High-orbit satellites can provide navigation services for travel to the moon. Currently, spacecraft in the region between the moon and Earth (known as cislunar space) lack a positioning service like GPS that is always available. To address this issue, the Laser Communications Group and Advanced Capabilities and Technologies Group at MIT Lincoln Laboratory are developing a concept called the Light High-Orbit Utility Signal Emitter (LightHOUSE). LightHOUSE would use a small constellation of satellites in high-altitude orbits as cooperative optical beacons. These beacons would exchange timing and communication signals with user spacecraft and use imaging against the stellar background to estimate each spacecraft's three-dimensional position and velocity. By providing timely, independent navigation data, LightHOUSE could reduce the need for corrective maneuvers, preserve spacecraft propellant, lessen the burden on onboard navigation sensors, and ease demand on existing ground-based systems. The concept of LightHOUSE is based on laboratory work demonstrated through NASA-sponsored programs such as TBIRD and O2O, as well as the Optical Time Transfer for Resilient Satellite Communications Networks project led by the Laser Communications Group. LightHOUSE beacons would be based in ultrahigh orbits, up to roughly 1 million miles in altitude, allowing communication with spacecraft on the far side of the moon as viewed from Earth. The central engineering challenge is making the asymmetry work across cislunar space. Blogger's Review: This technology has the potential to revolutionize navigation and communication between the Earth and the moon, reducing the energy consumption and improving the navigation accuracy of spacecraft, with a wide range of applications and potential.