AEROSPACE INDUSTRY
UPDATE
October
2017
McIlvaine Company
TABLE OF CONTENTS
What’s Hiding Underground at NASA?
Hidden beneath Chamber A at NASA’s Johnson Space Center in Houston is an area
engineers used to test critical contamination control technology that has helped
keep NASA’s James Webb Space Telescope clean during cryogenic testing.
This voluminous area is called the plenum, and it supports the weight of the
chamber above as well as houses some of the cabling and plumbing for it. Before
Webb’s cryogenic testing in the chamber commenced, engineers ventured to the
plenum’s depths to test NASA-developed technology designed to remove molecular
contaminants from the air.
Nithin Abraham, a coatings engineer at NASA's Goddard Space Flight Center in
Greenbelt, Md., is part of a contamination control team tasked with ensuring
Webb remains as clean as possible during its testing in Chamber A. Abraham is
the principal investigator of the coatings research team that has developed and
tested a highly porous material called molecular adsorber coating (MAC), which
can be sprayed onto surfaces to passively capture contaminants that could be
harmful to Webb’s optics and science instruments.
Not to be confused with absorption, adsorption is the process in which
microscopic materials (for example, atoms and molecules) adhere to a surface —
in this case, to the surface of a panel coated with the MAC. The MAC panel
secures contaminants released through outgassing, a process that occurs when gas
that was dissolved, absorbed, or otherwise trapped within a substance is
released into the surrounding environment. An example of this is the coveted
“new car smell” of a freshly manufactured automobile.
Even minute amounts of outgassed material within the plenum could have posed a
threat to Webb’s optics and science instruments located in Chamber A, so Abraham
and her team — engineers turned spelunkers — descended into the cave-like space
to place the MAC panels before cryogenic testing began.
To reach the plenum, the engineers walked single file along a narrow,
mineshaft-like passageway between the helium shroud that surrounds the Webb
telescope and the wall of the chamber, then descended a ladder into the
cylindrical room. Light along the passageway and within the plenum is sparse, so
the engineers donned headlamps before they made the journey. They also wore
oxygen sensors to warn them if oxygen levels inside the plenum were getting low.
The MAC panels in the plenum primarily captured hydrocarbons and silicone-based
compounds. These contaminants are ghosts of the Apollo era, when a mechanism
within the central cylinder of the plenum rotated the floor of the chamber
above. This rotation simulated the thermal roll used to evenly disperse heat on
the Apollo spacecraft during their journeys to and from the Moon. Nithin and her
team also placed MAC panels inside Chamber A, including on the outside of the
helium shroud.
“We do a thorough analysis on the types of contaminants that were collected and
how much,” says Abraham. “That data is very useful and shows that we are
protecting [the telescope] from molecular contamination.”
MAC panels are only one type of contamination control protecting the Webb
telescope from both microscopic and macroscopic threats. Engineers wear white
cleanroom suits to prevent particles of skin, hair, and clothing fibers from
depositing on the telescope. Similarly, Webb must move from cleanroom to
cleanroom because the rooms are specially designed to reduce the amount of
airborne particles present. Engineers enter the cleanrooms using airlocks, and
the rooms have positive air pressure compared to their surrounding environment,
so air flows out of the area and takes any potential contaminants with it.
When a spacecraft is exposed to the vacuum of space, outgassing occurs from
epoxies, tapes, lubricants, plastics, and other materials used to construct it.
For Webb, the biggest threat from outgassing comes early in its mission, shortly
after launch when the telescope is cooling down but is still warm.
“Fortunately, warm things outgas but cold things not so much, so once the
telescope and instruments go cold, the outgassing goes way down,” explains Lee
Feinberg, optical telescope element manager for the Webb telescope at Goddard.
Engineers will control the temperatures of the different parts of the
observatory as it cools so outgassed molecules from one part do not deposit
elsewhere, such as on sensitive surfaces like the optics, but instead escape to
space. Though the MAC is only being used terrestrially and peripherally for
Webb, engineers are researching ways to apply the coating directly onto elements
of future NASA spacecraft, as an added measure of protection.
After cryogenic testing at Johnson is complete, Webb’s combined science
instruments and optics journey to Northrop Grumman in Redondo Beach, California,
where they will be integrated with the spacecraft element, which is the combined
sunshield and spacecraft bus. Together, the pieces form the complete James Webb
Space Telescope observatory. Once fully integrated, the entire observatory will
undergo more tests during what is called "observatory-level testing." This
testing is the last exposure to a simulated launch environment before flight and
deployment testing on the whole observatory.
Webb is expected to launch from Kourou, French Guiana, in the spring of 2019.
The James Webb Space Telescope, the scientific complement to NASA's Hubble Space
Telescope, will be the premier space observatory of the next decade. It was
assembled in a Class 10,000 cleanroom at NASA's Goddard Space Flight Center.
Webb is an international project led by NASA with its partners, ESA (European
Space Agency) and CSA (Canadian Space Agency).
Source: NASA
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