Pure metallic hydrogen is predicted to have a specific impulse ( Isp ) of 1700 seconds , but the reaction temperature is too high for current engine materials . Diluting metallic hydrogen with liquid hydrogen can reduce the reaction temperature to levels compatible with current material limits and still provide an Isp greater than 900 s. Metallic hydrogen has not yet been produced on earth , but experimental techniques exist that may change this situation . This paper will provide a brief description of metallic hydrogen and the status of experiments that may soon produce detectable quantities of this material in the lab . Also provided are some characteristics for diluted metallic hydrogen engines and launch vehicles .