By Kim Smiley
On October 31, 2014, Virgin Galactic’s commercial space vehicle, SpaceShipTwo, tore apart over the Mojave Desert in California during its fourth rocket-powered test flight. One pilot was killed and the other seriously injured. An investigation is underway to determine exactly what caused the crash, but initial data indicates that the tail booms used to slow down the vehicle moved into the feathered position prematurely, increasing the aerodynamic force. This disaster has the potential to impact the emerging commercial space industry as regulators and potential passengers are reminded of the inherent dangers of space travel.
This issue can be analyzed by building a Cause Map, a visual method for performing a root cause analysis. An initial Cause Map can be built using the information that is currently available and then easily expanded as more data is known. The first step is to fill in an Outline with the basic background information of the incident. Additionally, the impacts to the overall goals are listed on the Outline to determine the scope of the issue. The Cause Map is then built by asking “why” questions.
Starting with the safety goal in this example: one pilot was killed and another was injured because a space vehicle was destroyed and they were onboard. (When two causes both contribute to an effect, they are both listed on the Cause Map and joined with an “and”.) SpaceShipTwo is designed to hold passengers, but this was a test flight to assess a new fuel so the pilots were the only people onboard. The space vehicle tore apart because the stress on the vehicle was greater than the strength of the vehicle. The final report on the accident will not be available for many months, but the initial findings indicate that the space vehicle experienced greater aerodynamic forces than expected.
The space vehicle used tail booms that were shifted into a feathered position to increase drag and reduce speed prior to landing. Video shows the co-pilot releasing the lever that unlocked the tail booms earlier than expected while the vehicle was still accelerating. It’s unclear at this time why he released the lever. The tail booms were not designed to move when unlocked and a second lever controls movement, but investigators speculate that the aerodynamic forces on the space vehicle while it was still accelerating caused them to lift up into the feathered position once they were unlocked. The vehicle disintegrated seconds after the tail booms shifted position, likely because of the aerodynamic forces in play.
After the final report is released, the Cause Map can be expanded to include the additional information. To view a high level Cause Map of this accident, click on “Download PDF” above.