Circling Antarctica in a balloon at an elevation between 110,000 and 120,000 feet, or 17 miles above a typical airliner's cruising altitude, the Galactic/Extragalactic ULDB Spectroscopic Terahertz Observatory, or GUSTO, will study the interstellar medium in our Milky Way and beyond by observing the sky above most of the atmospheric water vapor that otherwise would obscure its view.
Scheduled for launch on Dec. 15, 2021, the high-altitude, Ultralong-Duration Balloon, or ULDB, balloon will silently rise into the cold, dry air above Antarctica with an airborne observatory in tow. GUSTO's science payload consists of a 1-meter telescope and various instruments mounted to a platform known as the gondola. The GUSTO payload will weigh close to 2 tons and run on about 1 kilowatt of electrical power generated by its solar panels.
Christopher Walker, a professor of astronomy in the UA's Steward Observatory with joint appointments in the UA's Colleges of Optical Sciences and Engineering, is the principal investigator of the GUSTO mission. The mission's science aims at measuring emissions from the interstellar medium. The data will help scientists determine the life cycle of interstellar gas in our Milky Way galaxy, witness the formation and destruction of star-forming clouds, and understand the dynamics and gas flow in the vicinity of the center of our galaxy.
"If we want to understand where we came from, we have to understand the interstellar medium," Walker said, "because 4.6 billion years ago, we were interstellar medium."
The interstellar medium, it turns out, is the stuff from which most of the observable universe is made: stars, planets, rocks, oceans and all living creatures, and GUSTO is uniquely equipped to probe the conditions inside it.
The telescope is outfitted with carbon, oxygen and nitrogen emission line detectors. This unique combination of data will provide the spectral and spatial resolution information needed for Walker and his team to untangle the complexities of the interstellar medium, and map out large sections of the plane of our Milky Way galaxy and the nearby galaxy known as the Large Magellanic Cloud.
Walker, who is a longtime amateur radio (ham) operator, explains that carbon atoms, nitrogen atoms and oxygen atoms in the interstellar medium act like tiny, very-high-frequency radio transmitters, and GUSTO is engineered to listen to what they have to say.
"We do this by using cutting-edge superconducting detectors and other instruments that allow us to listen in at these very high frequencies," Walker explained.
In December, his team successfully launched the Stratospheric Terahertz Observatory, or STO, which served as a pathfinder mission for GUSTO, in Antarctica. Carried by stable, circumpolar winds, the airborne observatory completed a three-week flight and collected data from a portion of the Milky Way.
"With STO, we proved our team is capable of making a balloon payload capable of mapping the interstellar medium on a much larger scale," Walker said.
GUSTO will map the Milky Way and also the Large Magellanic Cloud, which has hallmarks of a galaxy more commonly found in the early universe, Walker said.
"Our measurements will provide the data to help develop a model for early galaxies and our own Milky Way, which together will serve as bookends to understand the evolution of stars and galaxies through cosmic time," he said.
"GUSTO will provide the first complete study of all phases of the stellar life cycle, from the formation of molecular clouds, through star birth and evolution, to the formation of gas clouds and the re-initiation of the cycle," added Paul Hertz, astrophysics division director in the Science Mission Directorate in Washington. "NASA has a great history of launching observatories in the Astrophysics Explorers Program with new and unique observational capabilities. GUSTO continues that tradition."
Launched from McMurdo, Antarctica, GUSTO is expected to stay in the air between 100 to 170 days, depending on weather conditions. It will cost approximately $40 million, including the balloon launch funding and the cost of post-launch operations and data analysis.
NASA's Astrophysics Explorers Program requested proposals for mission of opportunity investigations in September 2014. A panel of NASA and other scientists and engineers reviewed two mission of opportunity concept studies selected from the eight proposals submitted at that time, and NASA has determined that GUSTO has the best potential for excellent science return with a feasible development plan.
"This work is an example of the innovative cutting-edge ideas that our faculty are turning into reality every day," said Kimberly Andrews Espy, the UA's senior vice president for research. "We very much appreciate the support from NASA and confidence in Dr. Walker and his team to deliver this next generation space technology. Utilizing the stratosphere holds great promise to transform our approach to imaging and observing, and the UA researchers are leading the way forward."
The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, is providing the mission operations and the gondola. The UA will provide the GUSTO telescope and instrument, which will incorporate detector technologies from NASA's Jet Propulsion Laboratory in Pasadena, California; the Massachusetts Institute of Technology in Cambridge; Arizona State University; and SRON Netherlands Institute for Space Research.
NASA's Explorers Program is the agency's oldest continuous program and is designed to provide frequent, low-cost access to space using principal investigator-led space science investigations relevant to the astrophysics and heliophysics programs in the agency's Science Mission Directorate. The program has launched more than 90 missions. It began in 1958 with the Explorer 1, which discovered the Earth’s radiation belts, now called the Van Allen belt, named after the principal investigator. Another Explorer mission, the Cosmic Background Explorer, led to a Nobel Prize. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the program for the Science Mission Directorate in Washington.