Spacecraft Wall Thermal-Conduction Network (2D)

Orbit & Wall Design

Orbit altitude 550 km

Skin solar absorptivity α 0.50

MLI conductance G_mli 0.40 W/K

Electronics dissipation Q_int 40 W

Live State

☀ In sunlight

T skin

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T MLI

—

T structure

—

T electronics

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Orbit period

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Eclipse fraction

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Electronics ΔT (last full orbit)

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How it works

This is an independent 1-D thermal-node network, not a flattened 3D scene. Instead of one lumped spacecraft temperature, the wall is split into four real thermal nodes — outer skin, MLI insulation blanket, structural bus and internal electronics — each with its own heat capacity C, linked to its neighbours by a conductance G (this is the same resistor-capacitor "SINDA-style" node network real spacecraft thermal engineers build for transient analysis):

C_i · dT_i/dt = G_(i-1,i)(T_(i-1)-T_i) + G_(i,i+1)(T_(i+1)-T_i) + S_i(t)

skin (i=0):    S_0 = α·A·S_solar (sunlit only) − ε·A·σ·T_0⁴   (Stefan-Boltzmann loss to space)
electronics:   S_3 = Q_int   (constant internal dissipation, no direct radiation)

Orbit altitude sets the orbital period (Kepler's third law) and the eclipse duration via an exact in-plane shadow test — low orbits spend a large fraction of every revolution in Earth's shadow, geostationary orbit is nearly always sunlit.
Skin absorptivity α sets how much of the incoming ~1361 W/m² solar flux the outer node soaks up while sunlit; its fixed IR emissivity radiates that heat (and more) away via σT⁴ at all times.
MLI conductance G_mli is the thermal resistance between skin and structure — a real multi-layer-insulation blanket. Low conductance (good insulation) lets the skin swing through a huge day/night ΔT while the structure and electronics stay nearly steady; raise it and the skin's swing propagates straight through.
Electronics dissipation Q_int is heat the payload itself generates continuously — it must be conducted out through the same chain in reverse, which is why electronics boxes are usually bolted to structure with a high-conductance interface, unlike the deliberately low-conductance MLI layer above them.

Sending G_mli to a very large value collapses this four-node network onto the same 0-D lumped energy balance used by the companion 3D orbit-view simulator — a useful sanity check that the two models describe the same underlying physics at two different levels of detail.

Sun / solar flux Space (radiative sink) T skin T structure T electronics