Building the Webb telescope is a complex process. Over 100 companies around the world have worked with NASA and the European and Canadian space agencies to design, plan and construct the telescope's various parts, often creating new technologies to deal with the unique circumstances Webb will face.

Those parts are being brought together and assembled into the telescope's major components and tested to ensure that they can survive both launch and the extreme conditions in space. As they are completed, components go through testing to demonstrate that Webb will function precisely and effectively once everything is in place.

Webb's primary mirror is made up of 18 individual segments that fold up inside the rocket that carries it into space. Once deployed, they function as a single giant mirror. The mirror segments are made of beryllium, a metal that is both extremely strong and light. The segments are coated in a layer of gold - approximately 10 wedding rings' worth to coat the entire primary mirror, but spread ultra-thin - in order to best reflect infrared light. A series of smaller mirrors direct the light from the primary mirror to the instruments.

The challenging task of making, polishing and coating the mirror segments is now finished. All mirror segments have now undergone final cryogenic testing as well to ensure they will withstand the cold of deep space.  Now that the extremely challenging fabrication phase of the mirror segments is over, the next steps include assembling the actuators onto the primary mirror segments and assembly of the mirrors onto the support structure (backplane), and further testing.

Read more about the mirrors, from start to finish...

Webb's instruments carry within them several different components. Some have cameras, which take images. Some have spectrographs, which break light into its component colors and allow scientists to analyze details like the chemical composition of an object. Some have coronographs, which block the light from bright objects - like stars - so astronomers can observe dimmer objects - like orbiting planets.

Building Webb's instruments is a process of creating all the individual pieces and ensuring they work well together in the bitter temperatures of space. Webb's instruments are:

• NIRCam - NIRCam will be Webb's workhorse camera and is expected to be one of its most in-demand instruments. It will detect galaxies that are much too faint for Hubble to find.
• MIRI - MIRI will be Webb's most versatile instrument. It will be able to explore the widest range of infrared wavelengths and has spectrographs, giving it great range for scientific observations.
• NIRSpec - NIRSpec will be Webb's all-purpose spectrograph, capable of performing three distinct modes of spectroscopy. It allows astronomers to observe a large number of objects in a crowded field of stars and galaxies, to study just a few objects in greater detail, and to perform an intensive, in-depth examination of a small region.
• FGS/NIRISS - FGS/NIRISS will be a high-speed camera that also helps point and stabilize the telescope. It provides near-infrared images and spectroscopy.

Webb's sunshield will keep unwanted infrared light from the Sun, Moon and Earth from interfering with the telescope's observations, and prevent radiation from the telescope's own heat-producing equipment, such as the solar panels and computer, from reaching the science instruments and optics.

As with Webb's other components, the sunshield has to undergo testing to prove it's ready for space. But a full, tennis court-sized sunshield, consisting of five layers of Kapton coated in either silicon or aluminum, would be too big to be tested in a cryogenic chamber. None large enough exist, and building a chamber just to test the sunshield would be impractical. So engineers constructed a 1/3-scale model to perform the testing. That model was used to test the sunshield's deployment and was put through thermal testing. The data gathered was then used in computer models for further analysis.

Additionally, full-scale sunshield templates have been constructed and are undergoing 3D shape-testing, which tells the engineers how the sunshield layers will behave once deployed.  Next steps include manufacturing the flight sunshield membranes."

Webb's "bus" is home to the systems that keep the telescope running: the electronics, attitude and thermal control, communications, and propulsion. Webb's bus is one of the telescope's more standard technologies - a bus is part of all space telescopes and satellites - and thus requires less innovation than many of Webb's other pieces.

Once Webb's components are constructed, the major task of assembling and testing the full telescope remains. At key points throughout Webb's construction process, components are tested to make sure they function, then tested again as they are assembled with other pieces into larger components. Each part must function individually, then again as a group, then finally as a complete telescope. The testing ensures that all of Webb's pieces will withstand the stresses of launch and the extreme conditions of space.

Once they are assembled into larger components, Webb's science instruments and mirror segments will need to be tested to ensure that they can withstand temperatures up to -390 F° (-198 C°) and the vibrations they will encounter at launch. At Goddard Space Flight Center in Maryland, the science instruments will be brought together and assembled into a larger unit, which will be subjected to both temperature and vibration testing. Separately, the actuators will be attached to the individual primary mirror segments, and the mirrors will be mounted onto their support structure and tested.

Once those tests are passed, the mirror assembly and instrument package will be joined, and the entire assembly will be tested as a whole at Johnson Space Center in Texas. Because the Webb is so big, the chamber used for the testing must be equally large, so engineers are currently modifying an 120-foot-tall vacuum chamber originally used for the Apollo program. When that test is over, the sunshield and spacecraft bus will be added, the telescope will be tested again, and then Webb will be prepared for launch.