Beginning on flight day one, series of thruster burns were performed daily to bring Discovery in line with Mir. Original plan called for the orbiter to approach to no closer than 10 meters (33 ft) from Mir, and then complete a flyaround of the Russian space station. However, three of the 44 orbiter Reaction Control System (RCS) thrusters—small firing jets used for on-orbit maneuvering—sprang leaks prior to rendezvous. Shortly after main engine cutoff, two leaks occurred in the aft primary thrusters, one of which—called R1U—was key to rendezvous. A third leak occurred later in flight in the forward primary thruster, but the crew was able to fix the problem.