Psyche Mission Description and Design Rationale

Abstract

The Psyche spacecraft launched on October 13, 2023 to journey to the asteroid of the same name. Psyche is the largest M-class asteroid and possibly the remanent core of an early differentiated planetesimal that was disrupted by collisions. The Psyche mission will test that hypothesis as the 14th mission in NASA's Discovery Program. An alternative hypothesis is that the asteroid is unmelted primordial material. We describe the proposal competition process leading to selection of the mission and its context with other small body missions. This paper will briefly introduce the three science instruments, gravity science investigation, and Deep Space Optical Communications technology demonstration, leading into a detailed explanation of the science mission architecture. The orbital science phase is divided into a series of circular mapping orbits at four distinct altitudes, each selected to address specific science objectives. The requirements and objectives for each orbit are accompanied by an assessment of the effectiveness of each phase. We discuss the structure of the Psyche team during the operations phase along with the roles and responsibilities of the science and flight operations teams. Key elements of mission operations that are unique to the Psyche mission are provided. The Science Data Center manages and archives the Psyche mission data. The contents of the archive data sets for each instrument are outlined as well as the interfaces between the Science Data Center, the instrument teams, and the Planetary Data System.

Keywords: (16) Psyche; Asteroids; Mission operations; Psyche mission; Science operations.

Fig. 1

The Psyche baseline cruise trajectory includes a Mars gravity assist in 2026 with arrival at Psyche approximately three years later. The wide grey lines plotted over the trajectory indicate when the spacecraft is thrusting with its electric propulsion subsystem. The blue dots indicate weekly DSOC opportunities over the first two years of the cruise phase. There are multiple periods in cruise and in orbit around Psyche when the spacecraft is in solar conjunction and communications with the earth are disturbed by the sun. The grey-scale semi-circle beyond Psyche’s orbit indicates the percentage of illuminated surface at that time during orbital operations

Fig. 2

The Psyche mission’s four science orbit altitudes are designed to address the specific objectives of each of the four science investigations. The geometrical relationship between the sun, Psyche’s spin axis, and the spacecraft orbital plane has important implications for placement of imaging campaigns on the mission timeline. Psyche’s rotation axis (+Z) is tipped nearly into its orbital plane. At the time of this simulation, sunlight is coming from the left, and Psyche is at an equinox, so all parts of its surface are illuminated each rotation around its spin axis. At solstice, only half of the surface is illuminated. Orbits A, B, and C are polar orbits and Orbit D is inclined at 160° for stability. The three polar orbits enable global ground track coverage to support the mapping campaigns, although the extent of imaging coverage depends on Psyche’s orbital season

Fig. 3

Placement of science instruments on the spacecraft. The two Magnetometer sensor units are located on a 2-m boom with their electronics units (not shown) in a gradiometer configuration. The Gamma-Ray Spectrometer and Neutron Spectrometer are located on a separate 2-m boom with the Gamma-Ray Spectrometer at the 2 m point and the Neutron Spectrometer at the 1 m point of the boom. Each has its own electronics box mounted inside the spacecraft. The two Multispectral Imagers are mounted on the central cylinder of the spacecraft with views out of the −X direction of the spacecraft. Their electronics are packaged into a single box mounted inside the spacecraft. Gravity science is performed with the X-band HGA as well as three LGAs mounted on the +X, −X, and −Z decks of the spacecraft (not all are visible here). Blue components on the spacecraft drawing are provided by Maxar. Green components are from JPL or other partner institutions

Fig. 4

DSOC technology demonstration architecture showing the FLT on board the Psyche spacecraft, the ground laser transmitter and ground laser receiver on the ground with the DSOC mission operations system for coordinating operations. Coordination between the flight and ground assets in addition to the Psyche project was key to DSOC project success

Fig. 5

(a) Optical Transceiver Assembly (OTA) with photon-counting camera and floating electronics module integrated; (b) DSOC accommodation kit for accommodating OTA; (c) Laser transmitter assembly mounted separately on spacecraft panel and fiber coupled to OTA; (d) Stationary electronics module interfaces to spacecraft electronics and houses flight software and firmware

Fig. 6

Four recent Psyche shape models are shown for comparison. (a) Shepard et al. (2017) was the planning baseline for the 2022 launch opportunity. (b) Hanuš et al. (2017) was used to evaluate our plans in the “bounding cases” study. (c) Viikinkoski et al. (2018) was a second model used in the “bounding cases” study. (d) Shepard et al. (2021) is the current planning baseline for the 2023 launch mission. Our mapping campaign was shown to be successful with each of the shape models, demonstrating the resilience of our strategy for designing science orbits

Fig. 7

Simplified graphic of Psyche’s surface illumination as viewed from the north ecliptic pole. Psyche spin axis is the “positive pole” and that hemisphere is the basis of the seasonal references. The science orbit phases are shown on the inside circle. Orbits A through C are polar orbits and Orbit D is a near equatorial orbit. The best surface illumination is available during the two equinoxes. Orbit B2 is the only orbital phase that occurs during optimal illumination conditions

Fig. 8

The Psyche Approach phase, science orbits, and transfer orbits are shown on the mission timeline for the 2023 launch planning baseline. Illumination conditions are based on a model using a triaxial ellipsoid. The eclipse season for equatorial orbits is shown in pale blue and for polar orbits in pale violet. The period for optimal gravity science when the Sun-Earth-Probe angle is > 40° is shown in orange. Avoiding eclipse seasons while satisfying surface illumination and other observation requirements drove the design of the mission profile

Fig. 9

Variability in illumination conditions for Psyche assuming different spin axis orientations. The blue curve is for Psyche’s nominal pole RA/dec (36.3°, 6.1°) and maximum incidence angle of 90°. The salmon curve is for the nominal pole with maximum incidence angle of 70°. The yellow curve shows a worst case 3-sigma variation in Psyche’s pole RA/dec (51°, 21°) and the purple curve is the opposite worst case 3-sigma pole RA/dec (21°, −9°), both with maximum incidence angle of 70°. The science orbit phases are shown with respect to the lighting curves for both the nominal date for injection into Orbit A and a worst-case injection date. Imaging in Orbit B2 will satisfy the requirement to provide surface coverage of greater than 80% even with a worst-case injection date

Fig. 10

Six simulated OpNav images shown on approach to Psyche. Psyche’s diameter changes from 6.7 pixels to 2900 pixels between OpNav 1 and OpNav 28. For this approach trajectory, the phase angles range between 35° to 72° and all but OpNav 28 are taken from a northern sub-spacecraft latitude. Psyche surface texture is simulated

Fig. 11

Imaging in Orbit A taken from the perspective of the spacecraft as modeled by the Science Opportunity Analyzer software. (a) One Imager FOV is shown positioned near the dark-to-lit terminator in Orbit A. (b) One orbit of nadir imaging. The spiral shape of the orbit ground track and imaging swath results from the spacecraft orbit period being greater than the asteroid rotation period. (c) Four orbits of imaging, less than half of the 9-orbit cycle, provide nearly global surface coverage of the illuminated surface

Fig. 12

The spacecraft transitions between data downlink as it passes over the dark side of the asteroid during its orbit and science observing while passing over the lit side of the asteroid. The spacecraft enters the hit hemisphere in the south and travels to the north. Activities are planned relative to the terminator crossings of each orbit. This scheme allows the imaging sequences to be developed as a repeating template that can be adjusting if the timing of the terminator crossing changes. The magenta rectangle is a projection of the Imager field of view on the surface. The Psyche body-fixed axes are turquoise. The spacecraft is not to scale

Fig. 13

The operations time in Orbit A naturally divides into 4.5 ground track repeat cycles. Each 9-orbit cycle provides the opportunity to completely map the surface with the Imager and map gravity using the telecommunications subsystem. The time spent pointing the Imager nadir or off nadir is colored green and the communications periods are yellow. Cycle 3 is dedicated to off-nadir OpNav imaging

Fig. 14

Examples of different off-nadir imaging coverage for one orbit of Orbit A plotted on a latitude/longitude map. The background texture map is an artist rendering. (a) The spacecraft is pointing the Imager ahead of the orbital velocity vector. (b) The spacecraft is pointing the Imager behind the orbital velocity vector. The lightest orange indicates coverage with a single image and duplicate coverage is shown with increasingly dark colors until blue, which indicates coverage with six images or more covering the same area

Fig. 15

(a) The first cycle of Orbit A provides 81% surface coverage for incidence angles < 70°. (b) As the sun moves towards the southern hemisphere, overall coverage decreases by the end of the phase although additional terrain in the south becomes visible with good illumination. (c) The cumulative coverage is slightly above the required 80% for multispectral imaging, but this could change with small variations in spin axis or arrival date. Coverage is shown using a Mollweide projection

Fig. 16

Imaging in Orbit B1 taken from the perspective of the spacecraft. (a) One Imager FOV. (b) One orbit of nadir imaging. The spiral shape of the orbit ground track is evident. The twisting of the FOV is driven by the secondary pointing axis that strives to keep the solar arrays oriented towards the sun. (c) One complete cycle of 17 orbits of imaging provides global coverage of the illuminated portion of the surface

Fig. 17

(a) Graphical depiction of the 10 sequence cycles for Orbit B1. Each ground track repeat cycle is 17 orbits with additional orbits added for extra downlink and orbit maintenance maneuvers. Yellow indicates periods when the HGA is pointed to Earth for communications and shades of green and purple indicate when the Imager is pointed nadir or off nadir to observe. The illuminated surface is fully mapped 10 times in Orbit B1. (b) Summary timeline of all cycles in Orbits B1 and B2 demonstrating the ample science margin in the plan

Fig. 18

The illuminated surface available with incidence angles < 70° at the beginning and end of Orbits B1 and B2 is shown here. (a) Cycle 1 coverage for both Orbits B1 and B2 are shown. The improved surface illumination in Orbit B2 is evident in the coverage results. (b) Coverage results for the final cycle for Orbits B1 (Cycle 10) and B2 (Cycle 11) are shown. (c) The accumulated coverage over each science orbit phase for Orbits B1 and B2. (d) Coverage results from combining Orbits B1 and B2. (e) The addition of bonus mapping in the operations margin at the end of Orbit B2 brings the total mapping coverage to 99% for the mission

Fig. 19

Summary of Orbit B topography results. (a) Representation of off-nadir angles planned for Orbit B. The dashed green and purple rectangles emphasize the two sets of four off-nadir angles chosen. (b) Definition of “useable” stereo criteria used to evaluate expected performance in reconstructing topography from the planned imaging campaign for both stereophotoclinometry and stereophotogrammetry. (c) Stereo coverage on a latitude/longitude body map using the stereophotoclinometry criteria. Colors defined in legend show how many stereo views are available for each element of the surface. Coverage results are cumulative with the requirement being > 80% for four or more views. Results of 99.1% satisfy requirements with margin. (d) Stereo coverage using the stereophotogrammetry criteria. Results of 92.3% satisfy requirements with margin

Fig. 20

Illustrations of an example (a) orbit transfer from Orbit B1 to Orbit D and (b) orbit transfer from Orbit D to Orbit C showing the plane change at high altitude. Note that these transfer orbits reach altitudes of 29 and 35 Psyche radii, respectively, far exceeding the highest science orbit altitude. (c) This graphical timeline demonstrates the placement of the GRNS calibrations during the high-altitude periods of the orbit transfers before and after Orbit D. The purple curve is the spacecraft altitude in units of Psyche body radii. Thicker portions of the line are due to altitude fluctuations. The horizontal red line at 3.5 body radii is the altitude above which the GRNS can obtain useful background calibration data. The 40-day calibration requirement is satisfied by combining the 25 days from the first transfer with the 31 days from the second transfer. The orbit transfer durations are designed to have 50% margin as they are expected to increase in duration once all constraints are accommodated. The transfer to Orbit D includes a 10-day solar conjunction period

Fig. 21

Imaging in Orbit D taken from the perspective of the spacecraft. (a) One Imager FOV. (b) One nadir swath of 37 images covering about 25% of the lit-side pass. The trajectory hugs a band around the terminator for the entire phase. (c) The equivalent of 25 days (171 orbits) of imaging with 37 images/orbit. Placement of the images over features of interest viewable from a nadir attitude will be planned during Orbit B1 execution and the transfer to Orbit D

Fig. 22

Graphical depiction of the four cycles for Orbit D. Each ground repeat cycle is 196 orbits divided into roughly 75% nadir observing (green) for GRNS and 25% with HGA pointed to Earth for communications (yellow). The 18-orbit template was selected to provide the opportunity to evaluate spacecraft health every two days

Fig. 23

Surface sampling. The map shows the relative contribution of surface regions to the response of the GRNS while in the Orbit D with the Shepard et al. (2017) shape model. Since the orbit has high inclination, the equatorial band between +/−20° latitude contributes more than the mid-to-high latitude regions. This is primarily due to the solid angle of surface parcels at higher latitudes being lower than those at the equatorial sub-spacecraft points. When averaged over all orbital measurements, 76.5% of the surface contributes >5% of the maximum signal to the instrument response. This threshold criterion is used to evaluate coverage for different orbits. The sampling map is from an Orbit D “bounding cases” study for which several permutations of Psyche’s shape and corresponding orbits were considered. The map was normalized so that the maximum sampling intensity across all permutations considered was 1. The baseline orbit provides ample sampling of the equatorial region

Fig. 24

Signal intensity and spatial resolution for the Orbit D baseline. (a) A histogram of solid-angle-equivalent altitudes (h_eq) for a series of orbital locations sampled uniformly in time. (b) A histogram of the width of the GRNS instrument response (1-sigma arc length on the surface) determined for the same time series of locations

Fig. 25

Imaging in Orbit C taken from the perspective of the spacecraft. (a) One Imager FOV projected on the surface in the southern hemisphere; (b) One orbit of nadir imaging; (c) One cycle of nadir imaging coverage if every orbit was able to be imaged. The operations plan skips multiple orbits for communications passes as shown in a later figure. The northern hemisphere is not well illuminated

Fig. 26

Orbit C architecture showing observing periods (green), HGA communications (yellow), and orbit maintenance maneuver windows (blue). Each ground track repeat cycle is 45 orbits in duration and each operational repeat cycle is offset from the previous ground track repeat cycle by seven orbits to shift the HGA tracks

Fig. 27

Buildup of nadir coverage with incidence angle < 70° in Orbit C following the operations schema shown in Fig. 26. (a) Cycle 1 coverage: Top map shows individual Imager FOV and bottom map shows total coverage. Yellow indicates areas imaged only once and red indicates areas imaged more than once. (b) Combined coverage from Cycles 1 and 3. Top map shows individual FOV for Cycle 1 in red and Cycle 3 in orange. Bottom map shows total coverage. (c) Combined coverage from nadir Cycles 1, 3 and 5. Top map shows individual FOV with Cycle 5 in purple, and bottom map is total coverage. By Cycle 4, gaps from downlink passes and maneuvers in earlier cycles are filled in with robust redundant coverage. The northern hemisphere is not well illuminated during this period

Fig. 28

Colored boxes show the number of unique views in the Psyche-solar-orbit frame from which a given area on the body would be observed by the spacecraft during Orbit C. Each view corresponds to a different interaction between the solar wind and the same region of Psyche’s surface. Data are binned over longitude and latitude in the Psyche-body-fixed frame. Each bin is 10° × 10°, and the spacecraft position is sampled at 1-s intervals. The views in the Psyche-solar-orbit frame are also binned at 10° × 10°. Each view comprises tens of thousands of measurements taken during different segments of the orbit

Fig. 29

Project decomposition and external interfaces. The instrument investigation teams and the Science Data Center have responsibilities to both the science team and the flight operations team. While all NASA projects interface to the DSN and PDS, the interface to the DSOC project is unique to Psyche

Fig. 30

The working group organization within the science team. In practice, there is significant overlap in the membership between science working groups so it is the responsibility of the working group leads to ensure that each science objective receives dedicated attention and analysis. Members of the instrument science investigations and other groups are also included in the science objective working groups

Fig. 31

Psyche Phase E project organization for operations. Many aspects of the Psyche organization are common to deep space flight projects. Unique to the Psyche project is the partnership with Maxar. While the spacecraft is operated from JPL, Maxar provides on-call support for anomaly investigation and other studies as needed

Fig. 32

Top-down approach drives science planning. Activity plans and sequences flow from top-level science goals rather than instrument-driven requests. This approach eliminates time-consuming negotiations between instrument teams for resources and ensures that the science data collected addresses the primary science objectives

Fig. 33

Timeline for the uplink process from initial science plans through sequence development and execution. Progressive refinement of science activity plans leads to straightforward sequence implementation. Detailed science plans are developed pre-launch and then refined during cruise as additional information becomes available about the asteroid, the trajectory and arrival date, and spacecraft and instrument capabilities. The uplink planning process is designed to be strategic and iterative

Fig. 34

Layout of the activities for a typical periodic maintenance and calibration windows. The need to thrust with the SEP system for most of cruise leaves limited time to calibrate the science instruments or perform maintenance on the spacecraft. All activities must be efficiently integrated within the 4-day timeline

Fig. 35

Thrusting architecture for Mars gravity assist with the Trajectory Correction Maneuver (TCM) and windows for Mars Trim Maneuvers (MTMs). MTM-1 is deterministic and MTM-2 is a statistical correction. Both maneuvers include contingency cases shown in light green. This architecture was designed to achieve the most accurate delivery at Mars closest approach without overloading the flight team’s ability to generate the associated spacecraft command files

Fig. 36

Psyche science data flows from the GDS at JPL to the SDC, which coordinates all traffic of science data products between the GDS, the Psyche science team, and the PDS