WASHINGTON: The James Webb Space Telescope fully deployed its five-layer sunshield Tuesday, a critical milestone for the success of its mission to study every phase of cosmic history, US space agency NASA said.

"All five layers of the sunshield are fully tensioned," said an announcer at the telescope's control center in Baltimore, where team members cheered, a live feed showed.

The tennis court size, kite-shaped apparatus acts like a parasol, ensuring the observatory is kept in the shade so that it is able to detect faint infrared signals from the far reaches of the Universe.

Each of the layers was unfolded one by one over two days.

Because the telescope was too large to fit into a rocket's nose cone in its operational configuration, it had to be transported folded, origami style. Unfurling is a complex and challenging task, the most daunting such deployment NASA has ever attempted.

"When I get asked what keeps you up the most at night, it's the sunshield deployment," Bill Ochs, project manager for Webb, told reporters ahead of the operation.

The most powerful space telescope ever built, Webb blasted off on December 25, and is now more than halfway to its orbital point, a million miles (1.5 million kilometers) from Earth.

Powerful enough to see the first stars and galaxies that formed 13.5 billion years ago, it will give astronomers new insight into the early Universe. Its mission also includes the study of distant planets to determine their origin, evolution, and habitability.

The sunshield will be permanently positioned between the telescope and the Sun, Earth and Moon, with the Sun-facing side built to withstand 230 degrees Fahrenheit (110 degrees Celsius).

Each successive layer is cooler than the one below, allowing the telescope's sensitive instruments to operate at -370F.

It is made of lightweight material called Kapton, coated with treated silicon. It also has special "ripstop" seaming to limit damage from meteoroids.