Before every NASA mission is launched, the spacecraft is subjected to weeks of rigorous testing. It's attached to a large table that shakes as violently as a rocket launch. It is deafeningly louder than a stadium rock performance. In a vacuum room that resembles the extremes of space, it is frozen, baked, and irradiated. Surface Water and Ocean Topography (SWOT), a joint US-French program to monitor all water on Earth's surface, has passed these crucial criteria.
SWOT is now ready for its December launch, with the exception of a few last inspections. SWOT engineers at NASA's Jet Propulsion Laboratory in Southern California have worked on the mission for a decade, designing, constructing, and assembling it. It's been tough to watch the equipment they've worked on the go through the newest set of tests, but the crew has handled it in stride. That's because every component of SWOT, even down to the nuts and bolts, had been thoroughly tested before the satellite entered the thermal vacuum chamber for the final time. According to the engineers, the earlier experiments caused significantly greater worry.
JPL mechatronics engineer Phoebe Rhodes-Wickett has spent a quarter of her life working on SWOT. She originally concentrated on a minor component required to deploy the antennae on the primary instrument of the spaceship.
According to Rhodes-Wickett, "the first time I tested my mechanism, I was terrified." The component, which was about the size of a box of tissues, was tested on a full-scale shaker table. It was simply this small machine by itself. The test is audible, and you can see the mechanism in action. Our initial round of testing was a failure. To have the mechanism verified as spaceworthy, we had to redesign and retest it in a matter of months.
After passing the retest, the mechanism was linked to larger and larger systems before being fully integrated into the SWOT spacecraft. Every stage of spaceship construction involves the formation of new connections and the introduction of new opportunities for human mistakes, thus it concludes with another series of testing. Since that initial test, Rhodes-mechanism Wickett's has passed three further vibration tests.
She stated that passing each exam is a relief, but after the third or fourth test, your stress level is significantly reduced.
SWOT's new radar equipment, the first of its type in space, includes the mechanism. Two radar antennas are installed on mechanical arms on the Ka-band Radar Interferometer or KaRIn. SWOT's arms will unfurl from opposing sides of the spaceship and expand until the antennas are about 33 feet (10 meters) apart while in orbit. The gap between KaRIn's two antennas helps the device disclose more information about Earth's water, much as the space between your eyes helps you evaluate distance and depth better. However, if the procedure isn't quite ideal, if the mechanical arms don't fully stretch or the antennas are misaligned by even a few thousandths of a degree, KaRIn won't be able to make the desired measurements
According to JPL's Eric Slimko, a chief mechanical engineer on SWOT, "it's a unique part of a NASA career that we're always trying to build stuff that hasn't been built before."
This implies that each NASA cargo begins with an unknown risk element. Most missions get a feel of the danger level by flying prototype instruments and testing them in labs, but there's still the (literally) sky-high extra difficulty of modifying the equipment to survive launch and function in space.
He stated, "We don't have the capability of eliminating all of that risk with a piece of paper analysis." We must put it to the test. Even off-the-shelf components are OK.
Slimko stated that devising experiments to demonstrate that the folding arm and antenna assembly function as well in orbit as they do on Earth was quite difficult. For one thing, we can't deactivate gravity. However, we devised a verification program that, while we cannot recreate the precise flying condition on the ground, we are certain that it will operate in space. To finish the set of tests as the spacecraft was built, scores of JPL engineers spent weeks or months at the Thales Alenia Space facility in Toulouse, France, collaborating with colleagues from the French space agency Centre Nationale d'Études Spatiales (CNES). The spacecraft has gear from not just CNES and NASA, but also from the United Kingdom and Canada, with each team checking the performance of its own pieces throughout testing.
All that remains now is the final test: the launch itself. Engineers are more than prepared.
According to Rhodes-Wickett, it's exciting to have a kid that you actually thought up, helped to develop, and are now walking it to the finish line. It's thrilling to watch something you've put so much time and effort into make a difference in the world.