Three Forks Depot

The Mars 2020 Perseverance rover has been collecting a set of samples for potential future return to Earth through the joint NASA-ESA Mars Sample Return (MSR) Campaign. Near the end of the rover’s prime mission, an initial set of 10 samples was placed on the surface of Jezero Crater. This set of samples serves as a backup, in case the primary set of samples cached within the rover are unable to be retrieved for return to Earth. This set of samples and their location are collectively referred to as the “Three Forks Depot” by the Mars 2020 Science Team. The samples are:

A preliminary set of scientific observations and interpretations of the 10 samples in the Three Forks Depot is included in the Initial Reports collection of the Sample Dossier Archive. In most cases, these observations and interpretations have been revised and expanded on in a number of subsequent publications, not listed here.

Within the Analyst's Notebook

The Three Forks Depot archive is being integrated into the AN.

• An overview table of the Three Forks Depot (accessible from the Mission summaries tab) lists the ten samples dropped at the depot and a suite of Mastcam-Z panoramas taken during depot construction.
• The traverse map (accessible from the Map tab) shows sample locations in context of the rover traverse.
• Related images to individual samples at the depot are included in the the Sample Science pages.

In the Archive

The Three Forks Depot Archive is intended to record data related to both the construction and documentation of the Three Forks Depot, to allow for future reconstruction of environmental conditions experienced by the sample tubes both during the depot construction process and while sitting on the surface prior to retrieval for return to Earth. The Three Forks Depot Archive is intended to complement the Sample Dossier Archive, which records data related to the sample acquisition process.

Much of the data referenced in the Three Forks Depot Archive is formally archived in other PDS bundles associated with the Mars 2020 mission. As such, where possible the Three Forks Depot Archive references these products by PDS Logical Identifier (LID) and provides context such as the identity of the associated sample tube, instead of archiving a separate copy of existing products.

Data product collection

The archive includes these data products:

Orthorectified DEM/RZS Products

Orthorectified digital elevation models (DEM) and image mosaics (RZS) at an approximate resolution of 0.0025 m/pixel created from Navcam stereo images are included for each sample tube. Browse versions of all such products are included in the Browse collection.

Sample Drop Timestamps

The Sample Drop Timestamps product lists the times during each tube drop event when the tube was formally declared to be on the ground.

ACA Timeline

The ACA timeline products list the timestamps of events that occurred as each sample tube moved through the Adaptive Caching Assembly (ACA) during tube drop events. A high-level overview of the sequence of steps which occur during tube drop events is as follows, with further detail is available in Moeller et al. (see the Related Publications list below):

• The sample tube is removed from the Sample Tube Storage Assembly (STSA)
• The sample tube is moved to the Vision Station
• The sample tube is imaged by CacheCam
• The sample tube is moved to the Sealing and Drop Off Station
• The sample tube is dropped to the surface

Each product includes a list of commands executed during the tube drop event, the sequence ID from which each command was called, the start and end time of each command (in both SCLK and LMST), the duration in seconds, and the status code (SUCCESS or FAILURE) of each command. The table below summarizes the expected commands that may be observed during tube drop events.

Document collection

The archive includes this documentation:

Anomaly Summary

This document summarizes all known anomalies that occurred during Three Forks Depot construction.

Mastcam-Z Mosaics

Several mosaic products showing the Three Forks Depot were produced as special products by the Mastcam-Z team, outside the normal Mastcam-Z processing pipeline. As such, these products are archived here instead of in one of the Mastcam-Z-specific bundles. In some cases, additional versions of these products can be found in the Mastcam-Z’s 360° Panorama Collection. https://mastcamz.asu.edu/mastcam-zs-360-panorama- collection/

Mastcam-Z mosaic product names share a similar format, denoting the sol (or sol range) on which individual frames were acquired and camera eye (left or right) used to acquire the image frames. For example:

• mastcam_z_mosaic_sol_650_left.png: Mosaic acquired on sol 650 by the left eye
• mastcam_z_mosaic_sols_690_692_right.tif: Mosaic acquired from sols 690-692 by the right eye

Reduced-resolution browse versions of all Mastcam-Z Mosaic products are included in the Browse collection.

Hogwallow Flats Mosaic

Two Mastcam-Z mosaic products were acquired at the “Hogwallow Flats” location a few hundred meters away from Three Forks:

• mastcam_z_mosaic_sols_466_474_left.tif
• mastcam_z_mosaic_sols_466_474_right.tif

These products were included in the archive as the highest-resolution mosaics that show the entirety of the Three Forks Depot from an external perspective. In both mosaics, the Three Forks Depot is approximately located at lines 7500-8000 and samples 88,000-90,000.

WATSON Mosaic

One mosaic product showing the Three Forks Depot and the Perseverance rover was produced as a special product by the WATSON team, outside the normal WATSON processing pipeline. As such, this product is archived here instead of in one of the WATSON-specific bundles. A reduced-resolution browse version of this product is included in the Browse collection.

Science Community Workshop Report

The Science Community Workshop Report is a report produced following a joint M2020/MSR workshop to assess the samples cached at the Three Forks Depot. The joint workshop aimed to determine whether the planned sample collection was Scientifically-Return Worthy prior to the construction of the Three Forks Depot.

Browse collection

Quick look versions of image mosaics in the archive are included as browse products. As stated above, much of the data referenced in the Three Forks Depot Archive is formally archived in other PDS bundles associated with the Mars 2020 mission and can be found in those bundles.

Miscellaneous collection

Ancillary products in the archive are described below.

Campaign Sols

The Campaign Sols table gives the start and end sols for all rover campaigns involved in scouting the Three Forks Depot location and constructing the depot.

Depot Mosaics

The Depot Mosaics products are a set of three related products that summarize available depot-wide mosaics of the Three Forks Depot. The included mosaics were selected to provide the highest-resolution images of the Three Forks Depot available. There are other mosaics available but not listed here, such as:

• Lower-resolution mosaics acquired outside the Three Forks Depot (e.g. end-of-drive mosaics acquired for tactical planning during the Depot Reconnaissance campaigns)
• Mosaics acquired to document individual sample tubes, instead of the depot as a whole (these are included in the Documentation Image products)

Orbital Map

The Orbital Map is a clipped version of a larger orbital map showing the vicinity of Perseverance’s traverse, archived as part of the Mars 2020 PLACES bundle. The clipped Orbital Map has a black line drawn on it showing the traverse path of the rover during the Depot Creation campaign. A browse version of this product is included in the Browse collection.

Documentation Images

The Documentation Images tables list all images acquired as planned documentation images for each individual sample tube. The nominal set of images acquired for all sample tubes is as follows:

• CacheCam images of each sample tube prior to drop
• WATSON images of a subset of sample tubes in the Sealing Station prior to drop (these images are indicated by a comment in the Notes field)
• WATSON images of each sample tube on the ground after tube drop
• Front HazCam images of each sample tube on the ground after a short drive backwards
• Navcam images of each sample tube on the ground after a short drive backwards
• Mastcam-Z images of most sample tubes on the ground. For the sample tube M2020-00586-18 WB3/Amalik Witness, no standalone high-resolution Mastcam-Z documentation images were acquired. Instead, the high-resolution Mastcam-Z mosaic acquired on sol 693 provided similar quality coverage while also documenting the rest of the completed Three Forks Depot.

For each image product, the Documentation Images table provides the Sol, Site, Drive, Instrument, and LID. For most image products, an approximate Sample and Line coordinate of the sample tube in the frame is included. These are omitted for CacheCam, WATSON images of the sealing station, and some WATSON images of the ground (which were partially intended to confirm that the sample tubes were not underneath the rover’s wheels, so they imaged the wheels even if no sample tube was present). For some image products, an associated mosaic is provided in the Mosaic LID field.

Incidental Images

The Incidental Images tables list all known images of sample tube locations (both before and after tube drop events) that were not acquired as planned documentation for the specific sample tube, along with the coordinates of the sample tube in each image. Individual images may occur in multiple different Incidental Images products if multiple sample tubes were in the field of view simultaneously.

Mesh Files

Mesh Files tables list the known 3D mesh products generated from Navcam and HazCam data that include each sample tube within the mesh footprint. Along with the instrument and LID of each mesh product, the intent is given, which has one of three possible values:

• Documentation: these mesh products were generated from post-drop Navcam and Front HazCam images acquired as planned documentation of each sample tube
• Pre-Drop: these mesh products were generated from pre-drop Navcam images that were used to plan the tube drop
• Incidental: all other mesh products

Documentation and Pre-Drop mesh products are expected to have the highest quality data of all mesh products available for each sample tube.

Event Sols

The Event Sols table summarizes the sols on which various key events for each sample tube occurred. These include the Bump Sol, on which the rover drove to the final drop location, the Drop Sol, on which the tube drop actually occurred, and all of the planned documentation imaging.

Sample Tube Identifiers

The Sample Tube Identifiers table summarizes relevant identifying information for each sample tube. These include the formal designation, informal name (and any alternates), unique identifiers for the drop zone and the sample tube, and serial numbers for all parts of the sealed tube.

Sample Tube Locations

The Sample Tube Locations table summarizes available location information for each sample tube. These include the Site and Drive indices of the rover during drop events and the rover’s latitude, longitude, and elevation during drop events. For more details on these latitude, longitude, and elevation coordinates, see the Rover PLACES data product Software Interface Specification.

The Sample Tube Locations table also records the azimuth of the sample tube on the ground after tube drop, measured as the angle clockwise from the true north vector to a vector drawn from the seal end of the tube to the glove end of the tube.

Sample Tube Targets

The Sample Tube Targets table summarizes various strategic and tactical target names used during planning for each sample tube. These include:

• Drop Zone – Strategic: the drop zone target, defined strategically (for long-term planning purposes)
• Drop Zone – Tactical: the drop zone target, defined tactically (typically immediately prior to driving to the drop location, and used to plan the drive as precisely as possible)
• Drop Zone – End of Drive: the drop zone target, defined after arrival (typically used to validate the drive to the drop zone prior to dropping each tube)
• Drop Location – Glove: a target identifying the glove end of the sample tube post-drop
• Drop Location – Seal: a target identifying the seal end of the sample tube post-drop
• Imaging Target: a target used to plan post-drop documentation imaging.

Related publications

These papers describes in detail the overall Mars 2020 mission, the Sampling and Caching Subsystem, and the various cameras used to acquire image products mentioned in the Three Forks Depot Archive.

• Farley, K. A. et al. Mars 2020 Mission Overview. Space Sci. Rev., 216:142, 2020. doi:10.1007/s11214-010-00762-y
• Moeller, R. C. et al. The Sampling and Caching Subsystem (SCS) for the Scientific Exploration of Jezero Crater by the Mars 2020 Perseverance Rover. Space Sci. Rev., 217:5, 2021. doi:10.1007/s11214-020-00783-7
• Bell III, J. F. et al. The Mars 2020 Perseverance Rover Mast Camera Zoom (Mastcam-Z) Multispectral, Stereoscopic Imaging Investigation. Space Sci. Rev., 217:24, 2021. doi:10.1007/s11214-020-00755-x
• Bhartia, R. et al. Perseverance’s Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Investigation. Space Sci. Rev., 217:58, 2021. doi:10.1007/s11214-021-00812-z
• Maki, J. N. et al. The Mars 2020 Engineering Cameras and Microphone on the Perseverance Rover: A Next-Generation Imaging System for Mars Exploration. Space Sci. Rev., 216:137, 2020. doi:10.1007/s11214-020-00765-9