Astronaut 'A,' perhaps having grown a little negligent on his tenth and final EVA, steps through a seemingly solid crust on a Martian crater rim, plunging 10 meters down the 50 deg sloped crater wall. The fall is steep and a bad landing twists his left leg violently outward. Astronauts 'B' and 'C' hear their EVA teammate shout on their headset. Minutes later, they see their teammate at the bottom of the crater wall; he is not moving. Astronaut 'B' ties a rope to the team’s rover and rappels down into the crater. After assessing the situation, he realizes his teammate has a broken femur and requests that Astronaut 'C' repel down the EVA emergency stretcher. They secure their injured teammate onto the stretcher and use their rover to pull the stretcher up the slope with a secured rope. Once out of the crater, they tow their injured teammate back to the pressurized habitat, remove his suit and give him the required medical treatment. By acting quickly, they have saved their teammate's life and Astronaut 'A' makes a full recovery.
MDRS Emergency Simulation
Such an example could be an emergency scenario on a planetary surface EVA expedition. Future planetary surface exploration will require the use of extensive EVAs, which will involve inherently dangerous operations that can put crew safety at risk. The purpose of our research at the Mars Desert Research Station (MDRS) is to perform proof-of-concept demonstrations to test the feasibility of prototype EVA emergency equipment and procedures.
For our simulation, we used a modified four-wheeled emergency stretcher (we tested both 13” and 16” wheels), which incorporates an opening for the Portable Life Support System (PLSS) so that the injured astronaut can lie down in a supine position, and incorporated mountaineering rescue techniques.
A mountaineering technique used for a crevasse rescue was implemented, which uses a single pulley configuration, similar to a belay system. A single anchor point with an astronaut above the hill (i.e. belayer), and one astronaut below accompanying the injured astronaut in the stretcher was simulated. By using a single anchor/belay system, the accompanying astronaut (next to the injured astronaut) provided a minimal push to the stretcher as it moved up the slope or crater wall, and the belayer (at the top of the hill) used body weight, a gri-gri (Figure 1 - active belay tool which stops the rope from sliding out of the system) and an ascender (Figure 2.). The belayer used body weight to pull the stretcher up, draw the rope through the gri-gri, then extend his arm with the ascender to tighten the rope and to ready for the next pull. Unfortunately, this approach proved to be extremely challenging for the belayer, and we decided to attach the rope to the ATV and have it drive away, which resulted in the stretcher being able to be pulled up the slope without difficulty.
Two other mountaineering pulley systems will be further tested in future rotations: an inline two pulley system, and a two pulley “Z” system. The inline system uses two pulleys: one at the anchor, the other part way down the rope, between the rescuer and the stretcher (Figure 3). This is also a typical system used for crevasse rescue in mountaineering. This system has distinct advantages by increasing the amount of pull for the overall system. By incorporating this type of rescue into a scenario where an astronaut fell down a crater wall, the rescue simply assembles the single anchor (either cracks in the rock, a spire/outcrop, soil screws, or a rover), the 2 pulleys, and then attaches the rescuer line to him/herself and moves away from the anchor system. This can be done with no additional mechanical system attached to the astronaut, leaving his/her hands free, or to attach to a motorized vehicle which could raise the stretcher. This system, though somewhat longer to set up, is more advantageous than the single belay system (which uses just one pulley).
Though the Z-Type pulley rescue system (Figure 4) can also increase the amount of pull the overall system has, it requires two separate anchor points, which increases the set up time. In any environment, one location for a suitable anchor may be difficult enough, but finding two that are close (within a few meters) may be impossible at times. Thus, this system would be best used in a very dynamic area with hard, cracked rock, spires, or if multiple vehicles are present to anchor to. The Z-type system may also be advantageous where a crater rim is dotted with multiple boulders, or the rescuer cannot be in line with the stretcher.
Given the three systems that may be implemented, the one with the least amount of set-up time, and with the fewest required anchor points, would be the in-line pulley system. This scenario allows the rescuer to move him/herself away from the hazardous environment, while incorporating two pulleys to improve the amount of pull in the system, and decrease the rescuer’s strain. This method also allows the use of a motorized vehicle, such as rover. The Z-type pulley system should be implemented in a very dynamic environment with multiple hazards, multiple solid anchor points, and if the injury is non-life threatening (due to the increased set up time for the two or more anchor points required). Lastly, the belay-type rescue system should be implemented: it requires more force to raise the stretcher, and uses the most energy from the astronaut. A very serious injury requiring immediate response could use this system, though more strain will be put on the rescuer or the vehicle doing the pulling.
Regarding the wheel size configuration, the 16” wheels are recommended over the 13” wheels because they allow the stretcher to more easily maneuver changes in slope or go over rocks without the PLSS hitting the surface. However, it is recommended that the aggressive treading of the 13” wheels be incorporated due to its off-road design (i.e. individual knob patterns), which allow the tire to bite into the surface and lever the sides of the tread to get a better grip; especially useful on soft or loose surfaces.
Alex Diaz - Crew 141 Commander
Josh Borchardt - Crew 141 HSO