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Providing Energy for Space Systems

Steven E. Johnson United Space Alliance, LLC ISS Flight ControllerNASA Johnson Space Center

NASA/NTSA SymposiumLiving and Working in Space: Energy

4 November 2006

Photo taken January 26, 2003 by the crew of Space Shuttle Columbia

Copyright © 2006 by United Space Alliance, LLC.  These materials are sponsored by the National Aeronautics and Space Administration under Contract NAS9-20000 and Contract NNJ06VA01C.  The U.S. Government retains a paid-up, nonexclusive, irrevocable worldwide license in such materials to reproduce, prepare, derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the U.S. Government.  All other rights are reserved by the copyright owner.

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Overview

• Objectives• Energy• Energy Systems• Nuclear Power • Energy Storage• Solar Power• ISS• Summary• Theoretical Applications• Backup Material

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Learning Objectives

• After reviewing the presentation, participants will: – List the three types of spacecraft power systems. – State advantages and disadvantages of spacecraft power

system types. – Describe the ISS Electrical Power System. – Identify the type of power system theoretical spacecraft should

employ.

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SpacecraftPowerSystemOptions

Solar NuclearEnergyStorage

Photo-Voltaic*

SolarDynamic

Fission Radioisotope Chemical* Mechanical

Energy Systems 101Powering Spacecraft

*Current manned space systems use Photovoltaic and Chemical power

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Nuclear PowerApplications

Voyager

Galileo Ulysses Cassini

Viking

Since 1961, 40 RTGs have been used on 22 US space systems.

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Nuclear PowerEvaluation

• Nuclear Power Advantages• Radioisotope Thermoelectric Generators (RTG) use the natural decay of

plutonium to produce heat, which is directly transformed into electricity through a thermocouple device.

– Provides a very long-term energy source• Supports mission duration of tens of years

– Allows independent space system operation• Not dependent on illumination source

– Solar pointing system not required• Most space craft require control systems for attitude control

regardless of power system

– Currently the only viable option for non-solar missions longer than ~2 weeks and missions traveling beyond Mars

→ Best option for deep-space unmanned missions

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Nuclear PowerEvaluation

• Nuclear Power Disadvantages– Low power capability

• Highest power application: Cassini, < 1 kW• Not practical for manned space systems

– Expensive– Requires custom-built system for each application

→ Unfeasible option for manned missions

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Energy StorageApplications

Cassini ProbeCassini Probe

ApolloLunar Rover

Space ShuttleSpace Shuttle

ApolloCommand ServiceModule

Gemini

EMU

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Energy StorageEvaluation

• Energy Storage Advantages• Energy Storage devices include batteries, which stores chemical energy

and makes it available in an electrical form; and fuel cells, which produce electricity from an external supply of fuel (usually hydrogen) and oxygen.

– Allows independent space system operation• Not dependent on illumination source

– Solar pointing system not required• Most space craft require control systems for attitude control

regardless of power system

→ Best option for limited-duration manned missions

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Energy StorageEvaluation

• Energy Storage Disadvantages– Limited mission duration

• Fuel or battery life are limited-quantity consumables• Limits mission durations to ~2 weeks

– Requires custom-built system for each application– Fuel Cell systems produce by products (water) which

must be stored/dumped

→ Unfeasible option for long-duration missions

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Solar PowerApplications

ISS

Skylab

Mir

Mars Exploration Rover

Mir

GPS

Hubble

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Solar PowerEvaluation

• Solar Power Advantages• Photovoltaic Arrays convert sunlight into electricity by absorbing the energy of the

sun and causing current to flow between two oppositely charged layers of photovoltaic materials (usually silicon and gallium arsenide).

– Unlimited energy supply• Mission duration is not limited to on-board energy consumables

– Modular• Solar panel systems can be built independently of specific space

system

– Established manufacturing base– Cost effective

• Proven technology does not require significant research expenditures

→ Best option for long-duration near-sun missions

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Solar PowerEvaluation

• Solar Power Disadvantages– Requires a significant illumination source

• Sunlight strength diminishes as the distance from the sun increases

• Solar illumination insufficient for most applications beyond Mars

– Most solar-powered space systems require additional energy storage (battery) systems

– Most free-flight systems are dependant on a vehicle control system to point the space craft and/or solar arrays

→ Unfeasible option for deep space missions

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International Space StationPrior to STS-115/12A

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International Space StationSolar Array Deploy

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International Space StationAfter STS-115/12A

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International Space StationOverview

• International Space Station (ISS) is a manned Low-Earth Orbit vehicle– Launched in November 1998– Manned since October 2000– Mission Control Center (MCC) in Houston, TX maintains primary responsibility for

vehicle monitoring and operation• There’s no cockpit in ISS – its ‘flown’ from MCC

– Assembled in stages, estimated completion of 2010

• ISS is the largest space vehicle ever flown– Currently

• 170 feet long and 240 feet wide• Mass > 439,000 lbs

– Assembly complete • 240 feet long and 350 feet wide• Mass of > 1,000,000 lbs

• ISS utilizes a photovoltaic based power system– All electrical power is generated from solar energy

• Batteries charged by solar power are used during oribital eclipse

– Largest solar arrays ever flown– Each solar array is ~120 feet long– Each of the 8 [assembly complete] solar arrays generates up to 16 kW of user

power, up to 31kW of output power.

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International Space StationAssembly Sequence

STS-121/ULF-1.1

STS-115/12A

STS-116/12A.1

STS-117/13A

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International Space StationAssembly Sequence

STS-120/10A

STS-119/15A

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International Space StationElectrical Power System

• Energy is collected from solar radiation• Power is converted from collection (primary) power levels to

user (secondary) power levels– Primary power is also stored in chemical batteries to be used in eclipse

• Secondary power is distributed throughout the vehicle for system and user loads

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International Space StationElectrical Power System

MBSU

SARJ

BCDU BCDU

PFCA

PVCUPVCU

BattBatt BattBatt BattBatt

PVA

ECU

DCSU

DDCU

BCDU

IEA

Energycollection

BGA

SSU

Mast canister

Blanket Blanket

PVR

Users

Mast

Energystorage

Powerconversion

Powerdistribution

Power management andcontrol

Photovoltaic ThermalControl System (PVTCS)

Thermal cooling flow Control and data flowLegend:

SPDA

DDCU

RPDA

Users

PMCUPMCU

C&C MDMC&C MDMC&C MDM

From 2nd Power Channel

Various DDCUs,SPDAs & RPDAs

Batt (Battery) ECU (Electronics Control Unit) PVA (Photo Voltaic Array) BCDU (Battery Charge Discharge Unit) MBSU (Main Bus Switching Unit) PVCU (Photo Voltaic Control Unit) BGA (Beta Gimbal Assembly) RPDA (Remote Power Distribution Assembly) PVR (Photo Voltaic Radiator) C&C MDM (Command & Control Multiplexer-DeMultiplexer) PFCA (Pump Flow Control Assembly) SARJ (Solar Alpha Rotary Joint) DDCU (DC to DC Conversion Unit) PMCU (Power Management Control Unit) SPDA (Secondary Power Distribution Assembly)

SSU (Sequential Shunt Unit)

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Summary

• Space systems use three types of power systems

• Each system has advantages and disadvantages

• ISS utilizes a photovoltaic array power system to convert solar energy into electricity

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Theoretical Application 1

• Engineering is developing an Extra-Vehicular Activity (EVA) free-ranging, semi-autonomous robotic assistance device for ISS.

• The robotic device will need to operate for the duration of an EVA (~7 hours) or be operated independently from ISS for external inspection and have a mass of 8 kg or less.

• The robotic device will require the following systems– Video camera – 12 V, 40 W

– Still-picture camera – 12V, 25 W

– Flood light – 14 V, 250 W

– Attitude control system – 8 V, 25 W

– EMU-to-ISS Radio Signal Relay – 12 V, 80 W

– Command & Telemetry System – 12 V, 25 W

• What type of energy system should this system utilize?

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Theoretical Application 1

Energy Storage (battery)

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Theoretical Application 2

• A space system is required to investigate Jupiter moon Io

• The mission will have the following requirements– Payload up-mass: 850 to 2,200 kg– Payload Dimensions 3 m wide by 7 m long– Translate from Earth to Io in 16 months or less– Operate in orbit around Io for 2-4 years– Enter Io’s atmosphere on a ballistic trajectory and gather

atmospheric data and imagery– Send scientific data back to an Earth control center– Receive instructions from an Earth control center

• What type of energy system should this system utilize?

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Theoretical Application 2

Nuclear Power

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Theoretical Application 3

• A mission has been requested for sun surface observation and space environment sensing

• A space system is required which will have the following mission parameters– Operate in a solar orbit between Mars and Earth for 10+ years– Observe the sun with filtered video and photographic equipment– Sense space weather events– Monitor solar electromagnetic, ultraviolet, infrared, and x-ray

radiation– Send scientific data back to an Earth control center

• What type of energy system should this system utilize?

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Theoretical Application 3

Solar Power

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Back Up Material

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Low Earth Orbit (LEO)Overview

Insolation

(Sunlight)

Earth Orbit

Manned vehicle LEO altitude = 115-400 miles

Orbital Period = ~90 minutes

Insolation = ~45 minutes

Eclipse = ~45 minutes

Diagram Not to Scale

Eclipse

(Night)

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Manned Space Systems

• There are currently three US manned space systems– ISS– Shuttle– EMU

• ISS is powered by a solar power energy system– Also has an energy storage (battery) component

• Shuttle is powered by a energy storage system– Fuel cell

• EMU is powered by a energy storage system– Battery

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Space Transportation SystemOverview

• The Space Transportation System is an ascent, Low Earth Orbit, and return space vehicle– Comprised of 3 elements

• 2 Solid Rocket Boosters (SRBs) – Jettisoned ~2 minutes after launch and recovered by ship from Atlantic Ocean

• External Tank – Provides 500,000 gallons of hydrogen and oxygen fuel to Shuttle Main Engines, jettisoned after fuel expended and burns up in Earth’s atmosphere

• Space Shuttle orbiter – Orbits Earth for up to 18 days and then returns as a glider

– First and only operational space vehicle which is reusable• SRBs, Shuttle orbiter, and main engines are refurbished and resupplied for

subsequent missions– Only space system which allows heavy down-mass capability– Orbiter power is provided by 3 oxygen-hydrogen fuel cells

• Each fuel cell generates up to 7 kW of continuous power• Each fuel cell can generate up to 16 kW of short-term (15 min) power

• STS is the only manned US heavy-lift and ascent/return system– Weighs 4,500,000 lbs at lift off– Carries payloads up to 63,500 lbs– Crewed by up to 8 astronauts

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Extra-vehicular Mobility UnitOverview

• The Extra-vehicular Mobility Unit (EMU) is a self-contained ‘spacesuit’ used by crewmembers to perform Extra-Vehicular Activity (EVA)– The EMU contains all necessary elements for a crewmember to operate

outside of a pressurized vehicle• Battery power system• Pressurized environment• Life Support System• Communication system• Computer, data, and biomedical monitoring system• Urine collection device• Lighting and camera system• Drinking water

• EMU can operate independently for ~7 hours– The air scrubbing cartridge lifetime is the limiting factor in EVA

• Similar Russian designed and built spacesuit (“Orlan”) used on ISS

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Extra-Vehicular Mobility Unit Power System

• EMU battery operates at 16.8 V– Capacity = 26.8 A-Hr– Produces ~70 W of power– Useful power supplied

for ~7 hours

• Separate individual batteries are used for other EMU systems– Helmet light– Helmet camera– Glove heaters– Simplified Aid For EVA Rescue (SAFER)

(contingency jet pack)

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Extra-Vehicular Mobility Unit Power System

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Extra-Vehicular Mobility Unit Power System

EMUBatt

SSERCoolant Iso Vlv

Motor

Batt/SCU Sw

ISS Aux Power

Fan Pump H2O Sep

Fan Sw

Feedwater Iso VlvH2O Sw

CWS RTDS CCA

DCM

OBS

Display Sw

Batt (Battery) SSER (Space-to-Space EMU Radio) Iso Vlv (Isolation Valve) SCU (Signal Conditioner Unit) H2O Sep (Water Separator) Sw (Switch)CWS (Caution & Warning System) RTDS (Real Time Data System) CCA (Communication Carrier Assembly)DCM (Display & Control Module) OBS (Operational Bioinstrumentation System)

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References

• NASA Homepagewww.nasa.gov

• NASA Missions websitehttp://www.nasa.gov/missions/highlights

• NASA Human Spaceflight websitehttp://spaceflight.nasa.gov

• Wikipediahttp://www.wikipedia.com

• The magnificent brain of Steven Johnsonsteven.e.johnson@nasa.gov281-483-9534