<font color="yellow">Using the shuttle as an example...NASA requirements were for a shuttle with a 20,000 lb to LEO capability. The USAF wanted a 65,000 lb LEO capability. The AF requirement won out. these requirements are decided upon before contract selection. </font><br /><br />qso1,<br /><br />I appreciate your feedback. Your post reflects a well thought out process of your logical thinking. As you can see from your own statement above, defining "requirements", e.g. what you want/ need, is not a simple, nor a straightforward process. Technically, it's an iterative process at best. Everything is a trade off. First question is, is it technically feasible? Can I do it in a single stage reusable vehicle? If not, can I do it in two stages? Can my vehicle survive the reentry heating? WHAT are the reentry heat loads? (this answer alone depends on how heavy the vehicle is and the reentry trajectory --- which sets off a whole set of different analysis, or a whole set of research programs, etc.). Then you have another subset of requirements just on the Shuttle Orbiter TPS alone. How heavy can they be before it gets to be too heavy? How hot do they need to withstand on one side, then on the back side? Can they get wet? What technologies do I need to develop <i>before</i> I can deploy this "concept of operation"? How long will that take? etc.<br /><br />Then there's always the issue of money & politics. As you've stated, NASA think a 20K payload class was adequate for its Space Shuttle program, but in order to get the USAF's support (evidently a must before the Congress would approve its fundings), it has to increase the size of vehicle and thrust of its boosters to handle AF's 65K payload class requirement. <br /><br />So as you can imagine, NASA would need to input from contractors during its each "iteration" of defining requirements. You can't just say, okay we'll do it this way without first finding out if that way can be done or not. Contractors <div class="Discussion_UserSignature"> </div>