ASEN 5158 Space Habitat Design

12/9/2008

Chapter 22 (& Eckart Chapter IV.6.2) Extravehicular Activity (EVA) Systems

Learning Objectives

Classify different spacesuit operational environments
Outline suit performance and functional requirements
Identify the major subsystems of a spacesuit design and suit interface requirements
Describe relationship and design trade factors between vehicle and suit operating pressures and gas mixes

• What are the mission objectives?

– Do they require EVA? If so, how much?

• What are the environmental conditions (IV or EV) that require a spacesuit to be worn and what suited tasks will be performed?

– Performance Requirements (ConOps)

• What functionality does the spacesuit need to provide?

– Functional Requirements (Physiological and Operational)

• What are the major subsystems of a spacesuit?

– Solutions

• How many optional suit architecture configurations and suit-to-vehicle interfaces can be identified for a given mission scenario?

– Systems Integration

• What factors are involved in transitioning from the cabin to the suit operating pressure?

– Physiological Concerns

Suited Environments

• Launch, Entry & Abort (LEA)

• Orbital

• Lunar

• Mars

Top Level Spacesuit Requirements

Functional and Performance

Provide necessary life support functions to enable safe and effective mobile crew operations outside (and/or inside) of the pressurized spacecraft volume

Performance Requirements

Enable Suited Tasks

Accommodate Interfaces

Provide Personal Life Support

Environmental Control Parameters – essentially the same as for basic life support

• Pressure

• Oxygen provision (normoxic baseline)

• CO2 Removal

• Thermal Control – especially difficult for gloves

• Humidity Control

• Trace Contaminants Control

• Micrometeoroid Protection

• Food / Water

EVA Systems (EVAS)

• Suit subsystems

– Space Suit Assembly (SSA) and Portable Life Support Subsystem (PLSS)

• Suit-to-Vehicle and other system interfaces

– airlock, rover, tools, suit-to-suit, etc.

• Operational Concepts (ConOps)

– Orbital Construction or Satellite Repair

– Lunar Surface Exploration

Current US EVA Space Suit

• Extravehicular Mobility Unit (EMU)

• Built by Hamilton Standard (Sunstrand)

• 4.3 psia operating pressure

• 100% O2

• Weighs ~ 250 lbs on Earth

• Space Suit Assembly (SSA)

– Pressure vessel

– Thermal and MMOD protection

• Portable Life Support Subsystem (PLSS)

– Provides O2

– Removes CO2/Contaminants

– Provides cooling

Characteristic Trade Variables (for suit design)

Complexity – pressure and one gas or mixed delivery?

(physiological needs and engineering constraints)

Mobility – a spacecraft must also have this

Dexterity – differs from spacecraft, most challenging part - gloves

Physiology – must address suit internal environment (~ECLSS) and transition to/from spacecraft

Getting from cabin pressure (14.7) to suit pressure (4.3)

Decompression Sickness (DCS)

(a.k.a. Caisson Disease or the Bends, as occurs in diving)

Occurs when the inert gas (N2) that is normally dissolved in the tissue forms bubbles at a lower ambient pressure

N2 comes out of solution 2x faster than O2 and 50x faster than CO2

• So how to prevent DCS?

– Lower nominal cabin pressure

• Maintain normoxic conditions

• Concern with flammability

– Lower N2 content in atmosphere

• In suit prebreathe

– Lower N2 content in human

• Exercise, aspirin, O2 mask

• Prebreathe protocol – facilitate equilibrium

Rate of depress also important

slow enough to prevent barotrauma

Nominal = 0.1 psi/sec

Emergency = 1 psi/sec

EVA Equipment & Tools

Safety Tethers

Mini Workstation (MWS)

Body Restraint Tether (BRT)

Pistol Grip Tool (PGT)

Foot Restraints

Tool Stanchion

Manned Maneuvering Unit (MMU)

Provides N2 propulsion for untethered maneuverability

Simplified Aid For EVA Rescue (SAFER)

Self-rescue device designed for ISS

Advanced 8.3 PSI Space Suit Technology

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