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Marshall Perrin Profile picture
Marshall Perrin
@marshallperrin
Astronomer at STScI. Exoplanets, mirrors, systems, software. Specialist in synthetic starlight. Deputy Telescope Scientist for JWST; tweets my own. (He/him)
May 9, 2022 • 19 tweets • 5 min read
A new image from JWST, or rather a better, bigger look at some of the data we shared at the completion of telescope alignment. Here's MIRI's view of a tiny part of the Large Magellanic Cloud, a nearby satellite galaxy to our Milky Way. What do we see here, and what's it mean? A🧵 JWST MIRI image of molecular clouds in the LMC First, some context. By eye, the LMC is a faint cloud in the southern sky (seen here over @GeminiObs). A region near its center was chosen long ago as a calibration field for JWST, providing millions of stars carefully mapped out, in part of the sky JWST can observe year round. Night sky over Gemini observatory, showing Milky Way and MagDeep view of the Large Magellanic Cloud, from NOIRLab/CTIO.
Dec 31, 2021 • 10 tweets • 3 min read
Now comes the audacious part, the unprecedented part, what many consider one of the harder parts. Now comes the sunshield, and all its shiny purple gossamer glory and complexity. (1/9) All of the deployments thus far have involved rigid bodies: hard structures, kinematic mounts, hinges, motors. Carefully controlled and limited degrees of freedom. This hinge only moves in this one axis, and so on. The sunshield’s not like that. (2/9)
Dec 29, 2021 • 7 tweets • 2 min read
Yesterday something momentous happened, something long in coming. A motor whirred, a cable pulled, mechanisms pivoted on hinges, seven meters of metal and kapton pivoted. Lots of #JWST engineers smiled. But that’s not what I’m thinking about. No, something even longer in coming. Long ago and far away indeed, a star shone in the darkness. Light streamed out into the young universe. Countless years passed. And then, at the last moment, Webb’s forward UPS pallet swung out of the way, and those photons passed onward through its aft optics entrance aperture.
Dec 22, 2021 • 18 tweets • 4 min read
Well, seems we have an extra day (or more, pending weather) with these golden hexagons still on the ground. OK, that just gives us a bit more time to talk about how JWST’s mirrors work. Let’s go. (1/18) I mentioned already beryllium for lightness & stability. These mirrors are *really light*: each 1.5 m diameter hexagon is only 20 kg (with mechanisms on the back doubling it to 40 kg total per assembly). The whole primary is just 740 kg. That’s super light for a big telescope.
Dec 20, 2021 • 24 tweets • 5 min read
If you’re familiar with large telescopes on the ground, how they’re designed & operated - many of the design decisions made for JWST are very different. The overall architecture is in its own part of solution space, only kinda like a ground based 6 m. Let me explain: (1/25) First there’s choice of materials: Beryllium mirrors: super lightweight as well as super stable (low CTE) at cryogenic temperatures. Carbon fiber structures: big stiff hollow tubes and trusses. I’ve held samples of these and they’re impressively airy and light for their size.
Dec 20, 2021 • 9 tweets • 2 min read
How does JWST work? And why was it built that way? A thread, and start of a series. (Questions welcome! Especially from students) 1/9 A few days ago I wrote about how Webb is so astoundingly lightweight, barely 6 tons for a 6 meter observatory the size of a small house. That one fact has driven the engineering of the observatory in a thousand ways. Over the next few days, I’ll share a some of those. 2/9