Aerospace and Electronic Systems - May 2019 - 48

An Emergency Mitigation System for Safer Lunar Surface Exploration
Table 3.

CARBON DIOXIDE REMOVAL

Atmospheric Partial Pressure Limits
Compound

OVERVIEW-LIOH VERSUS METOX VERSUS RCA

Minimum
(kPa)

Preferred
(kPa)

Maximum
(kPa)

17.2

22.1*

60.7

CO2

0.653

1.03

H2 O

0.827

1.31

1.86

Total

20.7

29.6

117.2

*Nominal value used on the Space Shuttle.

while the emergency shelter is inflated provides the
astronaut the ability to continue using any working
functions of his damaged suit, which may include
the LCG and communication system. Of course, if the
driver needs to use the emergency inflatable, then
the two will have to change places, which will require
temporary hose reconfiguration.

ROVER ECLSS SYSTEM DESIGN
The design of the proposed system relies heavily on a
deep understanding of the requirements for human life
support. These requirements dictate acceptable temperature ranges, pressure levels, O2 levels, relative humidity, etc. These requirements vary greatly based on the
level of activity. However, for this paper, we focused
on EVA. (For ECLSS System requirements on longer,
overnight missions, refer to [5]). Values for EVA (and
other scenarios) have been published by NASA in its
Advanced Life Support Baseline Values and Assumptions Document [9] and its Human Integration Design
Handbook [10].

BASELINE CONSUMABLE VALUES
Table 1 gives the human life support requirements for various substances for EVA. In addition, food requirements
were also considered but not included in this paper due to
the scope of a one-day EVA mission (Although NASA
provides a food stick inside the space suit, our personal
communication with NASA astronauts suggested that not
eating for 8 h was common if enough drink was provided
and a good breakfast was had).
An additional role of the ECLSS system is to provide a
tolerable atmosphere for humans to live in. The habitable
ranges for the three most important gasses in an artificial
atmosphere as well as the habitable range of total pressure
are shown in Table 3. These values come from the Human
Integration Design Handbook [10].
48

The CO2 produced through respiration must be scrubbed
from the atmosphere in order to maintain acceptable CO2
levels for the astronauts. NASA has developed two CO2
scrubbing technologies, or Contaminant Control Cartridges
(CCC): a single EVA lithium hydroxide (LiOH) CCC
which can be replaced between EVAs and a reusable metal
oxide (MetOx) CCC which can be regenerated using a special oven, which requires considerable power and would
most likely be situated on the lander/habitat. Both systems
have canister life spans of 8 to 12 h. A third option currently
under development is Rapid Cycle Amine (RCA), which is
a continuous-operation system that does not require canister replacement. These three CO2 scrubbing technologies
are discussed and compared in the following sections.

LITHIUM HYDROXIDE (LIOH)-SPECIFICATIONS AND
DRAWBACKS
Lithium Hydroxide technology utilizes a chemical reaction in which carbon dioxide reacts with lithium hydroxide
to form water and an innocuous compound, lithium carbonate. Using this technology, carbon dioxide is removed
from the atmosphere by flowing carbon dioxide laden air
through a canister containing a packed bed of lithium
hydroxide granules. The spent LiOH is not regenerated
and the canisters are returned to Earth for replenishment
with fresh absorbent.
The amount of LiOH required to remove the average
daily output of carbon dioxide by one person is 1.35 kg/day.
The removal capacity of one LiOH CCC is 0.55 kg of carbon
dioxide with an enthalpy change of À100 834 J/mol carbon
dioxide [12]. The dimensions of one EMU LiOH canister
are: 25.4 cm height Â 3 34.19 cm width Â 8.71 cm depth,
and the mass of one full/mission-ready LiOH CCC is 2.9 kg.
The mission timeline was analyzed to determine the total
amount of CO2 that needed to be scrubbed. Using the size,
mass, and enthalpy change for the LiOH CCC's listed
above, a total requirement of four LiOH CCC's was calculated. This total includes the two CCC's in the suit PLSS,
which results in only two CCC's being located on the rover
(and thus inside the system boundary). This corresponds to a
mass of 16.13 kg for the four LiOH CCC's.

METAL OXIDE (METOX)-SYSTEM SPECIFICATIONS AND
DRAWBACKS
MetOx is an on-orbit regenerative carbon dioxide removal
system. The MetOx flight system consists of two assemblies: a metal oxide sorbent canister and a regeneration
assembly. The canister removes the carbon dioxide and
also contains charcoal to remove the trace contaminants

IEEE A&E SYSTEMS MAGAZINE

MAY 2019

Aerospace and Electronic Systems - May 2019

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