetic field measured at the L1 point by DSCOVR and ACE (obtained from SWPC).

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Figure 4: Similar to Figure 3, for the CMEs occurred during February 10-11, 2024.
The SWEEP and SWICAR sensors on PAPA-Aditya-L1 are currently making continuous observations of solar wind electrons and ions in the default mode, demonstrating that they are performing as per the design in all modes of operations. The observations made by PAPA emphasize its effectiveness in monitoring space weather conditions and its capability to detect and analyze solar phenomena.
The PAPA payload is developed by the Space Physics Laboratory and Avionics Entity of the Vikram Sarabhai Space Centre (VSSC)/ISRO.
 
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India's Aditya-L1 to track the Sun during Total Solar Eclipse
The Total Solar Eclipse will occur on April 8 as the Sun, Moon and Earth align in a straight line leading to a brief period of darkness during the daytime.
Aditya L1 mission solar eclipse

The Adiya L1 mission is equipped with six instruments as it observes the Sun from Lagrange Point 1. (Photo:ISRO)
In Short
  • The Total Solar Eclipse will occur on April 8
  • The coronagraph studies the Sun's outer layer, the corona,
  • During the eclipse, the Sun's corona is visible as the Moon blocks the solar disk
India's maiden solar probe, Aditya L1, will track the Sun as it gets cloaked by the moon, creating a brief period of darkness in several parts of North America, during the Total Solar Eclipse.
The Total Solar Eclipse will occur on April 8 as the Sun, Moon and Earth align in a straight line leading to darkness during the daytime. The cloaking will create a period of totality expected to last over four minutes, illuminating the enigmatic outer layer of the Sun that is not visible from Earth.
The Adiya L1 mission has six instruments as it observes the Sun from Lagrange Point 1, nearly 15 kilometres from Earth. Of the six, two instruments could be primed to observe the Sun during the eclipse. These are the Visible Emission Line Coronagraph (VELC) and the Solar Ultraviolet Imaging Telescope (SUIT).
Aditya L1

The Aditya L1 spacecraft entered its halo orbit at Lagrange Point 1 earlier this year. (Photo: India Today)
The coronagraph studies the Sun's outer layer, the corona, by blocking the Sun's disk and creating an artificial eclipse onboard the spacecraft. Meanwhile, the Suit images the Solar Photosphere and Chromosphere in near ultraviolet.
During the eclipse, the Sun's corona is visible as the Moon blocks the solar disk and reveals the outer bright layers shining, and can be seen from Earth for a brief moment. The corona is not visible, otherwise, from the planet.
"The eclipse presents a rare opportunity to observe the Sun from both space and on Earth and then go on to get a comprehensive picture by cross-relating the observations at a later stage. We would be planning to observe the Sun with Aditya L1's Suit instrument," Professor Durgesh Tripathi, Principal Investigator of Aditya L1's Suit instrument at the Inter-University Centre for Astronomy and Astrophysics (IUCAA) told inditoday.in.
Solar eclipse

The Aditya L1 spacecraft entered its halo orbit at Lagrange Point 1 earlier this year after leaving Earth in 2023. The spacecraft is being calibrated in the coldness of space at L1 and has begun science observations.
The Plasma Analyser Package for Aditya (Papa) payload onboard the Aditya-L1 detected the first solar wind impact of Coronal Mass Ejections in February. Meanwhile, the 6-meter-long magnetometer boom was deployed in January.
The Aditya-L1 mission aims to deepen our understanding of solar phenomena, including the solar corona, photosphere, and the impact of solar winds and related radiation. The spacecraft's instruments have been calibrated during its voyage, sending back X-ray images and particle counts, showcasing its healthy condition.
Solar eclipse

Aditya L1 will not be the only spacecraft to be looking at the Sun during the rare eclipse, Europe's Solar Orbiter, which conducted its closest approach to the Sun on April 4, will also have its instruments activated.
Solar Orbiter will be observing the Sun side-on compared to our perspective on Earth. This means that the structures in the corona (the Sun’s outer atmosphere) that we see on the right-hand side of the Sun from Earth will be seen directly face-on by the spacecraft.
The eclipse offers a rare opportunity for astronomers across the world to observe the Sun and conduct tag-team observations with ground-based observatories and space-based probes to better understand the physics powering the Sun.
 

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