Prof. Glenn Lightsey Selected by NSF to Help Solve Coronal Heating Question

Prof. Glenn Lightsey Selected by NSF to Help Solve Coronal Heating Question
Prof. E. Glenn lightsey
Prof. E. Glenn Lightsey

Prof. Glenn Lightsey has been selected by the National Science Foundation to collaborate with a team of universities and NASA on a new space mission that will employ novel CubeSat technology to expand our understanding of our own sun -- and, possibly in the future, to search for exoplanets around other stars.

Working on the VIrtual Super-resolution Optics with Reconfigurable Swarms (VISORS) mission, Lightsey will help design and deploy a 'distributed space telescope' - a three-piece CubeSat formation that will allow researchers to obtain high-resolution imagery of our sun's surface without ever leaving Earth orbit. The approximate price tag of this NSF venture – slightly over $4 million - compares with the $1.5 billion cost of the Parker Solar Probe, a NASA flagship spacecraft that traveled to within 15 million miles of the sun last month.

The two are not competing concepts, Lightsey explains. They are different approaches to conducting space science.

"This is a theme that I have pursued a lot in my research: how can we transform the way we use technology so that we can do more with less? The science doesn’t change, but as the technologies may cost orders of magnitude less to produce, they've opened up new opportunities for us to explore," said Lightsey.

"With VISORS, our team thought that if we could change the instrument gathering the data, we could get the high-resolution imagery that is needed from the Earth's orbit. So maybe you don't need to go to the sun to get very accurate images of the sun. Maybe you just need a more precise telescope at Earth."

An image of the fireball that is our Sun, courtesy of NASA

Solving an Unsolved Problem

A fundamental but unanswered question in heliophysics involves the solar wind - photons and other charged particles emanating from the sun. In keeping with the basic laws of physics, these particles become less dense and slow down as they spread farther away from the sun.

With one exception.

In the coronal region of the sun -- its outer halo -- the particles in the solar wind tend to gain energy, to speed up.

"There are a number of theories about this, but, in essence, it's still considered one of the unanswered questions," says Lightsey. "We know that the sun has a magnetic field, and that there might be some interaction with that field that causes this coronal heating. But, really, this has never been confirmed."

To answer that question, scientists need to more closely study the sun's surface, in part by gathering high-resolution images. That is where the VISORS mission comes in. Using spectroscopy to determine solar activity based on light frequencies, the three-part distributed space telescope should be capable of capturing filamentary coronal structures as narrow as 150 milliarcseconds -- that's roughly the size of a dime sitting atop the the Empire State Building as seen from a street corner in Paris.

"We are using this approach here to study the sun, to study this question about coronal heating," says Lightsey. "But, it is really transformational in what it can do for applications in astronomy, space physics, and space science. For example, we could also use this technology to detect new exoplanets."
Photo: Courtesy of NASA

The images this telescope delivers will help scientists tackle an unanswered question in heliophysics: why and how does the sun's coronal heating occur? (see box)

"That's the science question, and it's a good one," says Lightsey. "As an engineer, the problem is also quite challenging: how do you build an instrument that can study the sun at a resolution and at a distance scale that's never been done before?  We take images of the sun from the Earth all the time, but not at the resolution we'd need to study coronal heating."

A preliminary answer to this question was proposed this past February during the NSF's Ideas Lab Workshop. As one of the 40  scientists, engineers, and technologists invited to attend, Lightsey brainstormed ideas for advancing the use of CubeSat Formation Flying in the NSF's mission. The week-long incubator concluded with a Shark Tank-like competition, in which teams of participants vied to have their proposals funded by the NSF.

Lightsey was a participant in two of the proposals that were ultimately selected for funding: VISORS and SWARM-EX.

(stay tuned for a SWARM-EX update).

"Engineering Exquisite Choreography"

The novel architecture of the VISORS ultraviolet telescope is enabled by the CubeSat technology that Lightsey has helped develop during his career.  Three separately orbiting CubeSats - a lens, a detector, and a sunshade to block unwanted light - will each perform functions that contribute to the delivery of high-resolution images.

"There’s exquisite choreography that needs to take place between these three satellites to get the measurements we need. It's really amazing. Once, per orbit, they will come into alignment such that a beam of light will pass through all three at the same time," said Lightsey.

"We only need 10 seconds of alignment to get an image. And we just need one image, this time, to validate the technology."

The component CubeSats are precisely placed 40 meters apart, a distance that allows the right optical length for the light to travel. If they were housed in one unit, the resulting structure would be about half the size of the International Space Station, Lightsey observed

"That's an expense we're able to avoid with this," he noted.

Using spectroscopy -- an analysis of light frequencies and light absorption patterns -- scientists will use the distributed ultraviolet telescope to get a better idea of what is happening on the sun.

"The light frequencies are very important because they are very specific. We look at the light spectrum coming from the planets and the stars and we can tell things about their chemical composition by seeing what light is being absorbed before it reaches us."

Another novel aspect of this mission is the images it will produce.

The VISORS 'lens' is actually a 3D-printed metal plate with precisely-placed micron-sized holes that transform the entering light into diffraction patterns.The interaction of planned diffraction patterns creates a unique interference signature which can be measured by counting photons. Those measurements can then be transmitted to a computer that constructs a high-resolution image of what is happening on the sun at that particular frequency of light

Lightsey said that, as the systems integrator, the Georgia Tech-based team working on VISORS will play a significant role in its ultimate success.

"We will be the institution that puts the spacecraft components together, to make sure the complete system works as intended," he said. "And that's really a strength here at Tech. We are known for systems engineering."



Next Month: SWARM-EX


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