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SPACE TECHNOLOGY Acoustic shock rattles telescope


The Webb Telescope spacecraft is undergoing environmental testing with its first failure resulting from acoustic testing.


T


he spacecraft element of NASA’s James Webb Space Telescope recently completed its first two major launch environmental tests at


Northrop Grumman Aerospace Systems in Redondo Beach, California, and will soon undergo further tests to ensure it will handle the rigours of launch and the harsh environment of space. The spacecraft element’s first test


simulated the mechanical shock caused by the separation of the spacecraft’s payload adapter after launch. The second test simulated the extreme sound and resultant vibration of the launch environment. Detailed inspections of the hardware


after the acoustic test showed that fastening hardware that holds the sunshield membrane covers in place had come loose. “NASA is reviewing options for repair and the next steps in launch environment testing,” said Greg Robinson, Webb’s programme director. “The team is reviewing the test data and hardware configuration and is actively working towards corrective action. We expect to get back to the environmental test flow shortly and continue to move safely and methodically toward mission success.” Discoveries like this one are not uncommon in the development of a complex and unique spacecraft. “This is an example of why space systems are thoroughly and rigorously tested on the ground to uncover imperfections and fix them prior to launch,” said Robinson.


THE SHOCK OF PAYLOAD SEPARATION When Webb is launched into space, it must be folded like origami to fit inside its Ariane 5 rocket’s payload fairing, which protects it from the forces and heat of the atmosphere as the rocket accelerates into space. Inside the fairing, the payload adapter


physically attaches Webb to the top of the Ariane 5. The adapter has two halves – one that is permanently attached to Webb and the other that is attached to the second stage of the rocket. When the rocket reaches a specific altitude in Earth’s upper atmosphere, the payload fairing


20 /// Testing & Test Houses 2018


❱ ❱ The James Webb Space Telescope is undergoing


environmental testing to


simulate the rigours of launch


is jettisoned and falls back to Earth. Following this, the first stage of the Ariane 5 expends its fuel and also is jettisoned. After the second stage of the rocket


gives Webb a final nudge to send it on its way to its orbit, the two halves of the payload adapter separate, releasing Webb from the rocket. The release sends a mechanical shock through the observatory. To simulate this separation on Earth, engineers at Northrop Grumman first suspended the spacecraft element in the air with the payload adapter attached to it. They then remotely released the bottom half of the payload adapter.


SOUND AND VIBRATION TESTS After completing shock testing, engineers enveloped the spacecraft in a plastic tent and moved it into Northrop Grumman’s Large Acoustic Test Facility. The tent protected the spacecraft from contamination during the move and during the acoustic test. During the test, engineers subjected the spacecraft element to launch sound frequencies from 25 Hertz to 2,500 Hertz. It was also tested at loudness levels up to 142.5 decibels, about 3 decibels higher than what is expected during launch. Engineers mounted several


microphones inside and outside the tent to monitor the acoustic environment during testing. They also mounted about 500 accelerometers around the spacecraft element to monitor the vibration responses.


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