DeltaV wrote:Long, thin blades are difficult to stow cleanly for high speed ascent/reentry. While the blades are stowing, are you planning to freefall or accelerate under rocket thrust?
Freefall? Accelerate? Neither, use the rocket to maintain altitude while the rotor blades decelerate and stow (alongside the body).
Hope your rocket consumes less than the SSME:
Each engine consumes 1,340 liters (340 gallons) of propellant per second. If the engine pumped water instead of liquid oxygen and liquid hydrogen, an average-sized swimming pool could be drained in 75 seconds - or 25 seconds for the sum of the three used for the space shuttle launch.
And that's not counting the solids.
rjaypeters wrote:Before re-entry, we have the choice of lifting the blades away from the body and aligning them above the hub before starting their rotation or just leaving them along the body. I'd prefer to leave the blades along the body and use the sink rate airflow to help lift and auto-rotate them.
Deploying them before reentry guarantees they melt or break off.
rjaypeters wrote:I'm not saying VTOL fans won't work. I am saying for the equivalent lift, helicopter works better and is lighter.
Polywell should have power to spare before orbit boost. Lots of lift fans if needed. Two helo rotors can't lift that much, and only give one level of redundancy, assuming they're cross-connected. Eight lift fans can tolerate losing two or three. Don't forget the complexity of rotor heads, gearboxes and cross shafts compared to Halbach rim-drive motors.
rjaypeters wrote:The central concept here is to reduce the disk loading so the air we accelerate downward has the lowest velocity for less noise (did you listen to the Martin Jetpack?) and wear and tear on our backyards.
Eh. Pour a concrete pad out back, if China doesn't buy up all the concrete first. If "disk" loading is that big a deal for arbitrary sites (dust/gravel kicked up) use more, smaller lift fans.
rjaypeters wrote:Who needs VTOL fans + REB + rocket? Save the weight (and money BTW) and complexity by having one flight transition per ascent (helicopter to rocket) rather than two (fans to REB to rocket).
Rocket? Where did you get rocket? It's VTOL electric lift fans, transitioning to electric turbines up to ~M2.5, transitioning to REB from there to orbit. See Bussard's papers on hypersonic propulsion. I'm feeding air to the REB until the atmosphere thins out, only then
blending in onboard reaction mass. Jumping from helicopter to rocket means you'll need to carry a lot more reaction mass, especially with the hover time needed for blade stowage.
rjaypeters wrote:The helicopter removes the weight of the REB equipment
rjaypeters wrote:and lets us carry (in fact, requires) more reaction mass.
Carry more, no. Sikorsky Skycrane payload is 20,000 lb. Think you're going to go orders of magnitude beyond that? Require more reaction mass to reach orbit? Yes, since you are starting to consume reaction mass much lower/slower, but it won't be able to lift it.
rjaypeters wrote:I'm assuming water is our reaction mass, but tankage is a lot lighter than REB equipment.
Maybe when it's empty.
rjaypeters wrote:On another point, these vehicles are going to be heavy. I'm guessing around one million pounds. We're still going to need landing pads, but flame buckets won't be required.
So the low disk loading of helo blades becomes moot.
rjaypeters wrote:I don't see loiter or atmospheric cruise as requirements which should drive the design of the first generation Polywell SSTO. IMO, high speed and/or extended flight through the atmosphere is not what we should be designing for in the first generation Polywell SSTO.
That's trivial compared to getting to orbit. Atmospheric cruise lets you pick your orbit and your takeoff/landing locations. So you want to limit yourself to a few orbit inclinations and one or two launch/landing sites, like Shuttle?
rjaypeters wrote:Once we understand the Bussard better (and can make it better), follow-on vehicles should have more difficult to satisfy requirements. Else, what would the engineers do?
Go for broke. Before the daggum gubmint regulates it all away.