Directed-Call 2 Attachment 1 SMS GRACs.pdf

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Pre-Decisional

NextSTEP-3 Appendix B Attachment 1

Surface Mating System Ground Rules, Assumptions, and Constraints

2 October 2026

National Aeronautics and Space Administration Lyndon B. Johnson Space Center Houston, Texas 77058

TABLE OF CONTENTS

SECTION PAGE

1.0 INTRODUCTION

1.1 Scope ....……………………………………………………………………………………………5

1.2 Definitions

2.0 GENERAL (APPLICABLE TO ALL MISSION PHASES)

2.1 General Ground Rules

2.1.1 Redundancy & Recovery

2.1.2 Design Life

2.1.3 Active Mating / De-Mating Cycles

2.2 General Assumptions

2.2.1 Design-Agnosticism

2.2.2 Lander Payload Mass Capabilities

2.2.3 Mobility Asset Capabilities

2.2.4 Site Preparation

2.2.5 Survivability / Operability

2.2.6 Power & Data

2.2.7 Power………………

2.2.8 Checkouts

2.3 General Constraints

2.3.1 Operations

2.3.2 Atmosphere

2.3.3 Interface

2.3.4 Design Factors

2.3.5 Loads…………

3.0 LAUNCH, IN-SPACE, AND LANDING PHASE

3.1 Launch, In-space, and Landing Phase Ground Rules

3.1.1 Volume & Mass

3.1.2 No Assumed Environmental Protection

3.2 Launch, In-space, and Landing Phase Assumptions

3.2.1 Physical Restraint

3.3 Launch, In-space, and Landing Phase Constraints

3.3.1 Volume…

4.0 OFFLOADING PHASE

4.1 Offloading Phase Ground Rules

4.1.1 Mass & Geometry

4.1.2 Dynamic Envelope

4.2 Offloading Phase Assumptions

4.2.1 Responsibility

4.3 Offloading Phase Constraints

4.3.1 Orientation & Accessibility

5.0 SURFACE MOBILITY PHASE

5.1 Surface Mobility Phase Ground Rules

5.1.1 Traverse Slope

5.1.2 Environmental Protection

5.1.3 Mobility Interface

5.2 Surface Mobility Phase Assumptions

5.2.1 Mobility Asset

5.2.2 Capture Envelope

5.2.3 Stability…

6.0 MATING PHASE

6.1 Mating Phase Ground Rules

6.1.1 Capture Envelope

6.1.2 Release From Mobility Asset

6.2 Mating Phase Assumptions

6.2.1 Alignment

6.2.2 Power/Data Handover

7.0 OPERATIONS PHASE (MATED OPS)

7.1 Mated Ops Ground Rules

7.1.1 Sealing & Leakage

7.1.2 Minimum Transgressable Volume

7.2 Mated Ops Assumptions

7.2.1 Maintenance

7.2.2 Vestibule Pressurization/Depressurization

7.2.3 Power/Data Continuity

TABLES

Table 2-1: Mated Load Set Sources

FIGURES

Figure 2-1: Passageway Dimensions

1.0 INTRODUCTION

This document establishes the Ground Rules, Assumptions, and Constraints (GRACs) for the Surface Mating System (SMS) intended for lunar surface operations. It encompasses the conceptual framework, operational boundaries, and technical constraints that guide the design, development, and integration of SMS for lunar habitats and logistics elements.

1.1 SCOPE

The document serves as a foundational reference for Offerors, ensuring that all SMS concepts and proposals adhere to the established GRACs. It is intended to guide design trades, inform technical decisions, and support the development of robust, adaptable, and compliant surface mating solutions for lunar exploration missions.

1.2 DEFINITIONS

To guide SMS concept planning and development, the definitions of the Ground Rules, Assumptions, Constraints, Key Performance Parameters, Thresholds, and Goals are provided below.

• Ground Rule – A basic or governing principle adhered to the maximum extent possible during the study period. Ground rules set the bounding framework.

• Assumption – A basic or governing principle used as a point of departure for trades during a study. Assumptions establish “working truths.”

• Constraint – A requirement held by the Program/Project that imposes limitations on the architecture. Constraints define hard boundaries the system must not violate.

• Key Performance Parameter (KPP) – A capability or characteristic considered essential for mission success. KPPs are the highest priority system metrics or requirements.

• Threshold – The minimum acceptable value of a KPP or requirement, the “must meet” level. Falling below the threshold means the system fails to meet an essential requirement.

• Goal – The desired or optimal value of a KPP or requirement, typically above the threshold. The goal represents the “nice-to-have”, preferred performance level used to guide design trades when feasible.

2.0 GENERAL (APPLICABLE TO ALL MISSION PHASES)

The GRACs listed in Section 2 are applicable to all mission phases.

2.1 GENERAL GROUND RULES

2.1.1 Redundancy & Recovery

The SMS must be designed to allow for recovery from failed mating attempts, including the ability to re-attempt mating, and must be robust to partial failures (e.g., stuck latch, failed sensor).

2.1.2 Design Life

The SMS will be designed for a 10-year life on the lunar surface. Design life accounts for maintenance, degradation, redundancy, and natural and induced environments.

2.1.3 Active Mating / De-Mating Cycles

1. The SMS must be designed to a minimum of 3 full mating/de-mating cycles, including any required checkouts prior to mating, for “long-duration ports” (threshold). A long-duration port is one that is designed to only be mated once, and the 3 cycles include one nominal mating / de-mating, one contingency mating / de-mating, and one mating / de-mating checkout.

2. The SMS must be designed to a minimum of 60 full mating/de-mating cycles, including any required checkouts prior to mating, for “high-cycle logistics ports” (goal). A high-cycle logistics port is one that is designed to have two missions per year for 10 years, and the 60 cycles include one nominal mating / de-mating, one contingency mating / de-mating, and one mating / de-mating checkout per mission for 10 years.

2.2 GENERAL ASSUMPTIONS

2.2.1 Design-Agnosticism

Design concepts can include a standalone SMS, an integrated SMS, or both. A standalone SMS is a separate payload that connects two habitat/logistics elements together, whereas an integrated SMS arrives pre-integrated on a habitat/logistics element and performs the mating function when another habitat element arrives.

2.2.2 Lander Payload Mass Capabilities

The Commercial Lunar Payload Services (CLPS) lander and the Human-class Delivery Lander (HDL) are lunar landing system elements responsible for delivering cargo to the lunar surface. This cargo could include a standalone SMS or a lunar surface habitat/logistics element integrated with an SMS. The CLPS landers to be used in Moon Base Phase 3 are currently undefined; however, they have an expected payload mass capability up to 8 metric tons, inclusive of any cargo-unique adapters. The HDL has a payload mass capability up to 15 metric tons (including MGA and margin), inclusive of any cargo-unique adapters.

2.2.3 Mobility Asset Capabilities

The capabilities of the surface mobility assets (Lunar Utility Vehicle (LUV) or equivalent) are still being defined. SMS design concepts should explicitly state any assumed capabilities (e.g., fine alignment, lifting) that are necessary for mating.

2.2.4 Site Preparation

The need for site preparation (e.g., compaction, leveling) is not yet resolved. SMS design concepts should be robust to a range of site conditions. However, any assumed site preparation capabilities required for surface mating should be explicitly stated.

2.2.5 Survivability / Operability

The SMS must be operable after surviving all induced and natural environments during launch, on-orbit transit, landing, surface operations (e.g. transport, mating), and throughout its operational life including:

• Mechanical loads (shock, vibration, quasi-static, acoustic)

• Thermal extremes (vacuum, cold soak, sun exposure)

• Radiation (space and lunar surface)

• Micrometeoroid debris (MMOD) and lunar ejecta impacts

• Dust exposure (especially during landing, offloading, and traversing)

2.2.6 Power & Data

The SMS will be provided with power and basic data/command links by the host vehicle (launch vehicle, lander, mobility asset, and/or hab/logistics element) during on-orbit transit and on the surface, but must be able to survive periods without power/data if necessary.

2.2.7 Power

The SMS must have the ability to pass up to 6kW of 120 VDC bi-directional power via redundant power connectors.

2.2.8 Checkouts

The SMS should support (as feasible) health and status, continuity, and/or functional checkouts after major dynamic events such as launch, landing, offloading, and surface transit. This may be limited by available power and data.

2.3 GENERAL CONSTRAINTS

2.3.1 Operations

The SMS must be capable of operating independent of a crewmember present on the lunar surface (either IVA or EVA) and time-critical operations such as emergency de-mating is not expected.

2.3.2 Atmosphere

The SMS structure must be designed for up to 9.6 psia Maximum Operating Pressure (+ additional FoS) and compatibility with up to 34% O2. Moon Base is planning an operational atmospheric environment of 8.2 psia at 34% O2 to reduce EVA pre-breathe time and amount of consumables required, or 9.6 psia at 28.5% O2 if necessary for reduced materials flammability risk. Until the final atmosphere is determined, the SMS design must account for both possibilities.

2.3.3 Interface

The SMS must have a circular interface compatible with a minimum 1.7m diameter for the crew translation corridor and a minimum 2.0m diameter for host vehicle attachment, as shown in Figure 2-1: Passageway Dimensions. In the figure below, there are notional keep out zones on either side of the passageway that are available for umbilicals, sensors, targets, etc.

FIGURE 2-1: PASSAGEWAY DIMENSIONS

2.3.4 Design Factors

The SMS shall be compliant to NASA STD 5017 Design and Development Requirements for Mechanisms and JSC 65828 Structural Design Requirements and Factors of Safety for Spaceflight Hardware.

2.3.5 Loads

The SMS must account for seal closure force, design pressure, compressive axial load, tensile axial load, shear load, torsion moment, and bending moment. Table 2-1: Mated Load Set Sources, can be used as a reference for how the design loads are derived.

TABLE 2-1: MATED LOAD SET SOURCES

Load Set Source 1 Source 2 Source 3 Source 4 Source 5 Seal Closure Force 22 000 N - - - -

Design Pressure - 66.19 kPa - - - Compressive Axial - - - - - Tensile Axial Load - 205 000 N - - -

Shear Load - - 9 600 N - - Torsion Moment - - 9 600 Nm - - Bending Moment - - 43 500 Nm - -

Notes:

1. Values are design limit loads

2. Structural latch preload and tunnel stiffness will be such that, when under external loading within limits, there remains metal-to-metal contact in the local vicinity of the latches.

3. Shear loads may be applied in any direction in the SMS mating plane.

4. Bending moment may be applied about any axis in the SMS mating plane.

5. The outer seal bead is to be used for all pressure calculations.

6. Source descriptions:

a. Source 1 – Seal Compression

b. Source 2 – Maximum Design Pressure

c. Source 3 – Derived Bending Capability

d. Source 4 – Reserved

i. (e.g., Cargo Transfer (mass dropping))

ii. (e.g., Hatch Operation)

e. Source 5 – (reserved)

i. (e.g. Thermal)

Load Source Assumptions (ref only):

1. Source 1 (Seal Compression):

a. Seal Length

i. Outer – 245.512 inches

ii. Inner – 240.728 inches

b. Seal Force

i. ~10 lbf per linear inch of seal for a single seal bulb

2. Source 2 (Design Pressure)

i. 9.6 PSI

ii. Area 4796.64 in2

3. Source 3 (Combined loading based on latch capability)

i. To derive the allowable bending moment, we first determine the maximum latch load at 2 × MDP (pressure-only, FS = 2.0). Then, we analyze the combined pressure and bending case (FS = 1.4), adjusting the bending moment until the latch load equals the previously determined maximum. This ensures compliance with safety requirements and provides a clear, traceable limit for bending moment at the interface.

ii. This load is roughly equivalent to a 6000 KG mass cantilevered 4.5 m from the interface.

3.0 LAUNCH, IN-SPACE, AND LANDING PHASE

The GRACs listed in Section 3 are applicable to launch, in-space transit, and the landing phase.

3.1 LAUNCH, IN-SPACE, AND LANDING PHASE GROUND RULES

3.1.1 Volume & Mass

The SMS must fit within the mass and volume constraints of the launch vehicle and lander. If integrated with another element (e.g., MPH, Node, or future habitat), it must not exceed the host’s allocation.

3.1.2 No Assumed Environmental Protection

Except for rare cases (e.g., Starship), landers do not provide significant environmental protection.

The SMS must be robust to direct exposure.

3.2 LAUNCH, IN-SPACE, AND LANDING PHASE ASSUMPTIONS

3.2.1 Physical Restraint

All SMS components must provide protection to preclude propagating damage to the host element or to the mating asset.

3.3 LAUNCH, IN-SPACE, AND LANDING PHASE CONSTRAINTS

3.3.1 Volume

1. If integrated on a habitat (e.g., Node, MPH, etc.) the habitat and SMS combined must be contained within a dynamic volumetric envelope of 7.8-meter (307.1 inch) height, 6.2-meter (244.1 inch) diameter depth, and 4.85-meter (190.9 inch) width per HLS-SUP-920, HLS Program HDL Supplement for Lunar Surface Habitat Document. These envelope dimensions represent ranges of expected cargo for the HDL delivery. This is inclusive of any habitats that the SMS would be integrated with and any cargo-unique adapters.

2. If integrated on a Mated Carrier (MC), the MC and SMS combined must be contained within the dynamic volumetric envelope of the CLPS lander; however, the CLPS landers to be used in Moon Base Phase 3 are currently undefined.

4.0 OFFLOADING PHASE

The GRACs listed in Section 4 are applicable to the offloading phase only.

4.1 OFFLOADING PHASE GROUND RULES

4.1.1 Mass & Geometry

A standalone SMS must not exceed the maximum weight or size capacity of the offloader or surface mobility asset.

4.1.2 Dynamic Envelope

The SMS must stay within the dynamic envelope of the lander offloading system. The SMS must not interfere with surrounding hardware as it’s being offloaded.

4.2 OFFLOADING PHASE ASSUMPTIONS

4.2.1 Responsibility

Offloading from the lander to the surface is the responsibility of the lander’s offloading system, not the SMS itself. The SMS (if not already integrated on habitation/logistics element) should provide notional offloading interfaces (e.g., lifting points, brackets, fiducials for robotic handling).

4.3 OFFLOADING PHASE CONSTRAINTS

4.3.1 Orientation & Accessibility

If delivered as a separate/standalone SMS, the landed package must be compatible with the surface mobility system (e.g., Lunar Utility Vehicle) and configured to allow retrieval, transport, and positioning at the habitat/logistics element (if not support full mating operation).

5.0 SURFACE MOBILITY PHASE

The GRACs listed in Section 5 are applicable to the surface mobility phase only.

5.1 SURFACE MOBILITY PHASE GROUND RULES

5.1.1 Traverse Slope

The SMS must be able to withstand a traverse on slopes of up to +/- 20 degrees.

5.1.2 Environmental Protection

Dust and thermal covers may be required to protect sensitive interfaces from environmental conditions during mobility. There will not be a human/crew ability to remove or replace environmental covers prior to surface mating ops.

5.1.3 Mobility Interface

For a standalone SMS, the system will include notional mechanical and electrical interfaces to the mobility asset.

5.2 SURFACE MOBILITY PHASE ASSUMPTIONS

5.2.1 Mobility Asset

The SMS is assumed to be carried by a surface mobility asset (e.g., Lunar Utility Vehicle) or integrated with a habitat/logistics element, not self-mobile.

5.2.2 Capture Envelope

The mobility asset will place the SMS within a 20cm (goal) to 50 cm (threshold) diameter capture sphere and compensate for a 3 deg (goal) to 7 deg (threshold) misalignment between the adjoining habitable assets in all six degrees of freedom.

5.2.3 Stability

A standalone SMS must be stable during transport (not tip over) and may have mounting points and fiducials for secure attachment and robotic handling.

6.0 MATING PHASE

The GRACs in Section 6.0 are applicable to the mating phase only.

6.1 MATING PHASE GROUND RULES

6.1.1 Capture Envelope

The SMS must be able to perform final alignment and latching from within a 20 cm (threshold) to 50 cm (goal) diameter capture sphere and compensate for a 3 deg (threshold) to 7 deg (goal) misalignment between the adjoining habitable assets in all six degrees of freedom.

6.1.2 Release From Mobility Asset

A standalone SMS must be releasable from the mobility asset after mating, without leaving behind debris or failed fasteners or otherwise preventing future assets from using the mobility asset.

6.2 MATING PHASE ASSUMPTIONS

6.2.1 Alignment

The SMS must support both coarse and fine alignment. Coarse alignment to get into the initial capture envelope will be provided by the mobility asset; fine alignment could be the responsibility of the SMS (e.g., latches, guides, Stewart platform, etc.) or shared between the SMS and mobility asset. The required alignment tolerance is driven by the latching and sealing system, as well as the mobility asset capabilities (reference Section 5.2.2).

6.2.2 Power/Data Handover

The SMS receives power and data from the mobility asset or habitat/logistics element during mating operations. The SMS must support seamless handover of power and data connections from the mobility asset or host element to the other habitat/logistics element. This may require a handshake protocol and/or redundant connections.

7.0 OPERATIONS PHASE (MATED OPS)

7.1 MATED OPS GROUND RULES

7.1.1 Sealing & Leakage

The SMS maximum total leak rates for Beginning of Life (BOL) and End of Life (EOL) are TBD at this time. However, the NASA Docking System Block 2 (NDSB2) has a maximum Beginning of Life (BOL) total leak rate of 0.000385 kg/day and a maximum End of Life EOL) total leak rate of

0.0365 kg/day as an example.

7.1.2 Minimum Transgressable Volume

During mated operations the SMS should not protrude into the minimum 1.1m (43in) wide x 2.09m (82.3in) high translation path envelope, excluding translation aids (handrails/handholds) and provide a translation path free of equipment and protrusions that accommodates the volume of a suited crewmember in partial gravity. A suited crewmember would only translate through the SMS translation path in a contingency scenario.

7.2 MATED OPS ASSUMPTIONS

7.2.1 Maintenance

The SMS should be designed for minimal maintenance, as in-situ repair capability is extremely limited. Any required maintenance should be able to be performed in a shirt-sleeved environment only. Multi-use interfaces must be robust to repeated cycles.

7.2.2 Vestibule Pressurization/Depressurization

The vestibule pressurization and depressurization operation is assumed to be performed by the host element. In addition, the habitat is assumed to provide the vestibule gas necessary for the operation.

7.2.3 Power/Data Continuity

The SMS must maintain power and data continuity between mated elements, with redundancy as appropriate.