HyperScout-H: the hyperspectral imager for the ESA Hera mission

TL;DR

The paper presents HyperScout-H (HS-H), a hyperspectral imager aboard ESA's Hera mission, designed to characterize the Didymos-Dimorphos system after the DART impact in the $0.65-0.95\,
6m$ range. It details HS-H's technical design, 25 spectral channels, and a $5\times5$ macropixel detector architecture, along with pre-flight calibrations (dark, flat-field, distortion) and a plan for in-flight calibration. The science objectives focus on surface composition, space weathering, and potential exogenous material, with outputs including taxonomic maps and band-parameter analyses to support geology and dynamics studies. A data-analysis toolbox is described, including novel demosaicing methods and machine-learning–driven taxonomic classification trained on asteroid spectra, and a laboratory proof-of-concept using meteorite spectra validates the instrument concept. Overall, HS-H is positioned to deliver high-value spectral maps that complement other Hera instruments and enable constraints on surface properties, ejecta, and density through meteorite analogs.

Abstract

The HyperScout-H (HS-H) instrument is one of the payloads aboard ESA's Hera spacecraft. Hera is a planetary defence mission that aims to provide a detailed characterization of the near-Earth binary asteroid (65803) Didymos-Dimorphos after the NASA/DART mission impact. HS-H is a versatile dual-use payload, functioning as a hyperspectral imager that captures both images and spectral data within the 0.65--0.95 $μ$m wavelength range. The observations from this instrument will offer key insights regarding the composition of the two bodies Didymos and Dimorphos, space weathering effects, and the potential presence of exogenous material on these asteroids. Thanks to its wide field of view ($\approx 15.5^\circ \times 8.3^\circ$ in paraxial approximation), HS-H will be able to monitor the system's orbital dynamic and dust environment. At the same time, both components of this binary asteroid remain in the field of view for most of the asteroid phase of the mission. These results also complement the data obtained from other instruments in characterizing the geomorphological units. The data that will be obtained by HS-H will enable the creation of maps highlighting key spectral features, such as taxonomic classification, spectral slope, and band parameters. This article presents the pre-flight calibration of the instrument, outlines the science objectives, and discusses the expected investigations. The instrument's capabilities are demonstrated through laboratory observations of two meteorite samples and a dedicated software toolbox was developed specifically for processing the instrument's data.

Figures (14)

• Figure 1: The left and central panels: rendered CAD assembly of the HS-H, without the removable plate and the multi-layer insulation blankets. Right: 3D optical layout of the telescope. Credit: hshiac.
• Figure 2: The HS-H macropixel configuration. Each subpixel represents a narrow band filter, with a specific central wavelength and an optical transfer function. The legend of each subplot shows the central wavelength (computed as the maximum of the optical transfer function), and the figure layout is the same as the macropixel one.
• Figure 3: The variation in the median and standard deviation of pixel values of dark current as a function of temperature. Both plots are shown for three different exposure times, with the behavior approximated using an exponential function.
• Figure 4: The variation in standard deviation of dark current for each narrow band filter. (represented by the central wavelength of each filter). The curve is plotted at a temperature of 18$^\circ$C (as indicated by the internal sensor) and an exposure time of 0.9 s.
• Figure 5: The comparison between the median master dark obtained for an exposure time of 900 ms and the one for 0.1 ms.