Alignment of the James Webb Space Telescope optical telescope element

The optical telescope element (OTE) of the James Webb Space Telescope has now been integrated and aligned. The OTE comprises the flight mirrors and the structure that supports them – 18 primary mirror segments, the secondary mirror, and the tertiary and fine steering mirrors (both housed in the aft optics subsystem). The primary mirror segments and the secondary mirror have actuators to actively control their positions during operations. This allows the requirements for aligning the OTE subsystems to be in the range of microns rather than nanometers. During OTE integration, the alignment of the major subsystems of the OTE structure and optics were controlled to ensure that, when the telescope is on orbit and at cryogenic temperatures, the active mirrors will be within the adjustment range of the actuators. Though the alignment of this flagship mission was complex and intricate, the key to a successful integration process turned out to be very basic: a clear, concise series of steps employing advanced planning, backup measurements, and cross checks that this multi-organizational team executed with a careful and methodical approach. This approach was not only critical to our own success but has implications for future space observatories.