scope:

Description of Driving Event:

On February 19, 2002, an incident occurred during the hot-fire testing of the Army vortex thrust chamber assembly at MSFC Test Stand 115. This was the fourth hot-fire test of the hardware, but the first test flowing both LOX (liquid oxygen) and RP-1 fuel as the main propellants and GOX (gaseous oxygen) and GH2 (gaseous hydrogen) for the torch igniter. The first three tests, which were successfully completed, were hot-fire tests of the GOX/GH2 torch igniter only. For these tests, gaseous nitrogen was flowed through the main injector. The fourth test was to characterize start up transient conditions.

The objectives of the vortex chamber testing were to demonstrate the feasibility of vortex chamber technology for a liquid hydrocarbon/liquid oxygen system, demonstrate several ignition techniques (torch, laser and combustion wave), demonstrate two rocket plume measurement methods (emission/ absorption and Raman scattering), and characterize the chamber performance by means of thrust measurements and species uniformity in the plume flow field.

At approximately 5.3 seconds into the automated firing sequence, a catastrophic failure occurred to the test article. A redline cut initiated shutdown at that time. The facility proceeded to follow the normal shutdown sequence, which initialized the safeguarding of the facility and test article. The area was immediately roped off with quality monitoring activities. Once the facility safeguarding was completed, it was determined that there were no injuries to personnel, and damage to the test facility was minor. Most of the test article pieces were recovered and provided important information in the investigation and analysis of the incident.

A timeline was constructed from the high-speed video film, control sequence data, and both the low and high-speed instrumentation. Due to the lack of a time stamp on the high-speed video, there were some inherent inaccuracies in correlating the instrumentation data timing with the video. Although all data systems were operational at the time of the incident, the over pressurization/detonation occurred very rapidly and as a result there was limited evidence of the over-pressurization in the collected data. The test article failed at the mounting bolts as well as the injector and spacer, and hardware was recovered over a large area of the test facility and nearby fields/woods.

The scenarios developed by the incident investigation team pointed out that three significant events occurred during the start up transients: 1) surface burning of the chamber head end hardware, 2) surface burning of the injector module hardware, and 3) accumulation of propellants in the chamber. The primary cause of the incident was the propellant accumulation in the chamber during the ignition delay. The first two events are not believed to have caused the eventual over-pressurization.