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> Skipping forward, the basic controls of fully automated vertical landing were directly demo'd in a real flying 1/3 scale test bed (though important to note no

by tzs 2y ago

> Skipping forward, the basic controls of fully automated vertical landing were directly demo'd in a real flying 1/3 scale test bed (though important to note not an orbital one) with the DC-X in 1993. Why is it important to note that it was not orbital?

db48x 2y ago
An orbital craft is moving at hypersonic speeds, which is a especially tricky when going backwards. Things moving through fluids tend to want to flip over so that the part with the highest drag is at the rear, so that drag is minimized. Meanwhile the engine bay of a rocket is not generally shaped to have low drag when pushing through the air.
- tzs 2y ago
  Wouldn't any spacecraft designed to return to Earth non-destructively, regardless of whether it was going to land vertically or land like an airplane or land with a parachute, first slow down to subsonic speeds before getting to the phase of the flight where the landing system is invoked?
  - immibis 2y ago
    It slows down by burning stuff and making hot stuff go out one end. That end is the one worse for air drag, because it has all the bits where the hot stuff comes out.
  - db48x 2y ago
    No. Go watch a Falcon 9 booster recovery <https://www.youtube.com/watch?v=w-_90o1KLkM https://www.youtube.com/watch?v=w-_90o1KLkM> on Youtube; you’ll see that when it starts its landing burn it is ~5 miles up and flying engines first towards the ground at ~1300 miles per hour.
xoa 2y ago
>Why is it important to note that it was not orbital? Orbital is what actually provides any significant economic value. But the nature of the Rocket Equation, effects with atmosphere, and how those interact with the limits of our material science means that there is an absolutely enormous gulf between a sounding rocket and getting to orbital velocity and back again. All of that is what makes it so hard but it's also required to be of any real practical use. So the DC-X was a noteworthy historical milestone/demo and test bed but going from there to something like the Falcon 9 let alone Starship takes an tremendous amount of further innovation and engineering (and investment of course). The new engine work alone SpaceX has done is a hufe deal and is what defines the envelope for the rest of the system.

by tzs 2y ago

db48x 2y ago

An orbital craft is moving at hypersonic speeds, which is a especially tricky when going backwards. Things moving through fluids tend to want to flip over so that the part with the highest drag is at the rear, so that drag is minimized. Meanwhile the engine bay of a rocket is not generally shaped to have low drag when pushing through the air.

tzs 2y ago
Wouldn't any spacecraft designed to return to Earth non-destructively, regardless of whether it was going to land vertically or land like an airplane or land with a parachute, first slow down to subsonic speeds before getting to the phase of the flight where the landing system is invoked?
- immibis 2y ago
  It slows down by burning stuff and making hot stuff go out one end. That end is the one worse for air drag, because it has all the bits where the hot stuff comes out.
- db48x 2y ago
  No. Go watch a Falcon 9 booster recovery <https://www.youtube.com/watch?v=w-_90o1KLkM https://www.youtube.com/watch?v=w-_90o1KLkM> on Youtube; you’ll see that when it starts its landing burn it is ~5 miles up and flying engines first towards the ground at ~1300 miles per hour.

xoa 2y ago

>Why is it important to note that it was not orbital? Orbital is what actually provides any significant economic value. But the nature of the Rocket Equation, effects with atmosphere, and how those interact with the limits of our material science means that there is an absolutely enormous gulf between a sounding rocket and getting to orbital velocity and back again. All of that is what makes it so hard but it's also required to be of any real practical use. So the DC-X was a noteworthy historical milestone/demo and test bed but going from there to something like the Falcon 9 let alone Starship takes an tremendous amount of further innovation and engineering (and investment of course). The new engine work alone SpaceX has done is a hufe deal and is what defines the envelope for the rest of the system.