NASA’s Parker Solar Probe launched on August 12, 2018 has completed its fourth close approach — called perihelion very recently, whizzing past at about 3.93 lakh km/h, at a distance of only 18.6 million km from the Sun’s surface.

Aditya L1: Exciting ahead

• The ISRO is preparing to send its first scientific expedition to study the Sun.
• Named Aditya-L1, the mission, expected to be launched early next year, will observe the Sun from a close distance, and try to obtain information about its atmosphere and magnetic field.
• ISRO categorizes Aditya L1 as a 400 kg-class satellite that will be launched using the Polar Satellite Launch Vehicle (PSLV) in XL configuration.
• The space-based observatory will have seven payloads (instruments) on board to study the Sun’s corona, solar emissions, solar winds and flares, and Coronal Mass Ejections (CMEs), and will carry out round-the-clock imaging of the Sun.
• Aditya L1 will be ISRO’s second space-based astronomy mission after AstroSat, which was launched in September 2015.

What is L1?

• L1 refers to Lagrangian/Lagrange Point 1, one of five points in the orbital plane of the Earth-Sun system.
• Lagrange Points, named after Italian-French mathematician Josephy-Louis Lagrange, are positions in space where the gravitational forces of a two-body system (like the Sun and the Earth) produce enhanced regions of attraction and repulsion.
• These can be used by spacecraft to reduce fuel consumption needed to remain in position.
• The L1 point is home to the Solar and Heliospheric Observatory Satellite (SOHO), an international collaboration project of NASA and the European Space Agency (ESA).
• The L1 point is about 1.5 million km from Earth, or about one-hundredth of the way to the Sun.

But why is studying the Sun important?

• Every planet, including Earth and the exoplanets beyond the Solar System, evolves — and this evolution is governed by its parent star.
• The solar weather and environment, which is determined by the processes taking place inside and around the sun, affects the weather of the entire system.
• Variations in this weather can change the orbits of satellites or shorten their lives, interfere with or damage onboard electronics, and cause power blackouts and other disturbances on Earth.
• Knowledge of solar events is key to understanding space weather.
• To learn about and track Earth-directed storms, and to predict their impact, continuous solar observations are needed.
• Every storm that emerges from the Sun and heads towards Earth passes through L1, and a satellite placed in the halo orbit around L1 of the Sun-Earth system has the major advantage of continuously viewing the Sun without any occultation/eclipses.

Why are solar missions challenging?

• What makes a solar mission challenging is the distance of the Sun from Earth (about 149 million km on average, compared to the only 3.84 lakh km to the Moon).
• More importantly the super hot temperatures and radiations in the solar atmosphere make it difficult to study.
• NASA’s Parker Solar Probe has already gone far closer — but it will be looking away from the Sun.
• The earlier Helios 2 solar probe, a joint venture between NASA and space agency of erstwhile West Germany, went within 43 million km of the Sun’s surface in 1976.

Problem of Heat

• The Parker Solar Probe’s January 29 flyby was the closest the spacecraft has gone to the Sun in its planned seven-year journey so far.
• Computer modelling estimates show that the temperature on the Sun-facing side of the probe’s heat shield, the Thermal Protection System, reached 612 degrees Celsius, even as the spacecraft and instruments behind the shield remained at about 30°C, NASA said.
• During the spacecraft’s three closest perihelia in 2024-25, the TPS will see temperatures around 1370°C.

Hurdles for Aditya L1

• It will stay much farther away, and the heat is not expected to be a major concern for the instruments on board. But there are other challenges.
• Many of the instruments and their components for this mission are being manufactured for the first time in the country, presenting as much of a challenge as an opportunity for India’s scientific, engineering, and space communities.
• One such component is the highly polished mirrors which would be mounted on the space-based telescope.
• Due to the risks involved, payloads in earlier ISRO missions have largely remained stationary in space; however, Aditya L1 will have some moving components, scientists said.

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