Leitung
Prof. Dr. rer. nat. Alfred Krabbe

Assistenz
Barbara Klett

Geschäftsleitung
Dr.-Ing. Thomas Keilig

Deputy SMO Director (Kalifornien)
N.N.

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

 

Michael Lachenmann

Dr.-Ing. Michael Lachenmann
Optical Raytracing and Finite Element Models

This picture shows  Michael Lachenmann
Phone +1 650 604 4536
Room Building N211 Room 118
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Stratospheric Observatory for Infrared Astronomy - SOFIA
Deutsches SOFIA Institut - DSI
NASA Ames Research Center
Mail Stop N211-1
Moffet Field, CA 94035
USA

Subject:
  • Optical Raytracing
  • Environmental Tests
  • Small Satellite  Lunar Mission BW1
  • Small Satellite  Flying Laptop
  • Orbital simulations
  • Design of Imaging systems
Publications:
Environmental testing for new SOFIA flight hardware

M. Lachenmann, J. Wolf, R. Strecker, B. Weckenmann, F. Trimpe, and H. Hall.
SPIE Astronomical Telescopes and Instrumentation, 91452V, International Society for Optics and Photonics, 2014.

Abstract: The Stratospheric Observatory for Infrared Astronomy (SOFIA) uses three visible range CCD cameras with different optics for target acquisition and tracking. The Wide Field Imager (WFI with 68mm f/2.0 optics) and the Fine Field Imager (FFI with 254mm f/2.8 optics) are mounted on the telescope front ring and are therefore exposed to stratospheric conditions in flight. The Focal Plane Imager (FPI) receives visible light from the 2.5m Cassegrain/Nasmyth telescope via a dichroic tertiary mirror and is mounted inside the pressurized aircraft cabin at typically +20°C. An upgrade of these three imagers is currently in progress. The new FPI was integrated in February 2013 and is operating as SOFIA’s main tracking camera since then. The new FFI and WFI are planned to be integrated in summer of 2015. Andor iXonEM+ DU- 888 cameras will be used in all three imagers to significantly increase the sensitivity compared to the previous CCD sensors. This will allow for tracking on fainter stars, e.g. the new FPI can track on a 16mag star with an integration time of 2 sec. While the FPI uses a commercial off the shelf camera, the cameras for FFI and WFI are extensively modified to withstand the harsh stratospheric environment. The two front ring imagers will also receive new optics to improve the image quality and to provide a stable focus position throughout the temperature range that SOFIA operates in. In this paper we will report on the results of the new FPI and the status of the FFI/WFI upgrade work. This includes the selection and design of the new optics and the design and testing of a prototype camera for the stratosphere. We will also report on preparations to make the new FPI available for scientific measurements.

Upgrade of the SOFIA target acquisition and tracking cameras

J. Wolf, M. Wiedemann, E. Pfüller, M. Lachenmann, H. Hall, H.-P. Röser.
SPIE Astronomical Telescopes and Instrumentation, 91450W, International Society for Optics and Photonics, 2014.

Abstract: The Stratospheric Observatory for Infrared Astronomy (SOFIA) uses three visible range CCD cameras with different optics for target acquisition and tracking. The Wide Field Imager (WFI with 68mm f/2.0 optics) and the Fine Field Imager (FFI with 254mm f/2.8 optics) are mounted on the telescope front ring and are therefore exposed to stratospheric conditions in flight. The Focal Plane Imager (FPI) receives visible light from the 2.5m Cassegrain/Nasmyth telescope via a dichroic tertiary mirror and is mounted inside the pressurized aircraft cabin at typically +20°C. An upgrade of these three imagers is currently in progress. The new FPI was integrated in February 2013 and is operating as SOFIA’s main tracking camera since then. The new FFI and WFI are planned to be integrated in summer of 2015. Andor iXonEM+ DU- 888 cameras will be used in all three imagers to significantly increase the sensitivity compared to the previous CCD sensors. This will allow for tracking on fainter stars, e.g. the new FPI can track on a 16mag star with an integration time of 2 sec. While the FPI uses a commercial off the shelf camera, the cameras for FFI and WFI are extensively modified to withstand the harsh stratospheric environment. The two front ring imagers will also receive new optics to improve the image quality and to provide a stable focus position throughout the temperature range that SOFIA operates in. In this paper we will report on the results of the new FPI and the status of the FFI/WFI upgrade work. This includes the selection and design of the new optics and the design and testing of a prototype camera for the stratosphere. We will also report on preparations to make the new FPI available for scientific measurements.

Missionsanalyse und Nutzlastauswahl des Kleinsatelliten Lunar Mission BW1

M. Lachenmann.
PhD thesis, Universität Stuttgart, 2012.

Abstract: The small satellite Lunar Mission BW1, currently being developed at the Institute of Space Systems, will be the first spacecraft, built by a university, which will travel to the Moon. To achieve this goal, the approximately 1 m3 large probe with a launch mass of around 300 kg will be equipped with several electric thrusters. After reaching a low lunar orbit, the spacecraft will circle the Moon for more than six months, while gathering scientific data and transmitting it back to Earth. This thesis contributes to the mission analysis to define the payload of a lunar small satellite in general and of Lunar Mission BW1 in particular. Due to highly limited resources in developing a small satellite by a university, their development philosophy often differs from satellite missions developed by the space agencies and the industry. In the end, this leads not to the development of a satellite bus based on a specific payload but to the selection of a payload, which fit to a specific satellite capable of certain tasks. The payload selection is hereby influenced by four parameters, which are determined in this thesis: the scientific application in comparison to previous lunar missions, the transfer trajectory and the final orbit around the Moon, the communication link, and the observation strategy. These parameters are illustrated at an exemplary set of payload instruments, which includes a high-resolution camera in the visual spectral range, a thermal infrared camera, an instrument to detect lunar-transient phenomena, and a detector for dust in the cis-lunar environment. In order to define requirements on the payload and mission-critical sub-systems, several low-thrust trajectories were simulated and analyzed on their transfer time, mass, and radiation loads. Depending on the strategy, the transfer time ranges between 150 and 1 500 days and fuel consumption reaches between 166 kg to 111 kg, respectively. The fuel consumption is especially restricted in small satellites, which was also taken into account for at the research of the orbital lifetime. Low-altitude lunar orbits are usually very unstable, requiring the satellite to actively raise its orbit once in a while. The simulations use a lunar gravity model of 100th degree and order to determine a specific orbit, which features high ground coverage, small orbital fluctuations, and long orbital lifetime. It is shown that an inclination of 84 deg promises a particularly stable orbit, which only exhibits altitude changes of less than 30 km and thus requires no maneuvers within a year. This helps to reduce fuel and extends the observation time. Calculations of the expected radiation input during the whole mission period enables the selection of adequately resistant components and the dimensions of the required shielding. Imaging instruments are often expected to achieve a complete ground coverage, which is also the goal for Lunar Mission BW1. The conducted simulations regard different swath widths and operational constraints, as they result from the satellite geometry and the properties of the payload instruments. A swath width of 15 km shows the best trade-off 23 Abstract between signal-to-noise ratio, ground resolution, accumulated data, communication duration, and time. When using the maximum amount of possible communication links to one ground station, data rates of approximately 10 Mbit/s are sufficient to process and transmit the images. This could be adequately achieved with Ka-Band communication. Also the onboard memory unit was optimized regarding its capacity and size. The results of each chapter are summarized and combined to present a realistic basis for the payload selection.

A new backup secondary mirror for SOFIA

M. Lachenmann, M. Burgdorf, J. Wolf, and R. Brewster.
SPIE Astronomical Telescopes and Instrumentation, 84442S, International Society for Optics and Photonics, 2012.

Abstract: The telescope of the Stratospheric Observatory for Infrared Astronomy (SOFIA) is a Cassegrain design with a convex, hyperbolic secondary mirror. It is 352 mm in diameter, was made from silicon carbide and weighs only 1.9 kg. As this material is brittle, and the secondary mirror is indispensable to observations with SOFIA, a backup with the same mass and moments of inertia was made of aluminium in 2004. This mirror, however, allows diffraction-limited observations only above 20 μm and it produces double peaked images. In this paper we discuss the requirements for a new backup secondary mirror that can be employed also at near-infrared and even visible wavelengths and describe the most important aspects of the manufacturing process. The starting point of our analysis was a high-precision measurement of the surface properties of the existing aluminium secondary mirror, using the NANOMEFOS technique, which was recently developed by TNO in Delft, the Netherlands. With the exact shape of the mirror as input for a Zemax model we could reproduce the results of actual measurements of its optical performance that had been carried out on SOFIA in 2004. Based on these findings we determined then the specifications to be fulfilled by a new backup secondary mirror in order to meet the requirements on improved optical performance. Finally, we discuss the dynamic deformation of the aluminium mirror during chopping motions.

Analyses of orbital lifetime and observation conditions of small lunar satellites

O. Zeile, M. Lachenmann, E. Baumstark, A. Mohr, D. Bock, R. Laufer, N. Sneeuw, and H.-P. Roeser.
Acta Astronautica. Vol. 66(3-4):516-527, Februar 2010.

Abstract: The Moon's gravitational field shows large inhomogeneities that strongly influence the shape of an orbit and can severely influence the orbital lifetime and observation conditions of any spacecraft orbiting the Moon. Small lunar spacecrafts are especially affected by those unstable orbits because their limited mass leaves little to no fuel reserves for excessive orbit maintenance maneuvers. Therefore, it may be favorable to choose an orbit, which features not the ideal observation conditions, but requires less Delta-V for orbit maintenance. These limitations have to be considered during mission design as they affect both the potential capabilities and the lifetime of the satellite. To characterize these limiting factors, simulations and analyzes based on up-to-date high degree and order gravity models were conducted with regard to the upcoming small lunar satellite Lunar Mission BW1 of the Institute of Space Systems (IRS) of the Universitaet Stuttgart. The cubical-shaped spacecraft with an edge length of 1 m and a mass of approximately 200 kg will use its own all-electrical propulsion system to reach a high-inclined low lunar orbit. Due to the limited fuel mass and operational lifetime of the thrusters, we consider the orbit maintenance capabilities of the probe to be minimal. Measures to maximize orbital lifetime with the least amount of propellant have to be taken and target orbits have to be examined carefully. This paper shows the results of simulations, which analyze ground coverage and access times, as well as simulations of orbital lifetime and changes in orbital parameters. Additionally, suitable, long lasting target orbits for small lunar spacecrafts are discussed.

Analyses of orbital lifetime and observation conditions of small lunar satellites

O. Zeile, M. Lachenmann, E. Baumstark, A. Mohr, D. Bock, R. Laufer, N. Sneeuw, and H.-P. Roeser.
59th International Astronautical Congress (IAC), Glasgow, United Kingdom, 2008.

Abstract: The Moon's gravitational field shows large inhomogeneities that strongly influence the shape of an orbit and can severely influence the orbital lifetime and observation conditions of any spacecraft orbiting the Moon. Small lunar spacecrafts are especially affected by those unstable orbits because their limited mass leaves little to no fuel reserves for excessive orbit maintenance maneuvers. Therefore, it may be favorable to choose an orbit, which features not the ideal observation conditions, but requires less Delta-V for orbit maintenance. These limitations have to be considered during mission design as they affect both the potential capabilities and the lifetime of the satellite. To characterize these limiting factors, simulations and analyses based on up-to-date high degree and order gravity models were conducted with regard to the upcoming small lunar satellite Lunar Mission BW1 of the Institute of Space Systems (IRS) of the Universitaet Stuttgart. The cubical-shaped spacecraft with an edge length of 1 m and a mass of approximately 200 kg will use its own all-electrical propulsion system to reach a high-inclined low lunar orbit. Due to the limited fuel mass and operational lifetime of the thrusters, we consider the orbit maintenance capabilities of the probe to be minimal. Measures to maximize orbital lifetime with the least amount of propellant have to be taken and target orbits have to be examined carefully. This paper shows the results of simulations, which analyze ground coverage and access times, as well as simulations of orbital lifetime and changes in orbital parameters. Additionally, suitable, long lasting target orbits for small lunar spacecrafts are discussed.

Academic Small Lunar Satellite Mission Concept and Design

R. Laufer, D. Bock, M. Lachenmann, H.-P. Roeser, and Lunar Mission BW1 Project Team.
59th International Astronautical Congress (IAC), Glasgow, United Kingdom, 2008.

Abstract: Earth orbiting academic small satellites are without any doubt useful research platforms, technology demonstration tools as well as educational instruments for more than 25 years. On the basis of the increasing new and world wide interest in lunar exploration an academic lunar probe would be a next logical step in small satellite development. The Stuttgart Small Satellite Program of the Institute of Space Systems (IRS) of the Universitaet Stuttgart, Germany, consists of four different small satellite projects in the areas of technology demonstration, Earth remote sensing, astronomical observation, re-entry research and space exploration. The Lunar Mission BW1 is an all-electrical small lunar orbiter of approx. 1 m cube and around 200 kg launch mass. Planned to be launched as a piggyback payload into a Geosynchronous Transfer Orbit (GTO) later than 2010 the probe should use solar-electric propulsion systems to be transferred to the Moon into a highly inclined circular low lunar orbit. The orbiter will perform technology demonstrations, remote sensing and in-situ research experiments. The paper will describe the requirements, boundary conditions and challenges of implementing and accomplishing a lunar mission within an academic environment. Steps towards a small lunar satellite within a program with possibilities for verification and gaining experience will be shown. The integration within education and research activities will be presented as well as the established network of partners, facilities, cababilities and tools which were built up to achieve the program's goals.

Experiments and Instruments of Lunar Mission BW1

M. Lachenmann, R. Laufer, and H.-P. Roeser.
European Planetary Science Congress, Potsdam, Germany, Conference contribution, 2007.

Abstract: As part of the Stuttgart Small Satellite Program, Lunar Mission BW1 - a small lunar orbiter - is currently developed at the Institute of Space Systems (IRS) of the Universität Stuttgart, Germany. The cubical shaped spacecraft with an edge length of 1 m and a mass of approximately 200 kg will be launched into GTO and will use its own all-electrical propulsion system, consisting of a thermal arcjet and a cluster of instationary magneto plasma dynamical (IMPD) thrusters to reach a high-inclined low lunar orbit. This paper gives an overview about the mission of the satellite and some possible experiments during its 2 year journey in cis-lunar space as well as during its operational phase in lunar orbit. Being a technology demonstration mission, one of its main experiments is the operation of the propulsion system whose behavior in space environment has to be monitored carefully. This paper describes a possible payload of the spacecraft including a matrix camera operating in the visual and near infrared spectral range, a micro-bolometer array to detect thermal infrared radiation in high resolution, an instrument to count lunar impact flashes on the lunar surface, and dust and space debris sensors. Furthermore, it gives information about requirements and constraints including access times and possible data rates using the Ka-band communication link.

Video compression of the Flying Laptop for low bandwidth satellite links

M. Lachenmann, S. Walz, and H.-P. Roeser.
R. Sandau, H.-P. Roeser, A. Valenzuela, (ed.) Small Satellites for Earth Observation, Berlin, Germany, Conference contribution, April 2007.

Abstract: The Flying Laptop is the first micro-satellite of the Stuttgart Small Satellite Program. It is currently being developed at the Institute of Space Systems of the Universität Stuttgart. This paper describes the concept to highly compress a steady stream of Earth observation images for non-scientific usage. This lossy compression technique uses data reduction combined with post-processing in order to fit a low bandwidth requirement. It uses an approach known as "Motion compensation" but was especially developed for space application.

Curriculum vitae:
since 2011 Research engineer at the Deutsches SOFIA Institut of the University of Stuttgart at NASA Ames Research Center
2012 Doctoral degree
2006 - 2010 Research associate at the Institute of Space Systems of the University of Stuttgart

2000 - 2006

Study of Aerospace Engineering, University of Stuttgart
 
Diploma thesis at the Small Satellites Group at the Institute of Space Systems, University of Stuttgart:
"Utilization of Low-Cost-CMOS-/CCD-Cameras on a Small Satellite for Monitoring and Public Relations"
 
Study thesis at the Institute of Aerodynamics and Gas Dynamics, University of Stuttgart:
"High-order Boundary Discretization of a Discontinuous-Galerkin Scheme"
1999 University-entrance diploma at the Max-Planck-Gymnasium Nürtingen
Supervised Study, Diploma, and Bachelor Theses:

Design and analysis of the new mounting interface for the improved FFI of SOFIA
Philip Castelo Branco.
Advisors: P. Middendorf, M. Lachenmann, and K. Birkefeld. University of Stuttgart. Study thesis, June 2014.

Performance of SOFIA Optics at Low Temperatures
F. Trimpe.
Advisors: M. Lachenmann, J. Wolf, and A. Krabbe. University of Stuttgart, Deutsches SOFIA Institut. Study thesis, September 2013.

Setup and Use of a Thermal/Vacuum Test Chamber for the Stratospheric Observatory for Infrared Astronomy SOFIA
B. Weckenmann.
Advisors: M. Lachenmann, J. Wolf, and A. Krabbe. University of Stuttgart, Deutsches SOFIA Institut. Study thesis, 2013.

Design and Manufacturing of the Optical Baffle of the Multi-Spectral Camera System MICS of the Small Satellite Flying Laptop
N. Baurain.
Advisors: F. Böhringer, M. Lachenmann, M. Lengowski, F. Steinmetz, and H.-P. Roeser. University of Stuttgart, Institute of Space Systems. Diploma thesis, September 2011.

Analysis of the effects of the Van-Allen belts on a small satellite
C. Hill.
Advisors: M. Lachenmann, T. Kuwahara, R. Laufer, and H.-P. Roeser. University of Stuttgart, Institute of Space Systems. Study thesis, May 2010.

Design and Characterization of the Optical Test Facility for the Multispectral Imaging Camera System MICS of the Small Satellite Flying Laptop
A. Büttner.
Advisors: M. Lachenmann, F. Böhringer, and H.-P. Roeser. University of Stuttgart, Institute of Space Systems. Diploma thesis, February 2010.

Integration of a COTS Industrial Camera as Panoramic Camera for the Small Satellite Mission Flying Laptop
T. Aust.
Advisors: F. Böhringer, M. Lachenmann, and H.-P. Roeser. University of Stuttgart, Institute of Space Systems. Diploma thesis, August 2009.

Requirements of the TICS camera of Lunar Mission BW1 considering the application of SERTIS data
M. Horstmann.
Advisors: M. Lachenmann and R. Laufer. University of Stuttgart, Institute of Space Systems. Technical report, October 2008.

Detailed Design of the Primary Structure and Conception of the Engineering Model of the Lunar Mission BW1
V. Mariathasan.
Advisors: M. Lachenmann, R. Laufer, M. Lengowski, and H.-P. Roeser. University of Stuttgart, Institute of Space Systems. Study thesis, October 2008.

Prediction of the orbital elements and maneuver strategies of a low lunar orbit spacecraft in a non-spherical gravitational field 
E. Baumstark.
Advisors: M. Lachenmann, O. Zeile, and H.-P. Roeser. University of Stuttgart, Institute of Space Systems. Study thesis, August 2008.

Developement of a Low-Thrust Earth-Moon-Trajectory with STK
A. Zöllner.
Advisors: M. Lachenmann, O. Zeile, and H.-P. Roeser. University of Stuttgart, Institute of Space Systems. Study thesis, August 2008.

Lunar Mission BW1 Radio Experiment
A. Delgado González.
Advisors: M. Lachenmann and R. Laufer. University of Stuttgart, Institute of Space Systems. Technical report, September 2007.

Lunar Exploration in the thermal infrared
J. Kuhlmann.
Advisors: R. Laufer and M. Lachenmann. University of Stuttgart, Institute of Space Systems. Technical report, March 2007.

PGP Key:

PGP Key - Fingerprint 512E AD01 07B8 D8F0 86BE DBD2 E695 6310 EE93 8F8B