The Ultimate Tightrope: A Step-by-Step Guide to an ISS Spacewalk (EVA)
The Personal Spaceship
A spacewalk isn’t a stroll. It’s piloting a personal spacecraft that happens to be shaped like a person.
At 319 pounds, the Extravehicular Mobility Unit (EMU) is a pressure-sealed, life-supporting machine. Inside: the Primary Life Support Subsystem (PLSS) scrubs CO₂ and circulates oxygen; the Liquid Cooling and Ventilation Garment (LCVG) runs roughly 300 feet of chilled-water tubing against the skin; the Secondary Oxygen pack stands by for emergencies; and the SAFER thruster is the self-rescue plan (NASA 2019/2020).
The Unseen Ascent: Training & the 58-Hour Prep
Each EVA hides a week of work: about 58 hours of preparation, 6–8 hours outside, and roughly 15 hours of post-servicing — near a 100-hour ordeal with an estimated $1.3M crew-time signal (NASA OIG 2017).
Beating the Bends
Station air is 14.7 psi; the EMU runs at 4.3 psi. Drop too fast and nitrogen bubbles form in the blood — decompression sickness. The older Campout protocol pushed crews to sleep in a 10.2 psi airlock: isolating, uncomfortable, and easily reset by false alarms. Today’s ISLE (In-Suit Light Exercise) replaces isolation with physiology — light exercise and pure O₂ inside the suit (NASA JSC 2010; NASA JSC 2014).
Crossing the Threshold
“Switch to internal.” Pressure drops. The hatch opens to nothing. Inside the helmet, the fan hums, oxygen hisses, and comms chatter fills the ear. The gloves, now stiff balloons, turn dexterity into pain; fingertips press against hard thimbles and blood flow dips, sometimes ending in fingernail loss (NASA 2019).
The LCVG creates a thermal paradox: hot core from work, cold legs from microgravity’s fluid shift — biology arguing with engineering (NASA JSC 2014).
Precision Labor: The Poetics of the Toolbox
The PGT as a Character
The Pistol Grip Tool (PGT) isn’t a drill; it’s a microprocessor-controlled, battery-powered instrument that dials exact torque and turns while logging every move. On Earth, reaction torque bites your wrist; in microgravity, it spins the astronaut. The PGT anchors torque between fastener and structure, not human and void. Even its lubricant is re-engineered: dry-film for vacuum extremes (NASA 2009/2010).
Limits matter: during a Hubble repair, the PGT’s bulk blocked sightlines, pushing engineers to create the leaner Mini Power Tool (MPT) — frustration turned into innovation (NASA 2010).
Case Study: AMS-02 “Microsurgery”
The Alpha Magnetic Spectrometer (AMS-02) — a $2B detector hunting dark matter — wasn’t designed for repair. Engineers invented 29 custom tools, built a worksite where none existed, and trained astronauts to cut/splice lines with millimetric care. Four EVAs later, cooling was restored. Pain, risk, and ingenuity served a purpose larger than the discomfort: reviving a question we’re still asking the universe (NASA 2019).
Ambient Threat: MMOD & the 4 mm Nightmare
Much of EVA risk is statistical. NASA’s debris models show a ~4 mm impact can be catastrophic to a suit. A drifting bolt is a tool in one moment and a bullet in the next (NASA 2018).
Systemic Threat: EVA-23 Drowning & Lessons
Forty-four minutes into EVA-23 (2013), Luca Parmitano felt a cold trickle. It thickened, tasted metallic. Water flooded his helmet. The antagonist wasn’t “space”; it was a clogged water separator — the same suit had a smaller leak a week earlier, misdiagnosed as a drink bag (NASA MIB 2014).
Vision blurred to black. Ears filled. Comms died. Alone with the hiss of breath, he used the tether recoil like a winch to reach the hatch. Inside, Chris Cassidy squeezed his glove — one human pulse cutting through mechanical chaos. Repressurization popped the helmet: ~1.5 liters of water poured out. Calm procedure met raw survival (NASA MIB 2014).
The Human Sensorium
Repress brings smell first: ozone, hot metal, a gunpowder tang — dust chemistry meeting oxygen (NASA 2015). Inside the station: antiseptic, coffee, electronics. Touch returns as inertia against the harness; hands throb where gloves rubbed raw. The fan’s life-hum gives way to ordinary noise. Awe is physical.
Framing the Void
Technology keeps humans alive, and limits them. The EMU’s reliable legacy still demands ~100 human hours per EVA. Commercial suits chase the wait-less EVA: faster prebreathe cycles, smarter gloves, quicker airlocks — not for glamour, but because $1.3M crew-time per spacewalk won’t scale (NASA OIG 2017; NASA 2024).
Empowerment: Why We Go Out There Anyway
Spacewalking is presence, not ease. The AMS-02 fix proved ingenuity; EVA-23 tested vigilance. Every checklist and tool is written in learned grit. Meaning lives in the hum of the fan, the smell of ozone, and the ache of hands that built something fragile in a place trying to break it.
Reader Reflection
- When did a complex process finally “click” only after you saw the hidden prep?
- If you could remove one bottleneck from EVA — prep time, gloves, airlock — which would you choose, and why?
FAQs
Why does an ISS spacewalk take ~100 hours end-to-end?
Suit prep and prebreathe (~58h), EVA ops (6–8h), and post-servicing (~15h) — driven by safety and physiology (NASA OIG 2017; NASA JSC).
What changed from “Campout” to ISLE?
Overnight 10.2 psi isolation evolved to in-suit light exercise with O₂, cutting time and discomfort while maintaining DCS protection (NASA JSC).
What’s the EVA-23 lesson?
Small hardware + misdiagnosis can snowball. Vigilance and anomaly response culture matter as much as the gear (NASA MIB 2014).
Can debris really puncture a suit?
Models show ~4 mm impacts can be catastrophic; mitigation is statistical, procedural, and material (NASA 2018).
Will commercial suits make EVAs faster?
That’s the aim: shorter prep/cycles with better gloves and airlocks — without compromising safety (NASA 2024).
Continue Your Journey
About Penny Waite
When I was small, the night sky was a fairytale. The moon was bigger. The stars were brighter. Every pinprick of light felt like it was winking just for me, like the universe was telling me secrets.
I’d beg my dad to lift me so I could touch the moon — that luminous disc hanging impossibly close. My fingers would stretch toward the stars, reaching for magic I could almost taste. I never touched them, but the wonder stayed.
Now I help others see it too. I write experiment books for parents navigating homework panic at 8 p.m. I develop science curricula that turn school trips into adventures. I direct science fairs where thousands of kids discover their curiosity matters. I translate the cosmos into something you can explore in your kitchen, your backyard, with your kids — because wonder shouldn’t require a laboratory or a degree.
Here’s what I know: curiosity is the antidote to despair. When you genuinely try to comprehend the scale of a galaxy — really try — something shifts. The broken dishwasher, the empty petrol tank, the endless scroll of anxiety… they don’t disappear. But they shrink to their true size.
Through a child’s eyes, the moon is bigger. The stars are brighter. The night sky is a fairytale. I write to give you those eyes back. I’m still reaching for the stars. Come reach with me.
Citations (Government Space Agencies)
- NASA OIG (2017). Crew time valuation & EVA operations context — oig.nasa.gov
- NASA JSC (2010). EVA prebreathe protocols — Campout — nasa.gov
- NASA JSC (2014). ISLE prebreathe evolution & LCVG thermal notes — nasa.gov
- NASA (2018). MMOD/BUMPER risk modeling overview — nasa.gov
- NASA (2019/2020). EMU & PLSS/LCVG fact sheets; PGT/MPT tool notes — nasa.gov
- NASA MIB (2014). EVA-23 Mishap Investigation Board report — ntrs.nasa.gov
- NASA (2019). AMS-02 repair briefings & tool set summaries — nasa.gov
- Roscosmos (Archive). Salyut/Almaz & MIR historical imagery — roscosmos.ru
Official Resources (open in new tab)
- NASA ISS Facts — nasa.gov/mission_pages/station
- NASA ISS Transition Plan — nasa.gov/humans-in-space/iss-transition-plan
- NASA Deorbit Plans — nasa.gov/.../iss-deorbit
- FAA Commercial Space — faa.gov/space