NASA has advanced its work on a new all-glass telescope for the LISA (Laser Interferometer Space Antenna) mission, an observatory designed to detect gravitational waves. L3Harris Technologies will design, assemble and integrate the telescope, called the Engineering Test Unit, which NASA describes as a final step toward future production of flight hardware. The European Space Agency leads LISA, which is slated for launch in the mid-2030s, with NASA contributing telescopes, other hardware and engineering and scientific support.

LISA will place three satellites in an Earth-following orbit forming a triangle 1.6 million miles (2.5 million kilometers) on each side. Each satellite will carry two telescopes that send and receive infrared laser signals between neighboring spacecraft, measuring tiny changes in relative distance caused by passing gravitational waves. Ira Thorpe, NASA's project scientist for the mission at Goddard Space Flight Center, said the changes are smaller than the width of a helium atom but could reveal low-frequency gravitational waves undetectable from Earth, including mergers of distant black holes.

Each telescope is to be made entirely of Zerodur, an amber-colored glass-ceramic that resists shape changes across temperature ranges. L3Harris delivered a prototype telescope in 2024, and in June the team delivered a metal structural model. Ritva Keski-Kuha, who leads the LISA telescope program at Goddard, said testing lessons are being carried into the new unit, described as the last pre-flight unit and the first optical telescope delivery to ESA. NASA's other contributions include the laser system and data analysis.