Design of a Quasi Optical HEB Array
Phase grating to generate multiple LO beams
4.7 THz quantum cascade laser (QCL) local oscillator unit. The QCL inside is developed by MIT/Sandia

GUSTO is a NASA mission that will launch a high-altitude balloon including a one-meter telescope. With a scheduled launch in December 2023, the aim is to provide a comprehensive understanding of the inner workings of our galaxy and one of our companion galaxies, the Large Magellanic Cloud (LMC), by tracing all phases of the interstellar medium.

GUSTO (Galactic/extragalactic Ultra long duration balloon Spectroscopic Stratospheric THz Observatory) is complementary to the European Herschel space telescope (ESA, 2009-2013), and the SPICA telescope which is now one of the three candidates for the M5 mission in ESA’s Cosmic Vision science programme. SRON and the Kavli Institute of Nanoscience of the Delft University of Technology provide the key detector technology for GUSTO’s 1.4, 1.9 and 4.7 THz cameras.


The balloon is scheduled for launch in December 2023, from Antarctica. During its ~55 day flight it will spiral out from the Antarctic circling the Earth. As it drifts northward, more and more of the Milky Way will become visible, allowing a large scale survey to be performed. At its flight altitude of ~36 km there is only a trace amount of water vapor, the primary source of absorption at THz frequencies. Therefore, the observing conditions are nearly the same as in space.


The observations of key astronomic cooling lines allow astronomers to trace star formation and galactic evolution. The fine-structure line of electrically neutral atomic oxygen (OI) at 4.7 THz is the dominant cooling line of warm, dense, and neutral atomic gas. In strongly UV irradiated photodissociation regions (PDRs), the OI line flux is generally larger than that of the carbon CII line, making it an ideal diagnostic for probing the physical conditions in regions of massive star formation and galactic centers. The spectrally resolved OI line is necessary to untangle the complexities of the interstellar medium.

Dutch scientists will contribute to the science (i.e., astrophysics and data analysis) of GUSTO. Xander Tielens at Leiden University and Frank Helmich at SRON are members of the science team. Jian-Rong Gao at SRON and TU Delft is a key member of the team developing the 4.7 THz camera.


SRON and the Kavli Institute of Nanoscience provide the 8-pixel cameras for GUSTO’s channels at 1.4, 1.9 and 4.7 THz, based on a so-called superconducting Hot Electron Bolometer (HEB) mixer. They managed to get the noise performance close to four times the quantum noise limit. SRON and TU Delft teamed with the Massachusetts Institute of Technology to provide quantum cascade laser local oscillator technology to increase the spectral resolution. The detection technique is similar to what is used in SRON’s molecule hunter HIFI in the Herschel telescope, with the difference that HIFI worked only up to 1.9 THz.

Jose Silva is in Antarctica between November 2023 and January 2024 on behalf of SRON. Read his blog here.