Sunpassing Thermal Load Test
In the event of a satellite attitude control malfunction, a so-called "sunpassing" can expose optical components to extremely high thermal loads. Components located in the optical focus may experience irradiance levels of several MW/m². Within the EnMAP project, a dedicated test setup was developed and implemented to evaluate the sunpassing resistance of the slit component of an optical sensor under vacuum conditions. The setup was integrated with the solar oven and the Xenon high-power radiator at the DLR Institute for Solar Research, enabling testing with a representative solar spectrum.
Optical Sensors
To experimentally verify the mechanical integrity of a critical optical sensor element under separation and release shock conditions, a micro-structured silicon component—particularly sensitive to shock loads—was subjected to dedicated testing.
- A stiffness dummy representing the excluded parts of the assembly was developed using FE analyses to replicate the correct dynamic boundary conditions.
- Shock testing was conducted on the mechanical impact device (KRP-M shock bench), ensuring compliance with the specified shock response spectrum (SRS) and evaluating mechanical connection losses during testing.
Field Splitter
Optical components such as the micro-scale double-slit of the EnMAP Field Splitter, located in the telescope’s focal plane, demand the highest levels of particulate and molecular cleanliness. To meet these strict requirements during environmental testing, a dedicated vacuum-tight test box was developed. Using this enclosure, both thermal-vacuum and vibration tests were successfully conducted under controlled cleanroom conditions.
- Thermo-Elastic Deformation (TED) Testing
- FE Analyses
- Design Optimization
- Thermal Testing
- Mechanical Testing
Thermo-Elastic Deformation (TED) Testing
- Planned, performed, and evaluated thermo-elastic deformation testing for the ceramic (HB-Cesic®) star sensor bracket for the Meteosat Third Generation Satellite.
- Designed and developed a highly accurate deformation measurement test rig and measurement system to meet the strict TED accuracy requirements of better than 1 µrad/K.
- TED tests were performed under both homogeneous and asymmetric temperature conditions. For this purpose, a dedicated heating system based on flexible heater foils was developed and implemented.
- The TED tests were supported by corresponding thermo-elastic FEM simulations for result validation and correlation.
FE Analyses
Performed all finite element analyses required for qualification, including quasistatic, modal, sinusoidal and random vibration, thermal, and thermo-elastic analyses
Design Optimization
Focused on mass minimization and reduction of thermo-elastic deformations
Thermal Testing
- Conducted thermal vacuum cycling and thermal balance testing of the ceramic support structure
- Developed a test setup ensuring radiative boundary conditions closely matching operational environments, particularly considering the applied multi-layer insulation (MLI)
- Accompanied by detailed thermal FEM simulations to support and verify test results
Mechanical Testing
- Planned and executed all qualification tests
- Performed vibration tests including both qualification and acceptance testing of flight models
- Carried out sine and random vibration tests
- Experimentally approximated interface loads (forces/moments) using the mass operator method, based on a reduced mass matrix (Guyan reduction) and measured accelerations
- Computed and verified notching profiles based on the derived loads for both sine and random vibration tests
- Correlated test results with FE simulations for model validation