With the successful extension of Webb’s second sunshield mid-boom, the
observatory has passed another critical deployment milestone. Webb’s
sunshield now resembles its full, kite-shaped form in space.
Engineers began to deploy the second (starboard) mid-boom at 6:31 p.m. EST
and completed the process at about 10:13 p.m. EST.
The completion of the sunshield cover and mid-boom deployments over the past
two days marks a critical milestone for Webb: all 107 membrane release
devices associated with the sunshield deployment — every single one of which
had to work in order for the sunshield to deploy — have now successfully
released. Webb has 178 of these ‘non-explosive actuators’ in all; 107 were
used to keep the sunshield safe and folded prior to deployment.
As the mid-booms slowly pushed out horizontally from the spacecraft, each
driven by a motor, they pulled the folded membranes of the sunshield with
them. This extended the sunshield to its full 47-foot width all the way
across the observatory.
“The mid-booms are the sunshield’s workhorse and do the heavy lifting to
unfold and pull the membranes into that now-iconic shape,” said Keith
Parrish, Webb observatory manager at NASA’s Goddard Space Flight Center.
While the deployments took longer than expected today, that was due to the
operations team moving forward with caution and according to the protocols
they laid out for dealing with unpredictable situations.
“Today is an example of why we continue to say that we don’t think our
deployment schedule might change, but that we expect it to change,” Parrish
said. “The team did what we had rehearsed for this kind of situation – stop,
assess, and move forward methodically with a plan. We still have a long way
to go with this whole deployment process.”
The two mid-boom arms are now locked in their final position. They will hold
the sunshield membranes in their proper place, as the team turns to the
final stage in the sunshield’s deployment: tensioning.
In the coming days, the team will separate and then individually tension
each of the five sunshield layers, stretching them into their final, taut
shape. This will create space between the membranes to allow heat to radiate
out, making each successive layer of the sunshield cooler than the one
below.
Webb’s engineers will begin with the bottom layer – the largest and flattest
layer, which is closest to the Sun and will reach the highest temperatures.
They will proceed sequentially to the fifth and smallest layer, closest to
the primary mirror. Tensioning the layers involves sending commands to
activate several motors to reel in a total of 90 cables through numerous
pulleys and cable management devices. Sunshield tensioning will take at
least two days but may take longer, due to the complexity of the process and
the flexibility built into the timeline.
Source: Link
Tags:
Space & Astrophysics