Launch and DEPLOYMENT

There’s a perfect spot in space for an infrared telescope, and Webb is heading there

A key feature of Webb’s design is that it has a ‘cold side’ and a ‘hot side’. The cold side is the one that does the observing, while the hot side carries the spacecraft’s solar panels and an antenna for two-way communication with Earth. But this arrangement only works if the Sun and Earth are always in the same direction from the spacecraft’s point of view.

This wouldn’t be the case if it was simply placed in Earth orbit like Hubble, nor would it be true if the spacecraft orbited the Sun at a slightly different distance from Earth’s orbit. But it turns out there is one special distance at which an object can orbit the Sun and always see the Sun and Earth in the same direction. This is the so-called L2 point, and it’s where the James Webb Space Telescope will operate.

L2 is one of several locations called Lagrange points, after Joseph-louis Lagrange, who studied them in the 18th century. At these locations, the gravity of two massive bodies – in this case the Sun and Earth – conspire to keep a third, smaller body, such as an asteroid or spacecraft, in a fixed position relative to the first two.

These Lagrange points aren’t stationary, but they revolve around the Sun at exactly the same rate as Earth, so their distance from us always stays the same. In the case of L2, it’s around 930,000 miles away – around four times as far away as the Moon.

To get the telescope all the way out to L2 requires a powerful launch vehicle, which will be the European Space Agency’s Ariane 5 rocket. In just 26 minutes following liftoff from French Guiana, this will carry Webb free of Earth’s atmosphere and put it on course for L2. The spacecraft will then separate from the rocket and cruise for around a month before finally arriving at its destination.