After waking up on flight day four, the crew began preparations for the maneuver that would brake them into orbit. At an altitude of the scientific instrument module (SIM) bay cover was jettisoned. At just over 74 hours into the mission, the spacecraft passed behind the Moon, losing direct contact with Mission Control. While over the far side, the CSM's service propulsion system engine burned for 6minutes and 15 seconds, braking the spacecraft into an orbit with a low point (pericynthion) of 58.3 and a high point (apocynthion) of 170.4 nautical miles (108.0 and 315.6 km, respectively). After entering lunar orbit, the crew began preparations for the Descent Orbit Insertion (DOI) maneuver to further modify the spacecraft's orbital trajectory. The maneuver was successful, decreasing the craft's pericynthion to . The remainder of flight day four was spent making observations and preparing for activation of the lunar module, undocking, and landing the next day.