Instrument Lofted by Gigantic Helium Balloon to Near the Threshold of Space
By Edwin L. Aguirre
After two earlier attempts were canceled due to high winds, UMass Lowell researchers successfully launched a planet-finding telescope to the edge of the atmosphere from a NASA facility in New Mexico.
The 14-foot-long, 1,500-pound telescope – called PICTURE-C, which stands for Planetary Imaging Concept Testbed Using a Recoverable Experiment—Coronagraph – was carried aloft to the stratosphere by an unmanned, helium-filled balloon 400 feet wide and several stories high that was released from the Columbia Scientific Balloon Facility in Fort Sumner on Sept. 28.
PICTURE-C was designed, built and tested by a team of students, faculty researchers, scientists and engineers at the university’s Lowell Center for Space Science and Technology (LoCSST), with support from a $5.6 million grant from NASA. The team hopes the telescope will be able to detect debris disks or asteroid belts around exoplanets.
UML’s high-flying observatory spent 14 hours observing nearby stars at an altitude of 127,000 feet – roughly 3½ times higher than the typical cruising altitude of a passenger jetliner – to get above 99 percent of the Earth’s atmosphere.
“Atmospheric turbulence distorts and blurs our image of the stars,” notes Chakrabarti.
After completing its observations, ground controllers sent a command the following morning to release PICTURE-C from the balloon. A parachute was then deployed to slow down the telescope and allow it to land gently on the desert floor for reuse in a future mission.
Mendillo adds: “PICTURE-C used its deformable mirrors to create the first-ever high-contrast coronagraph image produced by an observatory not attached to the surface of the Earth. This is a huge step towards the goal of one day imaging and characterizing exoplanets from space.”
This mission was PICTURE-C’s second and final flight.
“The first one in 2019 was an engineering demonstration flight. That was also a big success, including the recovery,” says Chakrabarti. “This latest mission was the actual science flight, with the telescope gathering real scientific data for the project.”
The primary targets selected for this mission were Vega (Alpha Lyrae), which is one of the brightest stars in the sky, and Epsilon Eridani.
In the coming months, UML scientists will analyze the data that PICTURE-C captured.
Mendillo says balloons are well-suited to search for planets outside our solar system.
“We’ve used sounding rockets before, but balloons are an amazing platform to use for conducting cutting-edge exoplanet research because of their relatively low cost, ability to accommodate large payloads and long observing duration,” he says.
PICTURE-C features a coronagraph, a specialized optical imaging system coupled to a 24-inch-diameter telescope that is designed to “mask,” or block out, the direct light from the star so that faint objects very close to the star – such as planets and interplanetary dust, which otherwise would be hidden in the star’s bright glare – can be studied in great detail.
At this level of sensitivity and precision, maintaining the telescope’s ultrasharp focus is critical to the entire mission.
Thaddeus Potter, a Ph.D. student in physics working on his thesis research at LoCSST, is developing a time-dependent thermal model of PICTURE-C by attaching temperature sensors throughout the telescope structure. His goal is to characterize how temperature variation affects the telescope’s optical system as the balloon climbs. The temperature can drop to –40 degrees Fahrenheit at the telescope’s highest flight altitude.
“This is important in a very precisely aligned telescope,” says Potter.
According to Mendillo, the telescope’s performance will determine how many exoplanets the researchers will be able to detect.
High winds in the upper atmosphere buffeted the entire telescope during the observing session. To keep the coronagraph aimed precisely at the target, the instrument is mounted on a special NASA gimbal platform, called WASP (Wallops Arc-Second Pointer), located in the balloon’s gondola that can compensate for any unwanted movements. PICTURE-C used the platform in conjunction with an onboard active optical pointing control system designed and built by Mendillo and Physics Assoc. Prof. Timothy Cook, who is the project’s co-investigator.
“This control system can optically stabilize the light coming out of the telescope and keep the coronagraph centered on the target star to an accuracy of one milliarcsecond, or better,” says Mendillo. “A milliarcsecond is equivalent to resolving an object approximately 2 meters wide on the surface of the moon, which is about 385,000 kilometers away.”
For his part, Kuravi Hewawasam, who obtained his Ph.D. in physics from UML in 2020 and is now a postdoctoral researcher at LoCCST, co-wrote some of the software that makes the coronagraph work.
“The coronagraph has a deformable mirror that can change its shape at high speed and in real time according to the wavefront of the starlight that’s coming in. It first senses the wavefront and then applies the corrections to get the highest image quality possible,” says Hewawasam.
“We’re a small group. Everybody does everything. This is the only group in the entire world who’s actually putting instruments in near-space to validate all these technologies. That’s our contribution to the field,” he says.
“From building the coronagraph and adaptive optics to developing the telescope’s attitude control, temperature control and communications systems and flight software, what our people are doing at the level of precision necessary to accomplish a space mission is incredible,” Chakrabarti adds.
“We train all engineers to be scientists and all scientists to be engineers,” says Cook.
PICTURE-D: The Next Generation
Mendillo was recently awarded a five-year, $7 million grant by NASA to develop UML’s next generation of the planet-finding telescope, which will be dubbed PICTURE-D (Planetary Imaging Coronagraph Testbed Using a Recoverable Experiment for Debris Disks).
“It’s basically the same platform, same telescope,” he says. “We’re just making several major upgrades to the instrument to make everything work better. Currently, we can only look at one side of a star at a time. Adding a second deformable mirror allows us to look around the entire star at the same time at very, very high contrast. We’re also integrating a new type of coronagraph that will allow us to make polarization measurements of debris disks.”
NASA has also named Mendillo as a Nancy Grace Roman Technology Fellow, which gives early career researchers the opportunity to develop innovative technologies while growing the skills needed to lead astrophysics flight instrumentation development projects. He will receive $500,000 in funding as part of the fellowship program.
“The funding will help bring our research group to a new level,” Mendillo says, adding that it gives LoCSST the opportunity to add facilities or equipment to its lab and possibly hire new personnel.