Operational Problems With Subsystems

In order to achieve maximum penetration into the realms of hypersonic and space flight, the X-15 necessarily had to use many newly ccnceived, partially developed subsystems fabricated of new materials by new processes. The XLR99 rocket engine, the auxiliary power units (APU), and the stability augmentation (damper) system are examples. A host of new problems were encountered with the subsystems after the start of flight operations, and flight schedules were subject to innumerable delays (refs. 5, 7, and 21).

In retrospect, a great deal of money and lost time could have been saved through more imaginative and more elaborate ground testing of all major subsystems. This sounds like a serious general criticism. But one must remember that the only precedents available in the mid-fifties were those based on experience with ordinary aircraft and with the much simpler previous research airplanes. As it was, the initial environmental testing of the X-15 subsystems far exceeded that of any previous vehicle. In this area perhaps more than any other, the X-15 brought to light innumerable "real" problems which could not have been foreseen by any means other than involve ment with an actual flight vehicle. The program revealed the true nature of the difficulties encountered in an aerospace environment and identified many specific new requirements for developmental testing that were of value in subsystem development for the space program

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