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Notes from the Field

Knock, Knock, Knocking on BITSE’s Door

September 25th, 2019 by Lina Tran

Jason Budinoff, an aerospace engineer, cocked his head, listening for the sound of metal on metal. “Can you hear it?” someone asked. The room quieted, and a soft, tinny buzz whined from the instrument at the center of the crowd. Inside, a small electric motor was spinning. 

It was three weeks before launch, and the BITSE team was testing the door on their instrument, which was almost ready for its balloon flight to the top of the sky. Eventually, BITSE successfully flew on Sept. 18. But the work toward its launch started a couple years earlier — and continued with tests of each detail up to the very last weeks before launch. One key element: the door.

Slightly larger than a pie, BITSE’s door works like the lens cap on a camera to protect the instrument’s sensitive optics. Instead of scratches, it shielded BITSE from dust and bugs that could fly in during ascent. Once it climbed to float altitude, 22 miles up in much less dusty skies, the door opened and BITSE began taking pictures of the Sun. 

The BITSE balloon flight put a new coronagraph to the test, a kind of instrument that looks at the Sun’s dim atmosphere. The BITSE tech — short for Balloon-borne Investigation of Temperature and Speed of Electrons in the corona — is designed to look for clues to how the solar wind forms. That’s the stream of charged particles constantly blowing off the Sun. The solar scope takes images in certain wavelengths of light that are especially prone to scattering off dust, marking data with distracting bright spots. “The cleaner we are, the better science we’ll get,” said Budinoff, BITSE’s lead mechanical engineer. 

That morning was as much a test of the team’s nerves as it was of the door. It was the last time they’d run it before launch, and BITSE was decked out in flight configuration.

Software engineer Seonghwan Choi and his team wrote the code that tells BITSE to open sesame. They work for the Korea Astronomy and Space Science Institute, NASA’s partner in the BITSE mission. “If the software doesn’t work and the door doesn’t open, the mission will fail!” Choi said. He laughed nervously at the idea. Take a picture with a camera but forget to remove the lens cap first, and you just get the void — no data. 

By then, they’d already done the test at least eight times. This was BITSE’s biggest audience yet, since the entire team was gathered at NASA’s Columbia Scientific Balloon Facility’s New Mexico field site for the coming launch. “When literally the entire mission is saying, ‘Your door better work!’ — the more we test the door, the better,” Budinoff told me. “I’d do it 50 more times if I could.” 

NASA Goddard/Joy Ng

It works like this: A one-centimeter-long pin — about the width of a fingernail — keeps the door latched shut, while a screw moves the pin back and forth. When BITSE receives the word, a tiny motor starts running and the screw starts turning. And that pulls the pin out from the latch, allowing the spring-loaded door to flip open. The entire thing hinges — literally — on the pin moving just half a centimeter. From sending the command to opening the door, it all takes no more than 45 seconds. 

A few minutes before the test, the team gathered in front of BITSE. Scientists brought their phones out to film it. I did the same. “It’s not going to be nearly as exciting as everyone is thinking,” Budinoff warned. 

Regardless, someone began a countdown. (We at NASA love a good countdown.) “Here it comes!” another called. BITSE buzzed for a brief moment, and the door fell open with a neat, hollow thunk. Satisfied, Budinoff started a round of applause. 

Later, they ran a second test. It looked just like the first one, but there was one key difference. Instead of sending a command, the software team let BITSE guide itself. This was the back-up plan in case they lose contact with BITSE. Without instructions from the ground, the coronagraph was programmed to open its own door after a few hours — the amount of time it would take the 6,000-pound load to ascend 22 miles. Even if it couldn’t hear the team, BITSE would dutifully stick to the plan. 

NASA Goddard/Lina Tran

After the second test, while the door was still open, the engineers took the opportunity to vacuum BITSE’s mouth. They used an ultraviolet flashlight to spot individual specks of dust, which pop in electric blues and greens under the light. With the door thoroughly tested and the tidying done, it was time to shut it one last time. The software team ran the program backwards, turning the screw the opposite direction so it pushed the pin into the latch. We listened again for motor’s high-pitched whine. “Hopefully the next time we open, we’ll be 120,000 feet in the air,” Budinoff said. 

In the end, their worrying, testing and re-testing was worth it: On Sept. 18, BITSE’s door opened like a charm. 

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