NASA is developing a new test telescope consisting entirely of glass-based material for the LISA mission, which will measure gravitational waves in space. The Engineering Test Unit, announced by the institution on October 8, is the last testing unit before the production of equipment to be used in flight. In addition, L3Harris will undertake the design, assembly and integration of the telescope, while NASA will transfer its prototype experience to the new model.
NASA’s new LISA statement states that this unit will also be the first optical telescope delivery to ESA. On the other hand, the team advanced its development work by delivering a separate structural model made of metal instead of glass in June. Therefore, the announcement does not mean that LISA’s flight telescopes are complete, but rather describes a new step in the pre-production engineering phase.
LISA, managed by ESA, will operate three spacecraft in a triangle extending 2.5 million kilometers on each side. Two telescopes on each vehicle will send infrared laser beams to neighboring vehicles while also receiving beams from them. The mission will thus investigate low-frequency gravitational waves that cannot be monitored from Earth by measuring extremely small distance changes between vehicles.
Gold-plated mirror and Zerodur material support precise laser measurement
All of the telescopes will consist of an amber-colored glass-ceramic material called Zerodur, which changes its shape very little over a wide temperature range. NASA’s prototype announcement in 2024 states that the Schott company in Mainz, Germany, produced the material and used it in high-precision optical applications. In addition, this material is also used in telescope parts that need to maintain their precise shape, other than mirrors.
On the other hand, the gold coating on the surface of the primary mirror helps reflect the infrared laser beams used more efficiently. The coating also helps the telescope maintain its operating temperature by reducing heat loss on the mirror surface exposed to the cold environment of space. NASA states that the prototype works best in conditions close to room temperature and therefore attaches importance to heat management.
The first full-scale prototype arrived in the clean room of the Goddard Space Flight Center in Maryland in May 2024 and underwent inspections. In addition, L3Harris produced and assembled this development unit in Rochester, New York, and delivered it to NASA. The new engineering telescope will carry the details learned from the tests of this prototype to the next model before the transition to flight hardware.
LISA’s laser measurements require precision to track distance changes on the picometer scale, which is one trillionth of a meter. For this reason, the mirror’s ability to reflect and maintain its shape against temperature serves a different purpose than just image quality. NASA and ESA plan the launch of the mission in the mid-2030s and continue the development of six telescopes in line with this schedule.