Gussto satelite - SRON artist impression
TU physicists are building terahertz sensors for Nasa’s ballooning mission, Gussto, set for launch in 2017. The mission will study interstellar dust and gas clouds where stars are born.
Terahertz astronomy opens a new window on the universe. In between radio waves and infrared radiation, terahertz waves travel long distances through interstellar space. On Earth however virtually all radiation is absorbed by moisture in the atmosphere, which is why terahertz astronomy, which promises to give clues about how stars and planets are formed out of gas clouds, is only practiced from the highest mountain peaks (Alma in Chile) or from satellites (Herschel space telescope, launched in 2009). The proposed Gussto mission will use a balloon to reach the edge of space at an altitude of 36 kilometres above the South Pole. The mission’s duration is two periods of 50 days each, with a refill in between for topping up the cryogenic helium.
The Gussto (Galactic/galactic Ultra long duration balloon Spectroscopic Stratospheric THz Observatory) mission is led by Professor Christopher Walker (University of Arizona), who selected SRON (Netherlands Institute for Space Research), and TU researcher Dr Jian-Rong Gao, to serve as the mission’s detectors. Why? “Because we’re the best in the world,” Gao explains, referring to the experience that Professor Teun Klapwijk’s research group at the Kavli Institute of NanoScience has in building terahertz detectors. The group was also involved in making the Herschel and Alma detectors.
A single-pixel detector 0,2 mm across
The new imager will be 1 square inch in size and feature 16 pixels consisting of improved supersensitive and low-noise detectors. Each detector has an on-chip antenna (smaller than 0.1 millimetre), and a superconducting nanobolometer, with a ‘hot’ electron in the middle, that remains on the verge of normal and superconductivity. Incoming terahertz radiation causes large variations in the electrical resistance. Moreover, the antenna’s signal is mixed with a reference signal in order to bring the frequency down to a manageable level – a technique called heterodyne detection.
Recent advances have increased the maximum detection frequency up to 4.7 THz, which is of particular interest as this allows for the detection of oxygen, as well as carbon and nitrogen, in space.
Gussto is one of two finalists in a Nasa competition: in 2013 the US space agency will decide which of the two projects will win a 55 million dollar grant.
