@Reuven.Zalman 

Q1: I'd like, if it’s possible, to iterate the last bit with STAR and how you figured out the correction for temperature.

A1: Hi Reuven! I believe that your question sounds like something I covered in the slides during the webinar presentation. I know that there was a technical error during the webinar that prevented the slides on STAR and the details surrounding the temperature correction from being shown. At the top of this Community post, there is a new link for the on-demand webinar where this issue has been fixed! If you open the on-demand link and go to the last section of the presentation, the slides on STAR will now be visible. If you still have questions on the STAR Module or the correction for temperature, please reply here and I’ll be happy to answer.

Q2: And why the 3 temperatures? 12C, 15C and 18C?

A2: On this post, Aleksander Makarov asked a similar question. I recommend looking at the answer that I wrote for them to see if it answers your question! Aleksander’s question was about how the temperature was estimated at orbit. To add a few more details, once 15C was chosen as the nominal temperature, a range of +/- 3C was chosen as the possible fluctuation range for the operating temperature. In a space-based optical system, it is unlikely for the optics to remain soaked at the exact same temperature. There will usually be some drift in temperature over time. Looking at FEA data for 12C, 15C, and 18C allows us to examine data at the boundaries of this range and at the nominal temperature. If desired, FEA analysis can also be run with additional temperature data points to achieve a finer sampling of the data.

@ofir 

Q1: What is the reference for the mirror design?

A1: The optical design for this CubeSat example was referenced from the following paper: Optical Design of a Reflecting Telescope for CubeSat (Jin, Lim, Kim and Kim, 2013). This paper was published in the Journal of the Optical Society of Korea in 2013.

Q2: How many rays were you tracing during the stop analysis?

A2: When you refer to the “Stop Analysis”, I assume that you are referring to the analysis completed with the STAR module in OpticStudio’s Sequential mode. While Non-Sequential mode allows the user to define the number of analysis rays that will be traced through the system from a defined Source Object, Sequential mode (where the STAR module is used) works a bit differently. When FEA data is applied to the optics via the STAR module, no rays are traced during the fitting process. Once FEA data is loaded via STAR, the module can work in conjunction with Sequential analysis features. The loaded FEA data will now affect how rays behave when they interact with the optics. The number of rays traced through the system depends on the analysis feature being used. For example, the Standard Spot Diagram analysis has a setting called Ray Density which specifies the number of rays to be traced during the analysis. To provide one more example, the FFT MTF analysis has a setting called Sampling which refers to the size of the ray grid used to sample the pupil. For the CubeSat example, a Ray Density of 6 (which refers to 6 hexapolar rings that trace 126 rays overall) was used for the Standard Spot Diagram and a Sampling of 128 x 128 rays was used for the FFT MTF.

Q: What is the meaning of a spot smaller than the Airy Disc? How should we interpret and use this information?

A: In this example, the spot size was used as one of the metrics to judge the optical performance of the system. An optical system will have a performance limit based on the size of the Airy Disc, or the diffraction limit. The effects of diffraction are important to consider as the size of the Airy Disc represents the smallest size to which a spot can be focused down to. By achieving a spot size that is smaller than the Airy Disc, we determined that the CubeSat optical performance was limited by diffraction. No matter how small the spot is focused down to in the Spot Diagram, if the spot size is smaller than the Airy Disc, the Airy Disc size will remain the smallest achievable spot size for a given system. This means that for the CubeSat example, the smallest achievable spot size has a radius of 8.905um (the radius of the Airy Disc). The spot size should be interpreted as an example of a metric that can help determine a system’s optical performance. However, other metrics can and should be considered. Wavefront error, MTF, and detector resolution are all metrics that can be important when analyzing system level performance. For this webinar, the Standard Spot Diagram was used as an example to highlight how the STAR module can interact with OpticStudio’s Sequential analysis features.

@James.Sheil 

Q1: How does Convert to NSC know where to place the detectors in NSC? Is it based on the position where the chief ray strikes the detector in sequential mode?

A1: When the Convert to NSC tool is used, all sequential fields defined in the Field Data Editor are first converted into equivalent Non-Sequential Source Objects. Each generated Source Object will be paired with its own detector. All detectors are positioned at the same global Z position in NSC which is determined by the position of the image plane in Sequential mode. Each detector is then properly positioned in X and Y by being centered about that field’s centroid at the image plane.

Q2: Could you go over how the Invar keeps the mirrors at the same separation, even though the frame is expanding/contracting?

A2: The mechanical design allows the frame to expand independently from the invar rods which have a very low coefficient of thermal expansion. This is being realized by allowing one side of the rod to slide in and out of the frame while the other side is firmly connected. The mirror retainers are only connected to the invar rods and are therefore unaffected by the expansion of the frame.

@Aleksandr.Makarov 

Q1: Was this system in space? 

A1: The CubeSat system discussed in this webinar is a completely simulated system that was built to illustrate the OpticStudio → OpticsBuilder → FEA → STAR Module workflow. While this system was not manufactured and put into space, this workflow demonstrates how such a system could be simulated with Ansys Zemax software.

Q2: How was the temperature estimated at orbit?

A2: For this CubeSat example, we assumed that the system would operate in Low Earth Orbit at 700km. Originally, the operating temperature of the optics in the Hubble Telescope was used as a comparison point. For the Hubble, the operating temperature for the optics was at 21C, or room temperature. However, if 21C was used for the operating temperature of the CubeSat optics, the results using STAR would not have been very interesting. This is because the Sequential model as “built on Earth” was also assumed to be soaked at 21C. To showcase the advantages of the STAR module, an assumption was made to lower the operating temperature of the optics by a few degrees. By choosing an operating temperature of 15C +/- 3C, interesting results with STAR could be obtained. This is because the temperature condition in-orbit is now different to the temperature condition on Earth. While the external frame of the CubeSat will experience larger fluctuations in temperature, space-based optical systems will generally use a thermal control system to prevent the optics from experiencing those fluctuations.

@Andrew.Keys 

Q: After adding the mechanical supports and structure, what is the final usable aperture of the optical system?

A: As the mechanical components do not limit the optical aperture, the aperture is still same as set in the initial sequential mode in OpticStudio, which is defined by the Entrance Pupil diameter and limited by the STOP surface on the first surface. So in this case this would be 55mm.

Q: In the Opticsbuilder/creo, is it possible to import CAD files for structural parts and integrate with the lens design?

A: The usual workflow for a Optomechanical system working with both Zemax OpticStudio (OS) and Zemax OpticsBuilder (OB) would be the following: A optical system is designed, analysed and optimized within OS, after that it is passed on to the CAD Environment into OB with via a .ZBD file. Once the optical components are imported into the CAD Environment the mechanical components are added to the assembly making it a optomechanical assembly. This can be all sorts of CAD files (E.g. STEP files), these mechanical components can then be assembled to the optical parts with the native CAD tools such as assembly constraints.

@Guanghua.Wang 

Q: How do you verify the design simulations since so many tools used?

A: After the initial design within sequential mode of Zemax OpticStudio, the Convert to NSC Group tool can be used in order to automatically convert it to the Non-Sequential mode (To subsequently perform the boolean operation). Within that tool the Critical Rayset Generator can be used to verify the performance after the conversion.

Once the optical designed is finished within OpticStudio and the optical system was passed on via .ZBD file. The Optomechanical Engineer can verify the optical performance by running a simulation, within the results of that simulation OpticsBuilder will differentiate between the OS (OpticStudio) Baseline and the OB (OpticsBuilder) Baseline, so the optical performance without and with the influence of the mechanical components. 

@Sergey.Nikitin 

Q: Why for step #3 (Mechanical design) do you use CREO not Speos (Ansys)?

A: In order to show-case the workflow with mainly Zemax products, Zemax OpticsBuilder was used and as OpticsBuilder is an Add-in for Creo Parametric 4,5,6 and 7, the CAD Environment had to be Creo. However, the mechanical design could have also been done within Speos. In this case you would want to export a STEP file of the optical system out of Zemax OpticStudio and import it into Speos to assemble the optomechanical system. But please keep in mind that other than the .ZBD file, the STEP does not hold any optical data, but only the geometry of the optical components. 

@Christophe.Gaschet

Q: How to relate the number of Nodes to the quality of the mirror (in RMS)?

A: I’m assuming you were referring to the fit quality of the mirror within STAR. There are many different ways to influence the fit quality. Among other things, there are two adjustment screws in the STAR Fit Assesment tool, the Max Level and the Grid parameters. Internal research has shown that the default values for these work best with a mesh of roughly 10 thousand nodes. The exact behavior varies and differs from case to case, that is why the Fit Assessment tool is very helpful to assess the error.