Flying by the Waist of Your Pants
There’s a scene in Ron Howard’s wonderful film, Apollo 13, when the crew is preparing to fire the LEM engine in space and Commander Lovell is Seen ensuring that his socked feet are firmly attached to the velco floor. That might well be authentic, but it leaves audiences with a mistaken notion of when flying the LEM was like during a landing.
Landings were dangerous because there was a big moon outside, just waiting to smash into you. The LEM had to maneuver, and the crew could be tossed around as it did so, just as they needed precision control. If something went wrong (as it did in Apollo 10) such an upset could elevate a minor problem into a crisis, but even under the best of circumstances, landings could be hard, and the last thing you wanted was for a suited astronaut to bang to into a bulkhead, breaking the suit or the LEM.
NASA needed a way to hold the astronauts down so they could focus on their jobs while giving them the mobility needed to move about the cabin as needed. It had to be light, it had to be reliable, and it had to be dead simple. Their solution? The Apollo LEM Crew Restraint System:
The CRS involved a set of cables and small pulleys, all connected to a spring-loaded “constant force reel” mounted below the console. There were two restraints, one for each crew member on his side of the cabin. To use the CRS, a suited astronaut would turn to his side and unclip the two cable ends from a storage hook. He’d then step between the wires and clip them to a hook sewn into his suit at the waist. Then he’d unclip the center hook with its central pully, and clip that to the opposite side of his waist.
- The single force reel pulls on two lines [A and B], one to restrain the astronaut down and forward, the other down and aft. Each line (A & B) comes from the reel (1), is split via pulley [A2 & B2], and it routed to tug on hooks at both the astronaut’s hips (3).
- Each hip has a hook sewn into the spacesuit for attachment to one side of the restraint , where the inboard hook is on his left if he stands to the right and his right if he stands to the left and the outboard is opposite.
- The actual restraint is a single line which runs from his inboard hook (B3-in), through the fixed and tensioned pulleys, through a pulley connected to his outboard hook (3-out), through more fixed and tensioned pulleys, and back to the astronaut, attaching to the hip where it started (A3-in).
- When hooked into the restraint, the astronaut is held down by a continuous loop of line, fixed only at the inboard hip and free to move through the pulleys everywhere else.
- The lines from the constant force reel only extend or retract when he moves farther or closer to the bulkhead, and when he puts the rig away. In use, the spring in the reel only provides downforce, not movement. The lines in the restraint loop, on the other hand, move through the pulleys constantly, whenever he shifts around.
- When he wants to exit the harness, he unclips his outboard hook (3-out pulley) and clips it to a storage hook on the bulkhead. Then he unclips both inboard hooks (A3-in and B3-in), steps between the now seperate lines, and clips them to the same storage hook. The reel always takes up the slack, so there is plenty of freedom in the system, and accommodate to astronaut height, movement, and storage of the system when not in use.
Thus secured, the tension of the force reel was distributed through all the pulleys, and he was gently held down, needing the Velcro panels on the floor mostly for traction. Pins could be adjusted to allow a crew member to move from the flight station to the docking station above.
The machines that took us to the moon were enormously complex, and it’s sometimes easy to think they all had to be–or that anything the government does is inherently over complicated.
Here is a counterexample. The solution was simple, cheap and effective, and just a little ingenious.
Thanks for posting this! Fascinating.
I am trying to figure out how the system works. I assume the “constant force reel” is _pulling_ on both ropes? And is there a reason why they didn’t use two constant force reels (front and back, or left and right), instead of the complicated pulley system?
It’s actually not that complicated. Some of the pulleys are just to keep the lines out of the way. I’ve updated the text and diagram to better explain.
Yes, the reel pulls both lines. More specifically, there is only one line, a big loop, both ends of which connect to one hip. The reel makes that loop draw down toward the floor, restraining the astronaut, while the astronaut’s movements pull the loop this way and that, freely sliding through the various pulleys. Two force reels would not be needed and would only add extra weight.