The details of the webinar are below! This thread will be used to collect questions before the webinar, and to answer any questions we received during the webinar. Feel free to post your questions!
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Date: Thursday, February 24th
Time: 6:00am PST & 11:00am PST
@Jordan.Teich, Application Engineer II @Flurin Herren, Application Engineer II @Matthias.Schlich, R&D Engineer II
CubeSats are a class of nanosatellite that are designed to operate within standardized dimensions of 1U cubes (10 cm x 10cm x 10cm). They can vary in size from 1U to 6U payloads. In the aerospace market, CubeSats have emerged as a lower cost solution for space-based optical systems. To design a CubeSat system, a workflow needs to be defined for developing the optical design, opto-mechanically packaging the system, and modeling structural and thermal impacts that the system will experience in orbit. In this webinar, we will demonstrate how the Zemax software suite can be leveraged to take a CubeSat design through these modelling steps. Starting with an optical design in Zemax OpticStudio, we will showcase how to apply an opto-mechanical retaining system to the design with Zemax OpticsBuilder, run an FEA analysis with Ansys software, and how FEA data can be used to examine impacts on system performance with OpticStudio’s STAR module. Learn how these discrete modelling steps can be united with Zemax software.
Q: You mentioned that the telescope was simulated on-earth but will be utilized in low earth orbit. Are the effects of the vacuum of space considered when looking at performance in OpticStudio?
A: Yes, the vacuum of space can also be considered in an analysis like this. We did go through the process of analyzing the structural deformation effects that result from simulating the pressure environment of space. However, it was found that in comparison to the structural deformation experienced by the optics from the temperature change, the deformation that occurred from just changing the pressure was 2 orders of magnitude lower. Thus, pressure effects did not severely degrade optical performance. For a full analysis of a real space-based system, you will want to include pressure effects even if it has a small effect on performance, just for the sake of having a full engineering model. Simulating temperature and pressure effects also allows for a more accurate comparison when analyzing test results of a system soaked in a thermal vacuum chamber.
Q: Can you perform tolerances analysis on both the mechanics and optics in optic builder?
A: Currently it is only possible to carry out the tolerance analysis separately, meaning to do the tolerancing of the optics with the various tolerancing tools within Zemax OpticStudio and the mechanical tolerances within the CAD environment (E.g. with the Creo EZ Tolerance Analysis Extension).
Additionally: Within the sequential mode of OpticStudio it is also possible to tolerance your optical components with the assumption of a mounted side of the component, this will give you already valuable information in order to go on and assemble/manufacture the optomechanical system.
Q: Can the Prepare for OpticsBuilder tool in OpticStudio also be used in Sequential mode?
A: Yes, if the optical system in OpticStudio is still in sequential mode when running the Prepare for OpticsBuilder tool, OpticStudio will automatically convert the sequential file to a non-sequential one. This includes: converting the sequential surfaces to matching non-sequential geometry, check to make sure rays are positioned and angled correctly, confirm that spot size change has remained below an allowable value and allow the user to open and inspect the non-sequential.
Q: Were there any considerations in this model for stray light effects? If not, what could be done to the model to account for stray light?
A: Stray Light was not considered for simplification reasons. The optical model can be easily adjusted so that it captures stray light effects in non-sequential mode as well as within OpticsBuilder. With the non-sequential analysis, the absorbed flux can be determined which can act as a heat load in a thermal FEA.
Q1: What is the FOV?
A1: The FOV of this example system is ~0.38 degrees. Per the paper that was used as a reference for the optical design, this design can theoretically “take images of a ~4km x ~2.3km area of the Earth’s surface at 700km altitude”.
Q2: Since the mirrors in this design are aluminum wouldn't you want the housing to be the same aluminum so that the figure changes of the mirrors over temperature will be matched by the proper change in the airspace between the two mirrors? If the housing has essentially zero expansion, I would think that the system would go out of focus over temperature. Maybe it has something to do with the spring-loaded mounting bolts?
A2: This is a very interesting suggestion and our material choice was not impacted by the spring loaded mounting. There are designs where you would build the entire instrument from the same material, even machine it from one huge block. We have gone with a different material choice here to show the effect with the new capabilities within STAR. Furthermore, if you would look at a case with a temperature gradient across the assembly instead of the uniform temperature, aluminum would cause much larger deformations that don’t cancel out, so using the same material for all parts is not always the best choice.
Q1: What is the FOV?
A1: Hi Luis! I also answered this question for Harvey Spencer in the comment above. I recommend reading through my answer on this topic there.
Q2: Can spring loaded mirrors handle vibe loads without misaligning?
A2: I’m not an expert on that, but you should probably choose a spring that causes a force that is large enough to counteract the vibrations and accelerations during the launch. This could be verified in separate analyses that focus on the mirror and the spring-loaded bolts.
Q1: How does this CREO Ansys and FEA differ from the earlier Ansys product Sigfit?
A1: SigFit is not part of the Ansys portfolio, but an independent software product from Sigmadyne. The STAR Module is built directly into OpticStudio which enables you to use a majority of the OpticStudio tools and analyses and see the impact of the FEA data inside of the OpticStudio immediately after loading the FEA data. In addition, the STAR Module features visualizations and a UI that is easy to use and fit into a variety of workflows.
The CREO CAD package was used to create the mechanical geometry with the help of OpticsBuilder. Ansys Mechanical was used to perform the thermal structural FEA simulation.
Q2: Does this come in as different configurations, so like ambient vs colder?
A2: Currently STAR does not support the use of multiple configurations. Instead, each of the datasets is imported to a different OpticStudio file. You can swap the FEA data in one file, but you would have to do a fit each time you changed the FEA data file for a surface. A surface cannot be assigned more than one FEA dataset at a time.
If you are interested in the difference for STAR effects applied, there are several ways to disable the FEA data momentarily or evaluate the difference in a wavefront plot.
Q: When would structural deformation data need to be considered and modeled for this type of system?
A: The deformation we are seeing in the FEA is only caused by the thermal expansion of the parts compared to their original shape at 21°C. You could add pressure (or rather the absence of pressure in the vacuum of space compared to one atmosphere) to the loads acting on the assembly on orbit, but apart from that there are only few structural loads while on orbit. During the rocket launch it is obviously a different situation where you could do a FEA for random vibration and acceleration loads.
Q1: Can you control the sampling of the surfaces in case of shorter wavelengths?
A1: The fit generated by STAR creates a continuous surface deformation from the discretized FEA result, so there is no actual sampling that you need to worry about in case of shorter wavelengths. However, if you want to capture deformation effects on a very small scale you might need to increase the number of nodes of the FEA mesh. The fit could also be adjusted to capture the FEA node deformation more tightly by increasing the Max Level or the Grid parameters in the STAR Fit Assessment tool.
Q2: Have you validated with environmental test your model results?
A2: The CubeSat example was not validated with any hardware tests as the intent was to demonstrate the workflow with Ansys Zemax software. The STAR module itself has been used and tested by several costumers where the results matched their measurements. In addition, we've compared to the OpticStudio "Make Thermal" tool, to Grid GRINs (using .GGD files), as well as other known results - like deformations with a known shape, where we can verify that the fit is returning the expected shape.
This thread is now closed to new comments. If you have questions about the software, feel free to send them within the general forum here: https://community.zemax.com/got-a-question-7
For more information about STAR, check out the user group and our upcoming Ask an Engineer event.
For more information about OpticsBuilder, join the user group here: Zemax OpticsBuilder User Group | Zemax Community