(Originally published by TU Delft)
November 1, 2011
NASA has recently selected five Explorer Mission Program of Opportunity proposals for a Phase A-Concept Study. GUSSTO, which stands for Galactic/Xgalactic Ultra long duration balloon Spectroscopic Stratospheric THz Observatory, is one of two astrophysics missions selected. Of these two missions NASA plans to choose one for flight. This is exciting news for the Kavli Institute of Nanoscience of Delft University of Technology (TU Delft) and SRON Netherlands Institute for Space Research, who will provide the key detector technology for GUSSTO's 4.7 THz camera.
The GUSSTO mission, led by Prof. Christopher Walker (PI) of the University of Arizona at Tucson (USA), 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. In that respect GUSSTO is complementary to the European Herschel space telescope (ESA), launched in 2009, and the Japanese SPICA telescope (JAXA) which will be launched in about 10 years from now and will carry the SRON led SAFARI instrument.
100 day flight
The balloon will be launched from Williams Field, Antarctic. During its ~100 day flight it will spiral out from Antarctica 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 NASA kick-off meeting for GUSSTO was on October 2011. It is going to take 11 months to conduct the mission concept study. If all goes well, the first GUSSTO flight may take place in December 2017.
Apart from the advanced technology, Leiden University’s Alexander Tielens will contribute strongly to the science (i.e., astrophysics and data analysis) of GUSSTO as well as Frank Helmich of SRON. Jian-Rong Gao at TU Delft and SRON is a key member of the team developing the 4.7 THz camera.
GUSSTO will be equipped with three 16-pixel heterodyne cameras operating at 4.7, 1.9 and 1.4 THz respectively, will simultaneous provide astronomical observations of neutral oxygen (OI), singly ionized carbon (CII) and singly-ionized nitrogen (NII) lines during ~100 days of operation (1 THz equals 300 micrometers in wavelength). GUSSTO will map the structure, dynamics, energy balance, pressure, and evolution of the interstellar medium within the Milky Way and LMC with the spectral and spatial resolution needed to untangle the complexities of the interstellar medium. “The ability to carry out the first large-scale surveys with velocity-resolved imaging of key fine structure lines is going to be a landmark in astrophysics," remarked GUSSTO project scientist Paul Goldsmith from the Jet Propulsion Laboratory in Pasadena, California.
The Kavli Institute of Nanoscience of the TU Delft and SRON will provide the key detector technology for the 4.7 THz camera for GUSSTO, which is based on a so-called superconducting hot electron bolometer (HEB) mixer, making use of nanotechnology and operating at very low temperatures. TU Delft and SRON will team with the Massachusetts Institute of Technology (MIT) 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. TU Delft-SRON is a 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. The work at TU Delft-SRON has been financially supported by different funding agencies such as ESA, EU FP7, NWO, and KNAW. The last two are supporting a joint research activity between The Netherlands (SRON and TU Delft) and China (Purple Mountain Observatory, Nanjing) and play a crucial role for the most recent development.