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    { "id" : "http://dbpedia.org/resource/Liquid_rocket_propellant"
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        "http://www.w3.org/2000/01/rdf-schema#comment" : [ "The highest specific impulse chemical rockets (liquid-propellant rockets) use liquid fuel propellants.Approximately 170 different liquid propellants have undergone lab testing.  This estimate excludes minor changes to a specific propellant such as propellant additives, corrosion inhibitors, or stabilizers.  In the U.S. alone at least 25 different propellant combinations have been flown.  However, there has not been a completely new propellant used in flight for nearly 30 years." ] ,
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