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About sevenperforce

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    Physics Superhero

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  1. In theory, an SSTO has fewer engines, less maintenance, and fewer failure points. In practice, it's just unattainable, and the theoretical advantages are miniscule.
  2. Most rocket engines gimbal from 0 to 4 degrees in any direction, although early models (and NK's current models) use multiple control engines with only one axis of gimbal freedom each. The SSME engines had a ridiculous 10+ degree gimbal in every direction because of how much the CoM changed during ascent. All the engines on the Falcon 9 gimbal, but the center engines has more gimbal than the outer ones because it has slightly more clearance. Although all the engines on the Falcon 9 are reusable, only three are plumbed with ignition fluid for in-air restart. It uses one engine for most landings but it sometimes uses the other two for part or all of the landing burn when it needs extra thrust for low-margin suicide burns.
  3. The 1:1 glide ratio is with the Block 5 grid fins. That video was hella cool, though. I was amazed to see the transonic shock forming around the tail just before the landing burn ignition. Also surprised by how long the landing burn was.
  4. Indeed, but I made the challenge the way I did for a reason, haha. Otherwise people would just pile on the engines and forget. This requires people to be at least a little bit creative. Yes, it looks good in the movies. One of the things I was curious about is whether we'd end up with designs that look a lot like scifi, or designs that look more utilitarian. It may be that I should alter the requirements of this challenge to say that warp time is not counted, or counted differently...not sure of the best way to do it.
  5. Jet-drop staging can be good for polar orbits of small satellites that don't need to stay aloft for very long.
  6. You can do this, but it's a huge waste of dV.
  7. A cone with a sharp transition will have more parasitic drag than a cone with a smooth/rounded transition, due to boundary-layer separation at the interface.
  8. Looking good! I did mean that it needed VTOL engines on a separate thrust axis, but I won't fuss about it.
  9. It depends on your launch vehicle's thrust-to-weight ratio. As a good rule of thumb, I typically try to pitch over gradually enough that my heading always stays inside the prograde marker, but rapidly enough that I hit 45 degrees (halfway over) at around 500 m/s. That's for KSP, obviously; pitchover for real-world launch vehicles is going to be different. A vehicle with very high TWR can execute the pitchover much lower in the atmosphere than a vehicle with a lower TWR, but the curve of airspeed vs pitch angle is going to be pretty similar across the board.
  10. You're right. I dug up the old Falcon 9v1.0 user guide:
  11. Of note -- the F-35B has the radar cross-section of a 2 cm steel marble, if I recall correctly.
  12. I've seen it phrased this way: If you could drive the average sports car straight up through the air, without a roadway, then it would take just a little over two hours of driving to reach the altitude of the International Space Station. But you'd still only be moving at 0.7% the speed of the International Space Station.
  13. From Wikipedia: "The F-117A's faceted shape (made from 2-dimensional flat surfaces) resulted from the limitations of the 1970s-era computer technology used to calculate its radar cross-section. Later supercomputers made it possible for subsequent aircraft like the B-2 bomber to use curved surfaces while maintaining stealth, through the use of far more computational resources to perform the additional calculations." The B-2 was far more radar-invisible and has completely smooth surfaces.
  14. Common misconception, actually. Ugly angular shapes are no better at scattering radar signals than curved ones. The shape of the F-117 was due to the fact that computers of the era were not powerful enough to solve the equations for proper geometry of a smooth radar-scattering surface, and so they had to make do with a multiplanar solution.
  15. I'd like to see a 2.5-m or 3.75-m LANTR. Two operating modes; can run on fuel alone or on fuel + oxidizer. Slightly higher specific impulse than the LV-N in fuel-only mode, with a lower TWR, but massively improved thrust in fuel+oxidizer mode. Enough to make pure-nuclear SSTOs at least vaguely feasible.