rendezvous. This took place at 54:26:12.3, raising the craft's orbit to . The fourth day's program (March 6) was for Schweickart to exit the hatch on the LM and make his way along the outside of the spacecraft to the CM's hatch, where Scott would stand by to assist, demonstrating that this could be done in the event of an emergency. Schweickart was to wear the life support backpack, or PLSS, to be worn on the lunar surface EVAs. This was the only EVA scheduled before the lunar landing, and thus the only opportunity to test the PLSS in space. McDivitt initially canceled the EVA due to Schweickart's condition, but with the lunar module pilot feeling better, decided to allow him to exit the LM, and once he was there, to move around the LM's exterior using handholds. Scott stood in the CM's hatch; both men photographed each other and retrieved experiments from the exterior of their vehicles. Schweickart found moving around easier than it had been in simulations; both he and Scott were confident that Schweickart could have completed the exterior transfer if called upon to do so, but considered it unnecessary. During the EVA, Schweickart used the call sign "Red Rover", a nod to the color of his hair. On March 7, the fifth day, came "the key event of the entire mission: the separation and rendezvous of the lunar module and the command module". The lunar module lacked the capability to return the astronauts to Earth; this was the first time space travelers had flown in a vehicle that could not take them home. McDivitt and Schweickart entered the LM early, having obtained permission to do so without wearing their helmets and gloves, making it easier to set up the LM. When Scott in Gumdrop pushed the button to release the LM, it initially hung on the latches at the end of the docking probe, but he hit the button again and Spider was released. After spending about 45 minutes near Gumdrop, Spider went into a slightly higher orbit, meaning that over time, the two craft would separate, with Gumdrop ahead. Over the next hours, McDivitt fired the LM's descent engine at several throttle settings; by the end of the day the LM was thoroughly test-flown. At a distance of , Spider fired to lower its orbit and thus begin to catch up with Gumdrop, a process