At preciously the moment that the outer edge of the 3CM unit touches the lead edge of the Upper Rotational Module of the MMS-1 spacecraft the crew of Atlantis bring the unit to a full and total stop. Astronauts in EVA Thruster Suits now leave Discovery and make the short journey to the outer hull of the 3CM unit. Mounted on the 3CM unit are a series of eight slide-guide docking units which will, in the first instance allow the unit to slide squarely into place within the Lower Rotational Module of the MMS-1. With the 3CM ready and the slide-guide units extended onto the outer hulls of the Alpha, Bravo, Charlie and Delta spine sections of the MMS-1 the next phase of the mission can now commence. The “soft docking” of the 3CM unit to the Lower Rotational Module has created a pressure seal which NASA engineers plan to use to slowly pull the unit into place within the Lower Rotational Module unit. As air is slowly pumped from tanks mounted in the cargo bay of the Endeavour into the Lower Rotational Module the pressure slowly raises until it reaches what NASA engineers call a “critical point pressure”. Too much air and the pressure will dislodge the 3CM unit from its location. Too little air and the entire operation will have to be continued in stages and take far longer to complete than NASA has planned. As the crew of Endeavour report that the “critical pressure point” has now been reached and the pressure hoses leading from the Orbital Shuttle to the Lower Rotational Module are closed the astronauts positioned on the hull of the 3CM unit report that it is still safely in place on the outer edge of the Lower Rotational Module. With the pumping operation completed the Flight Director in NASA’s Mission Control far below gives the ok for the next phase of this complex operation to start.