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Old November 15 2012, 02:27 AM   #329
Location: Kentucky
Re: Envisioning the world of 2100

Why would NASA be interested in an idea that would throw most of them out of work and render much of their support structure obsolete, or can't you see that obvious consequence? They will build whatever the Senate tells them to build. They're not even trying to build a re-usable rocket anymore, much less innovate.

Apparently you also never saw the DC-X fly. It did loops. NASA didn't go for it. In fact, what they did go for is way crazier than horizontal launch, lighting two giant solids on the bet that they wouldn't have a differential thrust problem in a vehicle with no abort system at all, while using a piggyback configuration with wings where the aerodynamics and structural complexities were mind-boggling. They made whole chains of decisions on the Shuttle that carried greater risks and greater complexity than lifting a rocket into the air with rockets and then aiming it, which is something rocket folks have done ever since guidance systems were developed.

In contrast, horizontal launch wouldn't take but a couple of days to design, and Mythbusters could film it for an episode. You could do it with only two pre-determined fixed burns, one slightly forward of the center of mass that lifts and rotates around the center of percussion relative the thrust location (the majority of the Wiki references for the math on that are me), and one to slow the rotation after 90 degrees. I wouldn't use just one lift and rotate motor for structural reasons, but that's all there is to it.

By the way, the DC-X burned because it was a tail sitter that had a landing leg failure, and a re-usable tail sitter tips all the way over when that happens. A horizontal lander would just drop one end several feet and get dented. It's also a given that tail sitters can't have nice, shock absorbing landing gear like an airplane because then the gear wouldn't be stiff enough to hold it vertically without wobbling and tipping problems, which means they have to set down very, very gently. Almost all of Elon Musks problems with grasshopper are probably going to stem from the combination of balance and stiff narrow landing legs.

I don't know if any SpaceX engineers read where I comment (lots of former NASA and Rockwell people do) but the blogger who runs the site runs into Elon Musk pretty often. Maybe he'll mention it sometime.
gturner is offline   Reply With Quote