Engineering Calculator
Lockheed Equation Calculator
Predict MLI thermal performance using the most widely adopted semi-empirical correlation. Input your boundary conditions and get real-time heat flux predictions.
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Input Parameters
Enter your MLI system conditions below. The calculator computes total heat flux and breaks it into conduction, radiation, and gas conduction components.
Boundary Conditions
MLI Configuration
Material & Atmosphere
Results
Equation Reference
The Lockheed Correlation
Standard (High Vacuum)
Valid for vacuum < 10-3 Pa. Separates heat flux into solid conduction and radiation components.
Extended (With Gas)
For non-ideal vacuum. Adds gas conduction term scaled by interstitial pressure.
Correlation Parameters
| Gas | k (300K) mW/(m·K) | Cg | Exp | Source |
|---|---|---|---|---|
| N2 | 25.9 | 14,600 | 0.52 | Lockheed empirical |
| He | 155.7 | 48,900 | 0.26 | Lockheed empirical |
| H2 | 186.6 | 48,900 | 0.26 | Lockheed (same as He) |
| Air | 26.4 | 14,600 | 0.52 | ~ N2 (78% N2 + 21% O2) |
| CH4 | 34.4 | ~20,000 | 0.52 | Estimated from k ratio |
| CO2 | 16.6 | ~9,300 | 0.52 | Estimated from k ratio |
| Ar | 17.7 | ~10,000 | 0.52 | Estimated from k ratio |
| H2O (gas) | 35.8 * | ~10,100 | 0.52 | Estimated; * condensation risk |
| Mixed (air) | ~26 | ~14,600 | 0.52 | Typical seal-failure composition |
Note: Cg values marked "~" are estimated by scaling from Lockheed's empirical N2 data using thermal conductivity ratios at 300K (NIST REFPROP / Marcia L. Huber). Only N2, He, and H2 have direct Lockheed empirical data. Estimated values should be validated against test data for critical applications.
H2O Warning: Water vapor condenses/deposits on cryogenic surfaces below ~200K, forming ice layers with thermal conductivity of 150-400 mW/(m·K) — orders of magnitude higher than vapor. This phase-change effect cannot be captured by the linear Cg*P model. (The Aerospace Corp., SPIE 2025)
Mixed Gas Effects
In real MLI systems, the interstitial gas is rarely pure. Typical residual gas compositions after seal failure or during pump-down:
| Scenario | Dominant Gases | Effective k | Key Risk |
|---|---|---|---|
| Normal high vacuum | H2O, CO2, H2 (trace) | negligible | Outgassing from materials |
| Seal failure (air in) | N2 (78%), O2 (21%), Ar (1%) | ~26 mW/(m·K) | Rapid k_eff increase |
| He leak (from leak check) | He + air | dominated by He | He has 6x higher k than air |
| LH2 system | H2 permeation + He | very high | H2 permeates through metals |
| LNG system | CH4 + N2 | moderate-high | CH4 from cargo evaporation |
| Humid air ingress | Air + H2O vapor | ~26 + condensation | Ice deposition on cold layers |
Data sources: Gas thermal conductivities from NIST REFPROP (Marcia L. Huber); Lockheed empirical Cg from NASA/TM-2015-000199; Sun et al. MLI multi-gas experiments (Processes 2023, MDPI); NETZSCH GHP 456 measurements (2026); The Aerospace Corp. water vapor study (SPIE 2025, DOI: 10.1117/12.3065462); LNG tanker MLI data (MATEC ICCHMT 2018).
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