The Psyche Multispectral Imager Investigation: Characterizing the Geology, Topography, and Multispectral Properties of a Metal-Rich World

Abstract

The Psyche Multispectral Imager ("the Imager") is a payload system designed to directly achieve or to indirectly enable the key scientific goals and optical navigation requirements of NASA's Psyche mission, which will conduct the first up-close orbital investigation of the metal-rich Main Belt asteroid (16) Psyche. The Imager consists of a pair of block redundant cameras and electronics that are mounted inside the thermally controlled spacecraft body, with a view out the spacecraft -X panel that will be nadir-pointed during nominal asteroid orbital mapping operations. The two identical Camera Heads are connected to a separate Digital Electronics Assembly (DEA) box that interfaces to the spacecraft avionics and that provides power, commanding, data processing, and onboard image storage. The Imager system shares significant heritage with imaging instruments flown on the Mars Climate Orbiter, the Mars Science Laboratory and Mars 2020 rovers, and Juno. Each camera consists of a 1600 × 1200 photosensitive pixel charge-coupled device (CCD) detector and its associated electronics, a 9-position filter wheel assembly, a compact catadioptric $f$ /2.9 telescope with a fixed focal length of 148 mm, and a sunshade to minimize stray and scattered light. The Imager CCD, filters, and optics enable broadband polychromatic (∼540 ± 250 nm) imaging plus narrowband imaging in 7 colors centered from 439 to 1015 nm. An additional neutral density filter enables protection of the CCD from direct solar illumination. Each camera has a field of view of 4.6° × 3.4° and an instantaneous field of view of 50 μrad/pixel that enables imaging of the asteroid at scales ranging from ∼35 m/pix from 700 km altitude to ∼4 m/pix at 75 km altitude. The primary camera ("Imager A") is pointed along the spacecraft -X axis, and the backup camera ("Imager B") is toed-out by 3.7° to potentially enable greater surface area coverage per unit time if both Imagers are operated simultaneously during some mission phases. Stereoscopic mapping is performed by observing the same surface regions with either camera over a range of off-nadir pointing angles.

Keywords: (16) Psyche; Asteroids; Psyche mission; Space imaging; Space instrumentation.

Fig. 1

Examples of relevant high resolution visible to near-IR telescopic, meteorite, and laboratory mineral or mineral mixture spectra (solid lines) resampled over the bandpasses of the Psyche Multispectral Imager’s narrowband filters (green/yellow data points; Table 2). These examples include many of the “best matches” to the telescopic spectrum of (16) Psyche compiled in Table 3 of Dibb et al. (2023). All spectra have been scaled to 1.0 at 550 nm and then vertically offset for clarity. Spectra and sources: (a) 80/20 wt.% mixture of $<75$ μm grain size powders of the metallic meteorite Gibeon and troilite, from Dibb et al. (2021); (b) Powdered $>75$ μm grain size sample of Gibeon, from Dibb et al. (2023): (c) 90/10 wt.% mixture of $<45$ μm grain size powders of the metallic meteorite Odessa and olivine, from Cloutis et al. (2009); (d) 90/10 wt.% mixture of $<45$ μm grain size powders of the metallic meteorite Odessa and low-Fe pyroxene, from Cloutis et al. (2009); (e) Powdered $>75$ μm grain size sample of the $\mathrm{CH}/\mathrm{CBb}$ chondrite Isheyevo, from Dibb et al. (2023); (f) whole-disk telescopic spectrum of (16) Psyche from the SMASSII survey of Bus and Binzel (2002); (g) Powdered $<1\mathrm{mm}$ oldhamite-dominated clasts from the Norton County aubrite, from by Dibb et al. (2022); (h) 1200 grit polished troilite slab, from Dibb et al. (2023); (i) Low-Fe $<45$ μm pyroxene powder (PYX042) used in mixture (d), from Cloutis (2002): (j) Olivine < 45 umpowder (OLV003) used in mixture (c), from Cloutis et al. (2009)

Fig. 2

Flight Psyche Multispectral Imager Camera Heads (left) and flight Digital Electronics Assembly (right), prior to integration with the spacecraft. For scale, the pocket knife is 3.5 inches (90 mm) long

Fig. 3

Block diagram for the two fully redundant Psyche Multispectral Imager Camera Heads and their associated Digital Electronics Assembly (DEA) electronics

Fig. 4

(A) Cutaway CAD view of the Psyche Multispectral Imager, along with actual photos of some of the key hardware components, including the 57 mm diameter Primary Mirror M1 on a test bench, the ∼12 × 9 mm CCD sensor, and the 9.1 cm diameter filter wheel. (B) Ray trace of the Psyche Multispectral Imager catadioptric telescope, with lens and mirror elements as identified in (A) above. M1 is the spherical primary mirror, and M2 is the spherical secondary mirror, coated onto the back (CCD side) of lens element L2. The part of the front of L2 corresponding to M2 is coated with Z306 diffuse black paint. M3 is a flat-surface mirror coated onto the front of lens element L1 and used for laser alignment verification of camera boresight pointing during pre-flight testing

Fig. 5

(Top Right) CAD view of the locations of the Psyche Multispectral Imager Camera Heads, protruding out the −X panel of the Psyche spacecraft. The ends of the Imager Sun Shades are protected by a Mylar-blanketed “doghouse” assembly, shown in the CAD view inset and the actual flight configuration to the inset’s left. (Top Left) Cutaway CAD view of the inside of the Psyche spacecraft showing the Imager Camera Heads mounted to a rectangular camera plate that is attached by struts to the spacecraft’s central structural cylinder. The Imager Digital Electronics Assembly (DEA) is a separate box mounted to the spacecraft’s +Y panel. The DEA and Camera Heads are connected by a harness. (Bottom) JPL Engineer Stephen Partida finalizing the installation of Imager-A (right) and Imager-B (left) on the Psyche spacecraft [photo credit: Sean Howard, JPL]

Fig. 6

Examples of “real world” imaging with Imager A in pre-flight testing at MSSS in San Diego. (A) Full frame (1648 × 1200 pixels, including masked reference columns) color composite image of the view out a special cleanroom window of houses on a ridge ∼1 km away. RGB = 722, 548, and 439 nm. (B) Enlarged 548 nm view of power lines ∼2 km away and behind the houses, demonstrating good focus under typical terrestrial imaging conditions. (C) Subset of an Imager A night-time image of the Moon, acquired during relatively clear and dry conditions on Jan. 27, 2022 at 02:26 UTC. The Imager’s 50 μrad IFOV (∼10 arcsec on the sky) corresponded to a scale of ∼19 km/pixel on the Moon. Imager B performed similarly under terrestrial conditions

Fig. 7

Example of a 3 × 3 mosaic of images from Imager-B of a star field in the constellation Perseus centered on the famous double cluster NGC869 and NGC884 (also known as h and $\chi$ Persei). The images were acquired during initial checkout observations on Jan. 6, 2024. The clusters and some prominent stars are annotated. In-flight focus and performance of both Imagers are comparable based on cruise observations to date

Fig. 8

Images of 433 Eros from the NEAR-Shoemaker mission at the approximate pixel scales representative of those typically expected during the Psyche mission’s Orbits A, B1 and B2, C, and D, as labeled