Successful review of the German GREAT receiver for first observations with the US-German SOFIA airborne observatory
GREAT, the “German REceiver for Astronomy at Terahertz Frequencies”, is a receiver developed in Germany for the airborne observatory SOFIA (“Stratospheric Observatory For Infrared Astronomy”). In December 2008, GREAT successfully managed its pre-shipment review after extensive laboratory tests and will now be shipped to its first observing mission on board of SOFIA. GREAT is built by a consortium of German research institutes led by Dr. Rolf Guesten from the Max-Planck-Institut fuer Radioastronomie in Bonn. It is one of the two receivers to be used in the first scientific flights of the observatory summer 2009. SOFIA is a joint US-German research project for operating an airborne observatory in an altitude of 13-14 km in the stratosphere, thus allowing an investigation of the universe in far-infrared light, at wavelengths which are otherwise completely absorbed by water vapour in lower layers of the atmosphere.
The pre-shipment review for GREAT took place from December 4-5, 2008 at the Max-Planck-Institut fuer Radioastronomie (MPIfR). The review was led by the German Space Agency (DLR) under participation of experts from the American space agency NASA. The concluded that GREAT in its present configuration will be able to reach its scientific goals and does also meet the hard technical requirements imposed by NASA for flight worthiness and safety. “We are now ready for the transport of GREAT to the USA, to install the instrument to the SOFIA telescope and to use it for the first scientific observations”, says Dr. Stefan Heyminck from MPIfR, the project engineer responsible for GREAT.
The GREAT consortium comprises the MPIfR Bonn and the I. Physikalisches Institut, Universitaet zu Koeln. Additional partners are the DLR Institute of Planetary Research and the Max-Planck-Institut fuer Sonnensystemforschung. GREAT is a receiver with high spectral resolution for the flight observatory SOFIA, used in the stratosphere to observe far-infrared radiation in a frequency range of 1.2 to 5 Terahertz (THz) which is not accessible from ground. Thus GREAT extends the spectral range provided by the Atacama Pathfinder Experiment (APEX) to higher frequencies. The 12m APEX telescope at an altitude of 5100 m in the Chilean Atacama desert is complementary to SOFIA. It is managed by MPIfR with partners and observes in a frequency range between 0.2 and 1 THz still accessible from ground.
“Because of the water vapour absorption in the atmosphere it is extremely difficult if not impossible to observe radiation beyond a frequency of 1 THz from ground”, says Dr. Rolf Guesten from MPIfR who is in charge of the GREAT project. “Only at flight altitudes of 12 km or more the atmosphere becomes transient for far-infrared radiation from the universe.”
Thus, scientists of the GREAT consortium, supported by American and German astronomers, will open a barely explored frequency range for astronomical investigations and increase our insight of physical processes in the interstellar medium leading to the formation of young stars and planetary systems. GREAT will observe the strongest emission lines cooling the interstellar medium, in particular fine-structure transitions of ionized carbon and nitrogen, and trace the energy balance of the investigated objects. The balance between heating and cooling processes regulates the temperature of the interstellar medium and thereby the formation of new stars. The study of the physical and chemical environment of young stars, throughout the Milky Way and in nearby galaxies, will be in main focus for research with GREAT.
For planetary science, GREAT will allow unique investigations of, e.g., Venus, and how the atmosphere of our sister planet has diverged from our own. Titan will be studied, with its atmospheric chemistry resembling a low-temperature analog to pre-biological Earth.
The GREAT project, supported by the Max Planck Society, the German Space Agency and the Deutsche Forschungsgemeinschaft (DFG) through the “Sonderforschungsbereich 494”, utilizes borderline technologies where the participating institutes play a worldwide leading role. A vast technological progress in the development of extremely fast superconducting detectors enables the construction of very sensitive receivers for the Terahertz range to be used astronomically with GREAT. For the spectral analysis of the signals GREAT utilizes a number of spectrometers of the latest generation.
SOFIA is a joint project of “Deutsches Zentrum fuer Luft- und Raumfahrt” (DLR) in Germany and National Aeronautics and Space Administration (NASA) in USA. A Boeing 747-SP airplane was modified and a high-precision telescope with a mirror of 2.7 m diameter and 17 tons total weight was implemented in the rear part of the plane. The German contribution to the project includes development and construction of the telescope as core part of the observatory and support with implementation and operation in the expected lifetime of 20 years.
The American operation center for SOFIA is NASA Dryden Flight Research Center in California; the German part is operated by the “Deutsche SOFIA-Institut” (DSI) at Stuttgart University on behalf of DLR.
SOFIA: SOFIA, the “Stratospheric Observatory for Infrared Astronomy” is a joint project of the German Space Agency (Deutschen Zentrums fuer Luft- und Raumfahrt e.V., DLR) and the National Aeronautics and Space Administration (NASA). It is funded on behalf of DLR by federal (Bundesministerium fuer Wirtschaft), state (Baden-Wuerttemberg) and University (Stuttgart) means. Scientific operation in Germany is coordinated by the “Deutsches SOFIA-Institut” (DSI) of Stuttgart University, in USA by Universities Space Research Association (USRA).
GREAT: GREAT, the “German Receiver for Astronomy at Terahertz Frequencies”, is a receiver for spectroscopic observations at far-infrared frequencies between 1.2 and 5 Terahertz (60-220 um wavelength), not accessible from ground because of water vapour absorption. The receiver will be used at the airborne observatory SOFIA. GREAT has been built as one of two German SOFIA instruments of the first generation by a consortium of German research institutes (MPIfR Bonn, Universitaet zu Koeln, DLR-P Berlin, MPS Lindau). Project manager for GREAT is Dr. Rolf Guesten (MPIfR). The development of the instrument was financed by means of the participating institutes, Max Planck Society and German Research Society within the framework of SFB 494.
Pre-shipment Review: The pre-shipment review took place from December 4 to 5, 2008, at MPIfR in Bonn.
