Expanding the Human Factors Toolbox:  An Approach to Balancing Crew and Mission Design Parameters

Why It Matters

Accurate crew‑size sizing directly impacts mission safety, cost, and the feasibility of autonomous deep‑space operations, making the methodology critical for sustainable Mars exploration.

Key Takeaways

• New quantitative methodology for Mars crew size decisions
• Models show high mental workload for single‑crew EVA support
• Six‑plus crew needed for 9‑month transit workload
• Expertise level must exceed 99.985% to keep LOC/LOM risk low
• Trade‑space tools integrate mission architecture, operations, and human resilience

Pulse Analysis

NASA’s Human Factors Technical Discipline Team is extending its toolbox to address the unique challenges of crewed Mars exploration. Unlike low‑Earth‑orbit missions, a Mars voyage faces up to 22‑minute one‑way communication delays and multi‑week blackout periods, stripping away the real‑time ground support that has underpinned ISS operations. To fill this gap, the National Engineering and Safety Center (NESC) has built a quantitative methodology that blends human performance science with mission architecture. The approach creates a data‑driven trade space, allowing planners to evaluate crew size, workload, and expertise alongside vehicle design and operational concepts early in development.

The NESC framework rests on four calibrated human‑performance models. The IV Operations for Planetary Surface EVA model flagged unacceptably high mental workload for a single intravehicular crew member supporting an EVA, suggesting slower pacing, more automation, or additional crew. The Robotic Arm Assisted EVA Operator model indicated manual arm control would likely need two operators, and that sleep debt further raises workload. A Mars Transit Crew model projected that more than six astronauts are required to match the work‑hour capacity of a four‑person ISS crew over a nine‑month transit. The Personnel, Expertise, and Training model showed that only a 99.985 % crew response success rate drives LOC/LOM risk below 0.1 %.

By quantifying crew workload, expertise gaps, and risk thresholds, the trade‑space tools give NASA and its partners a reusable decision‑making asset for any deep‑space architecture. The methodology can be updated as new automation, habitat, or propulsion technologies emerge, ensuring that crew‑size recommendations remain aligned with evolving system capabilities. Moreover, the data‑driven approach sets a precedent for other safety‑critical sectors—such as defense and autonomous transportation—where human resilience must be balanced against technical constraints. Ultimately, the NESC’s human factors toolbox strengthens the business case for sustainable Mars exploration by linking crew design directly to mission success and cost‑effectiveness.