The James Webb telescope will be launched into space on December 18, and already the tension is palpable among the scientists who participated in its design, because there will be many critical moments following this launch, including the deployment telescope and its various components.
When in operation, the James Webb telescope will occupy a space the size of a tennis court. But to get it into space, it had to be made much more compact. It was thus designed in such a way that it can be folded, as we do in origami, in order to be able to fit in the most voluminous rocket that we currently have, namely the rocket. Ariane 5 whose fairing diameter measures only 5.4 meters.
The most delicate part of the mission will therefore be the one where the telescope will unfold, once it is in space, said mission craftsmen during a virtual technical briefing organized by NASA. This deployment will consist of approximately 50 major stages, and 178 release mechanisms will need to function properly for the telescope to reach operational condition.
Shortly after launch, it will be the solar panel and the transmitting antenna that will deploy to, respectively, supply power to the spacecraft and establish communications with the control center on Earth, located in Baltimore, in the USA. The rocket Ariane 5 will then place the Webb telescope in a precise orbit from which the latter will continue on its own path to its final destination, which will be the second point of Lagrange L2, located 1.5 million kilometers from Earth, that’s four times farther than the Moon. The Webb telescope will therefore be found much further from our planet than the Hubble telescope, which revolves around the Earth at an altitude of 590 km.
Point L2 was chosen because the temperature is stable there, the gravitational influences are weak and the telescope can be kept at an angle that is always constant with respect to the positioning of the Sun, unlike Hubble which is affected by large variations in temperature. to which it is exposed since it is sometimes in the shadow of the Earth, sometimes on the illuminated side, explains Martin Bergeron, manager of planetary exploration and astronomy missions at the Canadian Space Agency (CSA).
As the instruments on board the Webb telescope can only function properly at a very low temperature (- 233 ° C), it has been fitted with a huge sunscreen (21 meters by 15 meters) which will act as a parasol to protect mirrors and instruments from the heat of the Sun, and that emanating from the light of the Earth and the Moon.
Composed of five very thin sheets (about the thickness of a hair) made of reflective materials, this sunscreen is vital for the proper functioning of the telescope. Its deployment therefore represents another crucial moment that worries scientists. About a hundred release mechanisms, 400 pulleys, 90 cables and a variety of hinges, springs and other hardware will be involved in the unfolding of these protective tarpaulins.
We will then proceed to the opening of the mirror, which is composed of 18 hexagonal sections. These gold-plated beryllium units will be aligned precisely to form a large mirror 6.5 meters in diameter. The Hubble telescope was perhaps three times the size with its diameter of 2.4 meters, but the ability to pick up light from the Webb telescope will be 9 to 10 times more powerful, says Bergeron. Such power and the location of the telescope at point L2 will allow “to see even further, in the first moments of the Universe”.
The telescope will therefore search for the first stars and galaxies that formed after the Big Bang. “These very distant objects have a very low luminosity, because their light has traveled a very great distance during which it has faded a lot. To see them, you must therefore have a very large mirror, which is the case with the Webb telescope, and observe them for a very long time to accumulate as much light as possible. But to observe a point of low light for a very long time, the mirror must be very stable. However, as this telescope is in space and not firmly planted on Earth, it was necessary to find a way to point the telescope towards a target in a stable manner, this is what the precision guidance detector (FGS) will do ” , explains Bergeron.
“The FGS is a Canadian instrument that will keep the entire telescope stable with an accuracy of one sixtieth of a degree, the equivalent of a coin four kilometers away, for long hours,” even days, ”he explains.
The Canadian Space Agency is also providing another instrument designed by René Doyon’s team at the University of Montreal: a near infrared slitless imager and spectrograph (NIRISS) which will allow the composition of the atmosphere to be determined. distant exoplanets.
This Canadian contribution to the James Webb Telescope mission, which is the result of a collaboration between NASA, the European Space Agency (ESA) and the CSA, will guarantee privileged access to the telescope for Canadians throughout the life of the telescope. of the mission. “Canadians will be entitled to 5% of the observation time, which is exceptional because this telescope will be under enormous demand,” says Bergeron.
But these researchers will have to be patient, because it is only next summer (in 2022) that the first lights captured by the telescope will be transmitted to Earth for analysis by scientists. “Because once launched, the James Webb telescope will take four weeks to reach the second Lagrange point, where it will be fully deployed. It will then need to be cooled so that the instruments do not contaminate the infrared signal coming from celestial objects. It will then be necessary to test everything and validate. All of this will take around six months before the telescope is operational, ”points out Mr. Bergeron.
The James Webb telescope will be launched from the European base in Kourou, French Guiana, where it arrived by boat on October 14 from California where it was built and assembled. Scientists are currently carrying out the very last tests before D-Day.