Cryogenic MLI Heat Flux Calculator
Spacecraft thermal control & cryogenics: Calculate Multi-Layer Insulation (MLI) heat flux ($q$), radiation shielding, solid spacer conduction, and effective thermal conductivity ($k_{eff}$).
MLI Blanket Specifications
Thermal Isolation Performance
Total Heat Flux $q_{total}$
--
$\text{W}/\text{m}^2$
Total Heat Load $\dot{Q}$
--
Watts (across area $A$)
Effective Conductivity $k_{eff}$
--
$\mu\text{W}/(\text{m}\cdot\text{K})$
Radiation Component $q_{rad}$
--
$\text{W}/\text{m}^2$ (shield reflection)
Solid Conduction $q_{solid}$
--
$\text{W}/\text{m}^2$ (netting spacers)
Blanket Thickness $t$
--
mm ($N / N^*$)
Heat Transfer Breakdown (Radiation vs Conduction)
Compressing MLI blankets increases solid spacer contact conduction ($q_{solid} \propto {N^*}^{2.63}$), whereas too few layers increases radiative pass-through. Optimum density is typically 20–30 layers/cm.
The Modified Lockheed MLI Equation
The empirical Lockheed correlation (Keller et al.) models the three parallel heat transfer modes through double-aluminized Mylar/Kapton with Dacron netting spacers:
$$q_{rad} = \frac{C_r \, \epsilon \, (T_h^{4.67} - T_c^{4.67})}{N}$$
$$q_{solid} = C_s \, (N^*)^{2.63} \, \left(\frac{T_h + T_c}{2}\right) \, \frac{T_h - T_c}{N}$$
$$q_{gas} = \frac{C_g \, P \, (T_h^{0.52} - T_c^{0.52})}{N}$$
Where $N^*$ is layer density in layers/cm, and $P$ is interstitial vacuum pressure in Torr. Below $10^{-5}$ Torr, residual gas conduction becomes negligible, allowing effective thermal conductivities down to $k_{eff} \sim 10 - 50 \, \mu\text{W}/(\text{m}\cdot\text{K})$.
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