I suspect weight and aerodynamics play the most important part in determining shape. What I've always wondered is why we've never effectively used wings on our spacecraft to get part of the way there. Spaceship one used something like this with its "stage 1" vehicle.
I haven't done the math, but I always assumed it would be less expensive (as in fuel and weight) to start the orbital boosters from 50,000ft after climbing via traditional wings, as opposed to the brute force option of simply producing as much thrust as possible and climbing straight up.
Granted for extremely large payloads the structural requirements for building wings that can support the weight might be impractical, but wouldn't it have been easier for the space shuttle to "launch" from 50,000ft?
I haven't done the math, but I always assumed it would be less expensive (as in fuel and weight) to start the orbital boosters from 50,000ft after climbing via traditional wings, as opposed to the brute force option of simply producing as much thrust as possible and climbing straight up.
Granted for extremely large payloads the structural requirements for building wings that can support the weight might be impractical, but wouldn't it have been easier for the space shuttle to "launch" from 50,000ft?