What Would Happen if Astronauts Were Detached From ISS During a Spacewalk?

Becoming detached from the International Space Station (ISS) during an EVA (spacewalk) is a low probability occurrence. While not likely to happen, since it is possible, astronauts prepare for it.
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What would happen to astronauts if they got detached from the ISS during EVA? Would they fall back to Earth or drift away into space?: originally appeared on Quora: The best answer to any question. Ask a question, get a great answer. Learn from experts and access insider knowledge. You can follow Quora on Twitter, Facebook, and Google+.


Becoming detached from the International Space Station (ISS) during an EVA (spacewalk) is a low probability occurrence. While not likely to happen, since it is possible, astronauts prepare for it.

For each and every spacewalk, one of the first -- and most critical -- steps occurs before ever departing the station's airlock. With hatches still closed and locked, astronauts verify their individual safety tethers (85 foot braided steel cable with retractable reel) are appropriately "closed and locked" on their spacesuits. In addition, while inside the station's "porch," the two spacewalkers hook their safety tethers together, in a move we call the "daisy chain." Now, both astronauts are connected to each other, and one of them is also anchored firmly inside the station.

When the hatch finally opens, another critical procedure is executed. The lead spacewalker -- EV1 -- will exit the airlock headfirst and attach the other (free) end of their safety tether to an anchor point outside. Now, the two still-daisy-chained astronauts are anchored inside and out. At this point, EV1 will break the daisy-chain and hook partner EV2's safety tether to the external anchor point. Now both crew members are safely, and separately, anchored externally.

Exiting the ISS airlock, for my first EVA July 23, 2007.

It is now time for the still-inside EV2 astronaut, to disconnect his or her internal anchor point and exit the hatch. Voila! Two spacewalkers, each safely anchored outside the ISS, ready to go to work.

All of that effort may still not be enough if proper "tether protocol" is not exhibited by our brave spacefarers throughout the spacewalk. As they both move away from the airlock -- anchor points still firmly attached -- each must endeavor to keep their individual 85' lines separate and untangled, a task that seems simple, but isn't always so, during a 6.5 hour excursion outside in a micro-gravity environment. In addition, if the work site is more than 85' away from the starting point, additional safety tethers must be carried with them, and "tether swaps" must be appropriately and safely executed as needed.

I haven't really answered your question have I? If all of our "tether protocol" efforts still fail us (remember, this is an extremely low probability), and one of us totally detaches from the ISS structure, we will be ready; albeit a tad bit embarrassed.

While unlikely to fall all the way to earth as your question suggests, it is possible the rates imparted to a spacewalker who has lost physical contact with the station could be high. The resulting drift away from "home" and deeper into outer space would not be good. Rescue by another spacecraft would be futile, taking too long to undock, rendezvous, and capture the wayward astronaut. Another option was required.

The solution? It's pretty amazing. Like Buck Rogers, we have a jet pack attached to our suits and unlike Mr. Rogers, we have virtual reality (VR) to train for this exact scenario.

With Rick Mastracchio, performing a VR Lab session in preparation for STS-131.

The training venue is called the VR Lab original huh?! Home to the true geniuses behind the DOUG (Dynamic Onboard Ubiquitous Graphics) software system, we are trained to utilize our last resort -- the Simplified Aid for EVA Rescue (SAFER) backpack -- in a virtual world.

Images from NASA's VR Lab at the Johnson Space Center (JSC) in Houston, Texas.

Wearing special gloves and helmets creates a virtual world enabling a simulated "fall" from the station, where repetition is key to a safe return. Since the SAFER is our last resort, we must be ready to correctly deploy its hand controller (HC) and "fly" ourselves back to structure. Fly is a general term. In essence, we must learn to utilize and understand the nuances of orbital mechanics to get our EVA suit spaceship, back to the ISS spaceship. Practice makes perfect. We see the ISS virtually, and our inputs to the hand controller coupled with the software's execution, give us a video game of sorts that imitates what we would experience in space. As our ability to return safely progresses, we "fall off" with higher and higher rates, until we can consistently demonstrate that we can save ourselves repeatedly.

It was FUN to be an astronaut! Keep lookin' up!

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