Following the completion of critical mirror alignment steps, NASA’s James Webb Space Telescope team expects that Webb’s optical performance will be able to meet or exceed the science goals the observatory was built to achieve. The 18th of the telescope’s primary mirror segments were installed Nov. 16 and the 19th mirror segment was installed Nov. 20. Each primary mirror segment is about the size of a coffee table and weighs about 88 pounds.
The next step for the mirror installation team is to install the telescope’s secondary mirror, which is even smaller but weighs almost as much as the primary mirror segments. The secondary mirror is about 1.
On March 11, the Webb team completed the stage of alignment known as “fine phasing.” At this key stage in the commissioning of Webb’s Optical Telescope Element, every optical parameter that has been checked and tested is performing at, or above, expectations. The team also found no critical issues and no measurable contamination or blockages to Webb’s optical path. The observatory is able to successfully gather light from distant objects and deliver it to its instruments without issue.
The Fine Guidance Sensor team has performed a series of final tests of the component before shipping to Goddard. This component will help Webb navigate to celestial targets and keep them locked onto them during observations. The team has completed its mechanical integration, electrical testing, and successfully completed vibration testing with the Fine Guidance Sensor installed on the telescope’s Integrated Science Instrument Module. The component was returned to ITT Exelis in Rochester, New Hampshire, for thermal vacuum testing.
Although there are months to go before Webb ultimately delivers its new view of the cosmos, achieving this milestone means the team is confident that Webb’s first-of-its-kind optical system is working as well as possible.“It’s a great feeling when you see the images that come out,” said Eric Smith, optical telescope element manager for JWST at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We can see stars and galaxies and nebula, and we can also see a beautiful solar filter for the first time.”
“More than 20 years ago, the Webb team set out to build the most powerful telescope that anyone has ever put in space and came up with an audacious optical design to meet demanding science goals,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington. “Today we can say that design is going to deliver.”
While some of the largest ground-based telescopes on Earth use segmented primary mirrors, Webb is the first telescope in space to use such a design. The 21-foot, 4-inch (6.5-meter) primary mirror – much too big to fit inside a rocket fairing – is made up of 18 hexagonal, beryllium mirror segments.
Each segment is nearly 8 feet (2.4 meters) tall and weighs approximately 200 pounds (100 kilograms). The primary mirror has a total area of 25 square feet (2.3 square meters). Optical systems in each of the 18 segments work together as one large 21-foot mirror, giving Webb its unique, incredibly sharp vision.
“In addition to enabling the incredible science that Webb will achieve, the teams that designed, built, tested, launched, and now operate this observatory have pioneered a new way to build space telescopes,” said Lee Feinberg, Webb optical telescope element manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.”The very large primary mirror, the largest ever flown in space, is only one of Webb’s many novel features.
