The Optical Telescope Element (OTE) is the eye of the James Webb Space Telescope Observatory. The
OTE gathers the light coming from space and provides it to the
science instruments.
Webb needs a large mirror to collect as much light as possible to see galaxies
from the beginning of the Universe. Webb scientists and engineers have determined
that a primary mirror 6.5 meters (21.3 feet) across is what was needed to measure the
light from these galaxies.
The OTE has 2 other components: the Fine Steering Mirror (FSM); and the structural
pieces to hold everything together. The structural pieces include [the secondary mirror support structure
(SMSS) and the primary mirror backplane assembly.
The OTE tertiary
mirror and the fine steering mirror are both contained within an OTE subsystem
known as the Aft Optics Subsystem. The backplane, in addition to holding the OTE
together will be where the science instrument, in the Integrated
Science Instrument Module (ISIM), is installed in the Observatory.
Learn more about the different parts of JWST, and compare it to a simple telescope by playing our "Scope It Out" game!
More About Webb's Primary Mirror
No launch vehicle (rocket) is large enough to hold a 6.5-meter mirror if it was all one piece. The Webb team decided to build the mirror with 18 hexagonal primary mirror assembly segments, which can be folded up to fit into the launch vehicle and then unfold after launch.
This animation shows how the Webb can fold up to fit in the launch vehicle.
This animation shows the Webb unfolding and deploying in space.
So that the segments
work together as a single large mirror, the 18 segments have been divided into
3 groups of six mirrors, each group having a slightly different shape
(prescription). A system known as Wavefront Sensing & Control has been
developed, as well. The image at right shows the location of the different
mirrors within the primary mirror.
In addition to making the mirror small enough to fit into a rocket, the Webb
team also has to make it light enough to be launched. If the Hubble Space Telescope's
mirror (2.4 meters) was scaled to be large enough for Webb, it would be too
heavy to launch into orbit. The Webb team had to find new ways to build the
mirror so that it would be light enough. Read more about Webb's mirrors...
