on the Status of JWST

The James Webb Space Telescope isn’t actually complete yet, but its mirror is now together. As has been stressed repeatedly in places like Twitter, this sight isn’t an unfamiliar one, but this time it’s not a model or a computer animation… it’s the real thing. And that means the James Webb Space Telescope (JWST) is actually happening!

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The James Webb Space Telescope, in its hangar at NASA’s Goddard Spaceflight Center. From the James Webb Space Telescope’s flickr account.

To understand the community’s surprise at what would appear to have been inevitable, you have to realize that space projects – large space projects, particularly – move incredibly slowly. We’re talking on the level of Boston’s Big Dig, which took 25 years. The Hubble Space Telescope was being planned (as “Space Telescope”) since 1972, was ready to launch in 1986, and finally launched in 1990. Various forms of a Pluto probe were proposed, starting in the mid-1980s before the New Horizons project was successful up to launch. A successor to Hubble was proposed in 1989, before Hubble even flew; the first concept was eventually replaced with what is now called James Webb. (And the successor to JWST is already being planned)

The telescope itself is going to be a marvel. It will be the largest telescope to ever fly in space, with a 6.5 meter aperture: larger than most telescopes on Earth, and much larger than the 2.4 meter Hubble Space Telescope. As a result of that decision, JWST will only fit into a rocket if it’s folded up, which means large mechanical subsystems will have to work exactly right to unfold it and very precisely align it once it reaches its intended orbit around the Sun. Needless to say, that mechanism is incredibly important – no astronaut is going to be able to fix it like they fixed Hubble.

As a result of many technological challenges, the James Webb Space Telescope has been a very, very expensive one. According to JWST’s chronology over at the Space Telescope Science Institute, it was originally expected to be 8 meters in diameter, cost $500 million dollars (where the New Horizons spacecraft to Pluto has cost $700 million), and launch in 2008. Suffice it to say, those were wildly underestimated once actual engineering tests and instrument development began. Schedules slipped until they finally ended up at a 2018 launch, the telescope shrank to 6.5 meter mirrors so that it would be easier to launch, and the budget expanded to $8.7 billion dollars… Astronomers began to worry about JWST muscling other programs out of their budgets (which was the subject of my first two posts on this blog, actually*). Remember, NASA’s budget is tiny. It only has 0.5% of the national budget, or 17 billion dollars a year, to keep flying the Hubble, Spitzer, and Kepler Space Telescopes, both Voyager probes, New Horizons, Cassini, Dawn, the Juno Jupiter probe, Mars Odyssey, Mars Reconnaissance Orbiter, MAVEN (another Mars orbiter), two Mars Rovers, a couple of solar observatories, the International Space Station, an enormous number of weather satellites you rarely hear about, AND develop new rocket technology AND build JWST** (and more that I didn’t list, and don’t know of). Eventually, NASA was given an extra line item in their budget simply for JWST.

But now here we are: It’s been a few years since budgetary estimates and time estimates stopped creeping upwards, and now the first visible signs that it’s really going to launch in only two years are here. There are symposia and workshops dedicated to helping people use the data processing software. Instruments are being shipped to Goddard Spaceflight Center.

And there’s a physical telescope assembly, ready to go. It’s a real thing now. And once it’s up in space, it will be able to do amazing things well beyond anything we can do with Hubble. Remember, Hubble’s mirror would be considered fairly small if it was on earth, but it’s been so great because:

  1. The on-board instrumentation is absolutely amazing.
  2. It doesn’t have to worry about the blurring and distorting effects of the Earth’s atmosphere – stars don’t twinkle in space.
  3. It can see wavelengths of light (like ultraviolet and infrared) that the Earth’s atmosphere blocks.
  4. It can stare at objects for DAYS at a time (46 minutes on/46 minutes off as it orbits the Earth) without worrying about weather.

Practically everything Hubble can do (except study ultraviolet phenomena), James Webb will do better. It will see farther and clearer. Infrared light is great at looking through dust, so it will be able to see deep into the hearts of star clusters and through the plane of the Galaxy. It will be able to see finer details and fainter objects than we’ve ever been able to see before. JWST will be revolutionary, and it’s actually coming soon.

*I’ll note that I was wrong about two big thing in my second blog post:

One, JWST was never intended to be an optical mission to succeed Hubble. The confusion probably arose because it’s often billed as a successor to Hubble, but that’s often meant more in the sense of the science it’s going to do – probe the edge of the Universe, chart galaxies, study exoplanets – rather than the light it was supposed to be looking at. On the other hand, its near-infrared camera (NIRCam) and near-infrared spectrograph (NIRSpec) will be able to see light as blue as 600 nm, which is visible to the unaided eye as red light. And 600 nm to 1000 nm light is still commonly considered “visible” by astronomers, because it can be picked up with the same detector technology used to capture visible light – your cell phone camera, for example, can pick up infrared TV remotes (unless it’s got a filter to prevent exactly that).

Two, JWST does NOT need cryogenic cooling; it maintains an extremely low temperature with its sunshield. This is unlike Spitzer and WISE, whose cryogen ran out and left them unable to use their farthest-infrared detectors, or Herschel, whose mid-infrared mission was entirely over once its cryogen ran out. (In all cases, the spacecraft itself became warm enough that it started seriously glowing at those wavelengths) The limited lifetime of JWST is governed by the maneuvering propellant. Hopefully there will be ways to stretch that.

** NASA isn’t solely fitting the bill for most of those things, but the point still stands.

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One Comment Add yours

  1. Dragallur says:

    Wow, this is so cool, and so well written post! I am very excited about JWST!

    Like

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