1 Providing Energy for Space Systems Steven E. Johnson United Space Alliance, LLC ISS Flight Controller NASA Johnson Space Center NASA/NTSA Symposium Living 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 NAS 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.

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

3 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.

4 Spacecraft Power System Options Solar Photo- Voltaic* Solar Dynamic Nuclear FissionRadioisotope Energy Storage Chemical*Mechanical Energy Systems 101 Powering Spacecraft *Current manned space systems use Photovoltaic and Chemical power

5 Nuclear Power Applications Voyager Galileo Ulysses Cassini Viking Since 1961, 40 RTGs have been used on 22 US space systems.

6 Nuclear Power Evaluation 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

7 Nuclear Power Evaluation 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

8 Energy Storage Applications Cassini Probe Cassini Probe Apollo Lunar Rover Space Shuttle Space Shuttle Apollo Command Service Module Gemini EMU

9 Energy Storage Evaluation 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

10 Energy Storage Evaluation 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

11 Solar Power Applications ISS Skylab Mir Mars Exploration Rover Mir GPS Hubble

12 Solar Power Evaluation 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

13 Solar Power Evaluation 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

14 International Space Station Prior to STS-115/12A

15 International Space Station Solar Array Deploy

16 International Space Station After STS-115/12A

17 International Space Station Overview 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.

18 International Space Station Assembly Sequence STS-121/ULF-1.1 STS-115/12A STS-116/12A.1 STS-117/13A

19 International Space Station Assembly Sequence STS-120/10A STS-119/15A

20 International Space Station Electrical 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

21 International Space Station Electrical Power System 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)

22 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

23 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?

24 Theoretical Application 1 Energy Storage (battery)

25 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?

26 Theoretical Application 2 Nuclear Power

27 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?

28 Theoretical Application 3 Solar Power

29 Back Up Material

30 Low Earth Orbit (LEO) Overview Insolation (Sunlight) Earth Orbit Manned vehicle LEO altitude = miles Orbital Period = ~90 minutes Insolation = ~45 minutes Eclipse = ~45 minutes Diagram Not to Scale Eclipse (Night)

31 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

32 Space Transportation System Overview 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

33 Extra-vehicular Mobility Unit Overview 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

34 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)

35 Extra-Vehicular Mobility Unit Power System

36 Extra-Vehicular Mobility Unit Power System EMU Batt SSER Coolant Iso Vlv Motor Batt/SCU Sw ISS Aux Power FanPumpH 2 O Sep Fan Sw Feedwater Iso Vlv H 2 O Sw CWSRTDSCCA DCM OBS Display Sw Batt (Battery)SSER (Space-to-Space EMU Radio)Iso Vlv (Isolation Valve) SCU (Signal Conditioner Unit)H 2 O 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)

37 References NASA Homepage NASA Missions website NASA Human Spaceflight website Wikipedia The magnificent brain of Steven Johnson