The Aeolus mission will take an innovative wind lidar called ALADIN (Atmospheric LAser Doppler INstrument) into space to measure wind profiles in the lowermost 30 km of the Earth's atmosphere. ALADIN is a direct detection wind lidar capable of using the backscatter signal from both molecular (Rayleigh-) and aerosol (Mie-) scattering to retrieve independent wind information. To achieve the mission goal, two separate spectrometers have been manufactured. The Rayleigh spectrometer is using a Fabry-Perot etalon with 2 paths and works like 2 narrow band filters. The detector measures the power reflected by the atmosphere for each thin band. The Mie spectrometer core is a Fizeau etalon. A CCD matrix measures directly the spectral response with a very fine resolution.
For both etalons, the critical parameters are the FWHM (Full Width Half Maximum) and the Finesse. High optical quality and extremely narrow FWHM are needed to achieve mission performance but also request high quality system for the verification of those performances.
The optical performance predictions, the verification philosophy and the test results are presented. The description of the different measurement setups including a system able to do spectral measurement with a resolution of some femtometers, the characteristic of the equipment and mathematical method used for calibration and to optimize the measurement accuracy are described.
For the 2 spectrometers, a numerical model has been developed to analyse and predict the spectral response. The model and the results of the analysis are presented in the documents. The comparison between analysis and measurement results is discussed.
Within the ATHENA optics technology plan, activities are on-going for demonstrating the feasibility of the mirror module Assembly Integration and Testing (AIT). Each mirror module has to be accurately attached to the mirror structure by means of three isostatic mounts ensuring minimal distortion under environmental loads. This work reports on the status of one of the two parallel activities initiated by ESA to address this demanding task. In this study awarded to the industrial consortium, the integration relies on opto-mechanical metrology and direct X-ray alignment. For the first or “indirect” method the X-ray alignment results are accurately referenced, by means of a laser tracking system, to optical fiducial targets mounted on the mirror modules and finally linked to the mirror structure coordinate system. With the second or “direct” method the alignment is monitored in the X-ray domain, providing figures of merit directly comparable to the final performance. The integration being designed and here presented, foresees combining the indirect method to the X-ray direct method. The characterization of the single mirror modules is planned at PTB’s X-ray Parallel Beam Facility (XPBF 2.0) at BESSY II, and the integration and testing campaign at Panter. It is foreseen to integrate and test a demonstrator with two real mirror modules manufactured by cosine.
RUAG Space developed, manufactured and demonstrated an afocal mirror telescope for space applications. The
telescope is part of a Laser Communication Terminal (LCT) for GEO and LEO satellites. The design is off-axis and free
of central obscuration. Optical interfaces are provided by pupils outside the telescope towards space (ø=135 mm) and
towards the payload (ø=12.5 mm). The magnification is Γ=-10.8. The main characteristics are a WFE of ≤35nm,
transmission <96%, low extinction ratio of linear and circular polarization, low stray light and low mass. The
performance stability was demonstrated under various environments including vibrations, shock and thermal-vacuum up
to 55°C. These properties enable a broad use, not limited to space. The layout is composed of four mirrors (Zerodur and
Fused Silica) integrated in a nearly zero expansion Carbon Fibre (CFRP) structure. A detailed characterisation and
advanced understanding of the CFRP represents a main achievement. The water absorption of CFRP in air causes elastic
distortions of the structure until saturation. Certain optical performances are affected by this phenomenon which has to
be considered when testing the system in thermal-vacuum environment. These effects were characterised and precompensated
during integration in order to tailor the performance to the in-orbit conditions. The stability of the
performances confirmed the selection of the CFRP as nearly-zero CTE material. Combined effects of moisture release
and thermo-elastic distortions under thermal-vacuum loads were detected. The optical performances verification was
then consequently and successfully tailored in order to distinguish these effects and prove the telescope stability under
The BepiColombo Laser Altimeter (BELA) is selected to fly on board of the ESA's BepiColombo Mercury Planetary
Orbiter (MPO). The instrument will be the first European planetary laser altimeter system. RUAG Space is the industrial
prime for the Receiver part of the scientific instrument. The BELA Receiver is a joined effort of Swiss industries under
the leading role of RUAG and University of Bern as co-Prime. A core element is the light weighted Receiver Telescope
(RTL), to collect the laser pulse reflected from the planet’s surface. An innovative design was required to deal with the
very challenging Mercury’s environmental conditions and with the very stringent instrument’s mass budget. The Optothermo-
mechanical analyses lead to the design of a 1250mm focal length Cassegrain telescope made of Beryllium. It
provides an aperture of 204 mm diameter and a 2 mm thick primary mirror for a total mass of less than 600gr. The
manufacturing and the integration needed special developments.
This paper presents the design analyses and the major challenges which had to be solved. Discussing some aspects of the
telescope integration and test campaign, the finally achieved performances and lessons learnt will be presented.
To ensure the performance of optical systems for space applications, the design of the mounts for the optical elements
and the choice of materials are crucial. Beside this also the applied bonding techniques are playing a major role. The
alignment of the optical elements must remain after the loads of the launch phase and in the thermal environment of the
satellite. We present our achievements in alignment accuracy and stability during assembly and integration of optical
systems for space applications in the case of two very different examples:
In the first example we bonded prisms to a baseplate using a radiation activated optical adhesive. The achieved
alignment accuracy was better than 3". In the second example we bonded Zerodur mirrors with diameters up to 150 mm
and mass of 1 kg to Invar mounting frames using a slow curing two-component adhesive. Here the achieved alignment
accuracy was in the order of 10". Thanks to our sophisticated bonding techniques and specially designed mounts and
bonding jigs, these alignments were preserved during environmental tests like thermal cycling and vibration tests.