Space thermal environment

1. Space thermal environment Isidoro Martínez isidoro.martinez@upm.es 11 July 2008

2. Space thermal environment(Thermal characteristics of the space environment) • Environment = external conditions or surroundings • Space environment  room conditions (vacuum, mg, radiations, wind…) • Mechanical effects: gravitational, vacuum, meteorites, debris, drag… • Thermal effects (what is the space temperature?) • Electric & magnetic effects: ionosphere, magnetosphere, telecom, remote sensing…

3. Space thermal environment • Environment: vacuum and thermal radiations • Thermal: temperature, heat, and thermal energy • Space: at <100 km, at LEO, at GEO, interplanetary, planetary • FUNDAMENTALS • Energy balance. What is thermal balance? • Heat transfer. What is thermal radiation?

4. Thermal radiation

5. Heat transfer theory • What is heat? (≡heat flow) Q≡DE-W → Q ≡DH|p • What is heat flux? (≡heat flow rate) • Heat flux density (≈heat flux)

6. The environment. Ascent and low Earth orbit

7. Background radiations • Cosmic isotropic microwave radiation (2.7 K) • Solar wind • van Allen radiation belts • Cosmic radiation

8. Solar radiation • Amount: the solar constant • Spectrum • Absorptance • Transmittance • Reflectance

9. Thermal characteristics of planetary missionsPlanet IR emission

10. Planet characterization for thermal radiation

11. SIMPLIFIED THERMAL DESIGN COMPUTATIONS • Thermal modelling approach: continuous, discrete, stochastic • Global thermal balance. Isothermal bodies

12. Some space data to keep at hand • Sun-Earth distance: RS-E=150·109 m (1 AU) • Earth radius: RE=6.37·106 m • Sun radius: RS=695·106 m (RS=109·RE) • GEO radius: RGEO=42.16·106 m (RGEO=6.6·RE) • Solar constant: CS=1370 W/m2 (TS=5800 K) • Stefan-Boltzmann law: Mbb=sT4, withs=5.67·10-8 (W/m2)/K4 • Earth mean emissivity: e=0.59 (TE=288 K) • Earth mean albedo: r=0.30 (a=0.70) • Background microwave radiation: TB=2.7 K • Aluminium: r=2700 kg/m3, alin=24·10-6 K-1, c=890 J/(kg·K), k=200 W/(m·K), a=0.10, e=0.05.

13. Proposed exercises • Find the solar irradiance, E, near Mercury and Saturn • Find the heat flux between isothermal plates with n blackbody plates in between (radiation shields) • Find the steady temperature of an isothermal sphere at 1 AU • Find the steady temperature of a white ball and a black ball, at sea level and above the atmosphere • Find the steady temperature change from LEO to GEO of a spherical blackbody at noon • Find the steady temperature at 1 AU, for an isothermal blackbody with different geometries • Find the temperature evolution of a microsatellite 0.4 m in diameter when entering the equinox eclipse in GEO. • Find the two side temperatures of a white painted panel of k=0.1 W/(m·K) and 1•0.5•0.01 m3 in size, tilted 30º to sun rays, and deployed from a spacecraft orbiting Mars.

14. SUMMARYSpace thermal environment • Environment?: vacuum, radiations, meteorites? • Thermal?: temperature, heat, or thermal energy? • Space?: at <100 km, at LEO, at GEO, interplanetary, planetary? • FUNDAMENTALS • Energy balancethermal balance • Heat transferthermal radiation