Early this year, Ball Aerospace delivered a cryostat to the University of Arizona (U of A) for NASA’s Galactic/Extragalactic Ultralong-Duration Balloon Spectroscopic Terahertz Observatory (GUSTO). GUSTO is a long-duration balloon mission that will map out parts of the Milky Way and Large Magellanic Cloud galaxies to determine the life cycle of interstellar gas, witness the formation and destruction of star-forming clouds and understand the dynamics and gas flow in the vicinity of the center of the Milky Way. The Ball-built cryostat is a low heat leak dewar that contains liquid helium and is designed to keep the GUSTO instrument cool during the entire length of the planned balloon flight.
Cold Facts spoke with Ball’s David Glaister, Cryogenics Department manager, and Gary Mills, GUSTO technical lead, regarding the cryostat development.
“GUSTO is a terahertz observatory on a helium balloon in the Antarctic,” Glaister explains. “The atmosphere is low humidity and is ‘pulled down’ in that region for good astronomy conditions. The wind circulation around the continent brings the balloon back around to the launch site every 14 days, give or take about 100 km.”
Observing at a terahertz wavelength means that the instrument has to be cooled below 4.5 K. “Arizona’s Dr. Chris Walker, GUSTO mission principal investigator, was having trouble keeping the system at the necessary temperature for more than a couple of hours,” Glaister adds. “Ball has designed systems that last for years, so Walker and his team reached out for help.”
Ball’s aerospace cryogenics experience started with the Gemini and Apollo missions, leading to one of the largest bodies of cryogenic work in the industry. Glaister and Mills have worked together on space applications in the past on other 4 K systems. They’d even worked with U of A in the past.
“Our biggest problem is heat leak,” Mills states. “The dewar uses a Sunpower (CSA CSM) cryocooler to help cool the outer vapor cooled shield, removing 8 watts at 70 K. We used enthalpy from the cold gaseous helium to cool the outer and inner shields and relied on Ball’s MLI Center for Excellence to make struts and supports on our heritage systems. We had to reduce parasitic for wiring and tubing, but that was about it.”
“The tank and vacuum shell are from Meyer (CSA CSM),” Glaister adds. “External fixtures were made by Cryofab (CSA CSM) while American Magnetics (CSA CSM) added a superconducting liquid level probe and Lake Shore Cryotronics (CSA CSM) supplied the silicon diodes. Almost everything else was built in-house at Ball.”
Managed by Leslie Buchanan from Ball’s Civil Space business unit, with lead designer Brian Buchholtz, the dewar qualification testing was done at Ball’s cryo test facility.
According to Mills, the first helium fill had very high heat leak and boiloff. “Thermoacoustic oscillations were to blame,” he says. “We used existing research to design a damper for the system that had 600 milliwatts in heat leak. With a little fine tuning, our final tests showed 44 milliwatts of heat leak, which would give the system 103 days of operational time—which more than met the requirement.”
The dewar has been delivered to U of A, which is installing final flight instruments and conducting tests. GUSTO, which is part of NASA’s Astrophysics Explorers Program, is scheduled to launch from Antarctica in 2021. Only one flight is currently planned but there is a possibility for a re-flight. Johns Hopkins University’s Applied Physics Laboratory will provide the mission operations.
Ball has more than 60 years of experience developing cryogenic spaceflight systems. This cryogenic experience includes cryogenic cooling systems such as cryostats, cryoradiators, cryocoolers and thermoelectric coolers. For example, Ball developed the cryocooler for NASA’s Thermal Infrared Sensor-1 (TIRS-1) and TIRS-2 and the cryoradiators for the James Webb Space Telescope (JWST). TIRS-1 is flying onboard Landsat 8 and Ball delivered the TIRS-2 cryocooler in 2018 to NASA Goddard for the Landsat 9 satellite.
“We’d like to continue to support Chris on future Antarctic stuff, especially because he wants to take this research to space to look at the origins of the universe,” Glaister summarizes. “If they’re in space, we’d have to go to cryogenic refrigerator systems, which we also build. So, the future challenge is applying this technology to the environment of space.”