speed and attitude at separation, the guidance system malfunctioned and caused an unstable flight trajectory. Impact occurred only downrange. Vehicle N-13 was launched 13 days later and carried no standpipes, but it did have increased pressure in the first stage propellant tanks, which did cut down on vibration. In addition, the oxidizer feedlines were made of aluminum instead of steel. On the other hand, the exact reason for pogo was still unclear and a vexing problem for NASA. The tenth Titan II flight (Vehicle N-15) took place on 10 January, the only nighttime Titan II test. While it appeared that the pogo problem was largely contained on this flight, the second stage lost thrust again due to a restriction in the gas generator and so only achieved half its intended range. While previous second stage problems were blamed on pogo, this could not be the case for N-15. Meanwhile, combustion instability was still an issue and was confirmed by Aerojet static-firing tests which showed that the LR91 Liquid-propellant engine had difficulty attaining smooth burning after the shock of startup. Efforts to human-rate the Titan II also ran afoul of the fact that the Air Force and not NASA was in charge of its development. The former's primary aim was to develop a missile system, not a launch vehicle for Project Gemini, and they were only interested in technical improvements to the booster insofar as they had relevance to that program. On 29 January, the Air Force Ballistic Systems Division (BSD) declared that pogo in the Titan had been reduced enough for inter-continental ballistic missile (ICBM) use and that no further improvements needed to be made. While adding more pressure to the propellant tanks had reduced vibration, it could only be done so much before putting unsafe structural loads on the Titan and in any case the results were still unsatisfactory from NASA's point of view. While BSD tried to come up with a way to help NASA out, they finally decided that it was not worth the time, resources, and risk of trying to cut down further on pogo and that the ICBM program ultimately came first. Despite the Air Force's lack of interest in human-rating the Titan II, General Bernard Adolph Schriever assured that any problems with the booster would be fixed. BSD decided that 0.6 Gs was good enough despite NASA's goal of 0.25 Gs and they stubbornly