The size of JWST's sunshield is often compared to what?

The size of JWST’s sunshield is often compared to a tennis court. Its deployed, kite-shaped shield measures roughly 21 by 14 metres, making the comparison an easy way to visualize the scale of the observatory’s thermal-control system.

The sunshield is much more than a giant shade. Webb must remain extremely cold to detect faint infrared radiation from distant astronomical objects. The shield blocks and reflects heat from the Sun, Earth, and Moon, allowing the telescope and most of its instruments to cool to around 40 kelvins. MIRI, which observes the longest wavelengths, requires an additional cryocooler.

Five separate layers of thin Kapton membrane form the shield. Each layer is coated with reflective metal, and the gaps between layers allow heat to radiate away progressively into space. The layers were folded for launch inside the Ariane 5 rocket’s fairing and deployed after Webb reached space.

The tennis-court comparison describes the deployed footprint, not the compact launch configuration. Successfully unfolding the shield was one of Webb’s most intricate early-orbit engineering milestones.