Most of us would not go on a long hike in a brand-new pair of boots. You first want to put a few casual miles on them to soften the material and make sure they perform well. This preliminary effort can help you avoid a lot of misery out on the trail. If you think of a spacewalk as the ultimate hike (who doesn't?), then it's easy to understand why spacesuits undergo the same type of break-in process before they're ever sent into space.
About the Suit
Before getting into the specifics of how spacesuits are broken-in, a little background on the suit is warranted. The NASA suit that astronauts have used for spacewalks since the dawn of the space shuttle era is the Extra-Vehicular Mobility Unit (EMU). The EMU is a modular design comprised of a handful of interchangeable subcomponents (helmet, upper torso, lower arms, gloves, etc.). Many of the various subcomponents that make up the suit are available in multiple sizes.
When an astronaut gets sized for an EMU, they do not get a dedicated suit to call their own. Rather, the product of the arduous sizing process is a chart illustrating the specific subcomponent sizes which provide the best fit for that astronaut. Whenever the astronaut needs a suit for a training event or mission, technicians reference the chart to pull the appropriate hardware off the shelf and assemble a correctly-sized EMU. The suit is torn down after the event and the individual subcomponents are placed back into inventory.
Over time, worn-out subcomponents get retired and replacements are manufactured. This new hardware undergoes rigorous inspection and testing before it can be added to the inventory. Yet, even more must be done before these EMU bits are used on an astronaut's suit.
New EMU subcomponents are required to undergo a break-in process called "cycling". Whereas factory testing is typically performed using only the individual subcomponent, cycling introduces the piece into a complete EMU. The intent of this effort is to begin softening the stiff layers of new fabric and to verify that the part performs properly in all respects. This is done by exercising the hardware with repetitive, spacewalk-inspired motions. For those who participate in cycling events, the term "exercising" is particularly appropriate.
Tour de Pants
Cycling is one of the few EMU-related events that does not involve astronauts. The person who will wear the suit is selected from a pool of EMU test subjects. These are usually people who work with the EMU in some capacity, but being a test subject is not their primary job. Actually, being a test subject isn't anyone's primary job. The key factor here is that test subjects have voluntarily met the same suit-related health requirements and sizing prerequisites as the astronauts. If a test subject's sizing chart resonates with the sizing of new hardware, they may be invited to cycle those subcomponents. Whether they accept such an invitation depends on the hardware involved and their personal threshold for physical exertion.
Each type of subcomponent requires specific motions for the break-in process. Some are more demanding than others. For example, cycling an upper arm calls for several different sets of motions. This includes more than 600 elbow flexions and extensions through the full range of motion (basically a bicep curl). While there are no dumbbells involved, the numerous layers of EMU fabrics and undergarments offer a fair amount of resistance to this movement. And did I mention that the suit is pressurized to about 4psi, creating even more resistance?
The test subject's elbow-bending burden is somewhat alleviated by the fact that the EMU is fastened to a beefy stand that holds it upright. This stable platform allows them to relax most of their body and focus only on the necessary movements. The suit is attached to the stand by the Primary Life Support System (PLSS), which resembles a large, rigid backpack.
In space, the PLSS contains all of the components necessary to keep an astronaut alive during an actual spacewalk (breathing air, pressurization, temperature control, etc.). Most earthly EMU events, including cycling, use an emulated PLSS that is little more than an empty fiberglass shell. When an emulated PLSS is used, the necessary life-sustaining functions are carried out by various ground equipment that is attached to the EMU with umbilical cords.
Among the support staff at a cycling event is a quality assurance representative (QA). Armed with a mechanical tally counter, their job is to ensure that every motion meets the prescribed standard and that the required number of motions is completed. Shortcuts and bad form are not tolerated. If the QA says you didn't fully extend on that last curl, there's no point in arguing. Just do it again and embrace the burn. I'm convinced that QAs moonlight as personal trainers--or should.
I can't recall whether I ever failed to complete the necessary reps for upper arms on my own. I may have been able to muscle through. Either way, I'm sure I was out of breath and asking for technicians to crank up the suit's cooling system. I definitely cannot say the same for my attempts to cycle legs.
The motion for cycling EMU legs resembles a squat very similar to what you would do at the gym. 150 such movements are called for. This requires the test subject to be unshackled from the stand so they can walk freely in the suit…an awkward and cumbersome task when gravity is involved. Not only do you have to overcome the aforementioned bulk and pressurization when walking and squatting, you must also bear the additional weight and imbalance of the suit. When configured for cycling, an EMU weighs about 175 pounds (79kg) and is decidedly top-heavy.
The test subject is allowed to lean forward and steady themselves against a table. But they must endure the effort of squatting alone. There were times when I made it through the full set. There were other times that I had to beg for mercy. In those cases, EMU technicians placed me face-up with the emulated PLSS flat on the ground - making me as helpless as an overturned turtle. With one technician on each side, they pushed my legs back and forth to replicate the remaining squats. It was reassuring to see that the required effort also caused them to break a sweat.
I've always thought that getting placed on your back is one of the most awkward things you can do in an EMU. Actually, being on your back is fine. It's the process of getting there that is stressful. Two or more technicians hold on to the PLSS as you lean back from a standing position. Once you pass the tipping point, they take over and rotate you down gently. Inside the suit, however, there is no obvious indication that you are being steadied. You must take their word for it and lean back…knowing that you're encased in priceless space hardware. It's the granddaddy of trust falls.
Are We Done Yet?
There is a lot of overhead involved with any EMU event, so planners try to make the most of every cycling opportunity. A cycling test subject is likely to find themselves in an EMU with several different factory-fresh subcomponents, each requiring a discrete break-in script. There could even be multiple examples of the same subcomponent. You may complete cycling on one set of upper arms, only to have technicians depressurize the suit, swap in another set of arms, and start all over again. If you walk into the room and find an extra set of suit legs on the table, you know it's going to be a long, exhausting day.
During my time as a test subject, I quickly learned that talking about the physical demands of cycling (or any other kind of EMU event) is a lot like complaining about a bellyache from eating too much ice cream. People just don't have much sympathy for you. Sure, I get it. I never lost sight of how lucky I was to have such opportunities – even if I needed a few ibuprofen when an event was over.
Once cycling has been successfully completed, an EMU subcomponent is deemed broken-in and fit for use. That could mean that it is sent in to space. Or perhaps it will be used for training events. More likely than not, it will be utilized for both purposes during its lifetime. Whatever the future holds for that particular piece of space hardware, cycling helps ensure that it will perform well and be comfortable.
Terry is a freelance writer living in Lubbock, Texas. Visit his website at TerryDunn.org and follow him on Twitter and Facebook. You can also hear Terry talk about RC hobbies as one of the hosts of the RC Roundtable podcast.