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I read up articles on both types - EVA suits meant for spacewalks, and Escape Suits used in launch and reentry - but other than bright orange color for ACES making it easy to find and the fact that Sokol doesn't have life-support backpacks (only due to room limitations though, not as a desirable design choice) I couldn't really pinpoint which differences between EVA and Escape suits are just arbitrary engineering choices and which ones are deliberate distinction due to their intended purpose.

So - what design considerations and engineering details set an escape suit apart from an EVA suit?

PearsonArtPhoto
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SF.
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2 Answers2

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The main consideration is the lifetime. An escape suit only needs to function for maybe 10 minutes. While they do need some life support provided through launch, it can easily be disconnected if required. For only 10 minutes, you only need a small supply of oxygen, a thinner suit will do, that is more mobile, etc. Also, the reentry suits are designed to be small, they have to fit in the usually small reentry space, while larger suits are okay for EVAs. Heat probably isn't a major concern, one can survive okay for 10 minutes if required, although they do still use a similar system to EVA suits for cooling. The suit also needs to be able to be put on quickly. They are designed for more shock absorption than an EVA suit (See Wikipedia)

An EVA suit has to last for a longer time, usually around 8 hours. There has to be some kind of water/nourishment is such a process. Harder work is also required, along with higher levels of redundancy, to sustain such a lengthy excursion.

PearsonArtPhoto
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    Agreed. The differences are mostly in the attached life support system. In fact the suit proposed for Orion, which includes EVA capability, is a modified version of the shuttle escape suit. https://www.nasa.gov/content/astronaut-spacesuit-testing-for-orion-spacecraft – Organic Marble Nov 04 '15 at 15:01
  • I'm still wondering though - it's obvious in case of Soyuz; matters of space available, but couldn't the shuttle astronauts just launch/land in EVA suits and forfeit the escape suits entirely? – SF. Nov 05 '15 at 07:00
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PearsonArtPhoto's answer is correct, as far as it goes. I'd like to add two more major differences between the two types of suits in question (FYI, I'm basing my answer here on the Launch and Entry Suits (LES) and the Extravehicular Maneuvering Units (EMU) used during the Space Shuttle era).

Mobility: The EMU's were designed in such a fashion so as to allow the crewmember inside to perform rather intricate tasks during long spacewalks. The EMU gloves were custom fitted for to each astronaut, while the LES gloves were generic. Also, the EMU's were designed to allow relatively unhindered arm and leg movement when compared to the LES.

Fit: In general, the EMU's, being modular in construction, allowed for a better fit. One could mix and match torso, leg, arm, boot sections. The LES's, on the other hand were mostly of unit construction. Sometimes, this led to compromises being made. For example, a particular crewmember might have considered arm length the primary factor in choosing a size, even though said suit may have been too short in the shoulder to crotch dimension (ouch!). It was generally accepted that long EVA's would be quite difficult if one were wearing a standard LES.

Digger
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