Since its launch, the James Webb Space Telescope (JWST) has undergone meticulous fine-tuning to uphold its exceptional optical capabilities, paving the way for groundbreaking cosmic observations and future astronomical discoveries. As the largest and most powerful telescope ever sent into space, JWST’s design includes a mirror composed of 18 individual hexagonal segments, which are aligned with remarkable precision to operate as a unified 21.6-foot (6.5-meter) reflector.

The intricate task of aligning and maintaining this sophisticated system demands constant vigilance from a dedicated team of engineers and optics scientists. Dr. Marcio B. Meléndez, the principal astronomical optics scientist for JWST at the Space Telescope Science Institute, sheds light on the complexities involved in aligning the telescope’s mirrors post-launch, as well as the ongoing efforts to ensure its accuracy during scientific operations.

Following the successful launch and deployment of JWST, a detailed process commenced to align its large, golden mirrors. This alignment process spanned nearly three months, transitioning from the initial deployment of 18 unfocused segments to a fully aligned system, constrained only by the optical design parameters.

Although the precise alignment of the telescope was finalized in early 2022 during its commissioning phase, maintaining this alignment is not a static endeavor. Various factors, including temperature fluctuations and ’tilt’ events, can disrupt the alignment, necessitating a lifelong maintenance program. The wavefront sensing team, tasked with ensuring the mirrors remain in optimal condition, continually monitors, investigates, trends, and occasionally adjusts the primary mirror segments throughout the telescope’s scientific operations.

These activities are executed from the Webb Mission Operations Center, located at the Space Telescope Science Institute in Baltimore. The monitoring program consists of a series of observations utilizing specialized optical sensing equipment within the Near Infrared Camera (NIRCam) instrument. This setup includes a series of lenses designed to intentionally defocus the images of stars by a predetermined amount. The resulting defocused star images contain measurable features that allow the team to ascertain the telescope’s alignment through a technique known as phase retrieval, which helps determine what is referred to as the ‘wavefront error.’

Currently, telescope monitoring observations are scheduled every other day, interspersed with Webb’s scientific observations, with each session running for approximately 20 minutes. All telescope monitoring data is made publicly available through the MAST archive, enabling observatory users and other interested researchers to view and model the optical quality using specialized tools.

The NIRCam instrument plays a pivotal role in this monitoring process, producing in-focus images that are essential for understanding the telescope’s performance. By analyzing these images, scientists can make informed decisions about necessary adjustments to maintain the telescope’s high standards of optical fidelity.

As JWST continues its mission to unveil the mysteries of the universe, the ongoing efforts to maintain and enhance its optical capabilities are vital. The collaboration between engineers and scientists ensures that this state-of-the-art telescope remains at the forefront of astronomical research, ready to explore the cosmos and deliver unprecedented insights into the universe’s origins and evolution.

With its advanced technology and dedicated team, the James Webb Space Telescope is set to redefine our understanding of the universe, highlighting the importance of precision engineering and ongoing maintenance in the realm of space exploration.