Is it safe to assume a mixture ratio of 2.16 with an ISP of 313 s for the NTO/MMH, SuperDraco Engine manufactured by SpaceX?

I am referencing the 2.16 propellant mixture ratio, and estimating or more so assuming the ISP.

I am calculating the propellant mass required for NTO/MMH propellant rocket engine, SuperDraco to conduct a change of Delta-V. However the calculation relies on mixture ratio of the propellant and ISP of the rocket engine? Can I please get your input for more accurate values. [http://www.astronautix.com/n/n2o4mmh.html ][1]



1 Answer 1


You're already mentioning ratio to three decimal digits, which is plenty for engineering level of calculations.

I don't know exact ratio. I'd even assume that they can change that - slightly - by results of previous missions. The question is a bit strange because you have to be sure of many things to get optimal numbers. For example, propellant can contain some hydrazin or UDMH (e.g. Aerozine was a mixture). Optimal by Isp ratio slightly depends on pressure in the chamber, and we don't have exact number here. Ratio could be not Isp-optimal for reasons of e.g. lowering temperature. And many small modifications in the system - temperature of ullage gas, tank pressure, properties of piping system, valves etc. - may change the desired ratio slightly. On the other hand, changes in Isp would be pretty small - a percentage point if not less - so delta-V won't be affected that much.

  • $\begingroup$ Does not answer the question. $\endgroup$ Commented Apr 8, 2019 at 0:43

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