Steve VanSickle wrote:
> On Thu, 7 Jan 1999, Spike Jones wrote:
> >> If 350 sec is an average for the whole flight,
> > well, not down low. thats surely their vacuum isp. i would be interested
> > in the isp profile, given aerospike altitude compensation.
> Me too. You're right...350 averaged is probably high.
> > > The rotor blades will deploy upward before reentry (like an umbrella blown
> > > inside-out) and stay in the lee of the shock way, minimizing heating.
> > steve i remain skeptical on this scheme.
> Seems like it ought to still get a bit warm to me, too. However, they
> *are* doing extensive computational aerodynamics and are relying heavily
> on hypersonic rotor wind tunnel work that NASA did in the 60's. Amazing
> all the stuff gathering dust in their libraries.
Yes, the heat from reentry is mostly in the shock wave. The reason the shuttle needs its tiles is that so much of its surface is at the shockwave. A longer leaner vehicle will keep most of its surface away from the shockwave.
> > i tried to make it work with no despun section, but couldnt figure out
> > how to guide the turn, so, i end up with a despun platform forward
> > that holds the payload. problem im having is that the cross sectional
> > area is large, so i lose an awful lot to drag. i wonder if i could get
> > a mountain top launch site? a high one could get me out of half
> > the atmosphere. the environmental types wouldnt like it tho. spike
> Is it because the low denity fuel requires a large diameter? Higher
> density fuel can make it much more compact. And I would think that
> rotating the feul tanks are more trouble than they are worth...slow, low
> pressure rotating seals aren't *that* hard.
This is why I like the solid liquid hybrid motors, it allows for a very small cross section, and the fuel provides structural support just as normal solid fuels do. A small cross section with a dense fuel allows for a small vehicle size, and the aerodynamic savings of the small cross section are enormous at transonic to hypersonic speeds.
rotating seals are ok, because the pressure is generated by the centrifugal forces of the spinning blades, so at the point where the blades and the tanks meet, you can have a very low pressure seal, because there should be a significant vacuum pressure inside the seal.