from LC-15 on 7 June. First stage performance was near-nominal, but the second stage developed low thrust due to a restriction in the gas generator feed. The Range Safety officer sent a manual shutdown command to the second stage, causing premature RV separation and impact well short of the intended target point. The third launch, Missile N-6 on 11 July, was completely successful. Aside from pogo oscillation (the nickname NASA engineers invented for the Titan's vibration problem since it was thought to resemble the action of a pogo stick), the Titan II was experiencing other teething problems that were expected of a new launch vehicle. The 25 July test (Vehicle N-4) had been scheduled for 27 June, but was delayed by a month when the Titan's right engine experienced severe combustion instability at ignition that caused the entire thrust chamber to break off of the booster and fall down the flame deflector pit, landing about 20 feet from the pad (the Titan's onboard computer shut the engines down the moment loss of thrust occurred). The problem was traced to a bit of cleaning alcohol carelessly left in the engine. A new set of engines had to be ordered from Aerojet, and the missile lifted off from LC-16 on the morning of 25 July. The flight went entirely according to plan up to first stage burn, but the second stage malfunctioned again when the hydraulic pump failed and thrust dropped nearly 50%. The computer system compensated by running the engine for an additional 111 seconds, when propellant depletion occurred. Because the computer had not sent a manual cutoff command, reentry vehicle separation and vernier solo phase did not occur. Impact occurred downrange, half the planned distance. The next three launches Missile N-5 (12 September), N-9 (12 October), and N-12 (26 October), were entirely successful, but the nagging pogo problem remained and the booster could not be considered man-rated until this was fixed. Martin–Marietta thus added a surge-suppressor standpipe to the oxidizer feed line in the first stage, but when the system was tested on Titan N-11 on 6 December, the effect was instead to worsen pogo in the first stage, which ended up vibrating so strongly that unstable engine thrust resulted. The result of this was to trip the first stage pressure switch and terminate thrust early. The second stage then separated and began its burn, but due to the improper