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As the world marvels at the release of the first images from the James Webb Space Telescope, Paul Geithner, Associate Project Manager for Webb Monitoring, recalls another unique moment: when the Webb team thought of a brief (happily brief) moment that the observatory was broken.
A portion of Webb’s structure, specially fabricated from a graphite-epoxy composite, underwent vibration testing at NASA’s Goddard Space Flight Center in late 2016. The connection points of the instrument’s deployable components were shaken to see how they would hold up. Everything was going well until it wasn’t. There was a loud bang. The sound was not pleasant at all.
“People were like — oh my god, did we just bust it?” Think Geithner. “I mean it sounded bad. Then the test switched off automatically. That was probably the scariest part.”
It has not been damaged. Matched mass dampers were added to the telescope’s secondary mirror support structure to suppress any resonance that could threaten the structure’s survival during launch. Testing at that time and in the months and years that followed continued as the mission team evaluated the observatory’s resilience to the extreme conditions it faced both during launch and in its permanent “halo” orbit around Lagrange Point 2 ( L2), larger than the Moon’s orbit around Earth, gravitationally balanced between Earth and Sun.
The orbit into which the Webb was inserted is credited to the 18th-century Italian-born mathematician and astronomer Joseph-Louis Lagrange, who made important contributions to celestial and classical mechanics. Lagrange studied the “three-body problem” (named for the three bodies that orbit each other) of the Earth, Sun, and Moon. He identified five points in near space, L1, L2, L3, L4, and L5, where objects could be easily orbited.
The Webb Observatory, the most complex and powerful space telescope launched to date, is an example of how cutting-edge space designs and equipment can be tested in environments modeled after those found in a vacuum of intense, ultra-cold and/or ultra-hot Radiation that can protect against known and maybe even unknown dangers as much as possible.
Webb’s successful launch, orbital insertion, system checks, deployment and now the spectacular images underscore the value of testing. Such advances would not have been possible without extensive study and validation of all Webb systems and components prior to telescope launch and deployment. But an important question was how accurately the tests for such a large artifact could be conducted.
La división del observatorio
Testing the entire Webb in NASA’s largest vacuum chamber was not possible because of the need to accurately replicate the thermal environment on either side of the observatory in its deployed configuration. One possible approach was to build another, larger chamber, but the construction costs and schedule delays were prohibitive.
The solution: The observatory was literally split in halves that, with some facility adjustments and upgrades, could be housed in a variety of test chambers spread across NASA centers and prime contractor’s Redondo Beach, Calif., Northup Grumman facility . Verifying the inserts and the Webb’s heat balance would be the result of combining many tests.
Webb’s structures, components, electronics, instruments and systems have been studied, evaluated and validated by thousands of scientists, engineers and technicians who together have developed, tested and integrated Webb. A total of 258 companies, agencies and universities participated: 142 from the United States, 104 from 12 European countries and 12 from Canada.
“We couldn’t just put the entire observatory in a vacuum chamber and duplicate everything at once,” says Geithner. “So we tried two big halves. It turns out that our approach worked.”
The NASA facilities involved in the major Webb tests were located at NASA research centers: Goddard Space Flight Center, Johnson Space Center, Marshall Space Flight Center, and Jet Propulsion Laboratory. Cryogenic (ultra-cold) testing of the telescope, its components and instrument packages played a prominent role in this effort, as did vibrational and thermal equilibrium assessments.
“We had to figure out how to do the two-part test and trust that the software would certify the results of that test,” says Webb program scientist Eric Smith, now chief scientist in the Astrophysics Division at NASA Headquarters. “So when we put the pieces together, the observatory would work in space. Lo and behold, it worked wonderfully.”
Conseguir un entorno limpio pero tormentoso
Beginning in July 2017, scientists and engineers in Chamber A at the Johnson Space Center are also subjecting the Webb optical telescope and its integrated scientific instrument module, known as OTIS, to a series of cold soak tests. The studies included an extensive verification of the alignment of the 18 elements of Webb’s primary mirror to ensure that each of the observatory’s gilded hexagonal segments acted together as a single monolithic mirror.
This was the first time the telescope’s optics and its instruments had been tested together, although the instruments had previously undergone cryogenic testing in a smaller chamber at Goddard. Engineers from Harris Space and Intelligence Systems, based in Melbourne, Fla., worked with NASA personnel on the Johnson test.
Before installing the Webb, Johnson engineers built a large clean room around the entrance to Chamber A. The modification, according to Smith, “turned a ‘dirty’ chamber into a clean chamber. That was a great investment.”
The clean room allowed the telescope to be removed from its shipping case, unwrapped from its protective bag, unfolded, rotated from horizontal to vertical, placed on its test platform, and finally slid into the chamber on rails and attached to the six long rods to hang up the suspension.
“Chamber A was an obvious choice, as was building a whole new facility,” says Geithner. “It was much better than starting from scratch. It’s a really good installation where you can create a really big vacuum.”
While the Webb was in the chamber, isolated from outside visible and infrared light, engineers scanned it using thermal sensors and special camera systems. Thermal sensors monitored the telescope’s temperature, while camera systems tracked Webb’s physical position to see how its components were moving during the cooling process.
Not everything went according to plan. Although experienced testers learn to expect the unexpected, some events will test the patience of even the most prepared.
“Our testing plan was solid. We prepare a lot at JSC,” says Geithner. “We plan and improve to survive a 500-year hurricane. And guess what happened? Hurricane Harvey.”
Harvey made landfall on the Texas coast on August 25, 2017 as a Category 4 hurricane before stalling over east Texas and weakening into a tropical storm where up to 4 feet of rain fell in and around Houston. Despite the hurricane, members of Johnson’s Webb Telescope team stayed on site for 100 days, working three non-stop shifts.
Another problem arose: supplies of liquid nitrogen, essential for maintaining ultra-cold conditions in the chamber, were running out. Lead test technician, telescope manager Lee Feinberg, made an emergency call to the nitrogen supplier and explained the nature and urgency of the mission. Austin drivers rushed to deliver and refill the liquid nitrogen, arriving just in time.
“People went a step further to keep the test going and the hardware secure,” says Geithner. “We were all determined. We were engaged.”
La importancia de las pruebas
They didn’t have the effects of a hurricane, but two other incidents gave reviewers pause. Acoustic testing conducted by Northrop Grumman in 2017-18 caused several #4 locking bolts in the Webb’s sun visor to fall out. Though it was, Geithner recalls, “a colossal effort” as engineers worked to solve the problem, it turned out there was no messy ending. As he points out, “That’s why it’s being tested, right?”
Just before launch, in December 2021, when the Webb payload was encapsulated, a ring of the launch interface opened up and, says Eric Smith, “it flew away. Fortunately there was no effect. Still, it was pretty scary to see part of the rocket go off like that.”
Smith still remembers his visits to NASA’s Space Environments Complex at what is now the Armstrong Test Facility, part of the Glenn Research Center. There he was able to see the inner workings of the tests, including the variety and scope of the complex equipment required to evaluate and verify the robustness of the spacecraft, structures, systems, components and instruments.
Original news (in English)
Edition: R. Castro.
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