India’s Aditya-L1 mission

Sometime in 2019 or 2020, India will send ISRO’s solar mission Aditya-L1 to a vantage point in space, known as the L1 Lagrange point, to do imaging and study of the sun. This launch will happen in the early part of the next solar cycle – an occurrence in which sunspots form on the face of the sun, growing in size and number and eventually diminishing, all over a period of eleven years. It will be a mission of many firsts.

The so-called L1 point is 1.5 million kilometres away. Here, due to the delicate balance of gravitational forces, the satellite will require very little energy to maintain its orbit. Also, it will not be eclipsed from the sun. The 1,500-kg class satellite will be programmed to orbit this point and image the sun’s magnetic field from space for the very first time in the world. Scientists hope to capture the close-ups of the sun from here, uninterrupted by eclipses for years.

Few other space agencies have successfully placed their satellites at this location. Among the few, the Solar and Heliospheric Observatory (SOHO), a NASA-ESA collaboration involving America and Europe, and NASA’s Advanced Composition Explorer (ACE) are at L1 exclusively to study the sun and space weather, respectively. Aditya-L1 is expected to be the very first to study from space two months from the time of launch, the magnetic field of the sun’s corona.

The corona is the outer layer that we see during total solar eclipses. It will be the first 100% Indian mission which will not only negotiate a challenging orbit but will also benefit the global scientific community in understanding the sun.

Earlier, the NASA-ESA mission SOHO was launched in 1995, and while it made many discoveries, its coronagraph, meant to image the sun, broke down shortly after the mission commenced. Hence there is currently no satellite imaging the sun from space. Aditya-L1 will not only fill this gap it will also literally, look deeper into the sun than SOHO.

What is L1, L5?

Lagrange point is a location in space where the combined gravitational forces of two large bodies, such as Earth and the sun or Earth and the moon, equal the centrifugal force felt by a much smaller third body. The interaction of the forces creates a point of equilibrium where a spacecraft may be “parked” to make an observation.

These points are named after Joseph-Louis Lagrange, an 18th-century mathematician who wrote about them in a 1772 paper concerning what he called the “three-body problem.” They are also called Lagrangian points and libration points.

There are 5 such points between the earth and the sun namely – L1, L2, L3, L4 and L5.

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