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Letters

posted: 06 December 2007
02:32 pm ET













Little Mistake with Big Difference



This letter is in response to




the Commentary article “Dangers of Nitrous Oxide No Surprise” [




Sept.




3




, page 19]




. Many causes are mentioned in this article for the tragic accident that




occurred at the Scaled Composites test site




July 26, which









led to the huge devastation of equipment and personnel casualty.

Among other things it is claimed specifically that




“nitrous oxide sprayed on an HTPB fuel grain can saturate that grain and turn into a substance as volatile as TNT.”



Such an assertion is not acceptable from our point of view. At temperatures below 600 degrees




Celsius, nitrous oxide




is an inert substance. This means that it does not react with any hydrocarbon like HTPB to form a highly explosive compound. Diffusion claimed by Mark Holthaus, which would lead to a mixture of oxidizer and fuel in explosive concentration, also can




be excluded because only very small quantities of




nitrous oxide could be deposited into the hydrocarbon.

It seems that the effects mentioned are more related to nitrogen dioxide




, a highly corrosive and nitrating substance. But that has nothing to do with nitrous oxide




.

Our organiz




ation, the




Scientific Workgroup for Rocketry and Spaceflight




, a non




profit organization located at the Technical University of Munich, has more than




40 years of extensive experience in hybrid rocket propulsion systems. Over the past years we have worked with many different oxidizers and propellants including nitrous oxide.






We performed some practical tests to disprove this claim. For this purpose small solid samples of HTPB were exposed to liquid nitrous oxide




for




approximately 2 minutes




. Afterwards the samples were ignited by several methods among other things by the use of unshielded flames. None of these tests showed the explosive effect that




is postulated in the related article.

A second interesting point is that




nitrous oxide also is




used in other technical applications besides the aerospace industry.




The application of




nitrous oxide in the food industry is exceptionally interesting. There the




nitrous oxide is used as a food additive due to its steriliz




ing character;




within this application it




also is designated as E 942. In particular




nitrous oxide is used as an additive in milk products, for example




to froth up cream.

Looking at it from this aspect, the following statement of Mark Holthaus is very interesting: “If the oxidizer [




in this connection related to N2O




] is exposed to any organic contamination it can become explosive.”




Now if we combine Holthaus




statement with the aforementioned fact, we would reach the conclusion, that if we stir up cream with a plastic spoon, the spoon –




and also the cream




– could turn into an explosive,
which destructiveness is beyond that of TNT. This would indeed be good news for any terrorist who wants to blow up an airliner. All required components would be brought up directly to the seat of the terrorist by the inflight service. Fortunately, this scenario will not happen –




the allegations of Mark Holthaus in reference to the characteristics of HTPB saturated with nitrous oxide




have nothing to do with reality.

Scaled Composites should continue with its choice of hybrid engines – it is the right and safe rocket propulsion for public spaceflight.






Joachim Sturm Stefan Koeglmeier

Scientific Workgroup for Rocketry and Spaceflight

Munich, Germany