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Explained: What is the VELC payload on Isro's Aditya-L1 mission?

Designed by the Indian Institute of Astrophysics, the Visible Emission Line Coronagraph is one of the seven payloads on the Isro Aditya-L1 mission

Aditya-L1, the first space-based Indian observatory to study the Sun.
Aditya-L1, the first space-based Indian observatory to study the Sun. (ISRO/Twitter)

The Indian Institute of Astrophysics (IIA) on 29 August said it has designed, assembled, and tested the Visible Emission Line Coronagraph (VELC), one of the seven payloads on India's first dedicated scientific mission Aditya-L1 conceived to study the sun.

The Indian Space Research Organisation (Isro) is set to launch Aditya-L1 from Sriharikota in Andhra Pradesh on 2 September.

IIA said the VELC was developed in close collaboration with Isro. “IIA had to build India's first large sized 'Class to Clean Rooms' at (sic) its CREST campus in Hosakote to assemble VELC,” the institute said in a statement on X, formerly known as Twitter.

The Aditya-L1 solar probe will carry six other payloads — Solar Ultraviolet Imaging Telescope (SUIT), Aditya Solar Wind Particle Experiment (ASPEX), Plasma Analyser Package for Aditya (PAPA), SoLEXS-Solar Low Energy X-ray Spectrometer (SoLEXS), High Energy L1 Orbiting X-ray Spectrometer HEL1OS, and Magnetometer with enhanced science scope and objectives possible by extensive remote and in-situ observation of the Sun. According to Isro, the mission will help scientists get a deeper understanding of the sun.

A Press Trust of India report said: "Earlier, this mission was conceived as Aditya-1 with a 400 kg class satellite carrying one payload, the Visible Emission Line Coronagraph (VELC), and was planned to be launched in an 800 km low earth orbit," IIA added in its statement.

A satellite placed in the halo orbit around the first Lagrangian point (L1) of the Sun-Earth system has the major advantage of continuously viewing the Sun without any occultation/eclipses, IIA said.

Therefore, the Aditya-1 mission has now been revised to "Aditya-L1 mission" and will be inserted in a halo orbit around the L1, which is 1.5 million km from the earth towards the Sun, the statement explained.

"The VELC payload on-board Aditya-L1 is an internally occulted solar coronagraph with simultaneous imaging, spectroscopy and spectro-polarimetry channels close to the solar limb. VELC is designed to image solar corona," IIA said.

Both imaging and spectroscopic observations obtained by VELC payload are key to study the diagnostic parameters of solar corona and dynamics as well as origin of the coronal mass ejections and magnetic field measurements of the solar corona. Stokes vector measurements in the plane-of-sky and imaging in white-light are the unique features of this payload, it added.

The scientific studies by the satellite will enhance the current understanding of the solar corona and also provide vital data for space weather studies, IIA said. 

India scripted history when the Vikram lander from the Chandrayaan-3 mission made a soft landing on the surface of the moon on 23 August.

Earlier this month, Nasa's Parker Solar Probe, another mission designed to study the sun, completed a fly-by past Venus, and will now use the planet’s gravity to aim toward a record-setting series of flights around the Sun that start in September.

Also read: Chandrayaan-3: Isro and India create history as spacecraft lands on the Moon

(With inputs from the Press Trust of India)

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