RT-3: Crew Return¶
Summary. "Return crews safely to Earth while mitigating adverse impacts to crew health" (ADD Rev C, p. 83). ADD Rev C grounds crew safety in NASA's human-rating standards and splits the architecture's response into system capabilities and integrated mission operations. Its forward look is about Mars: return could take months, so missions will need far more autonomy, survival options and health support, and the lunar fault-tolerance approach "may need to be reassessed". One of the nine recurring tenets.
All page numbers below are ADD Rev C, Section 3.5.3 (pp. 88–91). The section heading words the tenet "Return crew safely to Earth while mitigating adverse impact to crew health" (p. 88).
The assessment¶
- "The wellbeing and safe return of astronauts are of the utmost importance. Considerations for safe crew return start well before the mission and are integrated into system design, test and verification, and end-to-end mission testing and training" (p. 89).
- Standards the architecture adheres to (p. 89): NPR 8705.2 Human-Rating Requirements for Space Systems; NASA-STD-8719.29 NASA Technical Requirements for Human-Rating; HEOMD-003 Crewed Deep Space Systems Human Rating Certification Requirements and Standards for NASA Missions; NASA-STD-3001 NASA Space Flight Human-System Standard (Volumes 1 and 2).
- Human-rated means: "A human-rated system accommodates human needs, effectively utilizes human capabilities, controls hazards with sufficient certainty to be considered safe for human operations, and provides, to the maximum extent practical, the capability to safely recover the crew from hazardous situations" (p. 89).
- A proposed new process. "In addition to the established risk structure that has an existing process for program/mission risk assessments, an additional process that supports architecture decisions and definition has been proposed, contributing to safe crew return" (p. 89). Compare MD-04, the Mars loss-of-crew risk methodology selected at the 2025 ACR (Key definition tasks; the ADD doesn't say they are the same).
- Layers. "Crew safety includes multiple layers: hazard controls (and control redundancy) prevent hazards; crew survival methods ensure the crew can return to Earth if a hazard does occur. The architecture derives contingency and abort use cases and functions based on the human rating standard" (p. 89).
The results fall into two categories (pp. 89–90), quoted in short form:
| Architecture/system capabilities provide | Integrated mission operations provide |
|---|---|
| "Failure tolerance to catastrophic hazards (e.g., similar/dissimilar redundancy, reliability, functional down-moding, etc.)" | "A strategy to minimize crew risk and/or the exposure duration during first-time operations or high-risk activities (including, e.g., pre-cursor uncrewed demonstrations and an incremental approach to build up capability)" |
| "Medical systems, emergency systems, and crew survival capabilities" | "Clear mission authority, roles, and responsibilities" |
| "Crew manual control (of vehicle dynamics and systems) and manual override (of software/automation)" | "Execution of launch commit criteria and go/no-go flight rules prior to critical events" |
| "Crew control of any uncrewed vehicle in the vicinity of the crewed vehicle" | "Ability to monitor, command, and control vehicles and assist the crew from Earth or another remote location" |
| "Abort of a mission phase and safe return of the crew" | "Operational constraints … (e.g., EVA and rover range/time limits to return crew within suit consumables)" |
| "Crew/vehicle autonomy to return without Earth communication" | Crew support of critical activities: rendezvous, proximity operations, docking and undocking; landing, ascent and EVA; emergency response; rover operations |
| "Vehicle operation and crew protection at vacuum" | "Contingency capabilities (e.g., mission phase termination, catastrophic/critical system failure responses)" |
| "Return of an incapacitated crew to Earth" | "Use of abort and crew survival methods (e.g., safe haven, pressure suits)" |
| Safe modes "with documented objectives, triggers, transitions, constraints, allowed crew actions, and recovery timelines" | |
| "Crew training and onboard products for crew to execute all nominal, contingency, and emergency operations with or without Earth communication" | |
| "In-flight assessments of crew health and readiness" |
Mission examples (p. 90): Artemis I "demonstrated launch and reentry systems prior to crewed flight"; Artemis II "will demonstrate life support and habitability in the lunar vicinity while minimizing return risk via a free-return trajectory"; Artemis III "will demonstrate complex operations, including transferring crew across vehicles and conducting an initial lunar landing and EVA"; "Crewed Gateway and lunar surface missions will demonstrate crewed and uncrewed mission capabilities in lunar orbit and on the lunar surface"; and "Future crewed missions will demonstrate landing all crew on the lunar surface, leaving the crew return vehicle (e.g., Gateway, Orion) unoccupied". See Changes since Rev C.
Future considerations¶
- Knowledge gaps remain. "Significant knowledge gaps about the adverse effects of long-term exposure to the deep space environment remain." Long-duration precursor missions in cislunar space and on the Moon "will address some knowledge gaps", but "may not be sufficient to provide the necessary data to fully understand the risk associated with roundtrip missions to Mars" (p. 91).
- Return times. "If problems arise in LEO, the crew can return to Earth within hours; for lunar missions, crew return will take days. However, crew return during the Mars campaign may take months … a mid-mission abort may not significantly shorten the return duration" (p. 91).
- Higher bar for Mars. "The missions will require higher levels of system reliability, system redundancy, vehicle/crew autonomy, critical sparing and in-flight crew maintenance, abort and crew survival options, crew health/performance/psychological support, and general robustness than previous missions. The fault tolerance approach described above is applicable to lunar missions but may need to be reassessed for Mars missions" (p. 91).
"The following challenges represent gaps in crew return capabilities … They cannot be solved through architecture alone; they require experience in increasingly complex operations" (p. 91):
- Mars missions "will need to operate with more independence from Earth to account for communications latency and time-to-effect events"
- after "an unrecoverable loss of communication with Earth", onboard autonomy "should provide a safe crew return", including resources for the crew's own "mission planning, skills training, return trajectory execution, psychological support, and more"
- "requirements should include validated onboard autonomy and crew procedures"
- Mars crews must be able "to monitor, command, and control any uncrewed vehicle in the Mars vicinity"
- "robust crew survival methods, which may include safe havens, additional resources, rescue systems/vehicles, and more"
- "advanced health and performance monitoring and response, both onboard and on the ground"
- "high-bandwidth telecom capabilities to upload video learning or instructional materials to guide medical procedures or critical equipment repairs"
Changes since Rev C¶
The p. 90 examples predate the March 2026 fact sheet. In its updated plan Artemis III is a "Human landing system & EVA suit test mission in Earth orbit — 2027" and Artemis IV "Astronauts return to the lunar surface — early 2028" (Going back to the Moon, pp. 1–2). The updated plan mentions no Gateway visit. See Human Lunar Return and open question 22.
Related pages¶
Technology gaps on the same subjects as the Mars challenges. The ADD doesn't link them; the pairing is the wiki's: #1003 Fault/Anomaly Diagnosis, #1004 Trustworthy Autonomy and #1002 Autonomous Monitoring (onboard autonomy); #0405 Exploration Medical Capabilities (health monitoring and response); #0102 Deep Space Communications (high-bandwidth telecom).
Recurring tenets · RT-4 Crew Time · Human Systems · Orion
Sources¶
ADD Rev C, pp. 75, 83, 88–91 · Going back to the Moon, pp. 1–2