Advanced EVA: airlocks, rescue and suit contingencies
Design extravehicular activity as a complete chain: preparation, airlock, mobility, tools, return, rescue and recovery after anomalies.
Mastery objectives
- identify the functions, interfaces and degraded scenarios specific to the subject
- repeat simple calculations and verify units, assumptions and margins
- turn a principle into a verifiable procedure or decision
- connect the subsystem to human, energy and logistics constraints
1. EVA begins before the hatch opens
The sortie begins with suit preparation, consumable checks, tools, communications, work plan and abort criteria. A defect missed inside the airlock becomes much more expensive once a crewmember is far from the habitat.
2. Airlock: pressure, contamination and operational throughput
The airlock transfers people, atmosphere and dust. Its cycle manages depressurization, repressurization, leak checks, purge, storage and contaminated equipment. Airlock time belongs in the EVA budget and can become a bottleneck when several teams need to work outside.
3. Suited mobility: fatigue and real geometry
A tool that is easy in shirtsleeves can become difficult with pressurized gloves and limited mobility. Design must test grip, torque, visibility, posture and access. Repetitive tasks are organized so that excessive physical effort does not turn simple work into a return-to-base risk.
4. Buddy system and mutual monitoring
Crewmembers monitor one another for suit state, mobility, behavior and consumption. The principle does not require them to stand side by side at all times, but ensures that a human or hardware anomaly can be noticed by another person.
5. Rescue when a crewmember cannot walk
The plan covers towing, rover transport, assisted airlock entry and medical handover. Reduced apparent weight on Mars helps some motions, but inertia remains. A suited person with equipment is still a large mass that must be accelerated, stopped and passed through limited openings.
6. Lost communications or a suit alarm
Not every alarm has the same response. Some demand immediate return, while others require work stop and diagnosis. Procedures distinguish a suspected sensor fault from a real system failure without asking the crewmember to take additional risk merely to confirm the problem.
7. EVA consumables budget: several limits at once
EVA duration is not set by one gauge. Oxygen, carbon-dioxide removal, battery energy, cooling water, thermal state and fatigue impose several simultaneous limits. The plan must preserve a return reserve and then an additional reserve for helping a crewmember. An excursion consuming 95 percent of theoretical capacity leaves almost no room for a detour, stuck tool or slower travel. The budget is therefore updated during the EVA and secondary tasks are dropped before return margin is compromised.
8. Crewmember rescue: design the return before the accident
An injured crewmember may be unable to walk, control posture or operate airlock interfaces. The EVA system needs a method to move the combined body-and-suit mass, secure the casualty to rescue equipment and bring two people through the airlock in degraded configuration. A procedure that assumes manual carrying for several kilometres is not credible. Operating radius must include this case; as distance grows, vehicles, communications and consumable reserve become increasingly necessary.
9. Airlocks and contamination: return without bringing the terrain inside
An airlock manages pressure and contamination at the same time. Martian dust accumulates on seals, joints and external surfaces and can then enter occupied volumes. Return procedures include inspection, dust removal or containment, seal monitoring and separation of dirty equipment. Repeated cycling is also a maintenance load: pumps, valves, sensors and seals are tracked by cycle count and symptoms. Changes in pump-down time or leakage can reveal degradation before failure. The airlock is monitored like a vehicle rather than treated as a simple door.
10. Worked example: rescue return endurance
A crewmember is 1.8 km from the airlock. Normal return speed is 3.0 km/h, so travel time is 0.6 h = 36 min. With a 40% assistance penalty, speed falls to 1.8 km/h and return takes 1 h. If emergency endurance is only 50 min, the location is incompatible with an assisted-return scenario unless a mobile rescue capability is available.
11. Exercise
Plan an EVA 2 km from habitat and sequentially inject radio loss, ankle injury and a pressure alarm. For each case state the abort criterion, return route and role of the buddy.
12. Reasoned solution
First calculate the radius permitted by nominal return, then repeat the budget assuming one crewmember requires assistance and average speed falls sharply. The mission uses the more restrictive radius and preserves consumable reserve. If there is no way to transport an immobile crewmember, distance must be reduced or a rescue vehicle added.
13. Validation mini-project
Create a complete EVA operations package: airlock cycle, consumables, tools, communications, weather limits, abort criteria, rescue, assisted return, medical handover and technical debrief.