The James Webb Space Telescope is set to launch into orbit on Dec. 18 after years of delays and billions of dollars in cost overruns, ushering in the next era of astronomy.

Webb's mission is to observe the universe's very first stars.

It is the successor to the Hubble Space Telescope, and its development cost $10 billion. It will be one of the great scientific achievements of the 21st century.

"We've checked everything over and I can report James Webb is in perfect condition," NASA instrument systems engineer Begoña Vila said.

Webb will be sent into orbit by a French Guiana-based Ariane rocket. Over the weekend, engineers began assembling the vehicle's numerous components. The Ariane's main core stage, which stands 30 meters tall, was raised into the vertical to allow the side boosters to be attached. The upper-stage of the rocket, which will power Webb's final ascension, will be attached in a few days.

It will be installed a week before the rocket's launch on Dec. 18.

After launch, the observatory's solar array, high-gain antenna, and mirror segments will be extended in a make-or-break series of deployments. Webb also features a five-layer sunshield that keeps the telescope cooler than minus 370 degrees Fahrenheit, or minus 223 degrees Celsius, by shading its mirrors, detectors, and science instruments.

Each sunshield layer is as thin as a human hair and is made of aluminum-coated Kapton. Once Webb is in space, the sunshade will extend to the size of a tennis court.

The observatory's infrared instruments will peek into the universe's oldest and farthest reaches to investigate some of the first stars and galaxies that arose after the Big Bang, which occurred more than 13.5 billion years ago.

Webb will also be used by astronomers to investigate how galaxies develop and evolve, as well as the birth of stars and the atmospheres of planets that may be habitable to life outside our solar system.

When it opens a few weeks after launch, Webb will be the largest space telescope ever launched, with a primary mirror composed of 18 gold-coated beryllium segments reaching to a diameter of 21.3 feet (6.5 meters). This is over three times the width of Hubble's monolithic primary mirror.

Telescopes like the Webb provide us with access to previously unexplored regions of the universe, hidden stars and planets, and new worlds, as well as the opportunity to make new discoveries. The Webb mission, with its promise of observing the development of galaxies, the birth of stars and planets, and the emergence of the very early universe, appears likely to yield fascinating and exciting revelations.