GUSTO is a balloon mission from NASA which will launch a high-altitude balloon with a one-meter telescope. 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 proposed SPICA telescope.
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. SRON and the Kavli Institute of Nanoscience of the TU Delft provide the key detector technology for GUSTO's 4.7 THz camera.
The balloon is tentatively scheduled for launch in 2021, from Antarctica. During its ~100 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. Prof. Alexander Tielens at Leiden University and dr. Frank Helmich at SRON are members of the science team. Dr. 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 of Delft University of Technology (TU Delft) provide the 8-pixel HEB-camera at 4.7 THz for GUSTO, which is based on a so-called superconducting Hot Electron Bolometer (HEB) mixer, making use of nanotechnology and operating at very low temperatures. SRON and TU Delft teamed with the Massachusetts Institute of Technology to provide quantum cascade laser local oscillator technology which helps the detector to measure the signal intensity with highly resolved frequency information. The detection technique is actually similar to what is used in SRONs molecule hunter HIFI, but the difference is that HIFI works only up to 1.9 THz.
The Hot Electron Bolometer mixer is the only sensitive coherent detector working at such a high frequency. The SRON-TU Delft collaboration is world leader in super-THz technology and has produced very high sensitivity mixers at ~4.7 THz., with noise performance just a bit more than four times the quantum noise limit. In addition, SRON and TU Delft will also provide 8-pixel HEB arrays for the 1.9 and 1.4 THz frequencies.