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The James Webb Space Telescope is planned to succeed the Hubble Space Telescope in 2018. It has a bigger primary mirror, can see further, and will travel deeper into space than its predecessor, sending back images of never-before-seen phenomena to help scientists better understand how galaxies, stars, and planets form.
The 14,300-pound telescope is equipped with 18 intricately engineered mirrors and carefully calibrated sensors, all of which have to survive a rocket launch and bruising ride through the atmosphere. To ensure the hardware can survive, engineers will strap the telescope to vibration tables and shake it in every direction. It's a process every spacecraft and satellite has gone through since NASA first began sending satellites into orbit in the 1950s. To test Webb, NASA turned to Burlington, WA-based Team Corporation, a company that has been instrumental in NASA's vibration testing since the beginning.
NASA Goddard commissioned and installed two new vibration testing devices. At 11 square feet, they are nearly twice as big as the one the center had in its basement vibration lab, also built by Team. “Our shakers downstairs are capable of being reoriented. The new shakers have a dedicated system to do the horizontal, and a separate system to do the vertical,” explained Brian Ross, lead structural dynamic test engineer for the new telescope.
“The horizontal system is more or less the same, just a lot bigger, but the vertical system is completely different. It actually has two shakers that drive the table, and then it has quite a lot of structure surrounding the table to help react out, or counterbalance, the large loads.” Each system generates up to 100 vibrations per second, mimicking the forces the telescope will encounter on launch day.
One of the new requirements Team had to meet was for a “soft stop,” ensuring that if anything went wrong during the testing, the vibrations wouldn't stop too abruptly. “Usually, the systems are designed to protect themselves first,” explained Ross. Most of the time, the item being tested is one of many, and easier to replace than the machine itself, which can cost millions of dollars.
That calculation is reversed with items like the Webb telescope, whose total cost is projected at around $8 billion. If the machine stops abruptly, that could transfer a shock to the telescope, causing damage. Team built in a system that would ensure the shaking would allow at least four-tenths of a second to slow down before stopping — enough to protect the telescope.
In the early days of the aerospace industry, certain aspects of spacecraft development remained fairly primitive, and one of those, explained Team's Curt Nelson, was the testing procedure. “Basically they built it, stuck someone into it, flew off, and saw what happened,” said Nelson, head of North American military and aerospace sales for the company.
Engineers recognized the need for better preflight testing, and Vern Tauscher, who started working in aviation after World War II, devised a machine to provide powerful vibrations, based on reverse engineering of a German rocket. “He developed our very first product, the HydraShaker,” Nelson said. “We still build variations of that device every day — bigger, smaller, but the core technology is basically the same.”
Tauscher founded Team, which stands for Tauscher Engineering and Manufacturing, in 1954. When NASA started testing spacecraft, it turned to Tauscher. Needing improved equipment for the demands of spacecraft, Team invented under a NASA contract what it calls Model 1830 T and V bearings, which are stiff and frictionless, and can carry both tension and compression.
In addition to a rocket launch, these devices can recreate conditions of a bouncing road or a massive earthquake. It's all aimed at determining just how well a structure will hold up in a moment of extreme stress or over a lifetime of wear and tear.
Updates on those same hydrostatic bearings first designed for NASA in the 1950s can still be found in vibration testers, including those used by some of the world's largest car companies. Using four small vertical shakers, one under each car wheel, automakers like Ford test how well the fully assembled car will perform once it hits the road.
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