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Andy Jean

EGM-323

Russell DeVore

The Thermodynamic Qualities of Extravehicular Activity

An astronaut on a space-walk must wear a special suit. This space suit, regardless of its

different types, purposes, requirements are to protect the individual from the universe exterior to

the planet as well as its thermodynamic characteristics, as the individual displaces towards the

attainment of certain tasks (Bessette R, 1968). The universe is not homogenous, with heat

sources having variable behaviors existing to the potential hazard of the individual

(http://www.damninteresting.com/outer-space-exposure). Therefore, those that design this

enclosure must be concerned with the many heat sources, sinks, the displacement of heat and its

manipulation, internal and external to the individual.

Before any treatment of the thermodynamic qualities of the universe, their concerns, and

how the design of the spacesuit accommodates this; the spacesuit itself is an innovative

invention. The qualifications and specifications of the modern incarnation of the spacesuit has to

accommodate a stable internal pressure; a mobility that corresponds with the physiology of the

human body and its mechanical properties at different environments both extraplanetal and

terrestrial; regulation of homeostasis, respiration, excretion and communication (Thomas &

McMann, 2011).

There exist three types of spacesuits for intravehicular activity, extravehicular activity

and intra/extravehicular activity. The intravehicular activity suits include the mercury USAF x-

20, NACA-NASA-X-15, Gemini G-T7, Shuttle Emergency Escape Suits, Shuttle/Escape R&D;

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Shuttle Advanced Crew/Escape Suit and Shuttle Launch Entry Suits. (Thomas & McMann,

2011) The functions of these spacesuits are to keep the astronaut alive if a drastic change of

pressure happens, if the cabin becomes contaminated, facilitating escape in the case of

emergency and etc. The first spacesuits sponsored by USSR, U.S, and China were IVA’s solely

for the arrival and departure to and from space without going outside the vehicle. (Thomas &

McMann, 2011)

For space-walking, new models were unleashed: Apollo AAP/Block III, USA FMOL

Station Suit, Zero Prebreathe Suit, Space Station Freedom Advanced EMU, Shuttle Enhanced

EMU, and Shuttle Baseline EMU. (Thomas & McMann, 2011) This model of space-suit is used

to accommodate displacement outside of the vehicle in space, and the bodies located external to

the plant. The transitionary model suits, also called IEVA suits included USAF MOL LFS/EVA

Suits, Skylab, Gemini (Except GT7), Apollo 7-14, Apollo 15-17 CMP &ASTP. (Thomas &

McMann, 2011)

The history of the spacesuit itself is important for the eventual discussions on its

thermodynamic aspects. As the individual increases his elevation from sea level air pressure

drops (Organization, 1993) and the amount of oxygen available to the pulmonary system

decreases as well. The advent of aviation technology in the early 20th Century gave us many

instruments. Alongside this including the “supercharger” and oxygen pipes that allowed

increasing elevation to be possible without subsequent hypoxia. (Thomas & McMann, 2011) The

1920s would being the development of flying thermal protection and the first known creation of

an aviation full pressure suit in 1931 known as the Chertousky Ch-1 suit. (Thomas & McMann,

2011) World War II saw many companies and organizations attempting to perfect and streamline

this high-altitude pressure suit including Arrowhead Rubber Company, Goodyear, US Rubber

Company, University of Minnesota Bell Company and US National Bureau of Standards. NASA

would use the Goodrich Mark IV model with minor modifications to spearhead its first manned

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space program, Project Mercury. The David Clark Company would win the contract for the

design, development and manufacture of X-15 experimental aircraft (which reached 6.72 times

the speed of sound and 108 km of altitude) tailored spacesuit, it becoming the first U.S spacesuit

design. The pivotal moment was when on October 4, 1957 the USSR launched, the world’s first

artificial satellite, Sputnik I into Earth’s orbit. From the ashes of surprise NASA was formed in

1957. NASA initiated America’s first manned exploration program, called Project Mercury. The

Gemini, Apollo and Shuttle programs possessed launch and entry specific suit systems as well as

parachute systems and survival gear for the latter two.

Allow us to delineate in the modern-day the design of the two main extravehicular

activity spacesuits used by the International Space Station, the Space Shuttle Extravehicular

Mobility Unit (EMU) and the Russian Orlan Spacesuit. The Space Shuttle Extravehicular

Mobility Unit was first unleashed in 1982 upon contract of Hamilton United and ILC Dover. The

Shuttle EMU has 14 layers which comprise the liquid-cooling-and ventilation garment. (Suited

for spacewalking a teacher's guide with activities for technology education, mathematics, and

science.) The unit consists of 18 items allowing (quoted for emphasis):

“Pressure, thermal and micrometeoroid protection, protection, oxygen, cooling water, drinking

water, food, waste collection, (including carbon dioxide removal), electrical power and

communications”. (Thomas & McMann, 2011)

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The units include Primary Life Support system (PLSS), Displays and Control Module

(DCM), EMU Electrical Harness (EEH), Secondary Oxygen Pack (SOF), Service and Cooling

Umbilical (SCU), Battery, Contaminant Control Cartridge (CCC), Hard Upper Torso (HUT),

Lower Torso Arms (left and right), EVA Gloves (left and right), Helmet, Liquid Coding-and-

Ventilation Garment (LCVG), Maximum Absorption Garment (MAG), Extravehicular Visor

Assembly (EVA), In-Suit Drink Bag (IDB), Communications Carrier Assembly (CCA), and

Airlock Adapter Plate (AAP). (Suited for spacewalking a teacher's guide with activities for

technology education, mathematics, and science.)

A typical EMU suit can support an individual for 8.5 hours. The Orlan Space suit (The

Encyclopedia Astronautica) was used as a counterpart in the USSR operational in 1978.

Maximum time was three hours and was first used on the Salyut 6. Orlan space suits have been

used by Russian, American, European and Chinese astronauts.

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When an individual endeavors to complete an extravehicular activity, one needs to know

the environment of the universe that he will encounter as well as its thermodynamic qualities.

“Space has no temperature”. At an altitude of 53 miles, the temperature decreases to about -120

F. As we increase our altitude to 398 miles, supposedly the oxygen molecules absorbing solar

radiation can reach 4500 degrees Fahrenheit. In space, heat is transferred in the form of direct or

reflected sunlight. The temperatures of objects in space when exposed to solar radiation with

reflected energy from surrounding surfaces can exceed 250 degrees Fahrenheit (121 degrees

Celsius). Without any radiant energy from the Sun, the temperature can drop to -387 degrees

Fahrenheit. Lunar crates facing the Sun may reach 250 degrees Fahrenheit while areas near deep

space reach -250 degrees Fahrenheit. (Thomas & McMann, 2011) Space also has forms of

radiation on Earth. The atmosphere is the usual filter protecting individuals from solar radiation.

Space has highly energized hydrogen, helium, carbon, nitrogen, silicon, calcium, iron, and

oxygen atoms. It also has solar ultraviolet and visible radiation, solar flare x-rays, cosmic rays,

and electron and proton radiations. The heat originating from sunlight is prevented usually from

the earth’s atmosphere and sunlight proper is prevented from the earth’s atmosphere and sunlight

proper is prevented from damaging eyesight by a gold reflective visor pulled down over the face.

Heat produced by aforementioned radiation is usually prevented or blocked by the Earth’s

atmosphere and the Earth’s magnetic field. The sun solar flares’ high –energy particles are

blocked by the shielding of the spacesuits as well as careful avoidance, such as the timing of

spacewalks.

As for heat sinks, when heat sinks are mentioned in terms of spacesuit technology, it is

mentioned concerning the control of homeostasis of the individual during extravehicular

endeavors. The Soviets had a “cooling system” that channeled heat away from the body using an

undergarment. The Americans relied on air-cooling for their spacesuits. Both models would later

progress in to what is known as the aforementioned Liquid Cooling and Ventilation Garment.

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The Liquid Cooling and Ventilation System is made to provide thermoregulation usually

provided through conduction, convection, and radiation in the body. The necessity arises to

replicate this natural function of thermoregulation since the closed enclosure (spacesuit) causes

heat to increase inside. To quote verbatim:

“Body temperature is controlled by negative feedback that requires sensors, a controller,

and actuators. In addition to the hypothalamus itself that also acts as a sensor, cold and

warm sensitive temperature receptors are located throughout the body. The body

temperature receptors are located in the skin and in the interior of the body, specifically

in the spinal cord, abdomen, larger veins, and thorax. The hypothalamus, primarily

neurons in the anterior hypothalamic-preoptic region, is generally recognized as the

body’s temperature controller or thermostat. The hypothalamic thermostat works in

conjunction with other hypothalamic, autonomic, and higher nervous thermoregulatory

centers to keep core body temperature constant. Temperature sensitive neurons in the

hypothalamus are stimulated by the temperature receptors. Warm sensitive neurons in the

hypothalamus increase their firing rate in response to an increase in body temperature to

promote heat loss. Cold sensitive neurons in the hypothalamus increase their firing rate in

response to a decrease in body temperature to promote heat conservation and increase

heat production. Additional thermoregulatory responses are involuntary, mediated by the

autonomic nervous system, some neurohormonal, and others semi-voluntary or voluntary

behavioral responses. If the core body temperature decreases below the set point, cold

sensitive neurons, primarily in the anterior hypothalamic-preoptic region, initiate the

following hyperthermic responses…” (Pisacane, 2007)

A mathematical treatment using thermodynamics proper of this would be:

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˙Qm=Qe+Qr+Qk+Qc+Q st+W CITATION Pis07 \l 1033 (Pisacane, 2007)

Q_M= metabolic heat rate

Q_E= evaporative heat loss positive, gain negative

Q_R= radiative heat loss positive, gain negative

Q_K= conductive heat loss positive, gain negative

Q_C= convective heat loss positive, gain negative

Q_ST= heat storage rate

W= mechanical work

The core temperature of the subject must be kept between 36-38 degrees Celsius and the

skin temperature between 32-34 degrees Celsius for the subject to be comfortable. Anything

outside that range will result in discomfort, cognitive impairment, and in more severe cases

death. (Pisacane, 2007). The Liquid Cooling and Ventilation Garment attempts to procure this

physiological condition by being “long underwear” with small tubes sewn in to the fabric of the

spacesuit. There have been alternatives to this artificial homeostatic system, but this remains the

main one used in NASA and the International Space Shuttle.

Another utility used conjoined with the aforementioned Liquid Cooling and Ventilation

Garment is the Water Coolant Loop System.

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The loops decrease the thermodynamic potential by removing his metabolic heat and any

heat that leaks into the suit from the environment. The sublimator that decreases the temperature

of the oxygen flow extracts heat from the water, which normally leaves the pack at 45 F. To

control cooling, the astronaut uses a valve on the pack to select any of the three water

temperature ranges. Another subsystem supplies 11.8 pounds of expendable water, stored in a

rubber bladder reservoir, to the heat-rejecting porous plate sublimator to help in excretion, for as

we see that also affects homeostasis. (Portable Life Support System )

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(Pisacane, 2007)

Other thermodynamic concerns we believe are mitigated with present technology and

international cooperation or will be addressed in the near future. In conclusion, an astronaut on a

space-walk, wearing a special enclosure, in the 21st Century has enough assurances that his extra-

vehicular activity will not be a danger to him or his mission. Поехали!

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Works CitedBessette R, C. M. (1968). Patent No. 3751727 . United States.

http://www.damninteresting.com/outer-space-exposure. (n.d.).

Organization, I. C. (1993). Manual of the ICAO Standard Atmosphere.

Pisacane, V. L. (2007). Use of Thermoregulatory Models to Enhance Space Shuttle and Space Station.

Portable Life Support System . (n.d.). Retrieved from file:///C:/Users/ASUS/Desktop/LM15_Portable_Life_Support_System_ppP1-5.pdf

Suited for spacewalking a teacher's guide with activities for technology education, mathematics, and science. (n.d.). DIANE Publishing.

The Encyclopedia Astronautica. (n.d.). Retrieved from Encyclopedia Astronautica: http://www.astronautix.com/

Thomas, K. S., & McMann, H. J. (2011). U. S. Spacesuits. Springer Science & Business Media.