ASHRAE Journal - July 2020 - 14

TECHNICAL FEATURE

decreases when they operate at elevated temFIGURE 1 Schematic of the active thermal control system for ISS.22
peratures.18 An additional radiator is used for
each of the four pairs of solar arrays for heat
dissipation and maintaining an appropriate
operating temperature.
Effective control of air quality and airﬂow
inside ISS is also of great signiﬁcance. The
Radiator
spacecraft maximum allowable concentrations (SMACs) for short term (up to 24 hours)
Radiators
and long term are determined and published
considering human space ﬂight requirements.19 Trace chemical contaminants resultRadiators
ing from equipment off-gassing and human
Radiator
metabolism and cleaning materials used prior
to the ﬂight must be properly addressed to
avoid air quality issues for spacecraft cabins.
For this purpose, a combination of passive and
active contamination control methods have
been successfully tested and used for ISS.20
External Ammonia Coolant Loops Remove Heat
Russian Internal Coolant is Triol Fluid
Through Radiators (36°F - 43°F)
Russian External Coolant is Polymethyl
The ability of the contamination control
Moderate Temperature Water Coolant Loops
Siloxane
system must be tested and veriﬁed using trace
Low Temperature Water Coolant Loops
Japanese External Coolant is Perﬂuorohexane
contaminant control (TCC) analysis. Through
(39°F - 50°F)
this analysis, the spacecraft is subjected to an
research studies and various improvement methods are
off-gassing test, and the trace contaminant
load is determined while comparing the load against the investigated.26-30
active contamination control system's capabilities.
Spacesuits and Environmental Control
The environmental control and life support system
Unlike on Earth, where HVAC is only considered a
(ECLSS) is responsible for water recovery and oxygen
21,22
The water recovery system (WRS)
necessity for the built environment, astronauts require
generation at ISS.
recycles crew member urine and cabin humidity conproper environmental control inside and outside the
densation into drinkable water. The oxygen generation
spacecraft cabin. Spacesuits allows astronauts to work
system (OGS) produces oxygen through electrolysis
outside the spacecraft for an extended amount of time
of water for the crew members at an adjustable level
by protecting them from excessive temperatures31,32
and space dust as well as providing the needed interior
according to need.
spacesuit pressure, oxygen for breathing and water to
The free convection process, which allows natural airﬂow circulation on Earth, does not occur in zero gravity. drink. The spacesuit currently in use by NASA for space
walks outside the ISS is the extravehicular mobility unit
Sufﬁcient airﬂow must be induced to avoid cold spots
and the resulting condensation and microbial growth.14 (EMU).33 The EMU consists of 16 layers of protection,
Maintaining a proper balance between the generation
including a liquid cooling garment with 300 ft (91 m) of
and removal of volatile trace contaminants is also essen- chilled water tubing woven to the garment to control the
tial in the indoor air quality of the spacecraft cabin.23
inside temperature; a pressure garment to maintain a
To enhance quality of life on ISS, crew quarters (CQ)
proper pressure; and thermal micrometeoroid garment
are personal spaces for sleep and leisure for the crew
to reﬂect solar irradiation and protect the astronaut
with lower levels of noise and enhanced thermal comfrom space dust.
24
fort and personalized ventilation. Addressing issues
The back of the EMU contains the life support system
such as noise, carbon dioxide and dust accumulaincluding oxygen and water storage, pressure and ﬂow
tion25 in ISS and particularly CQs are studied in several
regulator, electricity generator and carbon dioxide
14

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