NASA engineer Dustin Gohmert, who designed seat systems for the crew module of the Orion spacecraft, explains the military-civilian distinction in straightforward terms. “Comfort itself is difficult to quantify,” he says. “We look primarily at the safety of the crew.”
The standards are very high for NASA vehicles. Because a spacecraft can crash hours or days from help, “we have to make it such that the crew can self-rescue,” Gohmert says. And sometimes that means doing away with conventional amenities. In the Orion capsule plan, for instance, Gohmert’s team dispensed with seat cushions altogether. Cushions may separate the body from the hard seat underneath by just a few millimeters, but in a sudden deceleration, the body can close even that small distance with enough force to cause injury. The Orion seats fit each astronaut fairly closely, and the weight distribution makes for a more or less tolerable experience. But comfort isn’t the goal. The seats keeps the astronauts alive.
Of course, NASA also gets to be picky about who comes on board, a degree of selectivity that further limits what the agency can teach us about our own comfort. The Federal Aviation Administration requires commercial airlines to safely accommodate nearly the entire spectrum of humanity, from a 5th-percentile woman (about 5 feet tall) to a 95th-percentile man (over 6'3"). Not so at NASA. To make sure each astronaut fits the operating environment of the spacecraft, the agency assesses not just height and weight, but every measurement of every extremity. If you don’t fit, you can’t fly. “We do three-dimensional body scans of the astronauts as part of the screening,” Gohmert says. “If your femur is too long, it might disqualify you.” Air Force pilots must also properly fit their plane—legs longer than the engineered standard could break when the pilot ejects in an emergency.
Civilian passengers, no matter how tall or wide, expect gentle treatment. As a result, engineers must set extremely conservative tolerances. Rail system designers, for instance, consider the acceptable limit of linear and lateral acceleration (the force exerted on passengers by starting, stopping, and rocking from side to side) to be no more than 0.15 G—roughly what you’d feel on the moon. That limit allows passengers to dispense with seatbelts and walk around freely inside.single page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.