HOUSTON, TX (WHNT) — The Orion spacecraft reentered the moon’s sphere of influence Saturday on the 18th day of its unmanned mission.

NASA said the spacecraft re-entered the sphere of influence, which marks the area where the Moon is the main gravitational force acting on the spacecraft, at 4:45 p.m. Central Time on Saturday. Orion will exit the lunar sphere of influence for the final time on Tuesday.

The spacecraft entered the Moons gravity about 39,993 miles away from the lunar surface and will leave it after a return powered flyby about 79 miles away from the surface.

NASA gave updates on Orion’s close flyby of the moon on the spacecraft’s official Twitter. A video of the craft coming within 687 miles of the surface of the moon can be found here

Engineers also took the time on Saturday to perform a development flight test objective that change the minimum jet firing time for the spacecraft’s reaction control thrusters over a 24-hour period. The test was meant to model jet thruster firings that will be part of the crewed Artemis II mission.

The test used the reaction control system (RCS) thrusters on the spacecraft’s European Service Module, which were built by France-based ArianeGroup. So far all the firings of the RCS thrusters during Orion’s journey have been from the service module.

Another set of 12 RCS thrusters, built by Aerojet Rocketdyne which has a facility in Huntsville, are present on Orion’s crew module. These thrusters will be tested a few days before the spacecraft’s return to earth. Their primary purpose it to help orient Orion for re-entry into Earth’s atmosphere to help create a safe landing.