22.033 Final Design Presentation

22.033 Final Design Presentation

Vasek DostalKnut Gezelius

Jack HorngJohn KoserJoe Palaia

Eugene ShwagerausAnd Pete Yarsky

With the Help of

Kalina GalabovaNilchiani Roshanak

Dr. Kadak

June 16th, 2003 22.033, Mission to Mars Design Course

Outline

•Mission plan

•Space power system

•Surface power system

•Conclusions

•Future Work


Mission Design Goals

•Reduce costs– Minimize initial launch masses.– Make use of re-usable, scalable and

evolvable systems.

• Increase science yield– Increase surface stay times.– Provide power rich environments.

•Leverage advantages of nuclear energy to achieve these goals.


Mission Plan Summary

• Nuclear Powered Telecommunication Satellite in Mars orbit– Demo space reactor & Electric Propulsion

system

• Sample Return– Demo surface reactor & ISRU plant

• Manned Exploration– 2 distinct transfer types

•Cargo Missions

•Crew Transfer Missions


Cargo Missions

• Large cargo mass to transfer.– Efficient transfer desirable to reduce

propellant mass.– Transit time not critical (1+ year ok).– Reusable Mars Transfer System (MTS)

• Ideal application for Electric Propulsion technology.– High Isp (high efficiency)

– Low thrust (long transit is tolerable)


Cargo Missions


Electric Propulsion Options

Cargo missionsArray of advanced Ion / Hall thrusters

Power 10 – 80 kW

Isp3000 – 10000 sec

Thrust 1 – 3 N


Crew Transfer Missions

•Fast transit required– Reduces crew exposure to zero-gravity

& radiation.– Increases surface stay time.– Requires high thrust to achieve

•Propulsion Options– VASIMR (only viable EP technology)– NTR (Nuclear Thermal Rocket)– Chemical Rocket


Crew Transfer Missions

- 3 Reactor Systems- 3 VASIMR Engines- Hydrogen Fuel- Transfer Habitat


Electric Propulsion (Manned Mission)

Variable Specific Impulse Magnetoplasma Rocket – VASIMR

10 MW of power


SpacePower System


Nuclear Space Power System

• Ultra-compact high power density reactor – Fast Spectrum– Pu Fuel

• Molten salt or Li coolant– High temperature, low pressure coolant– Good heat transport medium

• Thermo Photo Voltaic (TPV) cells– High efficiency power conversion (up to

40%)– No moving parts


Space Power System Goals

• Design for multiple round trips– three 180 day round trips at full power

• Low mass <3 kg/kWe

• Scalable – 200 kWe - Precursor

– 4000 kWe - Manned

• Simple and reliable– No moving parts


Reusable System Strategy

• Cargo missions (Mars Transfer System)

– 1 new tank of propellant per transfer

– 1 new reactor core after 3 transfers

• Crew transfer (VASIMR System)

– 1 new tank of propellant per transfer

– 3 new reactor cores after 3 transfers


Pu as a Fuel

• Most reactive fuel in fast spectrum– Small core size and mass

• Critical mass is independent of isotopic composition– Proliferation resistant Reactor Grade Pu can be used

• Compact core – High leakage, allows ex-core control

– Small shield

• Widely available– Reduced cost (238Pu for Cassini mission was

imported)


Molten Salt Fast Reactor: Reference Core DesignReference Core Design

Power 11 MWth

Dimensions 202020cm

Total mass 185 kg - (50 kg Pu)

Reflector thickness 6 cm (Zr3Si2)

Coolant - molten salt (NaF-ZrF4)

- High Boiling Temp

Fuel - Reactor Grade Pu carbide,

honeycomb plates

keff BOL = 1.1

Core lifetime 540 FPD

Honeycomb Fuel

MSFR Core Layout


MSFR Technology Challenges

• Fuel performance (El-Genk et al. 1984)

– Coated particle dispersed alternative fuel form

• Fuel – Cladding – Coolant compatibility– Li as alternative to corrosive Molten Salt

• High temperature structural materials

Fuel Form Fissile Density

Thermal Conductivity

Swelling Fission Gas Release

Clad Compatibility

UC + + - - - - W/Re

UN + + + + W/Re

UO2 - - ++ - Mo/Re, W/Re


MSFR Technology Challenges (cont.)

• Pu fuel environmental concerns

• Water submersion accident– Launch in robust capsule

Cassini MSFR

Total Pu mass, kg 28.8 50

Activity, Ci 4.3E+05 4.5E+05

Radioactive Ingestion Hazard Index, Sv 3.1E+09 3.3E+08

Chemical Ingestion Hazard Index, m3 H2O 3.6E+07 6.3E+07


Space Power Conversion CycleReference Concept

1. Coolant transfers the heat from the core to the internal radiator

2. All power is radiated towards TPV collector

3. TEM self powered pumps circulate the molten salt coolant

4. TPV collectors generate DC from thermal radiation

5. Residual heat is radiated into outer space

reactor

shieldpump

TPV array

Internal Radiator

External radiator


TPV Technology Challenges• Relatively low operating temperature needed for high efficiency

0

200

400

600

800

1000

1200

1400

500 600 700 800 900 1000 1100 1200

TPV Operating temperature, K

Rad

iato

r Su

rfac

e Are

a, m

2

Rocket geometry temperature limit

TPV operating temperature limit

Titan rocket geometry radiator surface limit

Magnum rocket geometry radiator surface limit


TPV Technology Challenges: Potential Solutions

• Deployable radiator• Liquid Droplet Radiator


MSFR Scalability

Precursor mission

Manned mission

Electric power (kWth) 200 4000

Thermal power (kWe) 1928 11000

TPV efficiency (%) 14 40

Core mass flow rate (kg/s) 37.9 249.8

Core inlet temperature (K) 1250 1550

Core outlet temperature (K) 1300 1600

Pressure drop (kPa) 3.04 122.73

Pumping power (kW) 0.04 11.89

Thermal losses (kWth) 500 1000

Power density (kWth/l) 261 1490

Molten salt velocity (m/s) 0.88 6.39

Heat transfer area (m2) 13.43 13.43


Shielding MSFR

Radiation Detector

mR/hr

WLiH

W

Ĵo = 8.752 x 1013 n/cm2 s

Neutron Attenuation: LiHGamma Attenuation: W

Radiator


Shield Design Issues

•Structural Design– Radiation induced LiH

expansion

•Thermal Design– 6Li (n,) reaction

– 7Li enrichment

– Proximity to the reactor core

– Operating in temperature range 600-650 K


Surface Power System


Surface Power System Goals

•Sufficient power for all surface applications (i.e. ISRU, habitat etc.) Satisfy NASA DRM. ~200 kWe

•Develop long lasting Mars surface infrastructure – Lifetime of 25 EFPY


Surface Nuclear Power System

• Cooled by Martian atmosphere (CO2)– Insensitive to leaks or ingress

• Shielded by Martian soil and rocks– Low mass

• Hexagonal block type core – Slow thermal transient (large thermal inertia)

• Epithermal spectrum– Slow reactivity transient– Low reactivity swing


CECR Core Design

• Power 1 MWth

• Dimensions L=160 cm, D=40 cm– 37 hexagonal blocks

• Total mass 3800 kg

• Reflector thickness 30 cm (BeO)

• Coolant Martian atmosphere (CO2)

• Fuel 20% enriched UO2 dispersed in BeO

• keff BOL = 1.14

• Core lifetime >25 EFPY

CECR Core Layout

Fuel PinsControl Drums


CECR Thermal Hydraulics (fix it)

• System pressure 480 kPa

• Core inlet temperature 486 C• Core outlet temperature 600 C• Core mass flow rate 7.47

kg/s

• Channel diameter 30 mm

• Block flat-to-flat 63 mm

• Film temperature difference 2.5 C• Pressure drop 25 kPa


CECR

• Two Martian atmosphere Brayton cycle options investigated:– Open cycle - intake from and discharge to the

atmosphere – Closed cycle - intake from the atmosphere

through a Martian atmosphere storage tank

• Pressurized CO2 from atmosphere cools the core– Open cycle - ~ 100 kPa– Closed cycle - ~500 kPA

Both options are capable of achieving ~20% efficiency

CO2 Cooled Epithermal Conversion Reactor


CECRCO2 Cooled Epithermal Conversion Reactor

GENERATOR

RECUPERATORPRECOOLER

TURBINECOMPRESSOR

REACTOR

1 2

3

4

5

6

GENERATOR

TURBINECOMPRESSOR

REACTOR

1

2

3

4

Intake through filter Exhaust

OPEN CYCLE

CLOSED CYCLE

CO2 storage

tank


• Acceptable efficiency (20% achievable)– Open cycle

•Simple•Requires pressure ratio of 18

– Closed cycle•heat rejection is the weakest point of the

design•massive pre-cooler or a fan is required

– precooler increases the overall mass of the system

– fan reduces the efficiency to 20%– The design requires further optimization

CECRPower Conversion Cycle


Surface Reactor Shield

Martian soilCore

Place for shutters

Thickness (cm) 170 180 190 200 210

Corresponding dose rate, shield surface (mrem/hr)

75.5 31.7 13.3

5.6 2.4

Dose rate (GCR), Martian surface (mrem/hr) > 1.1


Conclusions

•Mission plan

– Technology demonstration

•Reliability assurance before

people are committed

– Long term, reusability strategy

•Reduces recurring costs to

future missions


Conclusions

MSFR Space Reactor Features:

– Very high temperature, low pressure

– Thermo Photo Voltaic energy

conversion

•Potential for High efficiency

– Ultra compact core

•Fast spectrum, RG Pu fueled

•Potentially reduced shield mass


Conclusions

• CECR Surface Reactor Innovations– Epithermal spectrum

•Slow kinetics (maintains large Λ and βeff)

•Enhanced conversion•Compromise between advantages of fast

and thermal systems

– CO2 coolant

•Local resource•Resistant to leaks or ingress

– Martian soil shield


Future Work

• Further Development of conceptual designs

• Molten Salt Fast Reactor Space System– Fuel performance and materials compatibility issues

with different coolants – TPV & Radiator Technology– Criticality with water submersion

• CO2 Cooled Epithermal Converter– Further Open Cycle & Closed Cycle Investigation– Development of low pressure and high pressure ratio

turbomachinery– Surface Reactor Heat Rejection

• Reactor startup & remote control strategy• Mission & Systems Integration


This surface reactor concept has been adapted for use with the Mars

Homestead Project.

For More Information, see:

www.MarsHome.org

Documents

22.033 Final Design Presentation