NASA — Follow, follow the Sun / And which way the wind…

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Along with the Korea Astronomy and Space Science Institute, or KASI, we’re getting ready to test a new way to see the Sun, high over the New Mexico desert.

A balloon — which looks a translucent white pumpkin, but large enough to hug a football field — will soon take flight, carrying a solar scope called BITSE. BITSE is a coronagraph, a special kind of telescope that blocks the bright face of the Sun to reveal its dimmer atmosphere, called the corona. BITSE stands for Balloon-borne Investigation of Temperature and Speed of Electrons in the corona.

Its goal? Explaining how the Sun spits out the solar wind, the stream of charged particles that blows constantly from the Sun. Scientists generally know it forms in the corona, but exactly how it does so is a mystery.

The solar wind is important because it’s the stuff that fills the space around Earth and all the other planets in our solar system. And, understanding how the solar wind works is key to predicting how solar eruptions travel. It’s a bit like a water slide: The way it flows determines how solar storms barrel through space. Sometimes, those storms crash into our planet’s magnetic field, sparking disturbances that can interfere with satellites and communications signals we use every day, like radio or GPS.

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Right now, scientists and engineers are in Fort Sumner, New Mexico, preparing to fly BITSE up to the edge of the atmosphere. BITSE will take pictures of the corona, measuring the density, temperature and speed of negatively charged particles — called electrons — in the solar wind. Scientists need these three things to answer the question of how the solar wind forms.

One day, scientists hope to send an instrument like BITSE to space, where it can study the Sun day in and day out, and help us understand the powerful forces that push the solar wind out to speeds of 1 million miles per hour. BITSE’s balloon flight is an important step towards space, since it will help this team of scientists and engineers fine-tune their tech for future space-bound missions.  

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Hours before sunrise, technicians from our Columbia Scientific Balloon Facility’s field site in Fort Sumner will ready the balloon for flight, partially filling the large plastic envelope with helium. The balloon is made of polyethylene — the same stuff grocery bags are made of — and is about as thick as a plastic sandwich bag, but much stronger. As the balloon rises higher into the sky, the gas in the balloon expands and the balloon grows to full size.

BITSE will float 22 miles over the desert. For at least six hours, it will drift, taking pictures of the Sun’s seething hot atmosphere. By the end of the day, it will have collected 40 feature-length movies’ worth of data.

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BITSE’s journey to the sky began with an eclipse. Coronagraphs use a metal disk to mimic a total solar eclipse — but instead of the Moon sliding in between the Sun and Earth, the disk blocks the Sun’s face to reveal the dim corona. During the Aug. 21, 2017, total eclipse, our scientists tested key parts of this instrument in Madras, Oregon.

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Now, the scientists are stepping out from the Moon’s shadow. A balloon will take BITSE up to the edge of the atmosphere. Balloons are a low-cost way to explore this part of the sky, allowing scientists to make better measurements and perform tests they can’t from the ground.

BITSE carries several important technologies. It’s built on one stage of lens, rather than three, like traditional coronagraphs. That means it’s designed more simply, and less likely to have a mechanical problem. And, it has a couple different sets of specialized filters that capture different kinds of light: polarized light — light waves that bob in certain directions — and specific wavelengths of light. The combination of these images provides scientists with information on the density, temperature and speed of electrons in the corona.

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More than 22 miles over the ground, BITSE will fly high above birds, airplanes, weather and the blue sky itself. As the atmosphere thins out, there are less air particles to scatter light. That means at BITSE’s altitude, the sky is dimmer. These are good conditions for a coronagraph, whose goal is taking images of the dim corona. But even the upper atmosphere is brighter than space.

That’s why scientists are so eager to test BITSE on this balloon, and develop their instrument for a future space mission. The solar scope is designed to train its eyes on a slice of the corona that’s not well-studied, and key to solar wind formation. One day, a version of BITSE could do this from space, helping scientists gather new clues to the origins of the solar wind.  

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At the end of BITSE’s flight, the crew at the Fort Sumner field site will send termination commands, kicking off a sequence that separates the instrument and balloon, deploys the instrument’s parachute, and punctures the balloon. An airplane circling overhead will keep watch over the balloon’s final moments, and relay BITSE’s location. At the end of its flight, far from where it started, the coronagraph will parachute to the ground. A crew will drive into the desert to recover both the balloon and BITSE at the end of the day.

For more information on how we use balloons for high-altitude science missions, visit: https://www.nasa.gov/scientificballoons

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