As it begins the delicate process of unfurling its fragile sunshield, the James Webb Space Telescope (JWST) will enter its most risky moment yet.

According to NASA, the spacecraft took another important step in its deployment on Tuesday (Dec. 28) when it unfolded the Forward Unitized Pallet Structure (UPS) of its massive sunshield.

It took four hours to complete the operation, which ended at 1:21 p.m. EST, the agency said in a statement. Webb then repeated the process with the Aft UPS, which completed deployment at 7:27 p.m. EST.

JWST, which was launched on Christmas Day, is a ground-breaking new telescope dedicated to researching the universe in infrared light. But first, it must make it through a month-long journey to its ultimate station and a meticulously orchestrated deployment procedure.

Webb has been in development for about three decades. In September 1989, a group of astronomers met at the Space Telescope Science Institute in Baltimore to explore a possible successor to the Hubble Space Telescope.

Hubble hadn't even launched yet, but because large space telescopes take a long time to plan and build, the astronomical community tries to plan ahead a decade or two. And, in this case, there was a strong desire to avoid a protracted observing gap between Hubble and a "Next Generation Space Telescope," as the successor was dubbed informally.

NASA officials wrote that unfolding the forward UPS required dozens of distinct processes. The successful maneuver is the first step in a five-day process of creating the sunshield, which will shield Webb's sensitive equipment from solar radiation.

Although each stage of the deployment sequence is controlled from the ground and the timing can be altered as NASA and its partners see fit, the sunshield deployment procedure is expected to end around Jan. 3.

Webb's next steps will be to unfold the Deployable Tower Assembly, release the sunshield cover, and begin unfurling the sunshield itself when the two UPS structures have been unfolded.

The observatory will be in its final configuration in orbit within one month of launch if all goes according to plan. The spacecraft will orbit Earth-sun Lagrange point 2, or L2, which is about 930,000 miles (1.5 million kilometers) out on the opposite side of the sun. This placement, like the delicate sunshield, is critical for allowing the equipment to collect infrared observations.

Webb will be on its own out there because L2 is too far away for astronauts to visit; Hubble-style service flights are not planned for the massive new telescope.