Sunshield Radiative Cooling Simulator

Solar Distance

Distance from Sun 1.01 AU

Sunshield Design

Shield layers N 5

Layer emissivity ε 0.030

Live Readouts

Sun-facing plate

120 °C

Optics-side shield

36 K

Attenuation of solar heat load reaching the telescope

×1

How it works

Each shield is a thin, low-emissivity sheet floating between the hot sun-facing plate and deep space. In steady state the same radiative heat flux q crosses every gap, so consecutive layers satisfy the parallel-plate radiation exchange law:

q = σ(T_i⁴ − T_(i+1)⁴) / (2/ε − 1)

which makes T⁴ fall in equal steps from the hot plate to the last shield. The last shield then radiates that same q straight to cold space (q = σεT_N⁴), which closes the system and gives a direct formula for the step size d = T_i⁴ − T_(i+1)⁴:

T₀⁴ = (Solar flux) / σ         (hot plate equilibrium)
d    = (2−ε)·T₀⁴ / [1 + (2−ε)·N]
T_i⁴ = T₀⁴ − i·d                for i = 1 … N
q    = σ·ε·T_N⁴                 (residual flux reaching the telescope)

N (shield count) — more floating layers means more radiation gaps in series, so the same total temperature drop happens in smaller, easier steps. This is why JWST uses exactly 5 layers rather than 1 thick shield.
ε (emissivity) — a lower emissivity (shiny aluminized Kapton, ε≈0.03) makes each gap a much worse conductor of radiant heat, so the step size d shrinks and the last layer runs colder.
Distance from the Sun — solar flux falls off as 1/r², so the hot plate's equilibrium temperature T₀ = (flux/σ)^¼ drops with distance too.
Attenuation × — how many times smaller the heat flux reaching the telescope (q) is compared to the raw solar flux hitting the front plate with no protection at all.

Real-world relevance: this is the exact mechanism behind the James Webb Space Telescope's tennis-court-sized 5-layer sunshield, which keeps the sun-facing side near 110 °C while the mirrors on the far side settle below 50 K — cold enough to observe faint infrared light without the telescope's own heat swamping the signal.

Hot (sun-facing) Cold (optics-facing)

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