everyman@gorn.santa-cruz.ca.us (arvey j. shier) (03/10/91)
In response to a query re composition of SRB propellant I erroneouly gave an approximation of the composite propellant as approximately 84% oxidizer (ammonium percholorate) and 16% fuel (aluminum) with some additives included. Subsequently, another source gave a much more accurate list of the ingredients which I found quite correct. I would like to comment that percentage of oxidizer given above is incorrect but represents a number in composite solid propellant mixtures known as "loading". This number represents the total of the oxidizer, ammonium perchlorate, and the fuel, aluminum. As noted in the more detailed and correct version the percent of AP is approximately 70% and with the 16% aluminun totals an 86% "loaded" propellant. The PBAN binder (approx. 12%) and burning rate catalyst with small amounts of other additives make up the total. Attempts to improve Isp are sometimes made by increasing the "loading". This is would increase the percentages of AP and/or Al at the expense of the binder. The physical properties of the propellant would be degraded somewhat but is nonetheless accepted in some cases. Not however on the SRB's at this time.