• Chris Baker

A quick Update on the JWT

Updated: Dec 22, 2021

The James Webb Space Telescope

Introduction

In my original article I explained how Santa would be coming early, December 22nd in fact, as the James Webb Telescope was due for launch that day. But here we are with a few more delays. However, there is good news as it is now scheduled for Christmas Day at 12:25 pm - after your first glass of wine but maybe just prior to lunch! (If you are in the northern hemisphere!)


In any case I will send you an update on Christmas Day so if you want to watch it LIVE then I will supply a link.


This is the launch date of the long-awaited James Webb Space Telescope (JWST) – the replacement for the Hubble Space Telescope, launched 30 years ago. It has been jointly developed by NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA).


Illustration of the James Webb Telescope


This hugely ambitious project is over-budget to the tune of ten billion $’s and at least a decade late, but here we are, finally ready to fly.


What is it?

Like the Spitzer, Kepler and Hubble observatories, it is a telescope based in space. Here, the seeing conditions are optimal as the weather never changes - there is none! And there is no atmosphere to look through and disturb the faint photons arriving from afar.

On one side of the instrument there is an array of mirrors, each individually controlled, forming one large mirror 6.5 metres in diameter. This compares to the Hubble mirror of 2.4 meters. This mirror captures the light and delivers it to a range of different cameras, each designed to measure different wavelengths of light.

The light being captured is extremely faint and primarily at infra-red wavelengths – basically that of heat- therefore the mirror and instruments need to be shielded from the light and heat generated from the sun, earth, moon and the telescope itself. So there is a huge shield between the sun-facing side of the observatory and the gigantic mirror, looking deep into space.


Illustration showing the enormous sun-shield.


The sunshield separates the observatory into a warm, sun-facing side which will reach approximately 230 degrees F, and a cold side where the instruments are located, down to -394 degrees F ! The five-layer sunshield keeps sunlight from interfering with the sensitive telescope instruments. The telescope operates at around-370F.


Where will it hang-out?

The JWST will be in a completely different orbit to any other space telescopes. For example, the Hubble telescope is in an orbit around the earth at a height of about 343 miles and completes one earth orbit every 97 minutes. This ‘low altitude’ orbit has allowed for service missions, including upgrading the cameras and fixing the mirrors over its 30 year lifetime.

However, the JWST is going somewhere completely different, at a point over 1 million miles from earth and will never be serviced at this vast distance. No human has gone beyond the distance to the moon which is about 250,00 miles.


Illustration showing the position of the JWST


The telescope will not orbit the earth but follow the earth’s path around the sun at a point called L2.

There are a number of what are called ‘Lagrange Points’ - these are specific positions around the earth where the gravity from the earth, moon and sun is in balance. Therefore objects placed at these points move in a continuous stable orbit around the sun and in a fixed position relative to the earth. This is important to maintain the shield in a fixed position against the sun(light).

The instruments operate at an exceptionally low temperature and the JWST will actually orbit the L2 point,