# Summary of Water Processing Trade Studies and Analysis of JSC Integrated Water Recovery System (IWRS) {#summary-of-water-processing-trade-studies-and-analysis-of-jsc-integrated-water-recovery-system-iwrs .unnumbered}

# [Abstract]{.underline} {#abstract .unnumbered}

Many different technologies have been proposed as solutions to "close
the loop" and provide nearly total water recovery for long-duration
space craft missions. In this trade study, the technologies used on the
International Space Station (ISS) are compared to the Integrated Water
Recovery System (IWRS) evaluated in tests at the Johnson Space Center
(JSC) in 2000 and 2001 and to the Vapor Phase Catalytic Ammonia Removal
(VPCAR) system. The systems were scaled to estimate the mass, power, and
volume of each system for a number of different mission scenarios. Based
on the assumptions made in this analysis, and the equivalent system mass
(ESM) technique for system comparisons, the IWRS system outperformed the
ISS technologies for very long duration missions, but the VPCAR system
outperformed both systems for all cases.

Using the ESM analysis performed to do the trade study, the system
drivers that most affect the mass, volume, and power consumption costs
in the IWRS system can be identified. Directing future research to these
critical areas can help the IWRS and similar systems be more competitive
in the future.

![](media/image1.png){width="7.125in" height="9.375in"}

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<tr class="odd">
<td colspan="12"><strong>JSC 62185A</strong></td>
</tr>
<tr class="even">
<td colspan="12"><p><strong>CREW AND THERMAL SYSTEMS
DIVISION</strong></p>
<p><strong>NASA–LYNDON B. JOHNSON SPACE CENTER</strong></p>
<p><strong>HOUSTON, TEXAS</strong></p></td>
</tr>
<tr class="odd">
<td colspan="2"></td>
<td colspan="8"><p><strong>Summary of Water Processing Trade
Studies</strong></p>
<p><strong>and Analysis of JSC Integrated Water Recovery
System</strong></p>
<p><strong>Document Number</strong> <u>CTSD-ADV-543</u>
<strong>Date</strong> <u>August 30, 2004</u></p></td>
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<td></td>
<td colspan="3"><strong>PREPARED BY:</strong></td>
<td colspan="7">Molly S. Anderson</td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td colspan="3"><strong>APPROVED BY:</strong></td>
<td colspan="7">Chin H. Lin</td>
<td></td>
</tr>
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<td colspan="12">Number of pages: <u>_____</u></td>
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<td colspan="12"><strong>REVISIONS</strong></td>
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<td colspan="4">APPROVALS</td>
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<td colspan="3">DATE</td>
<td colspan="2">AUTHOR</td>
<td>SECTION</td>
<td>BRANCH</td>
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<td colspan="3">REV. LETTER</td>
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<td colspan="3">10/28/04</td>
<td colspan="2">M. Anderson</td>
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<td colspan="3">A</td>
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JSC FORM 151C (Rev Sept 86) NASA-JSC

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# Table of Contents {#table-of-contents .unnumbered}

[List of Figures ii](#list-of-figures)

[List of Tables iv](#list-of-tables)

[Introduction 1](#introduction)

[1 System Descriptions 1](#system-descriptions)

[1.1 International Space Station Water Recovery System
1](#international-space-station-water-recovery-system)

[1.2 Integrated Water Recovery System
3](#integrated-water-recovery-system)

[1.3 Vapor Phase Catalytic Ammonia Removal System
3](#vapor-phase-catalytic-ammonia-removal-system)

[2 System Scaling and Assumptions 4](#system-scaling-and-assumptions)

[2.1 Making More Equal Comparisons 4](#making-more-equal-comparisons)

[2.1.1 Infrastructure Factors 5](#infrastructure-factors)

[2.1.2 Adding or Removing Components 6](#adding-or-removing-components)

[2.2 System Scaling Methods 6](#system-scaling-methods)

[3 Mission Assumptions 7](#mission-assumptions)

[3.1 Mission Summaries 7](#mission-summaries)

[3.2 Wastewater Flowrates 7](#wastewater-flowrates)

[3.3 Equivalent System Mass (ESM) Equivalency Factors
8](#equivalent-system-mass-esm-equivalency-factors)

[3.4 Makeup Water Mass 9](#makeup-water-mass)

[4 Trade Study Results 9](#trade-study-results)

[5 ESM Drivers for the IWRS 10](#esm-drivers-for-the-iwrs)

[5.1 Biological Water Processor ESM Sources
12](#biological-water-processor-esm-sources)

[5.2 Reverse Osmosis ESM Sources 14](#reverse-osmosis-esm-sources)

[5.3 Air Evaporation System ESM Sources
15](#air-evaporation-system-esm-sources)

[5.4 Post Processing System ESM Sources
16](#post-processing-system-esm-sources)

[6 A Sensitivity Analysis Case on the IWRS AES Results
18](#a-sensitivity-analysis-case-on-the-iwrs-aes-results)

[7 Conclusions and Recommendations 20](#conclusions-and-recommendations)

[8 List of Acronyms 21](#list-of-acronyms)

[9 Primary References 22](#primary-references)

[Papers and Reports: 22](#papers-and-reports)

[Data References: 22](#data-references)

#   {#section .unnumbered}

# List of Figures {#list-of-figures .unnumbered}

[Figure 1: Simplified schematic of the ISS Urine Processor Assembly,
which is a primarily distillation based system.
2](#__RefHeading___Toc87082174)

[Figure 2: Simplified schematic of the ISS Water Processor Assembly. The
primary processing technologies in the ISS WPA are multifiltration,
oxidation, and ion exchange. 2](#__RefHeading___Toc87082175)

[Figure 3: The Integrated Water Recovery System included the Biological
Water Processor subsystem that performed oxidation of organic
contaminants and nitrification of ammonia. Reverse osmosis and Air
Evaporation system provided most of the inorganic contaminant removal,
and a post-processing system provided polishing.
3](#__RefHeading___Toc87082176)

[Figure 4: The VPCAR system uses distillation as a primary processing
step, followed by oxidation and reduction reaction. The system is highly
thermally integrated. 4](#__RefHeading___Toc87082177)

[Figure 5: The summary ESM results for the three technologies (and one
variation) evaluated show that the VPCAR consistently outperforms the
ISS and IWRS systems. The IWRS system less suited for short duration
missions than the ISS system, but better suited for long duration
missions due to its greater water recovery rate and reduced use of
consumables. 9](#__RefHeading___Toc87082178)

[Figure 6: For the shorter surface missions considered in this trade
study, the AES system provides more than 50% of the ESM of the IWRS
system. 11](#__RefHeading___Toc87082179)

[Figure 7: The lower cost of cooling helps reduce the ESM of the AES to
less than 50% of the total for the 360-day transit mission, but the AES
still provides a significant fraction of the ESM in the longer duration
cases. 12](#__RefHeading___Toc87082180)

[Figure 8: ESM sources for the Biological Water Processor design based
on modifications of the original IWRS test bioreactors are shown for a
500-day Mars surface mission. 13](#__RefHeading___Toc87082181)

[Figure 9: The sources of system mass for the BWP system show that pumps
are a significant source of mass in the system. The values shown are for
the 500-day Mars surface case. 13](#__RefHeading___Toc87082182)

[Figure 10: The ESM of the RO system is primarily due to the mass of
components, followed by power consumption. The values shown are for a
500-day Mars surface case. 14](#__RefHeading___Toc87082183)

[Figure 11: Pumps provide the largest source of mass for the RO system
in the 500-day Mars surface case shown here.
15](#__RefHeading___Toc87082184)

[Figure 12: The AES is a large consumer of power, and consequently of
cooling, both of which contribute to the ESM of the subsystem. The AES
ESM also includes a large mount of consumable mass due to the short wick
lifetime, especially for the 500-day Mars surface mission considered
here. 15](#__RefHeading___Toc87082185)

[Figure 13: For a Mars surface mission and assumptions based on IWRS
test performance, most of the power consumption in the AES is due to
heater power. Only approximately 10% of this heater power is needed to
provide the heat of vaporization energy to the brine water.
16](#__RefHeading___Toc87082186)

[Figure 14: The ESM of the PPS system on the 500-day Mars surface
mission is primarily due to consumable mass.
17](#__RefHeading___Toc87082187)

[Figure 15: The resupply mass of the PPS is primarily due to the
consumable IX resin. 17](#__RefHeading___Toc87082188)

[Figure 16: Reducing the power and cooling required by the AES by 75%
does improve the results for the IWRS. More improvement would still be
needed from this iteration to be competitive with the VPCAR technology,
but the IWRS still consumes more resources than the ISS WRS on the
shorter 30 and 90 day surface missions. 18](#__RefHeading___Toc87082189)

[Figure 17: An alternate AES case was considered due to uncertainty in
the AES source data and the significance of the AES values to the IWRS
results. The AES still is the largest contributor of ESM to the IWRS,
even when the power and cooling are reduced by 75%.
19](#__RefHeading___Toc87082190)

[Figure 18: Reducing the assumed power consumption and cooling of the
AES makes the consumable mass of the system, totally attributed to the
replacement of the wicks, more important. Power is still significant,
and power and cooling together (as they are linked) still have greater
impact than the mass of the wicks. 20](#__RefHeading___Toc87082191)

# List of Tables {#list-of-tables .unnumbered}

[Table 1: A sample of the analysis used to derive the installation
infrastructure penalty factor for the Fluids Control and Pump Assembly
(FCPA) ORU in the ISS UPA. 5](#__RefHeading___Toc87082192)

[Table 2: Values for wastewater production rates from the ALS BVAD were
used to determine the total amount of wastewater processed daily in each
mission scenario. 8](#__RefHeading___Toc87082193)

[Table 3: Volume, Power, and Cooling equivalency factors used for the
ESM analysis of water processing technologies in this trade study.
8](#__RefHeading___Toc87082194)

#  {#section-1 .unnumbered}

# Introduction {#introduction .unnumbered}

Many different technologies have been proposed as solutions to "close
the loop" and provide nearly total water recovery for long duration
space craft missions. In this trade study, the technologies used on the
International Space Station (ISS) are compared to the Integrated Water
Recovery System (IWRS) evaluated in tests at the Johnson Space Center
(JSC) in 2000 and 2001 and to the Vapor Phase Catalytic Ammonia Removal
(VPCAR) system. The systems were scaled to estimate the mass, power, and
volume of each system for a number of different mission scenarios. Based
on the assumptions made in this analysis, and the equivalent system mass
(ESM) technique for system comparisons, the IWRS system outperformed the
ISS technologies for very long duration missions, but the VPCAR system
outperformed both systems for all cases.

Using the ESM analysis performed to do the trade study, the system
drivers that most affect the mass, volume, and power consumption costs
in the IWRS system can be identified. Directing future research to these
critical areas can help the IWRS and similar systems be more competitive
in the future.

# System Descriptions

Three systems were compared in this trade study. The first system
considered was the ISS Urine Processor Assembly (UPA) and Water
Processor Assembly (WPA). ISS technologies are frequently used as a
baseline for comparison when evaluating Advanced Life Support (ALS)
technologies. The second system evaluated was the IWRS evaluated at JSC
to produce potable water using a biological water processor (BWP) as the
primary organic removal step. The VPCAR system, evaluated as a third
option, is a highly integrated physical-chemical water processing
system.

## International Space Station Water Recovery System

The ISS Water Recovery System (WRS) processes urine and other
wastewaters separately. The UPA, shown in Figure 1, purifies pretreated
urine and flushwater with a vapor compression distillation (VCD) process
and filtration. The WPA, shown in Figure 2, processes the UPA distillate
and other wastewaters including condensate and hygiene waters with
multifiltration, partial oxidation, and ion exchange. The system
achieves approximately 95% total recovery, with most losses occurring in
the UPA.

![](media/image4.jpeg){width="5.000694444444444in"
height="3.9541666666666666in"}

[]{#__RefHeading___Toc87082174 .anchor}Figure 1: Simplified schematic of
the ISS Urine Processor Assembly, which is a primarily distillation
based system.

![](media/image5.jpeg){width="5.997222222222222in"
height="3.888888888888889in"}

[]{#__RefHeading___Toc87082175 .anchor}Figure 2: Simplified schematic of
the ISS Water Processor Assembly. The primary processing technologies in
the ISS WPA are multifiltration, oxidation, and ion exchange.

## Integrated Water Recovery System

The IWRS system, shown in Figure 3, processes a combined wastewater
stream. It uses biological reactors to oxidize organic compounds and
convert ammonia to nitrogen. A reverse osmosis (RO) system treats the
BWP effluent and is the primary inorganic removal system. The RO system
produces concentrated brine that is processed by the Air Evaporation
System (AES). In the AES, a wick absorbs the brine and a hot air stream
evaporates the water out while the contaminants accumulate in the wick.
That water is condensed from the air stream and combined with the RO
permeate to be polished by the Post-Processing System (PPS). The PPS
uses ion exchange beds to remove any remaining inorganic contaminants
and photo-oxidation to destroy any remaining organic contaminants. The
components are all separately designed and have not been optimized for
an ISS rack packaging. The IWRS system achieved 98% water recovery.

![](media/image6.jpeg){width="5.165277777777778in"
height="5.072916666666667in"}

[]{#__RefHeading___Toc87082176 .anchor}Figure 3: The Integrated Water
Recovery System included the Biological Water Processor subsystem that
performed oxidation of organic contaminants and nitrification of
ammonia. Reverse osmosis and Air Evaporation system provided most of the
inorganic contaminant removal, and a post-processing system provided
polishing.

## Vapor Phase Catalytic Ammonia Removal System

The VPCAR system, shown in Figure 4, is a highly integrated unit that
processes a combined wastewater stream to produce potable water.
Distillation of the wastewater occurs in the Wiped Film Rotating Disks
(WFRD) to remove many inorganic contaminants. The distillate is treated
in oxidation and reduction reactors to oxidize lightweight organic
components and ammonia and reduce any oxidized nitrogen compounds such
as N~2~O to nitrogen gas. The design is highly thermally integrated and
all components designed to be packaged in an ISS-like rack
configuration. The VPCAR system is assumed to achieve 98% water
recovery.

![](media/image7.wmf)

[]{#__RefHeading___Toc87082177 .anchor}Figure 4: The VPCAR system uses
distillation as a primary processing step, followed by oxidation and
reduction reaction. The system is highly thermally integrated.

# System Scaling and Assumptions

Because the water recovery systems evaluated may have been developed for
significantly different wastewater loads, each system must be scaled to
the appropriate size for the mission cases considered in this trade
study. Scaling relationships used in this study vary from the very
simple to the very complex. In addition to scaling the size of the
components in each system, it is important to make sure that each system
provides all of the same functions and attempt to equally account for
the mass of the infrastructure required to install and operate the
system.

## Making More Equal Comparisons

Whenever systems being developed in the ALS program are compared to
systems already optimized, packaged, and designed for spaceflight,
issues arise as to the fairness of the comparisons. It can be argued
that ALS systems are not optimized to the degree that systems at a
higher technology readiness level (TRL) are, and that their mass would
be reduced as they mature. It can also be argued that ALS systems do not
account for the additional mass due to additional safety requirements,
installation requirements, and reliability issues that flight systems
include.

To address the optimization issue in the IWRS, flight components from
other systems were substituted for commercial components in many cases.
Commercial components, such as pumps, were assumed to be used at their
maximum recommended flowrates to achieve a minimum reasonable mass for
each unit, unless directed otherwise by the system designer for
performance reasons, as in the case of membrane contactors that appear
to be overdesigned according to manufacturer recommendations.

The VPCAR system claims to be designed as a somewhat flight-like unit.
No modifications or adjustments were made to the current values to
account for optimization.

Oxygen consumption is not included in this trade study comparison, but
could impact the size of the ECLSS Architecture, as oxygen demands for
one system may be significantly larger than others.  Systems that
perform total oxidation through chemical or biological means will impact
consumable and oxygen production systems more than those that remove and
dispose of many organic contaminants before oxidizing the remaining
components.

### Infrastructure Factors

A detailed study of the ISS UPA and WPA was conducted to assess what
portion of the mass of each Orbital Replacement Unit (ORU) consisted of
components that performed water processing functions, and what portion
of the mass was due to components such as lines, packaging or acoustic
enclosures, brackets, bolts, and other miscellaneous hardware. After
this assessment, it was determined that on average, a factor of 1.6
would have to be assessed to the water processing components to include
the additional mass needed to install the units as ORUs in an ISS rack.
Table 1 shows an analysis of the Fluids Control and Pump Assembly (FCPA)
ORU as an example. This factor of 1.6 was applied to the mass of each
component in the IWRS system. A study of the VPCAR system, with slightly
less detail available, determined a factor of 1.4 would be derived from
comparing the mass of the water processing components to the mass of the
installed system, not including the rack and outside frame. Further
study may be helpful for determining how to assess penalties for
installation infrastructure to be applied to ALS systems in development.

+--------------------------+----------+----------+----------+----------+
| **Fluids Control and     | **Direct | **C      | **Water  | **Other  |
| Pump Assembly ORU**      | Water    | omponent | Pr       | Function |
|                          | Pr       | Mass     | ocessing | Mass     |
| **Subcomponents**        | ocessing | (kg)**   | Mass     | (kg)**   |
|                          | Fun      |          | (kg)**   |          |
|                          | ction?** |          |          |          |
+--------------------------+----------+----------+----------+----------+
| Motor Support            | NO       | 0.027215 |          | 0.027215 |
+--------------------------+----------+----------+----------+----------+
| Fluid Pump Control Assy  | YES      | 31.9282  | 31.9282  |          |
+--------------------------+----------+----------+----------+----------+
| Flex Line Assy           | NO       | 3.188738 |          | 3.188738 |
+--------------------------+----------+----------+----------+----------+
| Wire Harness Assy        | NO       | 2.313309 |          | 2.313309 |
+--------------------------+----------+----------+----------+----------+
| Seat Track Channel       | NO       | 0.240403 |          | 0.240403 |
+--------------------------+----------+----------+----------+----------+
| Coolant Loop Motor       | NO       | 0.072574 |          | 0.072574 |
+--------------------------+----------+----------+----------+----------+
| Bracket, Clamp           | NO       | 0.009072 |          | 0.009072 |
+--------------------------+----------+----------+----------+----------+
| FCPA Enclosure Base      | NO       | 4.499613 |          | 4.499613 |
+--------------------------+----------+----------+----------+----------+
| FCPA Enclosure Top       | NO       | 2.140945 |          | 2.140945 |
+--------------------------+----------+----------+----------+----------+
| Front Enclosure Assy     | NO       | 1.514991 |          | 1.514991 |
+--------------------------+----------+----------+----------+----------+
| Rear Enclosure Assy      | NO       | 2.236199 |          | 2.236199 |
+--------------------------+----------+----------+----------+----------+
| Misc Hardware            | NO       | 0.557916 |          | 0.557916 |
+--------------------------+----------+----------+----------+----------+
| FCPA Water               | NO       | 2.385883 |          | 2.385883 |
+--------------------------+----------+----------+----------+----------+
|                          |          |          |          |          |
+--------------------------+----------+----------+----------+----------+
| **Totals**               |          | **51     | **3      | **19     |
|                          |          | .11506** | 1.9282** | .18686** |
+--------------------------+----------+----------+----------+----------+
| **Factor = Total/Water   | **1.     |          |          |          |
| Processing**             | 600938** |          |          |          |
+--------------------------+----------+----------+----------+----------+

[]{#__RefHeading___Toc87082192 .anchor}Table 1: A sample of the analysis
used to derive the installation infrastructure penalty factor for the
Fluids Control and Pump Assembly (FCPA) ORU in the ISS UPA.

### Adding or Removing Components

Components were added to the current IWRS and VPCAR system to ensure
that the masses compared accounted for performing the same function. A
controller unit was added to the IWRS based on the ISS WPA controller.
The VPCAR system includes a controller already. A feed tank, microbial
check valve (MCV), potable water storage tank, and potable water
delivery system were added to both the IWRS and the VPCAR system.

## System Scaling Methods

The scaling methods used to size the ISS UPA and WPA, the IWRS, and the
VPCAR system were all slightly different.

For the ISS systems, commercial components of the same type were used to
determine how the size of these units varied with flowrate. It is
important to recognize that the flight unit sizes were used as the basis
for scaling, and only the rate of change was based on commercial units.
The ISS system was designed to be adaptable for varying loads of
wastewater. Increasing the daily processing time provides much of this
adaptability. For components such as pumps and heaters, which are scaled
based on flowrate, not daily load, both the maximum and minimum load
cases result in the same flowrate. For tanks, which depend on daily load
for sizing and are not replaced, the maximum case was used. For
consumables, such as multifiltration and ion exchange beds, it is
assumed that the stated design lifetimes are for the nominal case.

The JSC IWRS is built primarily of commercial components. The primary
goal of the IWRS test was to demonstrate that using a system with a
bioreactor as a primary processor to recover potable water from
wastewater was possible. The system was not optimized for mass or power
consumption. Some components were selected based on availability rather
than their ideal size, and some components were deliberately oversized
to provide plenty of margin. In this trade study, an attempt was made to
use more appropriately sized components where possible. This includes
selecting commercial pumps based on use at their maximum flowrate. Some
units, such as the membrane contactors used in the post-processing
system, were significantly oversized according to manufacturer
recommendations, but were used in the trade study as they were used in
the test according to direction from the system designer.

Significant adjustments were made to the designs of the bioreactors
themselves to provide more optimized designs than were used in the test.
The anoxic oxidation reactor used in the IWRS test used ceramic saddles
as packing. In this analysis, a bio-bale like material is used while
scaling to maintain the same surface area for microbial growth. The
nitrifying reactor used in the test was a tubular reactor that had
significant maintenance issues in the test. A new design for a
nitrification reactor using a bio-bale packed bed and external membrane
oxygenation was substituted for the tubular design. There is still a
large amount of uncertainty in determining what the correct sizing
methods for bioreactors should be, but as the mass of the bioreactors
does not appear to be one of the largest drivers of the IWRS mass, these
uncertainties can be accepted. New research beginning at JSC should help
address these bioreactor sizing questions for future trade studies.

The VPCAR system was not originally in the primary focus of this trade
study, but because updated information was made available, it was
included for comparison. The VPCAR processing components were scaled
based on a 40/60 assumption. Essentially, 40% of the mass of the system
is kept constant, while 60% of the mass scales linearly with flow. Power
was scaled linearly, based on the assumption that pumps and heaters
would maintain the same efficiency and specific energy to process the
wastewater. The controller was kept constant in all cases, as in the ISS
and IWRS cases.

# Mission Assumptions

Four separate mission scenarios were considered in this analysis. These
missions had crews of four or six, included surface and transit
scenarios, and had significant variations in the sources and amounts of
wastewater to be processed.

## Mission Summaries

The first category of missions considered is short-term surface stays.
These missions included a 30-day and 90-day scenario with four
crewmembers. For the 30-day scenario, the wastewater sources were
assumed to be crew urine, flushwater, oral hygiene, handwash and
facewash water, and condensate water for a load of 35 kg/day. For the
90-day surface mission, wastewater from a shower system is added for a
load of 49 kg/day. These missions are variations on the lunar outpost
scenario developed by the JSC water team, or possibly short-term Mars
surface stays.

The next mission scenario is a 360-day transit mission, used to estimate
the trip to and from Mars using current propulsion technologies. In this
transit mission, a crew of six is expected to produce wastewater from
urine, flushwater, condensate, and water recovered from CO~2~ reduction
in a Sabatier reaction. Only 29 kg/day of wastewater is produced.

The final mission scenario is a 500-day surface stay. This case is
similar to the Mars habitat or Early Planetary Base (EPB) scenario
developed by the JSC ALS water team with some modifications. The crew of
six produces wastewaters from urine, flushwater, oral hygiene, handwash
and facewash, shower, as well as condensate water and water recovered
from a Sabatier reaction. The total wastewater load in this case was 77
kg/day.

## Wastewater Flowrates

Wastewater flowrates from each source were taken from the ALS Baseline
Values and Assumptions (BVAD) document. For the 30-day and 90-day
surface cases values from the Early Planetary Base categories were used.
For the 360-day transit mission, values from the Transit Mission
category were used, including a reduction in the amount of flushwater.
For the 500-day surface stay, the Mature Planetary Base (MPB) case was
used, including an increase in the amount of condensate recovered. Table
2 shows these values as reported in the ALS BVAD.

![](media/image8.wmf)

[]{#__RefHeading___Toc87082193 .anchor}Table 2: Values for wastewater
production rates from the ALS BVAD were used to determine the total
amount of wastewater processed daily in each mission scenario.

## Equivalent System Mass (ESM) Equivalency Factors

The Systems Integration, Modeling, and Analysis (SIMA) element of ALS
frequently uses ESM as a technique for determining the least resource
intensive technology while trading the cost of mass, volume, power, and
cooling. Equivalency factors allocate the cost of structure, power
generation, and thermal control systems to the technologies based on the
use of these infrastructures. The equivalency factors for each system
depend on the mission and the technology selected, and are shown in
Table 3.

+-----------------+------------+-------+------------------------------+
|                 | **Equ      | **Un  | **Assumed System**           |
|                 | ivalency** | its** |                              |
+-----------------+------------+-------+------------------------------+
| **Mars          |            |       |                              |
| Surface**       |            |       |                              |
+-----------------+------------+-------+------------------------------+
| Volume          | 9.16       | kg    | Unshielded inflatable volume |
|                 |            | /m^3^ |                              |
+-----------------+------------+-------+------------------------------+
| Power           | 228        | kg/kW | 20% efficient photovoltaic   |
|                 |            |       | system                       |
|                 |            |       |                              |
|                 |            |       | with regenerative fuel cells |
+-----------------+------------+-------+------------------------------+
| Cooling         | 146        | kg/kW | Flow through radiators on    |
|                 |            |       | Mars                         |
+-----------------+------------+-------+------------------------------+
| **Mars          |            |       |                              |
| Transit**       |            |       |                              |
+-----------------+------------+-------+------------------------------+
| Volume          | 9.16       | kg    | Unshielded inflatable volume |
|                 |            | /m^3^ |                              |
+-----------------+------------+-------+------------------------------+
| Power           | 237        | kg/kW | Hybrid solar array           |
+-----------------+------------+-------+------------------------------+
| Cooling         | 60         | kg/kW | Internal coolant loop and    |
|                 |            |       | advanced lightweight         |
|                 |            |       | radiators                    |
+-----------------+------------+-------+------------------------------+

[]{#__RefHeading___Toc87082194 .anchor}Table 3: Volume, Power, and
Cooling equivalency factors used for the ESM analysis of water
processing technologies in this trade study.

For all of the surface cases, infrastructure factors based on a Mars
surface case were selected. The 30-day and 90-day surface cases could
also be representative of a lunar surface case. However, until a
reference mission for a lunar case is better established, it will be
difficult to determine the correct factors for that case. Also, it is
possible that these lunar cases will be simulations of Mars missions, in
which case it makes sense to select technologies most appropriate for
the Mars missions, and gain experience with them on the lunar surface.
For the transit case, the Mars transit factors are assumed. Table 3
documents the equivalency factors used in this trade study and the
assumed infrastructure technology that factor is derived from. These
values are used for calculating the ALS Metric annually and are listed
in the ALS BVAD.

## Makeup Water Mass

While all of the systems considered have nearly total recovery of
wastewater, over long durations small differences in the fraction of
water recovered can have a significant impact on the system mass as
replacement for lost water has to be provided. After the systems have
been sized to process the wastewater for each case, and the volume,
power, and cooling have been converted to equivalent masses, the final
addition of mass before comparison is from makeup water used to replace
water lost during processing. For the ISS systems, that is 5% of the
daily wastewater load multiplied over the mission duration. For the IWRS
and VPCAR systems, only 2% of the feed wastewater is lost.

# Trade Study Results

In an ESM based trade study, the system with the lowest ESM should be
selected. The three systems discussed above were compared, with the
addition of a fourth option. As later sections will show, the AES
contributes a large portion of the ESM of the IWRS system, but only
processes 10% of the wastewater. The fourth option simply subtracts the
ESM of the AES from the IWRS values and assumes that 10% of the daily
wastewater load must be replaced instead of 2%. Based on the results
shown in Figure 5, the VPCAR system is clearly the best performing
system in all cases. For short duration missions (30-90 days), the JSC
IWRS without the AES or the ISS UPA and WPA are the next best
candidates. The full JSC IWRS system had the highest ESM for short
duration missions. For long duration missions (360-500 days), the full
JSC IWRS system has a lower ESM than the IWRS system without an AES or
the ISS UPA and WPA.

![](media/image9.wmf){width="4.84375in" height="3.796527777777778in"}

[]{#__RefHeading___Toc87082178 .anchor}Figure 5: The summary ESM results
for the three technologies (and one variation) evaluated show that the
VPCAR consistently outperforms the ISS and IWRS systems. The IWRS system
less suited for short duration missions than the ISS system, but better
suited for long duration missions due to its greater water recovery rate
and reduced use of consumables.

These results show the benefit of systems with no or reduced consumables
over long duration missions. The performance of the VPCAR system
demonstrates the power of a highly integrated system in achieving
efficiencies over the less integrated ISS UPA and WPA or the IWRS units.

# ESM Drivers for the IWRS 

ESM analysis can be used as a powerful not just for comparing systems,
but for determining what are the most costly portions of the system for
an efficient use of time and effort to reduce the mass, volume, or power
consumption for the most benefit. The sections below compare the ESM due
to the system mass and stored consumable parts mass, the system volume
and consumable parts volume, and system power for the BWP, RO, AES, and
PPS subsystems of the IWRS. The most costly portion of each subsystem is
then analyzed in greater detail to determine which components would
provide the most payoff if efforts to reduce their size or power
consumption were made.

The relative contributions of each of the subsystems to ESM are
revealing as they show how the drivers for each mission shift or stay
the same depending on whether the mission is short or long. Figure 6
shows the ESM sources for the short duration missions, and Figure 7
shows the ESM contributions of the IWRS subsystems for the longer
duration missions. The AES contributes a large fraction of the system
ESM regardless of the mission. The significant power consumption of the
AES is expensive in every case. The relative contribution of the BWP
system decreases over time, as its resupply cost is smaller than the
initial investment in the system mass. The system described as "Potable"
in Figure 6 and Figure 7 is the mass of the MCV, potable water storage,
and potable water delivery system. These systems were not originally
included in the IWRS, but are required for a fair trade study between
the IWRS and the ISS systems. They do not change much over time. The RO
ESM increases for the very long 500-day Mars surface mission, but still
provides a relatively small fraction of the system ESM. The relative
contribution of the PPS increases over longer durations. The PPS
resupply cost increases beyond the initial investment in system mass
over long missions due the consumables designed into the system. The
amount of makeup water increases over long durations as well. This
makeup water increase has a significant impact on the total ESM values
displayed in Figure 5.

![](media/image10.wmf){width="4.33125in"
height="2.5208333333333335in"}![](media/image11.wmf){width="4.333333333333333in"
height="2.5194444444444444in"}

[]{#__RefHeading___Toc87082179 .anchor}Figure 6: For the shorter surface
missions considered in this trade study, the AES system provides more
than 50% of the ESM of the IWRS system.

Overall, it can be seen from Figure 6 and Figure 7 that decreasing the
AES ESM will have results for all missions. Decreasing the BWP system
mass would be helpful as well. Decreasing the resupply mass of the PPS
could have a significant impact, but primarily for long duration
missions. While increasing system water recovery would reduce the
resupply water, it is possible that 100% water recovery is not necessary
in all life support architectures. Increasing the water recovery is most
likely a more difficult process than decreasing the mass of the other
systems, considering the current TRL of the IWRS, and is not recommended
as the primary improvement in the system.

The IWRS seems most promising for the 500-day surface mission with a
long duration and large water load. In sections 5.1 through 5.4 the
sources of ESM for each subsystem will be analyzed to find promising
routes for reducing the ESM of the entire system.

![](media/image12.wmf){width="4.333333333333333in"
height="2.5194444444444444in"}![](media/image13.wmf){width="4.333333333333333in"
height="2.525in"}

[]{#__RefHeading___Toc87082180 .anchor}Figure 7: The lower cost of
cooling helps reduce the ESM of the AES to less than 50% of the total
for the 360-day transit mission, but the AES still provides a
significant fraction of the ESM in the longer duration cases.

## Biological Water Processor ESM Sources

The benefits of biological systems are advertised as low power
consumption because the system operates at ambient temperatures and
relatively low pressures, and low consumable usage rates. The
bioreactors used in this trade study were modified from the actual
designs used in the IWRS test, assuming packed beds for both the anoxic
oxidation denitrification reactor and the nitrifying reactor. The beds
are packed with Bio-bale material, and an external membrane oxygenation
unit is used. There is significant uncertainty in the sizing
relationships for the reactors due to these modifications, and
uncertainty in the correct basis for sizing the reactors. The resulting
numbers for these units have been verified by system developers as at
least reasonable values for reactor sizes, but improvements in future
trade studies will provide good information. Based on these assumptions,
it can be seen in Figure 8 that the original mass of the BWP system is
the largest source of ESM in the system, which shows that the advertised
benefits of the BWP system are valid.

![](media/image14.wmf){width="4.217361111111111in"
height="2.7506944444444446in"}

[]{#__RefHeading___Toc87082181 .anchor}Figure 8: ESM sources for the
Biological Water Processor design based on modifications of the original
IWRS test bioreactors are shown for a 500-day Mars surface mission.

![](media/image15.wmf){width="4.560416666666667in"
height="2.995138888888889in"}

[]{#__RefHeading___Toc87082182 .anchor}Figure 9: The sources of system
mass for the BWP system show that pumps are a significant source of mass
in the system. The values shown are for the 500-day Mars surface case.

Based on the results in Figure 8, an analysis of the source of the BWP
mass can be used to determine the components that will be the most
advantageous to reduce in mass. In Figure 9, the masses of the
components of the BWP are grouped by type. One of the largest sources of
mass is due to the pumps in the system. The BWP operated with a 20:1
recycle ratio in the IWRS test. Current research uses smaller recycle
ratios, on the order of 10:1. This change will reduce the size of the
pumps and should reduce the mass of the BWP system. This change could
also improve the size of the oxygenator units and gas-liquid separator
listed under "Misc" in Figure 9. Optimizing the pumps required for this
system may be an important engineering task as the IWRS matures.

## Reverse Osmosis ESM Sources

The RO system is the primary inorganic removal step in the IWRS system.
The contaminants are concentrated in a brine stream that is sent to the
AES. The RO system provides a relatively small amount of the mass of the
IWRS system. The mass of the system is the largest fraction of the RO
ESM, followed by power consumption, as shown in Figure 10. Based on
these results, and the assumptions in the study, such as using spiral
wound membranes with a one-year life, the RO system has relatively small
resupply requirements. The RO process requires high pressure provided by
pumps, so some significant power consumption is inevitable. Selecting
pumps with high efficiencies could be very beneficial for this system.
But any changes to the RO will likely have a relatively small impact on
the IWRS system mass because the RO is already small compared to the
other IWRS subsystems.

![](media/image16.wmf){width="4.219444444444444in" height="2.75in"}

[]{#__RefHeading___Toc87082183 .anchor}Figure 10: The ESM of the RO
system is primarily due to the mass of components, followed by power
consumption. The values shown are for a 500-day Mars surface case.

Like the BWP, the largest source of mass in the RO system is due to the
pumps. The RO system requires a low flowrate high-pressure pump, and a
high-speed low-pressure drop pump to handle the recycling of fluids in
the system. Finding membranes that operate at lower pressure, or
minimizing the flowrate in the recycle loop without fouling the membrane
may be beneficial routes of investigation for the RO system.

![](media/image17.wmf){width="3.1909722222222223in"
height="2.5006944444444446in"}

[]{#__RefHeading___Toc87082184 .anchor}Figure 11: Pumps provide the
largest source of mass for the RO system in the 500-day Mars surface
case shown here.

## Air Evaporation System ESM Sources

Examining and improving the AES may be one of the most efficient ways of
improving the IWRS system. The AES regularly provided on the order of
50% of the ESM of the IWRS system. Figure 12 shows that the majority of
the ESM for the AES system on the 500-day Mars surface is due to power.
Over this long duration, the resupply mass due to replacing wicks is
also significant. In this study, it is assumed that only the wick mass
is replaced, and not the container. If this is not feasible, the
resupply mass and the AES ESM would increase further.

![](media/image18.wmf){width="4.21875in" height="2.75in"}

[]{#__RefHeading___Toc87082185 .anchor}Figure 12: The AES is a large
consumer of power, and consequently of cooling, both of which contribute
to the ESM of the subsystem. The AES ESM also includes a large mount of
consumable mass due to the short wick lifetime, especially for the
500-day Mars surface mission considered here.

Previous studies of the AES assumed much less power would be needed to
recover water from the RO brine. In the IWRS test, approximately 1550 W
was needed to process 2.29 kg of brine each day. An earlier trade study
(Yeh 1999) assumed that 577 W would be used to recover 5.08 kg/day of
brine. An earlier analysis by Dr. Kevin Lange estimated that 490 W could
be used to recover 11.08 kg/day of water from the brine. Clearly, the
performance in test is significantly different from early estimates. If
there were reasons that the power consumption had to be increased in
test to make the system function successfully, those need to be
documented as lessons learned. Future efforts with the AES should focus
on reducing the power consumption of the AES. Most of this power
consumption is due to the heaters, as is shown in Figure 13. Based on
the ratio of airflow to water recovered, and the change in air
temperature from 7C to 58C used in the IWRS test, only approximately 10%
of the heater energy is actually used to vaporize water from the brine.

![](media/image19.wmf){width="3.201388888888889in" height="2.5in"}

[]{#__RefHeading___Toc87082186 .anchor}Figure 13: For a Mars surface
mission and assumptions based on IWRS test performance, most of the
power consumption in the AES is due to heater power. Only approximately
10% of this heater power is needed to provide the heat of vaporization
energy to the brine water.

## Post Processing System ESM Sources

The PPS provides final polishing of the RO permeate and the AES
condensate water. The system is designed to use ion exchange (IX) resin,
a consumable, to remove remaining inorganic components. The remaining
organic components are oxidized with ultraviolet light lamps.

![](media/image20.wmf){width="4.169444444444444in"
height="2.745833333333333in"}

[]{#__RefHeading___Toc87082187 .anchor}Figure 14: The ESM of the PPS
system on the 500-day Mars surface mission is primarily due to
consumable mass.

As a consequence of using the consumable IX resin, resupply mass is a
significant portion of the PPS ESM for a long duration mission, as shown
in Figure 14. Current PPS optimization efforts are focused on extending
the life of the PPS IX resin by removing CO~2~ that can fill the bed as
carbonate ions. The removal of CO2 is accomplished by adding additional
membrane contactors. The current contactors used to supply oxygen to the
UV units provide the second largest portion of the PPS system mass, and
are significantly oversized. The membrane contactors in the study are
based on the ISS membrane based Gas-Liquid Separator (GLS) ORU, not the
small plastic commercial units used in the test. The size and lifetime
of the membrane contactors added to the system should be considered to
ensure that they do not add as much mass as they save in IX resin mass.
Finding more support for using lightweight commercial membrane
contactors, or estimating the mass added to give them needed structural
strength, could improve the mass estimates for the PPS as well.

![](media/image21.wmf){width="3.198611111111111in"
height="2.4993055555555554in"}

[]{#__RefHeading___Toc87082188 .anchor}Figure 15: The resupply mass of
the PPS is primarily due to the consumable IX resin.

# A Sensitivity Analysis Case on the IWRS AES Results

The AES system clearly has significant impact on the ESM of the IWRS
design for water processing. A review of these results uncovered the
possibility that the system power consumption should be calculated as
significantly less than the values presented. The original goal for AES
performance in the IWRS test was to continuously process brine using a
coolant loop at a 18C-32C temperature. The coolant temperature was
changed to 7C, and the duty cycle of the unit may was reduced from
continuous operation to something less, though the cycle likely varied
with experimentation.

The previous results would be valid if the maximum power consumption is
the power scaling parameter of interest. This is especially true because
the maximum power is sustained for long periods of time, and does not
simply spike like actuating valves or other instantaneous power users.
However, the time averaged power value would be much lower. This
sensitivity analysis considers the results if the time averaged power
were used.

To look for impacts of this change, a second analysis of the IWRS was
done assuming that the power and cooling of the system is one quarter of
what was calculated in the results in previous sections. A comparison of
the modified IWRS values to the ISS and VPCAR systems is shown in Figure
16. The reduction does improve the ESM results for the IWRS, but not
change the qualitative results. The IWRS still consumes more resources
than the ISS WRS for the 30 and 90-day surface missions. The IWRS is
more economical on long duration missions, but still is not better than
the VPCAR system based on the current assumptions.

![](media/image22.wmf){width="4.938194444444444in"
height="3.876388888888889in"}

[]{#__RefHeading___Toc87082189 .anchor}Figure 16: Reducing the power and
cooling required by the AES by 75% does improve the results for the
IWRS. More improvement would still be needed from this iteration to be
competitive with the VPCAR technology, but the IWRS still consumes more
resources than the ISS WRS on the shorter 30 and 90 day surface
missions.

The AES is still the largest source of ESM in the IWRS when the power
calculations are reduced. For the 30 and 90-day surface missions, the
AES contributes 40% and 42% of the total ESM. For the longer cases,
shown in Figure 17 below, the AES contributes 34% of the IWRS ESM for
the 360-day transit case, and 39% of the IWRS ESM for the 500-day
surface case.

![](media/image23.wmf){width="4.288888888888889in"
height="2.502083333333333in"}![](media/image24.wmf){width="4.283333333333333in"
height="2.4993055555555554in"}

[]{#__RefHeading___Toc87082190 .anchor}Figure 17: An alternate AES case
was considered due to uncertainty in the AES source data and the
significance of the AES values to the IWRS results. The AES still is the
largest contributor of ESM to the IWRS, even when the power and cooling
are reduced by 75%.

With this change in the assumed power consumption, the replacement wick
mass becomes the most important ESM driver for the three shorter
duration missions. The power is still significant, especially if power
and cooling are considered together (as they are directly related). This
suggests that significant reductions in ESM for a long mission could
also be accomplished by extending wick life in the AES.

![](media/image25.wmf){width="4.4840277777777775in"
height="2.9194444444444443in"}

[]{#__RefHeading___Toc87082191 .anchor}Figure 18: Reducing the assumed
power consumption and cooling of the AES makes the consumable mass of
the system, totally attributed to the replacement of the wicks, more
important. Power is still significant, and power and cooling together
(as they are linked) still have greater impact than the mass of the
wicks.

# Conclusions and Recommendations

The performance of the JSC IWRS and the VPCAR system show that increased
water recovery and reduced use of consumables can provide significant
mass savings over long duration missions. Based on the values currently
available, the VPCAR system performs very well. This system has a lot of
potential and should be followed closely in development to ensure that
the assumptions made here are valid. The JSC IWRS system showed that the
biological technologies that perform a large portion of the water
processing are relatively low cost due to their low power consumption
and low resupply rate. There are opportunities to reduce the costs of
the BWP systems. However, systems downstream of the BWP, especially the
AES, contribute significantly to the total water recovery system design.
Reducing the ESM of the systems downstream of the BWP, especially the
AES, is imperative to make the system competitive with other ALS water
recovery technologies in development.

# List of Acronyms

Acronym Definition

AES Air Evaporation System

ALS Advanced Life Support

BVAD Baseline Values and Assumptions Document

BWP Biological Water Processor

EPB Early Planetary Base

ESM Equivalent System Mass

FCPA Fluids Control and Pump Assembly

ISS International Space Station

IX Ion Exchange

IWRS Integrated Water Recovery System

JSC Johnson Space Center

MCV Microbial Check Valve

MPB Mature Planetary Base

ORU Orbital Replacement Unit

PPS Post-Processing System

RO Reverse Osmosis

SIMA Systems Integration Modeling and Analysis

TRL Technology Readiness Level

UPA Urine Processor Assembly

VCD Vapor Compression Distillation

VPCAR Vapor Phase Catalytic Ammonia Removal

WFRD Wiped Film Rotating Disk

WPA Water Processor Assembly

# Primary References

## Papers and Reports: {#papers-and-reports .unnumbered}

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Campbell, Melissa, Barry W. Finger, Charles E. Verostko, Kristina R.
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Flynn, Michael, John Fisher, Mark Kliss, Badawi Tleimat, Maher Tleimat,
Gregory Quinn, James Fort, Tim Nalette, Gale Baker, Joseph Genovese.
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Parker, David S., Edward W. O'Connor, and Robert Bagdigian. "ISS Water
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Pisharody, Suresh, K. Wignarajah, and John Fisher. "Oxygen Penalty for
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Volk, Tyler, and John D. Rummel. "Mass Balances for a Biological Life
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No. 4 (1987): 141-148.

Walton, Timothy. "ECLSS Project Mass Properties Report." SLS-JA21-012
Rev A. National Aeronautics and Space Administration, George C. Marshall
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Wydeven, Theodore, and Morton A. Golub. "Generation Rates and Chemical
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TM 102799. Ames Research Center. August 1990.

Yeh, H. Y. "VPCAR and BWRS Trade Study." Lockheed Martin Nos. LMSEAT
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## Data References: {#data-references .unnumbered}

*ECLSS ORU List* (Excel spreadsheet)

Provided by Dave Williams, ISS ECLS System Manager, NASA JSC-EC

Source for ORU level mass, dimensions, and volume information

*Molly Anderson PL* (Excel spreadsheet)

Provided by Donna Grossman, Lead Designer for WPA, Hamilton Sundstrand

Source for detailed WPA component mass information, including actual
masses