Spacecraft Thermal control ystems Col John e Keesee Lesson Objectives 1. The student will understand thermal control processes 2. The student will be able to calculate thermal balances and equilibrium temperatures 3. The student will be able to size and select thermal control system
1 Spacecraft Thermal Control Systems Col. John E. Keesee Lesson Objectives: 1. The student will understand thermal control processes 2. The student will be able to calculate thermal balances and equilibrium temperatures 3. The student will be able to size and select thermal control systems
Outline Purpose of thermal control systems Review of heat transfer fundamentals Space system thermal analysis equations Models Analysis programs Thermal control sub-systems
2 Outline • Purpose of thermal control systems • Review of heat transfer fundamentals • Space system thermal analysis – Equations – Models – Analysis programs • Thermal control sub-systems
Purposes of Thermal control To control the operating temperature environment Sp ft syster Most systems become less reliable when operated outside their design operating environment Propellant freezes Thermal cycling damage Instrument/antenna/camera alignment Instrument requirements for very cold temperatures Example operating temperatures- SMAD Table 11-43
3 Purposes of Thermal Control • To control the operating temperature environment of spacecraft systems – Most systems become less reliable when operated outside their design operating environment – Propellant freezes – Thermal cycling damage – Instrument/antenna/camera alignment – Instrument requirements for very cold temperatures • Example operating temperatures – SMAD Table 11-43
Temperature requirements Operating temperature ranges Switch-on temperatures Non-operating temperature ranges Temperature stability Temperature uniformity
4 Temperature Requirements • Operating temperature ranges • Switch-on temperatures • Non-operating temperature ranges • Temperature stability • Temperature uniformity
Typical Spacecraft Design Temperatures Component/ Operating Survival System Temperature(C)Temperature(C) Digital electronics 0to50 -20to70 Analog electronics 0to40 -20to70 Batteries 10to20 0to35 iR detectors 269to-173 269to35 Solid-state particle -35to0 35to35 detectors Momentum wheels 0to50 20to70 Solar panels l100to125 l100to125
5 Typical Spacecraft Design Temperatures Solar panels -100 to 125 -100 to 125 Momentum wheels 0 to 50 -20 to 70 Solid-state particle -35 to 0 -35 to 35 detectors IR detectors -269 to –173 -269 to 35 Batteries 10 to 20 0 to 35 Analog electronics 0 to 40 -20 to 70 Digital electronics 0 to 50 -20 to 70 Survival Temperature (C) Operating Temperature (C) Component/ System
Review of heat transfer Fundamentals Convection- heat transfer via flowing flu uIds Conduction- heat transfer within materials other than flowing fluids Radiation heat transfer via electromagnetic waves
6 Review of Heat Transfer Fundamentals • Convection – heat transfer via flowing fluids • Conduction – heat transfer within materials other than flowing fluids • Radiation – heat transfer via electromagnetic waves
Convection g=h*A*AT h= heat transfer coefficient Important to spacecraft during launch after fairing separation Convective heat transfer is used in some pumped-liquid thermal control systems especially in manned spacecraft
7 Convection • h = heat transfer coefficient • Important to spacecraft during launch after fairing separation • Convective heat transfer is used in some pumped-liquid thermal control systems, especially in manned spacecraft q = h ∗ A∗ ∆T
Conduction q=(71-72 Rectangular 2kmL(71-T2) q Cylindrical ln(D。/D) 4mkRR(71-72) q (R。-R) k is the thermal conductivity
8 Conduction • Rectangular • Cylindrical • Spherical • k is the thermal conductivity ( ) 4 ( ) ln( / ) 2 ( ) ( ) 1 2 1 2 1 2 o i i o o i R R kR R T T q D D k L T T q T T x kA q − − = − = − ∆ = π π
Radiation g=EoT g=emissivity at the wavelength mix corresponding to temperature t o=Stefan-Bolzmann's constant =5670x108W/m2-K4 T is temperature in Kelvin Primary energy transfer mechanism for spacecraft Most spacecraft have large radiators to rid themselves of heat q is the heat transfer per unit area and T is the surface temperature
9 Radiation ε=emissivity at the wavelength mix corresponding to temperature T σ=Stefan-Bolzmann’s constant = 5.670 x 10-8 W/m2-K4 T is temperature in Kelvin 4 q = εσT Primary energy transfer mechanism for spacecraft. Most spacecraft have large radiators to rid themselves of heat. q is the heat transfer per unit area and T is the surface temperature
Planck's equation 2k ch/kT 入= wavelength h=Planck's constant c=speed of light kBolzmann's constant At any temperature above absolute zero, all materials emit thermal(blackbody) radiation For a perfect blackbody, the rate of total energy emission and the energy distribution across all wavelengths is strictly a function of the absolute temperature T For spacecraft and atmosphere covered planets these distributions are modified, but we usually use the perfect blackbody energy distribution at least as an initial estimate perfect blackbody. Eb is the energy per unit wavelength of a blackba on of a Plancks equation gives us the spectral energy distributio h=66260755e-34Ws2k=1380658e-23Ws/K
10 Planck’s Equation λ=wavelength h=Planck’s constant c=speed of light k=Bolzmann’s constant 1 2 1 5 / 2 − = ∗ b ch k T e hc E λ λ λ π At any temperature above absolute zero, all materials emit thermal (blackbody) radiation. For a perfect blackbody, the rate of total energy emission and the energy distribution across all wavelengths is strictly a function of the absolute temperature T. For spacecraft and atmosphere covered planets these distributions are modified, but we usually use the perfect blackbody energy distribution at least as an initial estimate. Planck’s equation gives us the spectral energy distribution of a perfect blackbody. Eb is the energy per unit wavelength of a blackbody. h=6.6260755e-34 Ws2 k=1.380658e-23 Ws/K