Human Travel into Deep Space Using Currently, or Imminently Available Technology A Design Study of long-duration interplanetary spacecraft

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Prof. David Hyland

Mech Aero – 2014

Hilton Philadelphia Airport Hotel

September 8 -10, 2014

Project Overview

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Design project for aerospace engineering students in final year of undergraduate program

Subgroups developed initial goals, which were later integrated into a final spacecraft

Presented to board of industry and academic reviewers in Dec. 2012

Mission Statement

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“To expand the domain of humanity beyond the earth for the betterment, preservation, and advancement of all humankind by

creating a self-sustaining, mobile habitat that ensures the physical and psychological well-being of its inhabitants.”

>24 Month Trip Time12 Crew MembersCapable of Interplanetary Space Travel

What’s the Purpose? Scientific

Advance the state of the art in diverse technological areas Innovations for space usually have important terrestrial

applications Economic

Mining of asteroids could yield many valuable materials High demand for space tourism, research opportunities

Exploratory Spark a new age of enthusiasm for the sciences Inspire next generation of scientists and explorers

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Ultimate goal Attain economic viability and sustainability of the interplanetary

habitat through a range of revenue-generating activities, primarily mining of asteroids

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Presentation Outline

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Design DriversDetailed DesignCompetitive Advantages

Design DriversDetailed DesignCompetitive AdvantagesPresentation Outline

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Design Goals Elements of a viable system

Livability – Crew must be able to function, survive Practicality – Magic solution will not appear, must deal with

proven feasibility of technology Modularity – Assembly must be simple, repairs must be efficient,

expansion must be an option

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Challenges of a Interplanetary Space Physiological Physiological

Weightlessness Livability Radiation

Cost barriers to entry

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Design Driver: Physiological Factors in Prolonged Spaceflight

No human being has ever traveled into interplanetary space In 5 decades of manned spaceflight, our understanding of

physiological change during long duration missions remains limited

Physiological impacts are significant and variedDuring the course of a mission: 0-g effects (bone loss, muscle

loss, immune system impairment, etc.), radiation exposure and immunological depression

Return to Earth: cardiovascular de-conditioning and orthostatic intolerance

Both in-flight and post-flight physiological issues must be countered

Design Driver: Countering 0-g Effects

There is no completely satisfactory approach to countering 0-g effects aside from sustained artificial gravity.

We do not know how much “g” is required to maintain human health indefinitely (besides zero g = bad, and one g = good)

We will not know the answer to this for a long time, since long term experiments are required.

Therefore, in this design study, we require: 1 g artificial gravity.Acceptable levels of Coriolis effectsExposure to 1g almost all the time

1g

0.035 g

Limit of low

traction

6 m/s rim speed

Apparent gravity

depends on direction of

motion

4 rp

mO

nse

t o

f m

otio

n

sick

ne

ss

Comfort zone

Artificial gravity becomes more “normal” with increasing radius

Countermeasures – Artificial Gravity

To avoid motion sickness, we must rotate below 4 rpm (while keeping the rotation radius as small as possible)

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Physiological Factors Size and Rotation Rate

1 g artificial gravity and acceptable levels of Coriolois forces motivate: Rotation rate = 3.5 rpm Rotation radius = 70m

(Thus max dimension can’t be less than 140m)Exposure to 1g almost all the time means entire s/c must rotate (a separate wheel with an attached zero-g component is not practical)

Design Driver: Interplanetary Space Environment

High levels of radiation present in interplanetary spaceMaterial must limit radiation exposure to levels on par

with ISS astronautsMicrometeorite protection must also be includedLivable temperature must be maintained

Design Driver: Mass

Support needed to keep structure togetherLaunch costs are around $2,000 per pound of materialStandard trusses would add unnecessary mass;

alternative solution needed

The crew has to breathe!

Atmospheric compositionpO2

22.7 +/- 9 kPa(170 +/- 10 mm Hg)

p(inert gas; most likely N2) 26.7 kPa

pCO2 < 0.4 kPa

pH2O1.00 +/- 0.33 kPa

(7.5 +/- 2.5 mm Hg)

Total pressure = ½ atm

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What Shape?

½ Atm pressurization & centrifugal loading Solids of revolution are the most efficient pressure vessels

Sphere

Large ratio of pressurized

volume to useful floor space

(projected area)

Long cylinder

Axis of minimum inertia = rotation axis

Energy dissipation results in disruptive nutation

Active attitude control of this = one more thing to go wrong

Torus

Minimum ratio of pressurized volume to

useful floor space

Rotation axis = axis of maximum inertia

Attitude is passively stable

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Space useSurface arearequired,m2/person

No. oflevels

Projectedarea, m2

Estimatedheight, m

Volume,m3/person

Residential 49 4 12 3 147

Offices 1 3 0.33 4 4.0

Assembly rooms & radiation storm shelter 1.5 1 1.5 10 15

Recreation andentertainment 1 1 1 3 3

Storage 5 4 1 3.2 16

Mech. subsystemCommunication distr.switching equipment

0.5 1 0.5 4 0.2

Waste and water treatmentand recycling

4 1 4 4 16

Electrical supply anddistribution 0.1 1 0.1 4 0.4

Miscellaneous 2.9 3 1 3.8 11.2

Subtotals 65.0 - 21.43 - 212.8

Agricultural space (a) Plant growing areas 44 3 14.7 15 660

(b) Food processingcollection, storage, etc. 4 3 1.3 15 60

(c) Agricultural drying area 8 3 2.7 15 120

Totals 121.0 - 40.13 - 1052.8Note: This is Table 3.2 of cited reference 2, but with several categories of space removed owing to the limitations of a 12-person vessel. The spaces removed are: Shops, schools and hospitals, public open space (500 m3) service industry space, transportation and animal areas.

How Much Space Do People and Plants Need?

Total Projected area per person

= 40 m2

Total Volume per person

= 1050 m3

Is a Complete Torus Too Roomy?

x, xb

z, zb

y, yb

R 2 r

With R=70m, r=5m and three “floors”:

Projected area ~ 10X2RX3 ~ 12,600 m2

Enough for 315 people! But we only need to sustain 12 …..

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Solution: Use only what you need!

• Modular pod configuration• Attach modules as needed to support volume requirements

• Addressing new challenges• Vibration damping using tensioned cables and compression

columns• Natural frequencies causing motion sickness are avoided

• Capitalizing new advantages• Engines may be placed along outer radius of structure

without interfering with livable area

Mission Requirements Minimize delta-v required for transportation 2-3 year mission duration

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Solution Constant thrust departure from LEO to Lagrange points “Grand Tour” of interplanetary space in Earth – Sun system

Drift along energy boundary of Earth-Sun system with little to no delta-v

Orbit cycle used by many asteroids, could allow for rendezvous and mining

Initial Deployment: Spiral out to E-M L1

3385 10 km

Start in 300 km circular orbit about Earth

Thrust always aligned with the velocity vector

Full thrust up until 11 days and coasting to L1 thereafter

Spiral out to a coasting trajectory to the E-M L1 “throat”.

Meld into the Lyapunov orbit of L1 Station and refuel

Propellant mass: 21 MTTrip duration: 5.6 months

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From E-M L1 to S-E L2: Start of the First Grand Tour

Moon

L1 Lyapunov Orbit

Orbit of the Moon

Earth-Moon Frame Sun-Earth Frame

L2

L2

L1

Sun

E-L1 to S-L2: V=12m/s, 50 days

122,720 km

After refueling, leave L1 on the outward invariant manifold.

Swing by the Moon and exit the E-M L2 throat in time to meld with a heteroclinic orbit leading to the Sun-Earth L2

Take one turn around the Lyapunov orbit and enter the external domain of the Sun-Earth system

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Asteroid Mining Tours: Exterior Realm

L1

1. Drop off cargo at L1 Station. Leave L1 Lyapunov orbit. Follow heteroclinic orbit to L2 (pink line, left to right) (drop off cargo at Earth-Moon system)

2. Meld into L2 Lyapunov orbit, follow for ¾ of a period, then follow the unstabile manifold (green line, heading down)

Sun-Earth Frame

L2

3.0 million km

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1

Through S-E L2 to the Grand Tour of the Exterior Realm

Sun

3-2 resonance

Apophis

3. Follow the homoclinic, exterior domain orbit (green path issuing from L2 and going clockwise)

4. Mine Amors and Apollos on the way (3 years)

Then: see next slide

1 AU

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1

Heteroclinic Transfer Between Exterior and Interior Realms

L1

5. Follow homoclinic exterior domain orbit to L2 on the stable manifold (green line, pointing down, left). Refurbish and repair at L2 Station

6. Meld into L2 Lyapunov orbit, follow for ½ of a period, then follow the heteroclinic orbit to L1 (pink line, right to left).

7. Deliver cargo to Earth-Moon system. Meld into L1 Lyapunov orbit, Exchange crew and refuel at L1 Station.

8. Follow Lyapunov orbit for one period, then follow the homoclinic interior domain orbit (blue line heading to the left).

L2

3.0 million km

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1

Through S-E L1 to the Grand Tour of the Interior Realm

Sun

3-2 resonance

Apophis

9. Follow the homoclinic, interior domain orbit (red path issuing from L1 and going counter clockwise)

10. Mine Atens and Apollos on the way (two years)

11. Then follow the stable manifold to L1 (blue line in previous slide, heading to the right).

12. Refuel and exchange crew at L1 station.

Go to step 1 and repeat.

Forbidden zone

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Presentation Outline

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Design DriversDetailed DesignCompetitive Advantages

SystemTeams

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Budget & Scheduling

ManagementPM: Ryan Haughey

Assistant PM: Blaise Cole

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

Goal:

Synergize design concepts to meet functional requirements

Challenges: Physiological: radiation, bone loss, air Psychological: confinement, productivity System stability

System Overview – ArchitectureMichael Pierce, Paola Alicea, Terry Huang, Luis Carrilo,

Christopher Roach, Mario Botros

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Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

Moment of Inertia Overview

x,y,z axes = Principal axes of inertia

Ixx = 203,300 MT-m2

Iyy = 463,600 MT-m2

Izz = 641,300 MT-m2

Total Mass = 350MT

xy

z

15MT

23MT

18MT

46MT

(total)4MT

Izz is largest moment of inertia; rigid body nutation of the spin axis due to energy dissipation coupling is suppressed

Architecture Overview

Inflatable Living Pod Modeled on NASA Transhab study (Inflatable pod) Nearly 2 dozen layers in 1-ft thick skin provide thermal, ballistic, and radiation

protection Radiation Protection: conservatively 30 rem/yr (ISS is 50 rem/yr) Ballistic Protection: Micrometeorite and Orbital Debris Shield Each pod provides living space for four crew members

8.4 m

13 m

32.5 m

10 m

6 m

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Auxiliary pods Identical to living pods Low-gravity environment: sufficient to allow for proper survival by plants One pod optimized for food growth, other for oxygen generation

Engine & Power Pods Provides housing for power plant and engine Power plant selected as nuclear reactor (further discussion later) Shielding for nuclear reactor assists structure in deep space

radiation and micrometeorite protection

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Water Ballast Stores system water Displace water along structure length to adjust

moments of inertia Thermal management of water could be accomplished

using heat pipes from power source High levels of redundancy needed to protect against

micrometeorite impacts on water column

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Docking Module Standardized module allows for docking of rendezvous craft ISS PIRS module may serve as good model

Combination docking port and airlock

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Image credit: NASA

Floor Space Summaries

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Living Pod Summary

Floor Area per Pod (m2) 79.48

Number of Pods 4

Number of Crew 12

Floor Area per Person (m2) 26.49

Stanford Study per Person Requirement2 (m2)

19.83

Agriculture Pod Summary

Floor Area per Pod (m2) 142.98

Number of Pods 2

Number of Crew 12

Floor Area per Person (m2) 23.83

Stanford Study per Person Requirement2 (m2)

18.70

Goal:

Synergize design concepts to meet functional requirements

Findings: Modular, inflatable habitation pods Water ballast Locate power, engine away from

the axis of rotation

System Summary – Architecture

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Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

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Goal:

Create an environment conducive to healthy human functions with minimal re-supply for duration of mission

Challenges:Crew nutrition & healthWater recycling & distributionWaste ManagementOxygen regeneration

Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Overview – Life SupportMegan Heard, Sarah Atkinson, Mary Williamnson, Jacob Hollister, Jorge Santana, Olga Rodionova, Erin Mastenbrook

Crew Nutrition Modeled on diet of residents of Greek island of Ikaria, noted for

exceptional health and longevity For missions past 21 months, more practical to self-sustain food Some portions of diet require bringing food along (meats, oils) Proposed solutions:

Aeroponically grow food in low-gravity agriculture pods Maintain cold storage for stowed perishable food

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Image credit: Tower Garden

Nutrition Logistics

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Aeroponics Farming: Tower Gardens

Height (m) 1.83

Base (m2) 0.58

Number of Towers 12

Plants per Tower 28

Max Plant Output 336

Aeroponics Farming: Shelf

Total Area (m2) 6.69

Tower gardens used to grow range of fruits, vegetables, and herbs.Shelf used to grow potatoes

Stored Farming (12 people, 2 years)

Total Stored Mass (kg) 8165

Total Stored Volume (m3) 13

Stored food consists of all which can not be grown in tower gardens. Includes: meats, grains, sugars, salts, & milk

Combination of produce and stored food allow for full sustainment of crew for around 3 years

Water Treatment Must handle waste-water and gray-water Prevent disease development Effective water recycling becomes advantageous after 0.5 months Proposed solution

Utilize ECLSS system currently in place on ISS (~95% efficient)

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Water Summary Mass (kg) Volume (m3) Power (kW)

Water for Humans: 5100 5.1 N/A Water for Algae: 7920 7.92 N/A Water for Agriculture: 1514 1.514 N/AECLSS Water Recycling System (2 units):

1782 6.51 4.42

Total: 14801.8

718.81 4.42

Waste Management Isolation of outpost requires full effective recycling Human waste can serve as effective crop fertilizers, reducing need

for artificial fertilization (added mass) Proposed solutions

Closed-loop system with high-efficiency composters & ECLSS water filtration system

Tie-in to agriculture system for fertilization

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Waste Summary

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Solid Waste Mitigation Summary

Solid Waste Production (kg/person/day)3 0.2

Number of Crew 12

Daily Waste Production (kg/day) 2.4

Waste Processor Performance (kg/unit/day)4 0.43

Number of Processors 10

Waste Capacity (kg/day) 4.3

Excess Waste Handling (kg/day) 1.9

Liquid Waste Migitation Summary

Liquid Waste Production (l/person/day)5 2

Gray Water Production (l/person/day)6 19

Number of Crew 12

Daily Waste Production (l/day) 252

Water Processor Performance (l/unit/day)7 140

Number of Processors 2

Waste Capacity (l/day) 280

Excess Waste Handling (l/day) 28

Oxygen Regeneration Standard CO2 scrubbing and Oxygen Generation Systems consume

water in production of oxygen After 21 months, a closed-loop system becomes more efficient Proposed solution

Convert CO2 into O2 using green algae (Spirulina) tanks

Mechanically filter other impurities Back-up system (in case of disease or catastrophic failure) would

be standard OGS/C02 scrubber similar to ISS

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Image Credit: California State University – Long Beach

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Goal:

Create an environment conducive to healthy human functions with minimal re-supply for duration of mission

Findings:High-nutrition, efficient dietRecycle, grow as much as possibleMultipurpose systems

Waste used as fertilizer

Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Summary – Life Support

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Goal:

Develop a stable structure capable of withstanding loading profile

Challenges:Rotational Loading & Rigidity

Truss design

Vibration Mitigation Cable design and placement

Thermal Environment Management

Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Overview – Stress & ThermalAlex Herring, Brendon Baker, Scott Motl, Keegan Colbert, James Wallace, Travis Ravenscroft

Structural Layout: Tensioned Cable

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Cables connect pods in rotation plane to central column Transfers centrifugal loads from rotation plane Significantly reduces need for trusses, total structure mass Manages vibration propagation Total compressive force: 782 kN

Vibration mitigation drives cable size

Why such a complicated design? Another structural configuration: “Bola”

Habitation areas connected by cable in rotation Suited to small structures, with few crew members Scale, mass of current structure would cause serious vibration

problems Tensioned cable with column gives structural rigidity in all 6 rigid body

DOFs Additional benefits

Thrust located off the spin axis More maneuverable, allows for easier docking

Much more expandable Pods can be more easily located at intermediate points in structure

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Structural Rigidity Trusses needed to maintain craft’s shape, operate in

case of no centrifugal loading (much lower loads) Dimensions of structure require advanced materials

to minimize weight Proposed solutions:

Composite (carbon-fibre) truss structure Outer connecting tubes enclose truss, prevents

outgassing & radiation degradation of composite

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Vibration Mitigation Torus has been segmented, resulting in vibration instability Cable dimension driven by vibration mitigation, not centrifugal

loading Failing to address vibrations could result in structure shaking itself

apart Augment tension cables to mitigate vibration in other planes Avoid natural frequencies which induce motion sickness (0.05 – 0.8

Hz), 8 Hz (need more detailed model to address)

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Cable Sizing Summary

X-translation mode minimum size (cm) 2

Y-translation mode minimum size (cm) 0.8

X-rotation mode minimum size (cm) 0.8

Thermal Management Nuclear reactor will produce large amounts of waste heat Near constant exposure to solar radiation once in deep space Simple white exterior to living pods renders a temperature on order

of -60oF Proposed solution

Black/white surface coating combination (43% white, 57% black) passively raises temperature to comfortable levels

Radiator of around 200 m2 sized using Idaho National Labs CERMET study (design basis for nuclear reactor)10

Heat pipes convey additional heat throughout structure to utilize as needed

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Goal:

Develop a stable structure capable of withstanding loading profile

Findings: Tensioned-cable structure reduces

truss mass, vibrationPassive cooling can accomplish

thermal control, with minor support

Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Summary – Stress & Thermal

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Goal:

Provide sufficient thrust to transport space craft into interplanetary travel

Challenges:Mission durationLong-duration thrust developmentAttitude control

Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Overview – PropulsionKyle Monsma, Benjamin Morales, Carl Runco, Paul Schattenberg, Mark Baker, Steven Swearingen

Engine Selection Continuous thrust system is most practical Electrodeless Lorentz Force (ELF) thrusters are emerging as

(relatively) high thrust, high Isp engine at a low weight & size

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Engine Comparison ELF8 VASIMR9

Engine Mass (MT) 3.8 7.6

Thrust (N) 66.5 47.5

Fuel Mass (% total) 8.74 7.84

Burn Time (days) 279 389

ELF Operation & Fuel

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Image credit: University of Washington, Dept. of Aerospace Engineering

Xeon provides maximum efficiency

Xeon has greater compatibility with existing spacecraft technologies

Spin-up & Attitude Control Need to attain 3.5 RPM for 1g conditions in given craft Engines are mounted on edge of rotation plane, allowing gimballing

to combine spin and forward propulsion Proposed solution:

During transit to Lagrange point, angle both engines to produce rotation

CMGs could also be used to provide heading maintenance

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Spin-Up Detail

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Properties Summary

Total Mass (MT) 350

Principle Moment of Inertia (kg m2)

6.63 E8

Required Angular Velocity (rpm) 3.5

Moment Arm (m) 70

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Goal:

Provide sufficient thrust to transport space craft into interplanetary travel

Findings:Low thrust, high-Isp engine (ELF)

Xeon fuelDeflect engines to obtain spin

Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Summary – Propulsion

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Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Overview – PowerCollin Marshall, Andrew Tucker, Carl Mullins, Jack Reagan, Colby Smith, Andrew Nguyen

Goal:

Provide reliable electrical power to meet spacecraft systems requirements

Challenges:High power requirements by enginesMass, size constraintsRadiation managementSystem redundancy

Powerplant Estimated power requirements around 2

MWe Solar array would be prohibitively large and

expensive INL CERMET study demonstrated conceptual

feasibility of space nuclear reactors of this rating10

Emergency power must be available for sustaining limited life support functions in event of outage

Power distributed using similar system to ISS

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Image credit (modified): Boeing Defense, Space &

Security

Reactor Core

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2 separate reactors placed on opposite arms of ship Each reactor supports minimum power requirements Location near engine reduces transmission cable mass

Passively stable with active control rods Allows for variable power output Conserves fuel and reduces overall mass

Shielding & Power Generation Be-W-LiH Layered Shielding covers broad spectrum protection Required thickness: 0.28m; mass of 1,450 kg per reactor

Shadow shielding – Only shield craft needing protection Power generated with standard Brayton cycle

High efficiency due to near 0K heat sink Helium is working fluid No regeneration

Each reactor-turbine combination produces

1.5 MWe Heat pipes circulate waste heat around structure

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Note: Cut-away view, shield is

hemispherical

To center of craft

Power Conversion

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Power Conversion Specifications10

Turbine Inlet Temperature (K) 1500

Pressure Ratio 15

Specific Mass (kg/kWe) 7.67

Total Mass (kg) 23,000

Efficiency 52%

Total thermal output (kWt) 5770

Total electrical output (kWe) 3000

Total waste heat (kWt) 2770

Emergency Power Solar panels capable of providing minimum life-support functionality

paired with each pod Back-up OGS system & heating will require 20 kW

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Solar Panel Array Specifications

Panel Efficiency11 0.29

Panel Area per Pod (m2) 16.7

Panel Mass per Pod (kg) 176

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Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Summary – Power

Goal:

Provide reliable electrical power to meet spacecraft systems requirements

Findings:Dynamic cycle power generationNuclear reaction heat productionSolar panels provide back up power

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Budget & Scheduling

Management

System Architecture

Life Support

Propulsion

Power

Stress & Thermal

System Overview – Budget & SchedulingBlaise Cole, Kevin Davenport, Lisa Warren

Goal:

Track the mass, power, and monetary requirements for the system, and prepare a feasible deployment plan

Challenges:Developing funding structureCreating deployment schedule

Systems Overview

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System Mass (MT)

Architecture 235.4

Structure 7.0

Propulsion 40.8

Power 28.3

Life Support 34.9

Total 346.4

System Power (MW)

Architecture 0.35

Propulsion 1.9

Life Support 0.3

Power Required 2.56

Power Produced 3.02

Funding Program would have extremely high costs for full integration Significant levels of government support would be unlikely,

undesirable due to loss of control Very risky nature of project would make significant levels of debt

unattainable, equity can lose direction Proposed solution:

Use bootstrapping plan: start developing core components of craft with terrestrial applications; provides revenue stream while supporting further R&D of technology

Develop LEO research, tourism platform for further partnerships & revenue streams

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Deployment Significant number of launches would be required to deploy full craft Assembling at Lagrange point would be extremely difficult and

impractical Proposed solution:

Assemble the structure in LEO, use as platform for research and tourism

After built, transfer to Lagrange point (while unmanned) Crew rendezvous with craft at Lagrange point, mission starts at

this point

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Design DriversDetailed DesignSummaryPresentation Outline

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Design Goals Livability

Artificial gravity, radiation shielding, diet ensure long-term health Internal architecture provides psychological comfort

Practicality All technology grounded in present or near-future developments

Modularity Assembly, repairs simple due to common pod Can incrementally grow station by adding modular pods Potentially attain full torus

Potential Applications Asteroid mining (would need further development of additional

spacecraft for use in mining)

Space tourism (deep space or near-earth)

Debris removal and recycling

Scientific research platform

Permanent space station at Lagrange point

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Acknowledgements Dr. David Hyland Department of Aerospace Engineering, Dwight Look College of

Engineering, Texas A&M University The Fall 2012 AERO 426 team leaders and team members

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Sources1 Hyland, David, “Class Lectures,” AERO 426, Texas A&M University, Fall 2012.

2 R.D. Johnson, C Holbrow, editors, Space Settlements: A Design Study, NASA, SP-413, Scientific and Technical.

3 “Feces,” Encyclopedia Brittanica Online Edition, 2013.

4 Oshima, T., Moriya, T., Kanazawa, S., Yamashita, M., “Proposal of Hyperthermophilic Aerobic Composting Bacteria and Their Enzymes in Space Agriculture,” Biological Sciences in Space, Vol. 21 No.4, 2007.

5 “Urinalysis,” Mercer University School of Medicine. 1994-2012 [http://library.med.utah.edu/WebPath/webpath.html#MENU].

6 Johnson, David, “Graywater Treatment and Graywater Soil Absorption System Designs for Camps and Other Facilities,” Alaska Department of Environmental Conservation, May 2005.

7 Beasley, Dolores, “NASA Advances Water Recycling for Space Travel and Earth Use,” NASA News, Nov. 2004

8 Slough, J., Kirtley, D., Weber, T., “Pulsed Plasmoid Propulsion: The ELF Thruster,” 31st International Electric Propulsion Conference. Sept. 2009.

9 Ad Astra Rocket Company, Company Website, 2009-2013, [http://www.adastrarocket.com/aarc/VX200].

10 Webb, J. A., Gross, B. J., “A Conceptual Multi-Megawatt System Based on a Tungsten CERMET Reactor,” Nuclear and Emerging Technologies for Space 2011, Idaho National Laboratory, Feb. 2011.

11 Gaddy, Edward M., "Cost performance of multi-junction, gallium arsenide, and silicon solar cells on spacecraft," Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE, IEEE, 1996.

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Questions?

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Thank you very much for your time!