Prof. Dr. rer. nat. Alfred Krabbe

Barbara Klett

Dr.-Ing. Thomas Keilig

Deputy SMO Director (Kalifornien)

Standortleiter AFRC & SOFIA Teleskop Manager
Dipl.-Ing. Michael Hütwohl

Standortleiter ARC & und Facility Scientist
Dr. rer. nat. Jürgen Wolf

Technology Advisor
Prof. Dr.-Ing. Jörg Wagner

Bildungs- und Öffentlichkeitsarbeit
Dr. rer. nat. Dörte Mehlert

Deutsches SOFIA Institut
Pfaffenwaldring 29
70569 Stuttgart

Tel. +49 (0)711/685-62379
Fax +49 (0)711/685-63596


Astronomical Telescope of the University of Stuttgart

The ATUS 0.6-meter Ritchey-Chrétien telescope

The Astronomical Telescope of the University of Stuttgart (ATUS) has been established by the university's Institute of Space Systems (IRS) with support of the Stratospheric Observatory for Infrared Astronomy (SOFIA), funded by the DLR Space Administration. The telescope is managed and operated by the German SOFIA Institute (DSI), a department of the IRS. For the university the telescope serves as a training platform for aerospace engineering students in basic astronomy and in remote control of complex systems.  M.Sc. and Ph.D. students use it as a research instrument for their engineering and astronomy projects. For SOFIA, it is used as a test platform to evaluate new hardware and software before the integration on the airborne observatory. In some cases, the telescope is also used to support SOFIA missions by providing preparatory or parallel measurements of a target or to conduct follow-up observations.

The ATUS is a 0.6 meter fully reflective telescope in Ritchey-Chrétien configuration made by Officina Stellare, Italy. Its primary and secondary mirrors are made of the ultra-low-expansion glass ceramics, CLEARCERAM-Z HS supplied by the Ohara Corporation, Japan. The primary mirror has a conically shaped backside to reduce its weight. The secondary mirror cell is motorized to shift the mirror along the optical axis for focusing. The optical tube assembly is a dual carbon fibre truss structure with titanium alloy joints. A German equatorial mount made by Astro-Physics (AP3600GTOPE) carries the telescope and allows slew speeds of up to 2.5 degrees per second. A precision encoder system at the polar axis of the mount provides nominal guiding accuracy better than 0.5 arcsec over periods of 20 minutes.

The fast Andor iXonEM+ EMCCD camera at the RC focus

The first and primary instrument at the Ritchey-Chrétien focus is a back-illuminated EMCCD camera made by Andor, Belfast combined with a 10-position filter wheel containing a Sloan filter set. The same camera and a similar filter set are used in SOFIA's new Focal Plane Imager (FPI+). It offers high quantum efficiency (ηPeak > 90%), high frame rates and virtually gap free imaging thanks to the sensor's frame-transfer architecture. Very low dark currents are achieved by the camera's thermoelectric cooler that cools the sensor as much as 95ºC below ambient. The main telescope is complemented by a piggy-back mounted Wide Field Imager which consists of a ProLine Camera made by Fingerlakes Instrumentation with an e2v CCD47-20 sensor and a commercial 135 mm Canon photo lens. This set-up is similar to the SOFIA Wide Field Imager. A 130 mm, f/6.2 refractor will eventually complement the instrument as a guide scope.

The ATUS is located at the Sierra Remote Observatories (SRO) in the foothills of California's Sierra Nevada, a location with seeing conditions in the 1 to 1.5 arcsec range in summer. The telescope's control computer and software are set up for remote access via an internet connection. It is remotely operated from the SOFIA Science Center in Moffett Field, California and from Stuttgart, Germany.


Optical characteristics of the ATUS and its instrumentation


ATUS Optical System

Free primary mirror diameter, D 0.6 m
Primary mirror focal ratio N = 3, f/3
Secondary mirror diameter 0.22 m
Secondary mirror obstruction, area          13 %
System focal length, f (nominal) 4.780 m 
System focal ratio (nominal) N = 8, f/8
System optical configuration RC
Diffraction limit, DAiry = 2.44 ⋅ λ/D 0.46 arcsec


Primary Instrumentation

EMCCD Camera in the RC focus             Andor iXonEM+ DU-888 BI
Sensor 1024 x 1024 pixels
Pixel 13 x 13 µm2
Field-of-view on sky 9.53 x 9.53 arcmin2
Pixel field-of-view 0.56 x 0.56 arcsec2
Frame rate 8.9 fps full frame, unbinned
with binning & subframing up to 400 fps


Wide Field Imager

Custom FLI ProLine Camera                    e2v CCD47-20
Sensor 1024 x 1024 pixels
Pixel 13 x 13 µm2
Lens f/2.8 f = 135 mm
Field-of-view on sky 5.65 x 5.65 deg2
Pixel field-of-view 19.9 x 19.9 arcsec2
Frame rate 1.5 fps full frame, unbinned
128 x 128, unbinned 5.6 fps