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8 Common Questions About Our James Webb Space Telescope

You might have heard the basics about our James Webb Space Telescope, or Webb, and still have lots more questions! Here are more advanced questions we are frequently asked. (If you want to know the basics, read this Tumblr first!)

Webb is our upcoming infrared space observatory, which will launch in 2021. It will spy the first luminous objects that formed in the universe and shed light on how galaxies evolve, how stars and planetary systems are born, and how life could form on other planets.

1. Why is the mirror segmented? 

The James Webb Space Telescope has a 6.5-meter (21.3-foot) diameter mirror, made from 18 individual segments. Webb needs to have an unfolding mirror because the mirror is so large that it otherwise cannot fit in the launch shroud of currently available rockets.

The mirror has to be large in order to see the faint light from the first star-forming regions and to see very small details at infrared wavelengths. 

Designing, building, and operating a mirror that unfolds is one of the major technological developments of Webb. Unfolding mirrors will be necessary for future missions requiring even larger mirrors, and will find application in other scientific, civil, and military space missions.

2. Why are the mirrors hexagonal?

In short, the hexagonal shape allows a segmented mirror to be constructed with very small gaps, so the segments combine to form a roughly circular shape and need only three variations in prescription. If we had circular segments, there would be gaps between them.

Finally, we want a roughly circular overall mirror shape because that focuses the light into the most symmetric and compact region on the detectors. 

An oval mirror, for example, would give images that are elongated in one direction. A square mirror would send a lot of the light out of the central region.

3. Is there a danger from micrometeoroids?

A micrometeoroid is a particle smaller than a grain of sand. Most never reach Earth's surface because they are vaporized by the intense heat generated by the friction of passing through the atmosphere. In space, no blanket of atmosphere protects a spacecraft or a spacewalker.

Webb will be a million miles away from the Earth orbiting what we call the second Lagrange point (L2). Unlike in low Earth orbit, there is not much space debris out there that could damage the exposed mirror. 

But we do expect Webb to get impacted by these very tiny micrometeoroids for the duration of the mission, and Webb is designed to accommodate for them.

All of Webb's systems are designed to survive micrometeoroid impacts.

4. Why does the sunshield have five layers?

Webb has a giant, tennis-court sized sunshield, made of five, very thin layers of an insulating film called Kapton.  

Why five? One big, thick sunshield would conduct the heat from the bottom to the top more than would a shield with five layers separated by vacuum. With five layers to the sunshield, each successive one is cooler than the one below. 

The heat radiates out from between the layers, and the vacuum between the layers is a very good insulator. From studies done early in the mission development five layers were found to provide sufficient cooling. More layers would provide additional cooling, but would also mean more mass and complexity. We settled on five because it gives us enough cooling with some “margin” or a safety factor, and six or more wouldn’t return any additional benefits.

Fun fact: You could nearly boil water on the hot side of the sunshield, and it is frigid enough on the cold side to freeze nitrogen!

5. What kind of telescope is Webb?

Webb is a reflecting telescope that uses three curved mirrors. Technically, it’s called a three-mirror anastigmat.

6. What happens after launch? How long until there will be data?

We’ll give a short overview here, but check out our full FAQ for a more in-depth look.

In the first hour: About 30 minutes after liftoff, Webb will separate from the Ariane 5 launch vehicle. Shortly after this, we will talk with Webb from the ground to make sure everything is okay after its trip to space.

In the first day: After 24 hours, Webb will be nearly halfway to the Moon! About 2.5 days after launch, it will pass the Moon’s orbit, nearly a quarter of the way to Lagrange Point 1 (L2).

In the first week: We begin the major deployment of Webb. This includes unfolding the sunshield and tensioning the individual membranes, deploying the secondary mirror, and deploying the primary mirror.

In the first month: Deployment of the secondary mirror and the primary mirror occur. As the telescope cools in the shade of the sunshield, we turn on the warm electronics and initialize the flight software. As the telescope cools to near its operating temperature, parts of it are warmed with electronic heaters. This prevents condensation as residual water trapped within some of the materials making up the observatory escapes into space.

In the second month: We will turn on and operate Webb’s Fine Guidance Sensor, NIRCam, and NIRSpec instruments. 

The first NIRCam image, which will be an out-of-focus image of a single bright star, will be used to identify each mirror segment with its image of a star in the camera. We will also focus the secondary mirror.

In the third month: We will align the primary mirror segments so that they can work together as a single optical surface. We will also turn on and operate Webb’s mid-infrared instrument (MIRI), a camera and spectrograph that views a wide spectrum of infrared light. By this time, Webb will complete its journey to its L2 orbit position.

In the fourth through the sixth month: We will complete the optimization of the telescope. We will test and calibrate all of the science instruments.

After six months: The first scientific images will be released, and Webb will begin its science mission and start to conduct routine science operations.

7. Why not assemble it in orbit?

Various scenarios were studied, and assembling in orbit was determined to be unfeasible.

We examined the possibility of in-orbit assembly for Webb. The International Space Station does not have the capability to assemble precision optical structures. Additionally, space debris that resides around the space station could have damaged or contaminated Webb’s optics. Webb’s deployment happens far above low Earth orbit and the debris that is found there.

Finally, if the space station were used as a stopping point for the observatory, we would have needed a second rocket to launch it to its final destination at L2. The observatory would have to be designed with much more mass to withstand this “second launch,” leaving less mass for the mirrors and science instruments.

8. Who is James Webb?

This telescope is named after James E. Webb (1906–1992), our second administrator. Webb is best known for leading Apollo, a series of lunar exploration programs that landed the first humans on the Moon. 

However, he also initiated a vigorous space science program that was responsible for more than 75 launches during his tenure, including America's first interplanetary explorers.

Looking for some more in-depth FAQs? You can find them HERE.

Learn more about the James Webb Space Telescope HERE, or follow the mission on Facebook, Twitter and Instagram.

Make sure to follow us on Tumblr for your regular dose of space!

10 Frequently Asked Questions About the James Webb Space Telescope

Got basic questions about the James Webb Space Telescope and what amazing things we’ll learn from it? We’ve got your answers right here! 

The James Webb Space Telescope, or Webb, is our upcoming infrared space observatory, which will launch in 2021. It will spy the first luminous objects that formed in the universe and shed light on how galaxies evolve, how stars and planetary systems are born, and how life could form on other planets.

1. What is the James Webb Space Telescope?

Our James Webb Space Telescope is a giant space telescope that observes infrared light. Rather than a replacement for the Hubble Space Telescope, it’s a scientific successor that will complement and extend its discoveries.

Being able to see longer wavelengths of light than Hubble and having greatly improved sensitivity will let Webb look further back in time to see the first galaxies that formed in the early universe, and to peer inside dust clouds where stars and planetary systems are forming today.

2. What are the most exciting things we will learn?

We have yet to observe the era of our universe’s history when galaxies began to form. 

We have a lot to learn about how galaxies got supermassive black holes in their centers, and we don't really know whether the black holes caused the galaxies to form or vice versa.

We can't see inside dust clouds with high resolution, where stars and planets are being born nearby, but Webb will be able to do just that. 

We don't know how many planetary systems might be hospitable to life, but Webb could tell whether some Earth-like planets have enough water to have oceans.

We don't know much about dark matter or dark energy, but we expect to learn more about where the dark matter is now, and we hope to learn the history of the acceleration of the universe that we attribute to dark energy. 

And then, there are the surprises we can't imagine!

3. Why is Webb an infrared telescope?

By viewing the universe at infrared wavelengths with such sensitivity, Webb will show us things never before seen by any other telescope. For example, it is only at infrared wavelengths that we can see the first stars and galaxies forming after the Big Bang. 

And it is with infrared light that we can see stars and planetary systems forming inside clouds of dust that are opaque to visible light, such as in the above visible and infrared light comparison image of the Carina Nebula.

4. Will Webb take amazing pictures like Hubble? Can Webb see visible light?

YES, Webb will take amazing pictures! We are going to be looking at things we've never seen before and looking at things we have seen before in completely new ways.

The beauty and quality of an astronomical image depends on two things: the sharpness and the number of pixels in the camera. On both of these counts, Webb is very similar to, and in many ways better than, Hubble. 

Additionally Webb can see orange and red visible light. Webb images will be different, but just as beautiful as Hubble's. Above, there is another comparison of infrared and visible light Hubble images, this time of the Monkey Head Nebula.

5. What will Webb's first targets be?

The first targets for Webb will be determined through a process similar to that used for the Hubble Space Telescope and will involve our experts, the European Space Agency (ESA), the Canadian Space Agency (CSA), and scientific community participants.

The first engineering target will come before the first science target and will be used to align the mirror segments and focus the telescope. That will probably be a relatively bright star or possibly a star field.

6. How does Webb compare with Hubble?

Webb is designed to look deeper into space to see the earliest stars and galaxies that formed in the universe and to look deep into nearby dust clouds to study the formation of stars and planets.

In order to do this, Webb has a much larger primary mirror than Hubble (2.5 times larger in diameter, or about 6 times larger in area), giving it more light-gathering power. It also will have infrared instruments with longer wavelength coverage and greatly improved sensitivity than Hubble. 

Finally, Webb will operate much farther from Earth, maintaining its extremely cold operating temperature, stable pointing and higher observing efficiency than with the Earth-orbiting Hubble.

7. What will Webb tell us about planets outside our solar system? Will it take photos of these planets?

Webb will be able to tell us the composition of the atmospheres of planets outside our solar system, aka exoplanets. It will observe planetary atmospheres through the transit technique. A transit is when a planet moves across the disc of its parent star. 

Webb will also carry coronographs to enable photography of exoplanets (planets outside our solar system) near bright stars (if they are big and bright and far from the star), but they will be only "dots," not grand panoramas. Coronographs block the bright light of stars, which could hide nearby objects like exoplanets.

Consider how far away exoplanets are from us, and how small they are by comparison to this distance! We didn’t even know what Pluto really looked like until we were able to send an observatory to fly right near it in 2015, and Pluto is in our own solar system!

8. Will we image objects in our own solar system?

Yes! Webb will be able to observe the planets at or beyond the orbit of Mars, satellites, comets, asteroids and objects in the distant, icy Kuiper Belt.

Many important molecules, ices and minerals have strong characteristic signatures at the wavelengths Webb can observe. 

Webb will also monitor the weather of planets and their moons. 

Because the telescope and instruments have to be kept cold, Webb’s protective sunshield will block the inner solar system from view. This means that the Sun, Earth, Moon, Mercury, and Venus, and of course Sun-grazing comets and many known near-Earth objects cannot be observed.

9. How far back will Webb see? 

Webb will be able to see what the universe looked like around a quarter of a billion years (possibly back to 100 million years) after the Big Bang, when the first stars and galaxies started to form.

10. When will Webb launch and how long is the mission?

Webb will launch in 2021 from French Guiana on a European Space Agency Ariane 5 rocket. 

Webb’s mission lifetime after launch is designed to be at least 5-1/2 years, and could last longer than 10 years. The lifetime is limited by the amount of fuel used for maintaining the orbit, and by the possibility that Webb’s components will degrade over time in the harsh environment of space.

Looking for some more in-depth FAQs? You can find them HERE.

Learn more about the James Webb Space Telescope HERE, or follow the mission on Facebook, Twitter and Instagram.

IMAGE CREDITS Carina Nebula: ESO/T. Preibisch Monkey Head Nebula: NASA, ESA, the Hubble Heritage Team (STScI/AURA), and J. Hester

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10 “Out of This World" Facts About the James Webb Space Telescope

Wouldn’t it be neat to see a period of the universe’s history that we’ve never seen before? That’s exactly what the James Webb Space Telescope (JWST) will be able to do…plus more!

Specifically, Webb will see the first objects that formed as the universe cooled down after the Big Bang. We don’t know exactly when the universe made the first stars and galaxies – or how for that matter. That is what we are building Webb to help answer.

Here are 10 awesome facts about this next generation space telescope:

1. The James Webb Space Telescope is the world’s largest and next premier space observatory. It will extend the discoveries of the Hubble Space telescope and observe the birthplaces of stars, galaxies, planets and life over billions of years.

2. It is named after James Webb, NASA’s second administrator and champion of our science.

3. At 3 stories high and the size of a tennis court, it will be 100 times more powerful than Hubble!

4. It is so big that it has to fold origami-style to fit in the rocket, which is only 5.4 meters wide...And then it will unfurl, segment by segment, once in space.

5. The telescope will observe infrared light with unprecedented sensitivity. It will see the first galaxies born after the Big Bang over 13.5 billion years ago.

6. Webb's infrared cameras are so sensitive they must be shielded from light from the sun, Earth, and moon. The 5-layer sunshield is like having sunblock of SPF 1 million.

7. Webb will orbit the sun 1 million miles from Earth, where the telescope will operate at temperatures below -390 F (-235 C).

8. Webb’s mirrors are coated with a super thin layer of gold only about 1000 atoms thick to optimize their reflectivity in the infrared.

9. Webb will launch from French Guiana in 2018. It is launched near the equator because the faster spin of Earth there gives the rocket an extra push.

10. Webb is an international mission, with contributions from the European Space Agency and Canadian Space Agency. Once operational, scientists from all over the world will be able to use Webb to explore our solar system, planets outside our solar system, stars and galaxies.

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com