SSTO Concept Design Project Team
Section 6.8.7.
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SSTO Aerodynamics

To determine the question of aerodynamic efficiency of the gumdrop shape on ascent, we'll need to propogate the entire trajectory using a digital simulation that includes atmospheric drag. Total delta-V won't tell us much about aero drag because that's the speed we're going at the end of the flight.

Since drag will slow us down, we also would want to include the change in engine thrust.

The trick is to guesstimate a drag coefficient for a 41-degree cone and push that gumpdrop through the soup (of the atmosphere). I'd assume a trajectory with mostly a vertical component until you're up around 300,000 feet. Air density at that altitude is only about 4x10-9 slugs/ft3, so aerodynamic drag up there is almost negligible. Then pitch over and start the downrange acceleration.

The Shuttle actually lofts its trajectory, peaking higher than its final orbit, to avoid air drag. I'll be quick to point out that ugly as it is, the gumdrop is a more aerodynamically efficient shape than all that claptrap hanging on the Shuttle stack. We don't have struts, wings, and tail hanging in the breeze. The vehicle doesn't have abrupt changes in cross-sectional area or stagnation points like the pilots' windows. And it doesn't have that venturi between four different main bodies looking like an enormous flat plate.

If you start streamlining the body you'll find skin friction drag along a long cylinder will exceed the flat plate drag. My guess is that it's not worth it to worry too much about streamlining on an otherwise aerodynamically clean vehicle that will spend only three minutes in the atmosphere during ascent, and those are at its lowest velocity. Essentially what we've done is to take a typical rocket shape and leave off the big cylinder at the back end.

Commercial SSTO Launch Configuration

SSTO Concept Design Project Team

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