Soyuz internal transfer docking unit. This system is used today for docking spacecraft to Mir. The active craft inserts its probe into the space station receiving cone. The probe tip catches on latches in the socket at the apex of the cone. Motors then draw the two spacecraft together. Latches in the docking collars catch, and motors close them. Fluid, gas, and electrical connections are established through the collars. After the cosmonauts are certain the seal is airtight, they remove the probe and drogue units, forming a tunnel between spacecraft and station. At undocking, four spring push rods drive the spacecraft apart. If the latches fail to retract, the spacecraft can fire