A record of questions asked during the Summer 2024 External Design Review on August 24, 2024, has been made. Answers are provided in italics.

Anonymous: optics - is the difference between the operating temperature requirements on p55 "withstand" vs "operate" based on imaging pass? Could you clarify the source?

• The “withstand” temperature refers to the range of temperatures the optical components should be able to endure without “breaking” during testing and in orbit.
• “Breaking” is defined as either physical fracture, loss in transmissivity, permanent warpage or inelastic changes to surface form, scratches or chemical changes to coatings, etc.
• The payload, in other words, will be capable of surviving the “withstand” temperature range from -40C to +70C. The camera is rated to be operational for the entire range too, so in theory, we could also operate in this range.
• However, requiring optical components to be “athermalized” over this very large temperature range is impractical. It would drive up costs, volume, mass, etc. It is also not necessary.
• Due to the thermal insulation and thermal control mechanisms available on board the satellite, we expect the temperature fluctuations of the payload will not be as drastic as they are on the exterior of the satellite.
• Hence, we specify an “operate” temperature range. This is the range we expect the payload will remain within, due to the thermal insulation and thermal control mechanisms. We estimate that this range will be 0C to 40C and are working on simulations to ascertain these numbers.

Adyn: Optics - are you at all worried about having a non-zero incidence angle for the light that falls onto the detector?

• No, this has not been a substantial concern of ours. It is commonplace with imaging optics that off-axis objects get imaged at a non-zero angle of incidence (AOI) onto the detector. Of course, it is advisable to avoid extreme ray angles at any point in the optical design in order to minimize aberration.

Anonymous: Optics/Firmware - any plans to test the sensitivity of the sensor pixels? weak/dead pixels on the "spectral axis" may affect data quality

• The FLIR Tau camera has built-in functionality that handles defective pixels (i.e., those that have very high responsivity or those that are “dead”). There is a built-in capability that the value of these “dead pixels” could be replaced with an “average” value of the neighboring pixels within the readout circuitry, before any post-processing.
• The product specification ensures that there are less than a handful of defective pixels in the main region of the photodetector array, e.g., less than 10 bad pixels in the center rectangle encompassing 90% of the area. The exact numbers can be found in the documentation.
• We will perform testing and be able to observe whether there are defective pixels, with the help of Data Processing. Particularly, we will be testing the (relative) Detection Efficiency of the camera sensor, since this information is needed and not publicly available.
• This and other tests will allow us to notice whether we have defective pixels, assess how “bad” the situation is, and collaborate with Data Processing / Firmware to resolve the issue.

David M: OPTICS - How is your optical performance looking in simulation? Are you anticipating a need for additional correction lenses beyond what is in design

• We are not ready to simulate the “full” optical system, in which we have all the SWIR space-grade components. The limitation is primarily with the lack of access to proprietary optical models (not all vendors are willing to share ZEMAX BlackBox models.
• Currently, we plan on making a base design with paraxial lenses and substituting them with real lenses to study the effect on spot size and MTF. We can get the models for the “real lenses” either by considering similar commercially available offerings or creating a surrogate model ourselves.