The James Webb Space Telescope will peer at
the first stars and galaxies as a cosmic time machine, look beyond to distant
worlds, and unlock the mysteries of the universe. But before it can do any of
those things, it needs to “train” for traveling to its destination — 1 million
miles away from Earth!
So how does Webb get ready for space while
it’s still on the ground? Practice makes perfect. Different components of the
telescope were first tested on their own, but now a fully-assembled Webb is putting all of its
training together. Here are 10 types of tests that Webb went through to prepare
for its epic journey:
1. Sounding Off
A rocket launch is 100 times more intense and
four times louder than a rock concert! (That’s according to Paul Geithner, Webb’s
deputy project manager – technical.) To simulate that level of extreme noise,
Webb’s full structure was blasted with powerful sound waves during its
observatory-level acoustic testing in August.
2. Shaking It Up
Webb will also have to
withstand a super-bumpy
ride as it launches — like a plane takeoff, but with a lot more shaking!
The observatory was carefully folded into its launch position, placed onto a
shaker table, and vibrated from 5 to 100 times per second to match the speeds
of Webb’s launch vehicle, an Ariane 5 rocket.
In July, Webb performed a rigorous test of its
software and electrical systems as a fully connected telescope. Each line of
code for Webb was tested and then retested as different lines were combined
into Webb’s larger software components. To
complete this test, Webb team members were staffed 24 hours a day for 15
After launch, Webb is designed to unfold (like
origami in reverse) from its folded launch position into its operational form. Without
recharging, the telescope’s onboard battery would only last a few hours, so it
will be up to Webb’s 20-foot solar array to harness the Sun’s
energy for all of the telescope’s electrical needs. To mimic the zero-gravity
conditions of space, Webb technicians tested the solar array by hanging it
The tower connects the upper and lower halves of
Webb. Once Webb is in space, the tower will extend 48 inches (1.2 meters)
upward to create a gap between the two halves of the telescope. Then all five
layers of Webb’s sunshield will slowly unfurl and stretch out,
forming what will look like a giant kite in space. Both the tower and sunshield
will help different sections of Webb maintain their ideal temperatures.
For these steps, engineers designed an
ingenious system of cables, pulleys and weights to counter the effects of
6. Dance of the Mirrors
Unfolding Webb’s mirrors will involve some
dance-like choreography. First, a support structure will gracefully unfold to
place the circular secondary mirror out in front of the primary
mirror. Although small, the secondary mirror will play a big role: focusing
light from the primary mirror to send to Webb’s scientific instruments.
Next, Webb’s iconic primary mirror will fully extend so that all
18 hexagonal segments are in view. At 6.5 meters (21 feet 4-inches) across, the
mirror’s massive size is key for seeing in sharp detail. Like in tower and
sunshield testing, the Webb team offloaded the weight of both mirrors with cables,
pulleys and weights so that they unfolded as if weightless in space.
Before a plane takeoff, it’s important for us to turn
off our cell phones to make sure that their electromagnetic waves won’t
interfere with navigation signals. Similarly, Webb had to test that its
scientific instruments wouldn’t disrupt the electromagnetic environment of the
spacecraft. This way, when we get images back from Webb, we’ll know that we’re
seeing actual objects in space instead of possible blips caused by
electromagnetic interference. These tests took place in the Electromagnetic Interference (EMI) Lab, which
looks like a futuristic sound booth! Instead of absorbing sound, however, the
walls of this chamber help keep electromagnetic waves from bouncing around.
How will Webb know where to go and what to
look at? Thanks to Webb’s Ground Segment Tests, we know that we’ll be
able to “talk” to Webb after liftoff. In the first six hours after launch, the
telescope needs to seamlessly switch between different communication networks and
stations located around the world. Flight controllers ran through
these complex procedures in fall 2018 to help ensure that launch will be a
After Webb reaches its destination,
operators will use the Deep Space Network, an international array of giant
radio antennas, to relay commands that tell Webb where to look. To test this
process when Webb isn’t in space yet, the team used special equipment to
imitate the real radio link that will exist between the observatory and the network.
Between 2017 and 2019, Webb engineers
separately tested the two halves of the telescope in different thermal vacuum
chambers, which are huge, climate-controlled rooms drained of air to match the
vacuum of space. In testing, the spacecraft bus and sunshield half were exposed
to both boiling hot and freezing cold temperatures,
like the conditions that they’ll encounter during Webb’s journey.
But Webb’s mirrors and instruments will need
to be colder than cold to operate! This other half of Webb was tested in the
historic Chamber A, which was used to test Apollo Moon
mission hardware and specifically upgraded to fit Webb. Over about
100 days, Chamber A was gradually cooled down, held at cryogenic temperatures
(about minus 387 F, or minus 232.8 C), and then warmed back up to room
When the Hubble Space Telescope was first sent
into space, its images were blurry due to a flaw with its mirror. This error
taught us about the importance of comprehensively checking Webb’s “eyes” before
the telescope gets out of reach.
Besides training for space survival, Webb also
spent time in Chamber A undergoing mirror alignment and optical testing. The team
used a piece of test hardware that acted as a source of artificial starlight to
verify that light would travel correctly through Webb’s optical system.
Whew! That’s a lot of testing under Webb’s
belt! Webb is set to launch in October 2021 from Kourou, French Guiana. But
until then, it’s still got plenty of training left, including a final round of
deployment tests before being shipped to its launch location.
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