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STO-2 launch configuration (from left to right: Helium balloon, parachute, launch vehicle and payload).
Above: STO-2 launch configuration (from left to right: Helium balloon, parachute, launch vehicle and payload).

Radio-Telescope

From Antarctica to the Stars

Jose Siles - Jon Kawamura - Darren Hayton
NASA deploys radio telescopes on balloons to gain fundamental insights into the origin and development of the solar system and of stars in distant galaxies. The Stratospheric Terahertz Observatory (STO-2), a balloon-borne radio telescope featuring cutting-edge MDL submillimeter-wave technology, was launched from NASA’s Long Duration Balloon Facility (LDB) in Antarctica in December 2016. STO-2 looked for carbon, oxygen, and nitrogen in star forming regions of our galaxy. Antarctica is a harsh continent, and assembling and preparing for flight one of the most advanced submillimeter-wave radio telescopes in the world, in just a few weeks, was certainly challenging. Having the opportunity to spend more than two months in one of the most beautiful places in the world, flying technology that the team developed was an extremely rewarding once-in-a-lifetime experience.

The JPL researchers were very inspired by the fact that the innovative technologies developed at MDL will help humankind better understand how the universe evolves and how stars and planets form. The submillimeterwave technology worked on at JPL is also used to develop instruments that are able to detect water in ocean worlds and analyze its composition, study the chemical composition of planet atmospheres, monitor Earth’s health, and even detect cancer. There is a unique team spirit at JPL. To quote one of the team, “I love having the opportunity to work with such an amazing group of people from so many different cultures, and with so many great qualities, both personally and professionally. I learn something new from them every day and this is certainly priceless to me.”

The Stratospheric Terahertz Observatory is a NASA-funded program led by the University of Arizona, with JPL, the Applied Physics Laboratory (APL), Arizona State University (ASU), and the Dutch Space Agency (SRON), as Co-I institutions. It is a balloon-borne 80-cm radio telescope consisting of five high-resolution heterodyne superconductive receivers to observe carbon ([CII] line at 1.9 THz), nitrogen ([NII] line at 1.46 THz), and oxygen ([OI] line at 4.7 THz) in our galaxy. These tracers are key to understanding the processes governing the formation of interstellar clouds and stars, which is crucial for unraveling the evolution of galaxies.

Carried by a ~400-ft-diameter helium balloon, STO-2 remained operative throughout its three-week baseline mission, gathering data 24 hours a day. Antarctica is an ideal location for balloon borne telescopes since the polar anticyclone keeps the payload circling the continent and makes it possible to land and recover the instrument once the mission is completed.

JPL delivered state-of-the-art four-pixel frequency multiplied local oscillator (LO) systems for [CII] and [NII] receivers featuring Schottky diode–based frequency multipliers. Local oscillators are the most critical components of these receivers and their fabrication at the MDL requires submicron precision. Unlike the superconducting detectors, the LOs were mounted outside the cryostat and totally exposed to the environment during launch, ascent, and mission operations, which made the design much more challenging. The flight of STO-2 was the first time room temperature; multi-pixel frequency-multiplied local oscillator sources above 1 THz have been successfully flown and operated in a stratospheric balloon environment. This confirms JPL’s leadership in the field and its ability to deliver multipixel LO sources for future NASA missions and platforms, such as SOFIA and the Cosmic Origins Space Telescope.

Based on the success of STO-2, NASA recently funded a follow-on mission: the Galactic/ExtraGalactic Ultra-long-duration Stratospheric Terahertz Observatory (GUSTO). GUSTO, a NASA Explorer Mission of Opportunity, will feature 24 receivers total (eight per band) and will be launched from LDB in December 2021. NASA’s brand-new Ultra Long Duration Balloon will carry it with a planned mission of 100 days.

These spectacular technical advances result from cooperation in JPL, not competition. To quote one researcher, “There is a unique team spirit at JPL. I love having the opportunity to work with such an amazing group of people from so many different cultures, and with so many great qualities, both personally and professionally. I learn something new from them every day and this is certainly priceless to me.”
Close-up view of the 4-pixel 1.9 THz local oscillator delivered by JPL.
Close-up view of the 4-pixel 1.9 THz local oscillator delivered by JPL.
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Left: STO-2 “first light” [CII] integrated intensity map of a small region in NGC 3567. <br/><br/> Right: STO-2 payload with solar panels attached, ready for launch. It is ~22 ft wide and ~34 ft tall and weighs ~5000 lbs.
Left: STO-2 “first light” [CII] integrated intensity map of a small region in NGC 3567.

Right: STO-2 payload with solar panels attached, ready for launch. It is ~22 ft wide and ~34 ft tall and weighs ~5000 lbs.
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