Lecture 7 power systems and thermal management
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Lecture 7: Power Systems and Thermal Management. Electrical Power Subsystem. Power Source. Energy Storage. Power Distribution. Regulation & Control. Power System Structure and Requirements. Typical Requirements Supply continuous electrical power to s/c loads during mission

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Lecture 7: Power Systems and Thermal Management

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Lecture 7 power systems and thermal management

Lecture 7:Power Systems and Thermal Management


Power system structure and requirements

Electrical Power Subsystem

Power Source

Energy Storage

Power Distribution

Regulation & Control

Power System Structure and Requirements

  • Typical Requirements

  • Supply continuous electrical power to s/c loads during mission

  • Control and distribute electrical power

  • Handle average and peak electrical load

  • Provide ac, dc power converters

  • Protect against failures in the EPS

  • Suppress transient voltages and protect against faults


Power system design process

Power System Design Process


Power sources

Power Sources

Power sources

Photovoltaic

Static

Dynamic

Planar

Concentrators

Thermionics

Thermoelectrics

Brayton

Stirling

Rankine

  • Photovoltaic solar cells convert incident solar radiation directly to electrical energy

  • Static power sources uses a heat source, typically plutonium- 238 or uranium-235 for direct thermal-to-electrical conversion

  • Dynamic sources also use a heat source – concentrated solar, plutonium-238, or enriched uranium – to produce power via Brayton, Stirling or Rankine cycles


Comparison of power sources

Comparison of Power Sources


Solar array design process

Solar Array Design Process

  • Determine requirements and constraints

    • Av. Power needed during daylight and eclipse

    • Eclipse durations

    • Design lifetime

  • Calculate power that must be produced, Psa


Solar array design process1

Solar Array Design Process

3. Select type of solar cell and estimate power output, P0 , with the sun normal to the surface of the cells

4. Determine BOL power production per unit area, taking account of inherent degradation:

And the cosine loss and life degradation:


Energy storage

Energy Storage

  • Primary batteries have higher specific energy densities but cannot be recharged. Thus, they typically apply to short missions.

  • Characteristics of some secondary batteries:


Energy storage1

Energy Storage


Black body radiation model

Black Body Radiation Model

A sea of photons is surrounded on all sides by high temperature atoms. These particles randomly absorb or emit photons, permitting all possible energy transitions compatible with conservation of overall energy


Black body radiation model1

Black Body Radiation Model


Black body radiation model2

Wien’s law

UV & Vis

Infrared

Microwave

Black Body Radiation Model


Cobe cosmic background explorer satellite data precisely verifies planck s radiation law

COBE (Cosmic Background Explorer) satellite data precisely verifies Planck’s radiation law


Black body radiation model3

Black Body Radiation Model


Thermal equilibrium of an isolated body in space

Thermal Equilibrium of an Isolated Body in Space

Electronics


Spherical spacecraft equations

Spherical Spacecraft Equations


Spherical spacecraft equations1

Spherical Spacecraft Equations


Putting the equations to work the preliminary design process

Putting the Equations to Work: The Preliminary Design Process


The preliminary design process continued

The Preliminary Design Process - Continued


Lecture 7 power systems and thermal management

Thermal Control Devices and Strategies - If special thermal control problems are encountered in step 9

  • Materials and Coatings

  • Optical Solar reflectors

  • Silver-Coated Teflon

  • MultiLayer Insulation

  • Electrical Heaters

  • Thermostats

  • Space radiators

  • Cold-Plates

  • Doublers

  • Phase Change Devices

  • Heat Pipes

  • Louvers

  • Temp. Sensors

  • Adhesive Tapes

  • Fillers

  • Thermal isolators

  • Thermoelectric Coolers

  • Cryogenic Systems

  • Active Refrigeration Systems

  • Expendable Cooling Systems


Thermal control devices and strategies

Thermal Control Devices and Strategies

  • Materials and Coatings: paints, silverized plastics, special coatings – all with special absorptivity & emissivity values– See Table 11-44

  • Optical Solar Reflectors (OSRs):

    • Highly reflective surface mounted on a substrate and overlaid with a transparent coating.

    • Reflects most incoming radiation back to space, IR emissivity = 0.8, solar absorptivity = 0.15

    • Expensive and fragile.

  • Silver-Coated Teflon - Cheaper alternative to OSRs.

  • MultiLayer Insulation (MLI):

    • The primary spacecraft insulation device.

    • Alternate layers of aluminized Mylar or Kapton, separated by net material, e.g. nylon, Dacron or Nomex

    • See Fig. 11-22 for the effective emmitance of MLI

  • Electrical Heaters

    • Used in cold-biased systems to bring selected components up to proper temp.

    • Thin electrical resister between two Kapton sheets

    • Typical power densities  1 W/cm2

  • Thermostats

    • Switches to turn heaters on/off

    • Typical operating range: -50 to 1600C


Thermal control devices and strategies1

Wicking material

Gas

Heat in - evaporation

Liquid flow via wick

Heat out - condensation

Thermal Control Devices and Strategies

  • Space radiators

    • Heat exchanger on the outer surface of the spacecraft that radiates waste heat

    • Can be structural panels or flat plates mounted on the spacecraft

  • Cold-Plates

    • Heat dissipated by electrical equipment is conducted across the interface to the cold plate. Fluid circulating through the cold plate Carries the heat to a space radiator.

  • Heat Pipes

    • Lightweight devices used to transfer heat from one location to another, e.g. from an electrical component to a space radiator

  • Temp. Sensors

    • Thermisters: Semiconductor materials that vary their resistance with temperature. They operate around -50 to +300 0C.

    • Resistance Thermisters: Uses a pure platinum conductor. Very accurate and expensive


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