2 thoughts on “Virgin Galactic’s Engine Issues”

1. The reason for the choice of the hybrid for the SS2 rather than a higher performance liquid-fueled engine was the idea that a hybrid engine could not explode. However, the accident in 2007 at Scaled Composites due to a nitrous oxide explosion has destroyed that misperception. Indeed because of the instability of nitrous oxide one team involved in developing a rocket propelled car suggests nitrous should not be used for passenger flight:

   Observations and comments on Cal/OSHA report (Inspection No: 31081103) on fatal accident at Mojave test site of Scaled Composites at the Mojave Air and Space Port, 26th July 2007.

   While it is most advisable to apply the established safety protocols relating to liquid oxygen, such protocols, in themselves are not sufficient to ensure the safe handling of Nitrous Oxide. The unique physical properties of N2O require further protocols above and beyond those used for liquid oxygen.
   Safety protocols for N2O, in a rocket motor system, should include (in addition to the protocols used for Liquid Oxygen)

   * The detailed study of materials compatibility of all components in the system
   * Avoidance of high temperatures at all points in the system
   * Stirring of large tanks
   * Avoidance of the gaseous phase both during apparatus filling and in use
   * Purging of lines and valves immediately prior to ignition
   * Not using any component that may have previously absorbed N2O – especially fuel grains

   We are not confident that, even with these additional precautions, that we yet know enough about N2O to consider it a safe oxidiser for use in passenger flight. In the light of what we do know, safety must remain a major concern.

   http://www.knightsarrow.com/rockets/scaled-composites-accident/

   1. Well, liquid N2O can possibly become a shock-sensitive explosive, and that’s never good for a passenger vehicle.

      Fromd Edwards AFB, 2008.

      N2O incidents indicates that safety practice understanding beyond current knowledge is needed.
      …
      Experimental investigation to gain recognition of large quantity N2O explosive and ignition traits may be the only way to ensure large N2O system safety. Prior hazard and monopropellant decomposition studies largely indicated that N2O was difficult to initiate into dangerous monopropellant decompositions. Based on prior studies and use of N2O for decades in dental practice without serious incidents, many people have considered use of N2O as safe. Early explosive hazard studies did not indicate a serious explosive nature for N2O. Inadequacy of historical N2O hazard study experiments was that they used too small volumes in their studies.

      So what may be safe on a small scale might not be safe on a big scale.

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