Ioonos

How do you make a telescope intended to be put into orbit?

The aim of a telescope is to catch light. So we have to have the largest possible diameter for the telescope’s mirror, because that is what does the “catching”. What’s more, having a large-scale mirror helps strengthen the entire structure. But here’s the problem: since we are working on space applications, we are constantly fighting against weight. Every kilo costs money! During manufacture you also have to take into account the rapid heating up of the satellite when exposed to the sun. The temperature differential can be fatal for the optical instruments. So between launch and the first contact with space, the telescope must be hermetically enclosed in a sealed compartment, refrigerated to space temperature. However, to avoid accidents that are always possible, we had to double up all the telescope’s key instruments.

What are the main differences between a land-based telescope and one in space?

Basic operation is the same. But a space telescope has to meet a larger number of constraints. I will not repeat the weight and thermal constraints. We also have to equip it with all the communications equipment that lets us control it from afar, which is what we call telemetry, and to protect it against any dust during launch. We can add that apart from having to handle the launch constraints, the hostile space environment, space telescopes must always retain the same precision. They must be very stable, knowing that they were tested on earth within a gravitational environment, whereas they will be operating in a weightless state up above. And finally, they have to be equipped with the full range of instruments to perceive the electromagnetic spectrum (X-rays, infrared), with the Earth’s atmosphere naturally filters out when we are on earth.

What fascinates you the most in the incredible Herschel project?

Technically it is undeniably a great achievement. In order not to be “dazzled” by the thermal rays, the telescope itself and all the instruments must be kept refrigerated throughout the satellite’s life at a temperature of –271 degrees Celsius, just two degrees Celsius from absolute zero, which is theoretically the lowest temperature possible. From a more astronomical point of view, I have to tell you that not only is it cold in space, but that the items located between the stairs are also very cold. That means that they are emitting in a part of the electromagnetic spectrum characterised by very long wavelengths. As a result, all the equipment onboard the satellite has to be as cold as the objects that interest us. Otherwise, you would not be able to observe them, because the radiation you are producing would be stronger than that emitted by these objects. In a word, you would be blind. It is extremely interesting to look at these objects, because they will teach us how stars are formed, a phenomenon often hidden in clouds of black dust. We will also be able to see clouds of interplanetary dust and from comets. Comets are my favourites because they are always surprising.