Editing Vanguard TV-3 (section)

== Cause of failure ==
The exact cause of the accident was not determined with certainty due to limited telemetry instrumentation at this early phase,<ref name="green">{{cite web|url=http://www.hq.nasa.gov/office/pao/History/SP-4202/cover.htm|title=Chapter 11: From Sputnik I to TV-3|access-date=2011-02-26|last=McLaughlin Green|first=Constance|author2=Lomask, Milton|year=1970|work=Vanguard – A History|publisher=NASA|archive-date=7 October 2018|archive-url=https://web.archive.org/web/20181007015322/http://www.hq.nasa.gov/office/pao/History/SP-4202/cover.htm|url-status=dead}} {{PD-notice}}</ref> but [[Martin Marietta]] concluded that low [[fuel tank]] pressure during the start procedure allowed some of the burning fuel in the [[combustion chamber]] to leak into the fuel system through the [[injector]] head before full propellant pressure was obtained from the [[turbopump]]. [[General Electric]], on the other hand, argued that the problem was a loose fuel connection. In hindsight, the first problem appeared to cause the second. The investigation concluded that tank and fuel system pressure were slightly lower than nominal, which resulted in insufficient pressure in the injector head. As a result, hot combustion gas backed up into the injector head and caused a large pressure spike. The injector rings completely burned through, followed by the rupture of the combustion chamber. At T+1 second, a shock wave in the thrust section of the booster ruptured a fuel feed line, completely terminating engine thrust. GE technicians had failed to catch this design flaw during testing and a temporary fix was made by increasing tank pressure. Eventually, a further modification was made by using [[ethane]] gas to increase fuel force and prevent rough start transients.<ref>{{cite web |url=https://www.scribd.com/document/46133829/The-Vanguard-Satellite-Launching-Vehicle-an-Engineering-Summary|title=The Vanguard Satellite Launching Vehicle an Engineering Summary; Rocket; International Geophysical Year}}</ref> The X-405 engine did not fail again on subsequent launches and static firing tests.