Telescope

Warning: If you are interested in astronomy and astrophysics, you might find this interesting (or you might not). If you are not interested in astronomy and astrophysics, you will probably find this to be an excellent cure for insomnia. And that’s okay. I’m writing this more for me than anyone else because I think the science behind this is incredible!

I saw a fascinating program the other night and I just watched it again. It has my inner nerd bouncing off the walls. The program is called “Telescope” and it is about the design and construction of the James Webb Space Telescope (JWST). The JWST is the next step in the evolution of space telescopes beyond Hubble. It is necessary because, believe it or not, the Hubble Space Telescope (HST) has already reached some of its design limitations.

Hubble

To understand just how far JWST can take science, you first need to have an appreciation for just how far HST has already gone.

Hubble, the telescope and the man, are both incredible stories in and of themselves. The Hubble Space Telescope is named after Dr. Edwin Hubble, one of the few scientists to ever successfully convince Albert Einstein that he was wrong about something and needed to change his theories. Hubble was the man who discovered that there were other galaxies beyond our own Milky Way and that the universe was expanding.

Conventional science of the early 20^th century held that all matter in the universe existed within this one galaxy (it wasn’t even called a galaxy yet). Astronomers noticed that there were odd smudges at certain locations in the sky and they named one of the largest Andromeda. Even though it was unusual, it was just presumed to be some sort of gas or dust cloud that existed within the bounds of the Milky Way and no-one paid much attention to it. But it interested Edwin Hubble.

On closer examination of Andromeda, Hubble found that there were more than ordinary stars within “the dust cloud.” Hubble also found variable stars called Cepheid stars – stars that vary in brightness. In 1912, a Harvard scientist named Henrietta Leavitt had discovered that you could use Cepheids to measure distance. Hubble used Leavitt’s formula to calculate that Andromeda was approximately 900,000 light years away – well beyond the boundaries of the Milky Way.

Later on, other scientists would discover that Hubble had actually been comparing two different kinds of Cepheids – bright ones in Andromeda and dimmer ones in the Milky Way. When they began comparing like to like, they discovered that Andromeda was actually more than twice as far away as Hubble had determined – 2,000,000 light years. As the techniques to measure celestial distances have improved, we now know that Andromeda is actually 2.5 million light years from Earth. (Here’s a term you might use to impress your kids (but probably not). Tell them that that’s 780 kiloparsecs. (Just a tad further than the Kessel Run))

After his Andromeda discoveries, Hubble went on to measure the Doppler shift on these newly discovered galaxies and discovered something else that no-one was expecting. The galaxies were shifted well into the red and were actually moving away from us. And the further away they were, the faster they were moving. This was groundbreaking. At the time, Einstein had proposed a closed universe with immense but finite dimensions. Hubble had just proved that the universe was not only vastly larger than previously believed but it was also still expanding – potentially infinite. As a consequence, Einstein changed his theory and threw away the idea of a closed universe.

In his book, A Brief History of Time, Stephen Hawking wrote that “Hubble's discovery that the Universe is expanding was one of the great intellectual revolutions of the 20th century." High praise, indeed. Hubble’s work also allowed scientists to make the first calculations on the age of the universe.

These are just the tip of the iceberg on Edwin Hubble’s accomplishments so it should be little wonder that when the first space telescope was built it was named after him. Unfortunately, the HST got off to a less than auspicious start. Launched in April, 1990, and costing over $2,000,000,000 (that’s billion – with a “b”), the HST was expected to rewrite our knowledge of the universe. When it transmitted its first images back to Earth they were fuzzy and out of focus. The telescope was, for all intents and purposes, useless. The primary mirror had something called a spherical aberration. If you are into photography, you might know something about aberrations. There are two basic kinds, spherical and chromatic. They are the main reason that professional grade camera lenses (the kind I lust after on a regular basis) cost as much as they do. Lens manufacturers spend a fortune on special glass made of special materials, grind it to the highest accuracy possible and align the elements to tolerances measured in microns. And Hubble, the most complex and expensive camera and lens ever built, had a spherical aberration. The shallow dish that brings light to a focus was a little too shallow, by roughly half the width of a human hair. But when the focal point is trillions of miles away, that was all it took to render the telescope unfocusable.

A Trip To The Optometrist

The way they fixed Hubble was a stroke of genius. They essentially gave it glasses!

Light from the primary mirror enters a camera (if you want to be technical, it’s called the WFPC for wide field and planetary camera). There it strikes another mirror that creates the final image. They designed a new secondary mirror for the camera with an identical but reversed aberration – just like fitting your eyes with a pair of corrective lenses. And just like that the problem was solved. Hubble was designed to undergo routine service every 3 years by shuttle astronauts, so changing out the camera was not an insurmountable task. And the HST has been taking science “where no-one has gone before” ever since. It has been a spectacular success!

Hubble gave us our first look at exoplanets (planets outside our own solar system). It gave us images of galaxies colliding and helped scientists understand the kinds of energies being released in these collisions. It discovered the existence of 2 moons near (the no longer a planet) Pluto. It showed us the first proof of black holes at the centre of galaxies and was the key tool used to gain an understanding of the increasing rate of expansion of the universe and the need for some kind of force to power this expansion. That force has since been named “dark energy.”

But its greatest achievement (IMHO) is the Hubble Deep Field.

The Deep Field is arguably one of the greatest accidents in the history of science. And it happened totally on what can only be described as a whim. One of the people in charge of the Hubble program decided it might be interesting to image a spot in space where there appeared to be nothing at all – just a big black empty. They pointed the telescope at a dark spot in the sky roughly the size of a drinking straw. Imagine looking up at the night sky and holding up a straw and looking through that. That’s the size of the spot they looked at. They focused the camera on that one spot and left it there for 10 days.

The man who made the decision to do this was heavily derided for it. It was a waste of valuable telescope time… we already know there’s nothing there…. yada yada yada. That all changed when they saw the result. Hubble did discover three new stars within the Milky Way but it was what was behind the three stars that astonished everyone. Fading off into the distance beyond the Milky Way were over 10,000 galaxies! Ten THOUSAND! In an area the size of a drinking straw! Prior to this, astronomers believed that there were thousands of galaxies in the entire universe. If there were 10,000 in this tiny space, extrapolate that to the entire sky and…. with a single image, thousands became billions. Astronomers now estimate that there are roughly 100 billion galaxies in the universe and the current estimate of the total stellar population is roughly 70 billion trillion (7 x 10²²) stars.

So, in terms of swinging for the fence, the Deep Field was Hubble’s home run. It nailed it. Out of the park. But in doing so, it also moved the fence much further away. It demonstrated that there is much more to see out there but to do so we will have to look much further away and much deeper into the past and, unfortunately, Hubble has now seen as far as it will ever see.

Hubble’s biggest limitation (if you can call it a limitation) is that it only sees visible light and very slightly into the infrared and ultraviolet. In the Deep Field it saw as far as you can see using visible light. To see even further, it is necessary to move to the end of the spectrum – the infrared. And that’s where the JWST comes in. Long before the Deep Field, scientists were already working on the next generation of space telescope, one that would only see infrared. They knew the day would come and the Deep Field just illustrated that the day had arrived.

James Webb

The JWST is designed to capture infrared light. Where the Hubble stops, the James Webb begins. It uses the most sensitive sensors ever developed. Its sensors are over 100 times more sensitive than Hubble’s. How sensitive is that? It can detect the heat of a child’s nightlight from the moon.

The further away from the Milky Way another galaxy is, the faster it is moving away from us and it reaches a point where all light emitted from it is so heavily shifted into the infrared that there is nothing to see in the visible spectrum at all. This is called the Doppler Effect. It’s the reason that the sound of cars and trains change pitch as they pass by. It works the same way for light. If something is moving away, it shifts into the red and, if moving fast enough, into the infrared. If it is moving toward you, it shifts into the blue or the ultraviolet.

Since Hubble only sees the visible spectrum, it can’t detect the farthest galaxies. But the JWST’s infrared sensors can. The deeper you look into space, the further back in time you are looking. For example, if Andromeda is 2.5 million light years away, that means that we are seeing light that was emitted 2.5 million years ago. The JWST will be capable of looking across billions of light years and that means looking back billions of years in time. The universe is 13.7 billion years old. Scientists expect that they will be able to see back to when the universe was a mere 250 million years old. Almost the initial moments of the universe. If Webb can pull off the infrared equivalent of the Hubble Deep Field, well, wouldn’t that be cool to look at!

The two telescopes are extremely different and those differences are very important to how they function. Hubble’s mirror is 8 feet in diameter, made of polished glass and only gathers visible light. Webb’s mirror is 32 feet in diameter, made of beryllium coated with a thin layer of gold and only sees infrared. Hubble orbits the Earth 354 miles up – easily accessible via space shuttle for repairs, adjustments and routine service. Webb will orbit the sun, not the Earth, at a place called L2, one of Earth’s five Lagrange points, located 930,000 miles outside Earth’s orbit. At a location 4 times further away than the moon, there will be no service calls and no second chances to get it right. If it doesn’t work right the first time, it’s done.

Lagrange

Just by way of definition, a Lagrange point is simply a point in space where the gravitational forces of two large objects work together to precisely balance the motion of a third, smaller object. The Earth has 5 such points. In simplest terms, if an object much smaller than Earth was orbiting the Sun in an orbit outside the Earth’s, it would move much more slowly than Earth. If it was a satellite, the Earth would quickly leave it behind and contact would be lost. But the L2 Lagrange point is different because there are 2 gravitational forces working in unison there. If you draw a straight line from the centre of the Sun through the centre of the Earth and keep going for an additional 930,000 miles, you will reach a point where the aligned gravitational pulls of the Sun and the Earth combine to create a point of stability. Any satellite placed at this point will stay fixed in place in relation to the Earth’s orbit. 

If you are familiar with Arthur C. Clarke’s Space Odyssey series of books and/or the movies (and you probably are if you’re still reading this and haven’t bailed out to go in search of something more interesting like funny cat videos) then you’ve heard of Lagrange points before. The 3^rd monolith orbits Jupiter at a Lagrange point between the planet and its moon, Io.

The decision to locate the telescope at L2 was made for several reasons. The Hubble Space Telescope orbits the Earth where it goes in and out of the Earth's shadow every 90 minutes. Hubble's view is blocked by the Earth for part of each orbit, limiting where the telescope can look at any given time. By placing Webb at L2, the sun and the Earth will be in the same part of the sky. The telescope will be oriented away from the inner solar system where it will have an unimpeded view of the universe and be insulated from both direct and background radiation from the Sun, Earth and Moon.

Secondly, the JWST views the universe entirely in infrared light and infrared is essentially another word for radiated heat. To give the telescope the best chance of detecting distant, dim objects in space, it needs to be kept as cold as possible. Even heat from its own on-board electronics could potentially affect its ability to see. When hidden from direct sunlight, the temperature at L2 is a balmy -225C. Even with temperatures that low, the telescope will still require an elaborate, 5-layer heat shield to protect it from sunlight and earthlight. Its electronics will also be located on the back of the heat shield to further insulate the sensors from extraneous sources of heat.

The Origami Telescope

The other major difference between Hubble and Webb is that Hubble‘s 8-foot mirror is made from a single piece of glass. Webb’s 32-foot mirror is segmented into 18 pieces and folds up. This is necessary because there is no launch vehicle currently capable of carrying something that wide into orbit. So, in order to get it into space, it must be folded up and then unfold itself once it reaches its destination. The Webb team has nicknamed their telescope “the origami telescope.” There are 189 unfolding operations that must be completed before Webb is ready to begin operation. And they all have to work perfectly. Fortunately, technology has made huge advancements in the almost 30 years since Hubble’s mirror was made. Earlier, when I was talking about Hubble’s spherical aberration, I mentioned “when the focal point is trillions of miles away…..” Trillions is actually grossly understating it. One light year is approximately 5.8 trillion miles. Hubble has already looked out 13.2 billion light years. Multiply 13.2 times 5.8, then add 9 zeroes, then add 12 more. That’s a lot of zeroes. Webb is going to look even further. Hubble was rendered inoperative by an aberration that was measured in fractions of the width of a human hair. Webb’s mirrors are so perfect that, if you spread one of them out from New York to California, there would be no deviation, no hill or valley, greater than 3 inches.

When they were interviewing engineers during the documentary, I was surprised to hear a few of them refer to DK². That is a term that I am all too familiar with. I used it a lot when I was a techie. It refers to things that are so far out there that you don’t even know that you need to know them – you don’t know what you don’t know. When you are working on something new and innovative, there are lots of unknowns. It’s one thing to know that there are missing pieces of information. You can do the research and get the answers you need as long as you know you need them. But what about the things that you don’t even realize you need to know? Questions that no-one even thinks about asking?

When I worked in I.T., I was involved in some pretty bizarre application designs and I was responsible for a lot of new technology development and deployment. When I was a techie at GWL in the ‘80s and ‘90s, we were technology cowboys. The company was way out ahead of the curve on technology and we did things that even IBM told us were impossible. We wrote code that intercepted and modified mainframe operating system service calls called SVCs. I personally wrote 9000 lines of (perfectly documented) code that inserted itself between database access requests and the actual DataBase Management System to change the way the DBMS managed itself and the way it delivered data back to the application. They were “impossible”, we were told. But we did them anyways and we made them work. We did some really cool stuff but, at the end of the day, we were just writing computer code, child’s play compared to the Webb telescope. They have the best people on the planet building Webb and even they worry about potential problems that they have failed to anticipate. One of them referred to it as a “failure of imagination. A failure to imagine something that we could have fixed on the ground.” I can’t even imagine the kind of pressure they feel knowing that they have to get it absolutely right the first time. Batting .999 isn’t good enough. They have to bat 1.000.

What’s Next

The JWST has four primary goals:

• Detect some of the very first star formations in the Universe. To do this, Webb will have to see objects when the universe was only 2% of its current age – more than 13.5 billion years ago and over 13.5 billion light-years away.
• Determine how galaxies evolved from their formation until the present. This will entail significant studies of dark matter including gaining a deeper understanding of the amount and nature of dark matter in galaxies and the role that dark matter plays in galactic evolution.
• Observe the formation of stars from their initial stages through to the formation of planetary systems.
• Measure the physical and chemical properties of planetary systems and investigate the potential for life in those systems.

The JWST launches in October, 2018. It will take about a month to reach L2 and then spend about 4 months undergoing initial tests. Then the real science will begin. And it doesn’t end there. Webb’s successor is already on the drawing boards. WFIRST, the Wide-Field Infrared Survey Telescope (what a mouthful!), is a space observatory designed to answer questions in both exoplanet and dark energy research.

The knowledge that is about to be unlocked is staggering. Personally, I cannot wait!