3 ms·

One of the weirdest aspects of Crew Dragon is the total lack of precision controls for manual docking. There's a reason that most aircraft, even the most comput

by kunai 5y ago

One of the weirdest aspects of Crew Dragon is the total lack of precision controls for manual docking. There's a reason that most aircraft, even the most computerized and automated ones like the F-35 and Airbus A350 still rely on a joystick for fine control. A touchscreen interface like this seems like a really clunky way to implement manual control, and offers less flexibility for alternate and abort flight modes where automated control may not be possible. The Soyuz is fully automated from liftoff to touchdown and still has a cockpit with a plethora of manual controls and two joysticks for RCS control. I guess the idea was to make it look all sleek and sci-fi on the interior... but at the expense of precision and versatility. It just seems to demonstrate a lack of consideration for tactility and the importance of it in a mission-critical environment like space.

_moof 5y ago
It's definitely unusual but the idea was actually not to waste time building things that aren't needed. Dragon is fully automated, has fault-tolerance in pretty much every subsystem, and there's a stack of procedures five feet high that operators would try before telling the crew to go manual. (Well, not literally. All the procedures are electronic.) This "simulator" is a marketing gimmick and bears almost no resemblance to real-world docking ops.
- kunai 5y ago
  That's fair, but traditionally the rule of thumb in aerospace and avionics is to compensate for every single possible edge case into consideration. (Obviously there are diminishing returns past a certain point, but assuming modified and emergent flight modes is important for a reason.) In an edge case where avionics failure is inevitable, fully automated aircraft with flight envelope protection like Airbus, Dassault, and Lockheed still retain "direct law" and "alternate law" modes that allow direct control of aircraft control surfaces. It just seems like an oversight. In 99.99% of normal flight law situations there will be no issue with touch controls. That 00.01% however is even more important in space than it is in the air, which is why Crew Dragon's avionics design philosophy strikes me as particularly odd. If there was ever an Apollo 13 style disaster on board, it would be an uphill battle to retain control compared to a traditional spacecraft like Orion or Soyuz.
  - kevin_thibedeau 5y ago
    In space mass and volume are at a premium. The Dragon approach produces a spacecraft that isn't stuffed with instrumentation like Soyuz. The extra capacity is available for more productive use.
    - kunai 5y ago
      I suppose if I had to pick between having a flight control stick or a bathroom, I'd probably pick the bathroom as well. Good point.
  - _moof 5y ago
    You seem to be confusing a stick with mechanical linkage. Airbus aircraft don't have mechanical linkage; there is no "direct control of aircraft control surfaces." Even in the degraded modes, you're still going through the computers. Apollo and Shuttle didn't have mechanical linkage either. So the "direct control" you're describing isn't actually direct; it's mediated by the avionics, just like Dragon. Even without mechanical linkage, a stick makes sense in an aircraft because its surfaces and powerplants have continuous ranges. But Dragon's propulsion doesn't--it makes discrete pulses. A continuous control in Dragon wouldn't actually be able to provide output over a continuous range. The pace of operations in space is also much, much slower than it is in the air. These aren't ace top guns doing split-second maneuvers with lightning reflexes. They aren't even airline pilots switching off the autopilot at 100' AGL. Docking is slow. Don't let the orbital velocities or the excitement of launch and reentry fool you--spaceflight is much more like sailing than it is like aviation. In any case, the proof is in the pudding: Dragon crews train for manual docking on the (real) simulator, and it works.
    - kunai 5y ago
      > So the "direct control" you're describing isn't actually direct; it's mediated by the avionics, just like Dragon. Very true, but I'm more describing the difference in the UX of how pilots access the avionics rather than arguing for fully manual control. Most pilots raised on FBW would find fully manual flight rather tricky (think an F-16 pilot stepping into a P-51), so I'm not suggesting we do that. It's just that Dragon's design philosophy seems like kind of an interesting departure from conventional wisdom. > The pace of operations in space is also much, much slower than it is in the air. These aren't ace top guns doing split-second maneuvers with lightning reflexes. They aren't even airline pilots switching off the autopilot at 100' AGL. Docking is slow. Don't let the orbital velocities or the excitement of launch and reentry fool you--spaceflight is much more like sailing than it is like aviation. This is a pretty solid point, and one I hadn't really considered. Leave that up to Hollywood and Kerbal Space Program for misleading everyone on how fast-paced spaceflight really is, heh!

by kunai 5y ago

_moof 5y ago

It's definitely unusual but the idea was actually not to waste time building things that aren't needed. Dragon is fully automated, has fault-tolerance in pretty much every subsystem, and there's a stack of procedures five feet high that operators would try before telling the crew to go manual. (Well, not literally. All the procedures are electronic.) This "simulator" is a marketing gimmick and bears almost no resemblance to real-world docking ops.

kunai 5y ago
That's fair, but traditionally the rule of thumb in aerospace and avionics is to compensate for every single possible edge case into consideration. (Obviously there are diminishing returns past a certain point, but assuming modified and emergent flight modes is important for a reason.) In an edge case where avionics failure is inevitable, fully automated aircraft with flight envelope protection like Airbus, Dassault, and Lockheed still retain "direct law" and "alternate law" modes that allow direct control of aircraft control surfaces. It just seems like an oversight. In 99.99% of normal flight law situations there will be no issue with touch controls. That 00.01% however is even more important in space than it is in the air, which is why Crew Dragon's avionics design philosophy strikes me as particularly odd. If there was ever an Apollo 13 style disaster on board, it would be an uphill battle to retain control compared to a traditional spacecraft like Orion or Soyuz.
- kevin_thibedeau 5y ago
  In space mass and volume are at a premium. The Dragon approach produces a spacecraft that isn't stuffed with instrumentation like Soyuz. The extra capacity is available for more productive use.
  - kunai 5y ago
    I suppose if I had to pick between having a flight control stick or a bathroom, I'd probably pick the bathroom as well. Good point.
- _moof 5y ago
  You seem to be confusing a stick with mechanical linkage. Airbus aircraft don't have mechanical linkage; there is no "direct control of aircraft control surfaces." Even in the degraded modes, you're still going through the computers. Apollo and Shuttle didn't have mechanical linkage either. So the "direct control" you're describing isn't actually direct; it's mediated by the avionics, just like Dragon. Even without mechanical linkage, a stick makes sense in an aircraft because its surfaces and powerplants have continuous ranges. But Dragon's propulsion doesn't--it makes discrete pulses. A continuous control in Dragon wouldn't actually be able to provide output over a continuous range. The pace of operations in space is also much, much slower than it is in the air. These aren't ace top guns doing split-second maneuvers with lightning reflexes. They aren't even airline pilots switching off the autopilot at 100' AGL. Docking is slow. Don't let the orbital velocities or the excitement of launch and reentry fool you--spaceflight is much more like sailing than it is like aviation. In any case, the proof is in the pudding: Dragon crews train for manual docking on the (real) simulator, and it works.
  - kunai 5y ago
    > So the "direct control" you're describing isn't actually direct; it's mediated by the avionics, just like Dragon. Very true, but I'm more describing the difference in the UX of how pilots access the avionics rather than arguing for fully manual control. Most pilots raised on FBW would find fully manual flight rather tricky (think an F-16 pilot stepping into a P-51), so I'm not suggesting we do that. It's just that Dragon's design philosophy seems like kind of an interesting departure from conventional wisdom. > The pace of operations in space is also much, much slower than it is in the air. These aren't ace top guns doing split-second maneuvers with lightning reflexes. They aren't even airline pilots switching off the autopilot at 100' AGL. Docking is slow. Don't let the orbital velocities or the excitement of launch and reentry fool you--spaceflight is much more like sailing than it is like aviation. This is a pretty solid point, and one I hadn't really considered. Leave that up to Hollywood and Kerbal Space Program for misleading everyone on how fast-paced spaceflight really is, heh!