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I cannot find an authoritative resource that describes how to estimate base drag for a missile or space launcher during powered flight. There are plenty of resources that describe how to estimate the common types of drag (form, induced drags) but nothing reliably describes base drag. Some papers are even contradictory.

FYI: Base drag is most commonly seen in the empty space behind the base of an artillery shell in flight. The air in this space forms a recirculation zone at lower than ambient pressure. This lower pressure acts like a drag force. Some shells even have a small rocket engine just to fill in this pressure to reduce overall drag and increase range. For rockets, if the stage diameter is bigger than the nozzle of the rocket, there is an annular base drag zone. Many people ignore it but some calculations show it may not be trivial depending on design. Some simulation models even give unphysical results (like discontinuites in speed). Of course, after flight tests everyone ignores the simulation estimates and models from the flight data -- if they get enough data.

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  • $\begingroup$ Related: space.stackexchange.com/q/38780/6944 space.stackexchange.com/q/38787/6944 $\endgroup$
    – Organic Marble
    Dec 10, 2022 at 16:04
  • $\begingroup$ Thank you for these citations. I've read these and some of the physics is similar to the effect I seek to capture. Indeed, the plume filling the ET void is an example of the "base bleed" artillery method I mentioned. Moreover, there is nothing predictive in these citations for the general case, IIRC. I was just hoping somebody knew far more than I without resorting to CFD methods and a giant multicore computer. I am compelled to live in a world of empirical methods whenever possible. $\endgroup$
    – Chris Ison
    Dec 10, 2022 at 19:31
  • $\begingroup$ There are some attempts to calculate a base flowfield here, but it's definitely in the CFD realm. semanticscholar.org/paper/… I don't think there is an easy + good way. Shuttle certainly had issues trying to predict it back in the 70s. $\endgroup$
    – Organic Marble
    Dec 10, 2022 at 19:41

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The book Missile Design and Engineering by Eugene Fleeman has exactly what you are looking for, including other "drag contributions" at different flight regimes too. It's in chapter 2.

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