Dragon ballistic/drag coefficients?

Question

I'm looking for some estimates of Dragon's ballistic or drag coefficients in its reentry (heat shield forward) configuration. Estimates for other spacecraft would be useful also as they would give me some intuition of what's normal and what's not. I know the exact numbers depend on many factors like air density, velocity, etc, but it's OK if you know them for just some (any) particular configuration. Ballpark figures OK. Thanks!

Answer 1

This may be of help to you: Planetary Mission Entry Vehicles Quick Reference Guide. Version 3.0. It contains lots of data on various entry probes (including ballistic coefficients) although it only goes up until 2003 (MER-A & MER-B).

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Edit:

User has retired but question is still likely to be of interest, and I have found an accurate estimate while working on an answer to Dragon re-entry flight profile?

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While in general a function of Mach number, these values are (pretty much) invariant in the hypersonic regime (Mach >= 5) and can reasonably be treated as constants in low-mid fidelity simulations.

I was able to infer a drag coefficient from the abstract of A. A. Gonzales et al., "Mars Sample Return using commercial capabilities: Mission architecture overview" and its associated presentation focusing on EDL.

The presentation contains this slide on methodology showing that NASA Ames did some CFD on a representative Dragon 2 / Crew Dragon model:

From abstract:

Total entry masses between 7 and 10 mt were considered

Plot from presentation:

Where $\beta$ is the ballistic coefficient $\beta=\frac{m}{C_D S}$:

Area, S ($m^2$)	Mass (kg)	$\beta$ ($kg/m^2$)	$C_D$
12.6	7,000	450	1.24
12.6	10,000	650	1.22

Thus $C_D=1.23$ (and $\beta=622$ $kg/m^2$).

References:

• A. A. Gonzales et al., "Mars Sample Return using commercial capabilities: Mission architecture overview," 2014 IEEE Aerospace Conference, 2014, pp. 1-15, doi: 10.1109/AERO.2014.6836421.
• L. G. Lemke et al."Mars Sample Return Using Commercial Capabilities: Propulsive Entry, Descent and Landing," 2014 IEEE Aerospace Conference, 2014 (retrieved from NTRS id: 20140013203)

Answer 2

Not knowing how much you already know about this, I'll just point out that drag coefficients at high speeds (10-25 Ma) are still Mach number dependent, though far less so than at low Mach number (less than 3 Ma). They are also dependent on air density and pressure (Reynolds effect). Most modeling takes a simplified approach and ignores much of this. Suggest looking at John Anderson's book on introduction to flight or fundamental aerodynamics to see some graphs of coefficient of drag vs Mach that make this point. The topic you ask about is referred to as "blunt body" aerodynamics.