James Webb Space Telescope has turned on it’s high-gain antenna

NASA’s James Webb Space Telescope has just reached its final destination, around a point in space with special gravitational properties known as the second Lagrange point, or L2. The $10 billion observatory could spend 20 years or more there, peering into deep space and gaining unprecedented insights into the Universe.

The James Webb, the most complex telescope ever built, made its way to L2 on Christmas Day. Finally, on January 24, it ignited a set of thrusters and placed itself in orbit around that point. There, it will complete a spin every six months or so.

L2 is located on the opposite side of the Earth from the Sun and about 1.5 million kilometers from our planet, a distance four times greater than that which separates us from the Moon. At that point, the joint gravitational pull of the Sun and Earth offsets the centrifugal force pulling the telescope in the opposite direction.

There are only a handful of space missions that have traveled to L2, one of the five Lagrange points of the Earth-Sun system. But more is planned, as it is an exceptional location for sensitive astronomical observatories like James Webb.

“There are a couple of unique details about L2 that make it ideal for astronomical missions,” confirms David Milligan, director of operations for the European Space Agency’s Gaia spacecraft.

One of them is the possibility of observing almost the entire sky without obstacles. Observatories that orbit the Earth, such as the Hubble Space Telescope, see the planet blocking a sizeable fraction of their field of view much of the time.

Instead, the James Webb Telescope faces away from the Sun and always has our star, Earth, and Moon behind it. “L2 is great because the brightest objects — the Sun, Earth, and Moon — are on the same side of the spacecraft,” says Karen Richon, an engineer who leads the James Webb Telescope Flight Dynamics team at the Center for Astronomy. NASA Goddard Space Flight. “You can build a big sun shield and block all three at all times.”

And that’s just what the James Webb does. From L2, its tennis-court-sized shield constantly blocks out the Sun, while its 6.5-meter-wide primary mirror peers into the darkness of deep space. The observatory will study a number of astronomical objects, such as the most distant galaxies in the Universe, the atmospheres of exoplanets and the dusty places where stars are born.

The importance of cold

The other big advantage of L2 is that it’s cold. Missions orbiting the Earth sometimes get sunlight and sometimes don’t, experiencing huge temperature swings that cause equipment to expand and contract.

Thus, devices that need to remain cold work better in L2, where the temperature is much more stable. The four science instruments on the James Webb Telescope operate at temperatures of about −233 degrees Celsius (40 degrees above absolute zero) to detect faint flashes of heat from stars, galaxies, and other cosmic objects.

Lagrange points are named after the mathematician Joseph-Louis Lagrange, who in 1772 discovered them as places where a small body can orbit in concert with two larger masses. That makes L1 and L2, the closest Lagrange points to Earth, obvious places to develop space exploration.

“There’s a natural route from Earth to those places,” says Kathleen Howell, an aerospace engineer at Purdue University. However, “until recent decades we have not understood that it was there.”

The first spacecraft to travel to a Lagrange point was NASA’s International Sun and Earth Explorer 3 (ISEE-3), which launched in 1978 and headed for L1, a point between the Sun and Earth. . That mission showed that it was possible to put a spacecraft into orbit around a Lagrange point, Howell says. In 1995, ESA also sent the Solar and Heliospheric Observatory (SOHO) to L1; that and other missions continue to study the Sun and space weather from that point.

Howell. In 1995, ESA also sent the Solar and Heliospheric Observatory (SOHO) to L1; that and other missions continue to study the Sun and space weather from that point.

The first mission to operate from L2 was WMAP, a NASA satellite that studied the afterglow of the big bang between 2001 and 2010. ESA has sent several spacecraft to L2, including the now-defunct dedicated Herschel space observatory (like the James Webb) to infrared astronomy. There are currently two other spacecraft at L2: ESA’s Gaia mission, dedicated to mapping our galaxy, and the Russian-German Spektr-RG observatory. The three instruments are in different orbits, Milligan says, so there’s no danger of them colliding with each other. Besides, “the space is enormous,” he adds.