The James Webb Space Telescope

Podcast Transcript

Sometime within the next week of my recording this episode, hopefully, a rocket will be launched from the European Space Agency’s launch facility in French Guyana.

On it will be NASA’s latest and greatest space telescope. It is unlike anything which has ever been launched into space before, and if successful, it will allow us to see further than we ever have.

Learn more about the James Webb Space Telescope and how it will radically advance astronomy, on this episode of Everything Everywhere Daily.

If you are familiar with space telescopes, you are probably familiar with the Hubble Space Telescope. The Hubble looks like a telescope. There is a mirror at the bottom of a long tube, has some solar panels on the side, and it zips around in Earth’s orbit.

The Hubble’s mirror is 2.4 meters or 7 feet 10 inches in diameter. Since it was launched into orbit on the Space Shuttle 31 years ago, it has revolutionized astronomy.

Putting a telescope in space has tons of advantages over ground-based telescopes. Space telescopes operate in the vacuum of space and never have to worry about atmospheric interference. There is no dust that will collect on the mirror. You never have to worry about cloud cover.

The Hubble is located in low Earth orbit about 570 kilometers above the surface of the Earth, and it is zipping around the world about once every 90-minutes.

If you have ever seen an image with hundreds of galaxies in it, it was probably taken by the Hubble.

The Hubble hasn’t been the only space telescope. There have been dozens of space telescopes of many different varieties which have been launched that observe everything from gamma rays to radio waves.

Before the Hubble was even launched back in 1990, there were already plans for a successor space telescope. Throughout the 90s, astronomers debated about what a Hubble successor would look like.

At first, the plan was to create a $500 million dollar low-cost telescope.

However, as these things tend to do, the scope and budget of the project increased. What they ended up proposing was something incredibly audacious.

The proposed telescope was called the James Webb, which was named after NASA’s second administrator, who lead the space program through the Apollo era. The telescope is a joint project of the Canadian Space Program, the European Space Agency, and NASA as the lead organization.

The telescope would be designed to observe the infrared spectrum of light.

Here I should explain why they wanted to observe infrared light as opposed to visible light.

If you’ve ever heard an automobile or a train approach you and then move away, you’ve probably experienced the Doppler effect. As the vehicle approaches you the pitch gets higher, and as it goes away the pitch gets lower. The sound isn’t actually changing, but the sound is perceived to change to you because the sound waves are compressed as it approaches, and elongated as it goes away.

Light is also a wave, and when a light-emitting object moves away from something, its wavelength will also elongate in the same way that sound waves do.

This is called a redshift. The light waves are elongating and move to the red or infrared parts of the spectrum.

The light sources from the most distant parts of the universe are moving away from us the fastest and it is the light that is the most redshifted.

So, if we want to observe things extremely far away, we have to create a telescope designed for infrared light, because that is what all the visible light has turned into.

The next thing about the James Webb is that mirror is really large. Light from the farthest reaches of the universe is extremely faint, and you need a large mirror to gather that much light.

The James Webb’s mirror is 6.5 meters in diameter, which means it will have a light gathering area over 6 times larger than Hubble’s mirror. The total power of the telescope, once everything is considered, will be 100x that of the Hubble.

The problem is, how do you get a mirror that large into space? The Hubble mirror is one solid, circular piece of honeycombed glass coated in aluminum.

A 6.5-meter diameter mirror can’t fit on a rocket.

The solution was to create a collection of hexagonal mirrors, 18 in total, made out of beryllium and plated in gold. The reason why the mirror is segmented like a honeycomb is that it can be folded for launch.

Because the mirror is folded, it can’t be put into a tube, like the Hubble. It is exposed to open space.

Because it isn’t in a tube it creates another problem.

Infrared light is what we also call heat. If you put a mirror in space, it is going to be exposed to extraneous infrared light from the sun, the Earth, and even reflected light from the moon.

In order for the instruments to work and not be overwhelmed by heat coming off the spacecraft itself, it has to be kept cool. Very cool. To be specific, it has to be kept to under 50 K, or ?223 °C, or ?369 °F.

So, how do you keep everything cool? Even though space is pretty cold, for something like this you need to block the heat coming from the Earth and the Sun.

That is why the James Webb is equipped with a large sun shield. The shield is about the size of a tennis court and is made of five layers of a lightweight material called Kapton E, which is thinner than a human hair.

As with the mirror, a sun shield the size of a tennis court can’t be put into a rocket. Just like with the mirror, the solution was to fold it.

There is one other thing that the James Webb is doing that is rather unique. It isn’t going to be put in Earth’s orbit. It is going to be located at Lagrange point 2.

Now you might be asking, what are Lagrange points? Lagrange points are areas in a system of two gravitationally massive bodies where the attraction of the bodies and the centripetal force of the object balance out.

There are five Lagrange points for any two-body system. There are five for the Earth-Sun, and there are five for the Earth-Moon. They are known as L1 through L5.

The James Webb will be located at the L2 for the Earth-Sun system. This is located well beyond the moon, approximately 1.5 million kilometers from Earth. Once it is parked there, it will basically sit there, gravitationally bound. It will be far enough away that, together with the sun shield, it shouldn’t have too much exposure from heat from the Earth or the Moon.

If this all sounds really complicated, that’s because it is.

There are a whole bunch of things going on, many of which have never been done before. That is why the James Webb has been chronically late with constant delays. The original launch date was supposed to be in 2011.

One study of the program found that there were 344 single-point failures with the telescope. That means 344 things which if any of them went wrong, the entire mission would fail.

The big reason for the delays is that $10 billion dollars and 20 years of astronomy are all riding on this one mission.

The first obstacle is that the whole thing has to be launched into space, which is never a risk-free endeavor. If it blows up on the launchpad.

Then it has to go to Lagrange Point 2. To put this into perspective, the moon is 385,000 kilometers away, and L2 is 1,500,000 kilometers away. The entire transit time will take a month given the difficult orbital dynamics of getting to L2.

While it is en route, it will begin to deploy. This is basically unfolding everything in a version of space origami. It will take most of the month of traveling to L2 for the telescope to unfold. First, the delicate sun shield will slowly unfold, and then finally the mirror itself.

Assuming everything goes right, it will be another 6 months of testing and calibrating everything before the first real observations can take place.

Unlike the Hubble, which is in low earth orbit, we can’t really send astronauts up to fix it if something goes wrong. There were five different space shuttle missions sent to service the Hubble. That is impossible for something which is over four times the distance from the moon.

So, if you are listening to this around when this episode was released, hopefully on Christmas Eve the James Webb will be launched into space.

…and, if everything goes according to plan, and I hope it does, sometime around May or June 2022, we should be getting our first glimpses of the most distant reaches of the universe.