AE323_Electrical Power Subsystem

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• EMBRY-RIDDLE Aeronautical University

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• Aerospace Engineering Department / College of Engineering

• Spacecraft Systems – AE323 Spring 2025

• Course: Spacecraft Electrical Power

• Instructor: Dr. Cagri Kilic

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• Importance of Power Systems in Space Missions:

  • Consider the necessity of power systems in spacecraft.

  • Identify various applications of power systems.

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• Requirements Flowdown:

  • Electrical Power System Requirements

  • Power Profile

  • Power Margin

  • Bus Voltage Levels

  • Cycling-Charging

  • Component Denotation

• Spacecraft Requirements:

  • Orbit Definitions

  • Mission Life Considerations

  • System Architecture

  • Environmental Factors

  • Size and Weight Constraints

  • Basic Power Needs

  • Mission Requirements including:

    • Primary Mission Science Needs

    • Mission Length

    • Cost and Scheduling Constraints

  • Source: Cunningham et al, 2018

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• Types of Power Sources:

  • Primary Batteries: Non-rechargeable, single-use.

  • Secondary Batteries: Rechargeable, multi-use.

  • Fuel Cells: Converts chemical energy to electrical energy.

  • Regenerative Fuel Cells: Reversible energy storage.

  • Chemical Dynamic Systems: Thermal-to-electric conversion.

  • Nuclear Power: Fission-based systems.

  • Electrodynamics Tethers: Utilizing magnetic fields for electricity.

  • Radioisotope Systems: Decay heat electricity.

  • Thermionic Converters: Direct conversion of heat to electricity.

  • Thermoelectric Converters: Power from temperature difference.

  • Photovoltaic Systems: Energy from solar light.

  • Solar Dynamic Systems: Mechanical power from solar heat.

  • Flywheel Storage Systems: Kinetic energy storage.

  • Propulsion-Charged Tether Systems: Utilizing electromotive force for orbit changes.

  • Source: Miller and Keesee, Lecture Notes

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• In-depth Characteristics of Power Sources:

  1. Batteries:

     • Non-rechargeable (Primary) to predominantly rechargeable (Secondary).

     • Key metrics include energy and charge cycles.

     • Operate via oxidation/reduction reactions.

  2. Photovoltaic Cells:

     • Predominantly used in unmanned spacecraft.

     • Evaluated based on power output and efficiency.

     • Interaction between n-type and p-type materials.

  3. Fuel Cells:

     • Used in manned short-term missions.

     • Produces electricity by combining hydrogen and oxygen.

     • Water is the main byproduct.

  4. Radioisotope Thermal Generators (RTGs):

     • Ideal for long-duration missions in space.

     • Electricity generated via the Seebeck effect.

     • Features low power output with prolonged operational life.

  5. Nuclear Fission Reactors:

     • Involves requirements for refueling, shielding from radiation, and heat management.

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• Photovoltaic Cells and Fuel Cells Overview:

  • Featured images and references from NASA.

  • Importance highlighted for each type of power source.

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• Solar Power Systems Metrics:

  • Power decreases in relation to the inverse square law:

    • Formula: P = 1370 W/m² x (1 AU / Rsun-s/c)²

  • Sources: NASA/Boeing, Visual Capitalist/Jeff Desjardins.

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• Photovoltaic Cells Measurements:

  • Insolation constant of ~1370 W/m² at 1 AU.

  • Measurements considered around different planets:

    • Mercury: ~0.4 AU

    • Venus: ~0.7 AU

    • Earth: ~1.0 AU

    • Mars: ~1.5 AU

    • Other planets with respective AU.

• Astronomical Units (AU) defined: Average distance from Earth to the Sun (~150 million km).

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• Continued Measurements and Effects:

  • Additional calculations concerning power relative to distance from the sun were repeated.

  • Made clear emphasis on solar power efficiency along various planets.

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• Mars Opportunity Log Example:

  • Battery status indicated low power and impending darkness.

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• Photovoltaic Cells Example Problem:

  • Assessment to calculate needed area for PV array and corresponding mass based on given power requirements (3kW Si cells).

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• Incorporated images for context, credits listed from NASA.

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• Fuel Cell Characteristics in Spacecraft Systems:

  • Process Overview:

    • Hydrogen and oxygen react in a fuel cell to produce water and energy:

      • Reaction equation: 2H₂ + O₂ → 2H₂O + energy.

  • Diagram showing anode/cathode setup.

  • Source: Miller and Keesee, Lecture Notes.

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• More on Fuel Cells:

  1. Electricity Generation:

     • Combines hydrogen and oxygen chemically to produce electricity.

  2. Material Utilization:

     • High energy density; harmless water byproduct.

  3. Advantages over Solar Panels:

     • Consistent power output, energy density.

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• Key Points on Fuel Cell Outputs:

  • Output voltage approximately 0.8 volts per cell.

  • Hydrogen consumption and water production rates.

  • Specific power metrics around 275 watts/kg with examples.

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• Radioisotope Thermoelectric Generators (RTGs) Reliability:

  • Historical reliability across various NASA missions:

    • Apollo, Viking, Pioneer, Voyager, etc.

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• Energy Release Fundamentals:

  • Concept summarized through Einstein's equation E=mc².

  • Notation for decay and energy implications.

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• Decay Process Descriptions:

  • RTGs utilize Pu-238 decay for heat production.

  • Transformation process and resultant heat significance.

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• Seebeck Effect Overview:

  • Explanation of the process and its implications:

    • Temperature differences yielding electrical voltage (science of thermocouples).

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• Structure of Multi-Mission RTGs:

  • Visual representation of GPHS/RTG modules.

  • Significant components described and the interactions explained.

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• Advantages and Disadvantages of RTGs:

  • Key advantages include:

    • Independence from sunlight, long life, efficient power relative to size, reliability.

  • Noted drawbacks include:

    • Continuous decay, heat management, high costs.

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• Historical Reference of Radioisotope Power Systems:

  • Overview of spacecraft missions utilizing radioisotope power.

  • Diverse types of missions represented.

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• Summary of Power Source Characteristics:

  1. Photovoltaic Cells: Utilized in unmanned missions; considered for power and efficiency.

  2. Fuel Cells: Best suited for manned missions with hydrogen/oxygen setup.

  3. RTGs: Excellent for long missions; capitalize on Seebeck effect.

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• Exercise Background Information:

  • Design requirements for a spacecraft in Low Earth Orbit (LEO), including operational power needs and solar array efficiency.

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• Exercise Tasks:

  • Series of calculations required to determine energy needs, battery mass, additional power requirements, etc. detailed stepwise.

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• References Cited:

  • Extensive list covering many aspects of spacecraft power systems from credible sources.