When the sunshield for the James Webb Space Telescope underwent deployment testing, it unfolded exactly like it would in space. At least, it did if you ignore the people, cranes, air, warmth, gravity, and conspicuous absence of the rest of the telescope. Even so, it looks really cool, and provides an SPF one million coverage.
Top image: A human in a cleanroom bunny-suit will not be anxiously peering out of the sunshield during orbital deployment. Credit: Northrop Grumman/Alex Evers
Gravity can be decidedly inconvenient when attempting to test spacecraft under realistic conditions. Image credit: Northrop Grumman/Alex Evers
The sunshield for the James Webb Space Telescope is designed to travel into space tightly wrapped around mirrors and fragile instruments, blossoming into an enormous origami kite once in orbit. Its purpose is simple: separate the observatory's hot, sun-facing side (up to 200°C) from the cold, shaded side(-120°C). The sunshield will keep delicate instruments carefully shielded and cool, allowing the James Webb Space Telescope to search for planets most likely to support alien life.
The sunshield for the James Webb Space Telescope is large enough to host a tennis court, if the engineers didn't instantly vaporize you with death-glares. Image credit: Northrop Grumman/Alex Evers
As NASA explains:
The sunshield's membrane layers, each as thin as a human hair, are made of Kapton, a tough, high-performance plastic coated with a reflective metal. On orbit, the observatory will be pointed so that the sun, Earth and moon are always on one side, with the sunshield acting as an umbrella to shade the telescope mirrors and instruments from the warmer spacecraft electronics and the sun.
Five layers of Kapton will shelter sensitive instruments from unforgiving sunlight. Image credit: NASA/Chris Gunn
The real trick is making sure the sunshield will unfold in practice nearly as well as the modelled plans in theory. It underwent its first practical tests this summer at Northrop Grumman in southern California. Here's a timelapse of the epic procedure:
The test unfolded, separated, and spread all five sunshield layers for the first time. It was a critical stage in the telescope's development, checking on how reality matched up (and more importantly, diverged from!) models, and identifying any problem-spots that require modifying the design before full production.
After spreading, each layer needed to be carefully separated for full deployment. Image credit: Northrop Grumman/Alex Evers
Understandably, this test didn't exactly match the telescope's intended operating conditions. To start with, we have gravity. And air. And people everywhere. Really, we have a lot of things that just aren't a problem over a million kilometers above the Earth.
The Mark 1 human eyeball confirms the sunshield is fully deployed and tensioned. Image credit: Chris Gunn/NASA
Jim Flynn, the Webb sunshield manager, explains how our environment complicates practical testing, and how they worked around it:
"Tests on the ground are a little bit tricky because we have to account for gravity. Webb won't face those same challenges in space. To overcome challenges on the ground, our technicians came up with the idea to rest the layers on a structure of metal beams covered by plastic."
Theory and practice are inconveniently in disagreement upon occasion. Image credit: Northrop Grumman/Alex Evers
It took seven engineers and six technicians 20 hours to unfold the sunshields over three days of work; the telescope's real deployment in orbit will stretch over multiple days. The shield will fold and wrap around the mirrors and instruments during launch, staying tucked away until the space telescope reaches an orbit one million miles from Earth (I love metric measurements, but "1,609,344 kilometers" is far less poetic). Then, the sunshield will unfold and deploy in five precisely stacked layers, forming the largest part of the observatory.
Five layers, all shiny... Looks good! Image credit: Northrop Grumman/Alex Evers
Sunshield layers are currently being manufactured by Northrop Grumman subcontractor NeXolve in Alabama, with a delivery date in 2016 when they will undergo another battery of tests. Other portions of the telescope were packed off to Maryland for additional assembly and testing, destined for Texas for low-temperature testing. The entire telescope is currently slated to launch in 2018.
I bet five layers of carefully-spaced Kapton would make an excellent thermos. Image credit: Northrop Grumman/Alex Evers
Tip via Alberto Conti.