Experimental set-up of a thermal vacuum chamber for thermal model in-house correlation and characterization of the HYPSO hyperspectral imager

Space environment with changing temperatures and vacuum can affect the performance of optics instruments onboard satellites. Thermal models and tests are typically done to understand the optics performance within large space projects, but less often in nanosatellites projects. It is even more rarer for an optics payload inside a CubeSat platform, made by a third provider, to do functional tests on their optics during space environment test campaign. In this research, an in-house made vacuum chamber with the possibility to warm up (TVAC) the devices under tests, and wall-through transparency for optics experiments is set-up. In parallel, a thermal model of the HYPerspectral Small satellite for ocean Observation (HYPSO) Hyperspectral Imager (HSI) is developed. The HSI, which is a transmissive grating hyperspectral instrument ranged in the visible to near infrared wavelength, has been tested in TVAC. As thermal control is based on heating the device under test, a new method for fitting the thermal models inside vacuum chambers with only heating capability is proposed. Finally, the TVAC set-up and the thermal model fitting method have been demonstrated to be appropriate to validate the HSI thermal model, and to characterize the optics performance of HSI in vacuum and in the range of temperatures found inside the in-orbit HYPSO-1 CubeSat.Research Council of Norway | Ref. 223254Research Council of Norway | Ref. 270959Norwegian Space Agency and the European Space Agency | Ref. 4000132515Ministerio de Universidades | Ref. CAS21/00502Universidade de Vigo/CISU

Structural thermal optical performance (STOP) analysis and experimental verification of an hyperspectral imager for the HYPSO CubeSat

The evaluation of space optical instruments under thermo-elastic loads is a complex and multidisciplinary process that requires integrating thermal, structural, and optical disciplines. This thorough analysis often requires substantial resources, leading small satellite projects to exclude it from their schedules. However, even though the instrument discussed in this paper is compact, its complex design and stringent dimensional stability requirements demand a comprehensive evaluation of its performance under thermal loads. The hyperspectral camera, which comprises 18 lenses, a grating, a slit, and a detector, is especially vulnerable to thermo-elastic distortions, as the deformation of even a single lens could significantly impact its performance. In this paper, we present the experimental validation of the STOP analysis applied to the HYPerspectral Small satellite for ocean Observation (HYPSO) Hypespectral Imager (HSI) model. Both the HSI Structural Thermal Optical Performance (STOP) numerical model and the HSI engineering model were subjected to identical thermal conditions in the simulations and in a Thermal and Vacuum Chamber (TVAC), and subsequently the optical results derived from simulations and the test campaign compared. To characterize the thermal field, an infrared camera and thermocouples were used. Moreover, to assess the thermal performance of the HSI, we measured the Full Width at Half Maximum (FWHM) of the main peaks in the intensity-wavelength spectra when the hyperspectral camera targeted a known spectral lamp. After individually calibrating the STOP models so that the FWHM and index of the intensity peaks are in close alignment with the experimentally measured FWHM and index, the lenses most sensitive for displacements were characterizedMinisterio de Universidades | Ref. CAS21/00502Research Council of NorwayNorwegian Space AgencyEuropean Space AgencyUniversidade de Vigo/CISU

HYPSO-1 CubeSat: First Images and In-Orbit Characterization

The HYPSO-1 satellite, a 6U CubeSat carrying a hyperspectral imager, was launched on 13 January 2022, with the Goal of imaging ocean color in support of marine research. This article describes the development and current status of the mission and payload operations, including examples of agile planning, captures with low revisit time and time series acquired during a campaign. The in-orbit performance of the hyperspectral instrument is also characterized. The usable spectral range of the instrument is in the range of 430 nm to 800 nm over 120 bands after binning during nominal captures. The spatial resolvability is found empirically to be below 2.2 pixels in terms of Full-Width at Half-Maximum (FWHM) at 565 nm. This measure corresponds to an inherent ground resolvable resolution of 142 m across-track for close to nadir capture. In the across-track direction, there are 1216 pixels available, which gives a swath width of 70 km. However, the 684 center pixels are used for nominal captures. With the nominal pixels used in the across-track direction, the nadir swath-width is 40 km. The spectral resolution in terms of FWHM is estimated to be close to 5 nm at the center wavelength of 600 nm, and the Signal-to-Noise Ratio (SNR) is evaluated to be greater than 300 at 450 nm to 500 nm for Top-of-Atmosphere (ToA) signals. Examples of images from the first months of operations are also shown.publishedVersio

Hyperspectral Imager Calibration and Image Correction

Hyperspektrale kameraer, ombord blant annet droner og småsatellitter, skal detektere algeoppblomstring og andre havfenomener langs norskekysten. Dette er en del av prosjektet HYPSO, som står for "hyperspektral småsatellitt for havobservasjon". For at bildene skal være brukbare må kameraene være kalibrert og karakterisert før bruk. Det første målet i denne oppgaven var derfor å sette opp prosedyrer for spektral og radiometrisk kalibrering, og deretter kalibrere to hyperspektrale kameraer. Det andre målet var å detektere kjente feileffekter kalt "smile" og "keystone", samt korrigere for disse. Prosedyrer for spektral og radiometrisk kalibrering ble utviklet, og de hyperspektrale kameraene HSI V4 og HSI V6 ble kalibrert. Etter spektral kalibrering ble spektral rekkevidde regnet ut, og estimert til 299 til 1015 nm for HSI V4, og 378 til 851 nm for HSI V6. Videre ble et oppsett for å detektere "smile" og "keystone" utviklet, bestående av en kollimator, et stripete mønster og spektrale lyskilder. Effektene ble detektert ved å bruke skjæringspunktene dannet i spektrogrammet og videre korrigert for ved å transformere skjæringspunktene over på et referansegitter. Korreksjon av bilder fra HSI V4 viste en klar forbedring, men feilmodellen kan bedres. I tillegg ble spektral båndpass og lineæritet av sensorresponsen karakterisert. Spektral båndpass for HSI V4 ble estimert til 2.66 nm, og 2.84 nm for HSI V6. Resultatene viser at HSI V4 har tilnærmet lik lineær sensorrespons

Real-time Corrections for a Low-cost Hyperspectral Instrument

The development of a hyperspectral imager (HSI) made from commercial off-the-shelf (COTS) parts enables the use of hyperspectral imaging on smaller low-cost platforms such as cubesats, drones, or other autonomous vehicles. However,HSIs built from COTS parts often suffer from more pronounced optical distortions, such as ‘smile’ and ‘keystone’,due to the shifted balance between cost and image quality.In this proceeding, radiometric, spectral, and geometric calibrations of a COTS HSI are presented. Furthermore, the calibrations are used to develop a real-time software-based spectrogram correction. The corrections will enhance the capability of small, autonomous platforms in using hyper-spectral imaging

Pre-Launch Assembly, Integration, and Testing Strategy of a Hyperspectral Imaging CubeSat, HYPSO-1

Assembly, Integration, and Verification/Testing (AIV or AIT) is a standardized guideline for projects to ensure consistency throughout spacecraft development phases. The goal of establishing such a guideline is to assist in planning and executing a successful mission. While AIV campaigns can help reduce risk, they can also take years to complete and be prohibitively costly for smaller new space programs, such as university CubeSat teams. This manuscript outlines a strategic approach to the traditional space industry AIV campaign through demonstration with a 6U CubeSat mission. The HYPerspectral Smallsat for Ocean observation (HYPSO-1) mission was developed by the Norwegian University of Science and Technology’s (NTNU) SmallSatellite Laboratory in conjunction with NanoAvionics (the platform provider). The approach retains critical milestones of traditional AIV, outlines tailored testing procedures for the custom-built hyperspectral imager, and provides suggestions for faster development. A critical discussion of de-risking and design-driving decisions, such as imager configuration and machining custom parts, highlights the consequences that helped, or alternatively hindered, development timelines. This AIV approach has proven key for HYPSO-1’s success, defining further development within the lab (e.g., already with the second-generation, HYPSO-2), and can be scaled to other small spacecraft programs throughout the new space industry