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Aditya L1 successfully undergoes fourth earth-bound manoeuvre: ISRO

Aditya L1 successfully undergoes fourth earth-bound manoeuvre: ISRO

by | Sep 15, 2023 | Science


Aditya L1 spacecraft, India’s first space-based mission to study the Sun, during the early hours on Friday, underwent the fourth earth-bound manoeuvre successfully, ISRO said.

“The fourth Earth-bound manoeuvre (EBN#4) is performed successfully. ISRO’s ground stations at Mauritius, Bengaluru, SDSC-SHAR and Port Blair tracked the satellite during this operation, while a transportable terminal currently stationed in the Fiji islands for Aditya-L1 will support post-burn operations,” the space agency said in a post on X, a platform formerly known as Twitter.

The new orbit attained is 256 km x 121973 km, it said: “The next manoeuvre Trans-Lagragean Point 1 Insertion (TL1I) — a send-off from the Earth — is scheduled for September 19, around 02:00 Hrs. IST.”

Also Read | Deep dive into Aditya L-1: Some questions and answers 

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

The first, second and third earth-bound manoeuvre was successfully performed on September 3, 5 and 10 respectively.

The manoeuvres are being performed during the spacecraft’s 16-day journey around the Earth during which the spacecraft will gain the necessary velocity for its further journey to L1.

With the completion of four earth-bound orbital manoeuvres, Aditya-L1 will next undergo a Trans-Lagrangian1 insertion manoeuvre, marking the beginning of its nearly 110-day trajectory to the destination around the L1 Lagrange point.

Upon arrival at the L1 point, another manoeuvre binds Aditya L1 to an orbit around L1, a balanced gravitational location between the Earth and the Sun.

Aditya-L1, destined for the Sun-Earth L1 point, takes a selfie and images of the Earth and the Moon.
| Photo Credit: PTI

The satellite spends its whole mission life orbiting around L1 in an irregularly shaped orbit in a plane roughly perpendicular to the line joining the Earth and the Sun.

ISRO’s Polar Satellite Launch Vehicle (PSLV-C57) on September 2 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 that day, the Aditya-L1 spacecraft was successfully injected into an elliptical orbit of 235×19500 km around the Earth.

According to ISRO, a spacecraft placed in the halo orbit around the L1 point has the major advantage of continuously viewing the Sun without any occultation/eclipses.

Also Read | Checking out the Sun: Why ISRO’s Aditya L-1 mission is unique in many ways

This will provide a greater advantage in observing solar activities and their effect on space weather in real-time.

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

The payloads are to observe the photosphere, chromosphere and the outermost layers of the Sun (the corona) using electromagnetic 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, and 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 Probleme des Trois Corps, 1772.”

Also Read | Who was Lagrange?

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.





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UR Rao—the man behind the solar mission

UR Rao—the man behind the solar mission

by | Sep 5, 2023 | Science


Many scientists involved with the Aditya L-1 mission have given credit to Udupi Ramachandra Rao (1932-2017), ISRO’s former Chairman between 1984 and 1994, for the mission’s success.

But why? The idea of the mission was born in 2006, when a group of scientists of the Astronomical Society of India and the Indian Institute of Astrophysics made a presentation to ISRO, stressing that it would be useful to have a satellite in the Low Earth Orbit, from where it would be observing the sun and taking pictures, whenever the sun is in view.

Dr Dipankar Banerjee, Director, Aryabhatta Research Institute of Observational Sciences, Nainital, and Dr Sankarasubramanian, Principal Scientist, Aditya L-1 mission, say that it was Dr UR Rao, who suggested that the sun-observing coronagraph should not be put in a satellite that is orbiting the earth, but should be put at the Lagrange-1 point, where it would have an uninterrupted view of the sun. With this, the scope of the mission was expanded.

Rao, an alumnus of the Massachusetts Institute of Technology in the US, guided India’s space program in the initial days. He received the Padma Bhushan for his contributions by the Government of India in 1976.





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Readying an alternative landing spot for Vikram

Readying an alternative landing spot for Vikram

by | Sep 5, 2023 | Science


Now that Chandrayaan-3’s Vikram lander has touched down successfully on the moon and its rover, Pragyan, has been rolling around on the lunar surface, sending home some fabulous pictures and intriguing data, such as the temperature variation between the surface and near-surface, here’s a peek into an alternative history.

This is the story of the selection of an alternative landing site (ALS), the backup site for the mission in case the primary landing site (PLS) proved elusive.

A paper by K Durga Prasad et al, titled ‘Chandrayaan-3 Alternate Landing Site: Pre-landing Characterisation’, describes the selection methodology, which was based on factors such as proximity to the PLS, conditions for safe landing, and whether it was of interest for scientific purposes. The ALS is an approximately 4 km x 2.4 km area in the same latitude (about 69 degrees South) as the PLS and about 450 km away. A hazard map was plotted using data from the Chandrayaan-2 orbiter’s high-resolution camera, which confirmed that 75 per cent of the ALS was hazard-free, making it suitable for landing and rover operations. Variability within the local terrain, illumination, and surface temperatures were studied to enable safe operations.

The ALS was found to be a scientifically interesting site with scope for sampling ‘ejecta materials’ from the lunar craters Tycho and Moretus formed during the Eratosthenian age (3.2-1.1 billion years ago).

An ‘ejecta blanket’ is formed when material ejected from a crater during an impact fall back on the lunar surface. It can extend for several kilometres beyond the rim of the crater and can be studied to determine the geology of the surrounding area.

The Eratosthenian age is a geological epoch of the Moon that occurred between 3.2 and 1.1 billion years ago. It represents a period of intense geological activity on the Moon, including the formation of large impact basins and the emplacement of volcanic deposits. 

To help interpret observed in-situ data, a set of studies were carried out:

Geomorphological characterisation, which was based on observations from the Chandrayaan-2 orbiter, particularly the best spatial resolution (25 cm) images from its high-resolution camera and the derived digital elevation model.

Thermophysical characterisation, which is the study of how materials respond to changes in temperature, was used to determine the temperatures and thermal behaviour of the ALS. The study used datasets from the Diviner radiometer aboard the lunar reconnaissance orbiter and a three-dimensional thermophysical model to understand the temperatures and thermal behavior of the alternate landing site.

Mineralogical and compositional characterisation, which is the study of the minerals and other chemical composition of a material, to understand the variations within the ALS. The study used data from the Moon Mineralogy Mapper (M3) of Chandrayaan-1.

Given that the same level of rigour would have been applied to the PLS, now known as Shiv Shakti Point, it was inevitable that ChaSTE (Chandra’s Surface Thermophysical Experiment) was the first direct measurement of the topsoil and subsoil near the lunar south pole.

As we wrap-up the story of where Shiv Shakti might have been, a quick appreciation of why the mission is important: knowledge from these missions help us better in better lunar exploration planning including designing better equipment and calibration; exploring resources and solar power generation; and establishing energy bases for future space missions.





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Chandrayaan-3 findings show moon is habitable

Chandrayaan-3 findings show moon is habitable

by | Sep 3, 2023 | Science


Ever since the Vikram lander touched down on the lunar surface, there has been a steady flow of data and information from the instruments onboard the lander and the rover.

Separately, the information may look like some scientific hickery-pockery, but when you stitch them together you can read one message: the moon is more habitable than thought earlier.

The biggest supporter of this notion is the data point thrown up by the lander, which sent a probe down 10 cm into the lunar surface and measured the temperature there. It came up with the revelation that when the lunar surface is about 50o C hot, just 8 cm below the surface, it is as cold as minus 10o C. There is more to this data point than the ‘wow’ feeling it evokes.

For a while now, scientists have known that the lunar subsurface is cold. Vikram has only provided proof that the lunar topsoil is a super-insulator.

Regolith shielding

In a 2015 paper titled ‘Determination of temperature variation on lunar surface and subsurface for habitat analysis and design’, published in the journal Acta Astronautica, the authors, Ramesh B Malla and Kevin M Brown, of the University of Connecticut in the US mathematically determined that “the outermost layer of regolith fluff has very strong insulating capabilities causing the temperature to drop 132.3 K (-140.85o C) from the maximum daytime magnitude of 387.1 K (113.95o C) within the first 30 cm at which point it then remains constant with increasing depth.”

The moon, which has no atmosphere, is directly exposed to the sun. It gets extremely hot (123o C) during daytime and incredibly cold during night (-233o C). To build a habitat there calls for a stupendous amount of insulation. Imagine carrying all the insulating material all the way from the earth! But now, as Vikram has shown, we see that it is not really necessary.

A layer of processed regolith spread on top of the habitat can make the inhabitants nice and comfy inside. Malla and Brown further say that when you have a regolith shielding atop a lunar habitat, the reflection of sunlight from the surrounding area (albedo) raises the temperature of the shielding, with a corresponding drop below a foot of the regolith cover.

Now that the Vikram lander has shown that the temperature drops by 60o C from the top of the 2 cm-thick ‘fluff’ to 8 cm below the ground, one can design a habitat accordingly. The fluff has very low thermal conductivity.

In another research paper, titled ‘Energy requirements of a thermally processed ISRU radiation shield for a lunar habitat’, authors Christopher Spedding et al of the Open University, Walton Hall, UK, note that it is possible to set up MW-scale solar or nuclear power plants and use the energy to “thermally process” construction material (with lunar regolith), “making large, permanent human presence on the moon more easily realisable.”

More good news

The Pragyan rover, on its part, has also helped confirm something heartening — the presence of oxygen in the lunar soil. The ‘Laser Induced Breakdown Spectroscopy’ (LIBS) instrument on the rover, threw laser beams on to the soil and analysed the reflections. It has shown the presence of sulphur, calcium and many metals such as iron, chromium, titanium, manganese and aluminium and oxygen.

The presence of oxygen in the soil, in the form of ilmenite (FeTiO3), means you have an alternative to ice for oxygen production. So, you don’t have to build your house only near an ice-source if you were to settle on the moon. Ice is not present everywhere, but soil is. Ilmenite can be reduced to make oxygen for breathing.

The findings from the lander and the rover go to strengthen a growing branch of science called In-situ resource utilisation (ISRU), alternatively known as ‘space resource utilisation’ (SRU).





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 Aditya L-1: Reading the Sun’s resume 

 Aditya L-1: Reading the Sun’s resume 

by | Sep 2, 2023 | Science


To know about a distant object, you need something to start from that object and reach you—a letter, voice, or reflected light. Astronomers learn about distant stars by analysing the electromagnetic radiation, including visible light from the stars and reaching their telescopes or other instruments. 

Luckily, the Sun is not as far as the other stars. It is ‘only’ 151 million km. And, again, it sends not just electromagnetic radiation, but also ‘matter’, mostly in the form of particles—positively charged protons, alpha particles (two protons and two neutrons) and a little bit of electrons. 

By sending (a) electromagnetic radiation, such as infrared, visible light, ultraviolet, X-rays, and (b) matter, in the form of particles—the Sun is sending us its resume. If we are able to read them, we know who our Sun is. 

Aditya L-1 is meant to do precisely  that – read Sun’s resume. The spacecraft was successfully launched by India’s ISRO into an Earth orbit and, over the next 125 days, will be slowly ‘pushed’ towards its parking slot—the Lagrange-1 point, 1.5 million km from the earth in the direction of the Sun—where it will have an uninterrupted view of the Sun, 24×7. 

With the Aditya L-1 solar, ISRO has ticked many boxes.  

The mission is the first of its kind, not only for India on some counts but for the whole world on others. 

When the spacecraft reaches L-1, it will make ISRO only the third space agency in the world to park a spacecraft at that point – after US NASA and the European Space Agency.  

Aditya L-1 will be the fifth object to be positioned there, the fourth for Sun observation.  

(NASA and ESA jointly were the first to put up a spacecraft at L-1 when they sent up the Solar and Heliospheric Observatory (SOHO) into L-1 in 1995. (Against an estimated mission life of 2 years, the SOHO is still alive and functioning even after 27 years.) The Advanced Composition Explorer (ACE), also of NASA, was the second to go to L-1. Again, NASA’s Wind spacecraft was the third—it was launched in 1994, but after being stationed at different places, it reached L-1 in 2004, where it is still functioning. The Deep Space Climate Observatory (DSCOVR) is the fourth spacecraft to be put up into L-1, but it is meant to observe the earth rather than the Sun. And now, Aditya L-1 will become the newest tenant of L-1.) 

Only one in the world 

Dr Anil Bharadwaj, Director, Physical Research Laboratory, Ahmedabad, observes that the spacecraft is “absolutely unique” because it is only fitted with instruments designed to measure particles, fields and radiation. There is none today that can do all three. 

As for particles, there are ground-based observatories, but the particles they receive have already undergone scattering by colliding with other particles in the earth’s atmosphere, whereas the Aditya L-1, being stationed in space, can check out on virgin particles—which can tell more.  

As for fields, the spacecraft can look at the Sun’s magnetic field, observe variations in the field and see how the variations impact the Sun’s activities, such as throwing up billions of tons of mass (coronal mass ejection) and sending gusts of solar winds (streaming particles.)  

As for radiation, Aditya L-1 is designed to pick up a wide range of electromagnetic radiation from the Sun, from near-infrared to visible light to near ultraviolet to soft and hard X-rays. If you imagine an electromagnetic radiation spectrum to be a string stretched between your hands, Aditya L-1 cuts a big length in the middle. 

Technology demonstrator 

Aditya L-1 is the first time that India is positioning a spacecraft at Lagrange-1 point. Injecting a spacecraft at this point calls for extreme precision. Once there, it also calls for skillful station-keeping, as the spacecraft would constantly be subject to many pulls and pressures (though not as much as at other, non-Lagrange points.) Apart from generating knowledge, the Aditya L-1 is a veritable technology demonstrator.  

The two major instruments – Solar Ultraviolet Imaging Telescope (SUIT) and Visible Emission Line Coronagraph (VELC) — are entirely designed and built in India by Indian scientists. Interestingly, they are complementary to each other. While the SUIT keeps looking at the central disc of the Sun, the VELC ‘blocks off’ the central disc and looks at the rim—the corona—the way we see the Sun during the solar eclipse. The corona is a million times fainter than the disc, points out Dr Annapurni Subramanian, Director, Indian Institute of Astrophysics. With the disc blocked, VELC can ‘see’ the corona better. Further, since both VELC and SUIT are looking at different parts of the Sun at the same time, scientists can infer the effect of any activity in the Sun on the corona. 

Unique data 

According to Dr K Sankarasubramanian, Principal Scientist for the Aditya L-1 mission, notes that the seven instruments on spacecraft will generate a “unique set of data currently not available.” 





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After the moon, India begins mission to study the sun

After the moon, India begins mission to study the sun

by | Sep 2, 2023 | Science


Indian Space Research Organisation’s workhorse Polar Satellite Launch Vehicle – PSLV-C57/Aditya Mission had a successful lift-off from the second launch pad of the Satish Dhawan Space Centre SHAR, Sriharikota.

ISRO’S Aditya-L1 lifts off aboard the PSLV-C57 rocketVideo Credit: TE Raja Simhan

After a successful landing on the Moon recently, the Aditya-L1 mission is to study the Sun. Aditya-L1 is the first space-based observatory-class Indian solar mission to undertake a comprehensive study of the Sun.

At 11.50, the ISRO’s workhorse PSLV blasted off from the second launch pad. On a hot and sunny day, PSLV-C57 emerged behind the trees – as visible from the terrace of the media centre about three km from the launch pad – and soared with a thunderous sound in the clear sky. The rocket with its orange flame in its tail left behind thick smoke as it soared.

The 1,420-kg spacecraft (PSLV XL) carried 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.





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