4 ms·

The thrust vector control method in this case is gimbaling, and it basically means using linear actuators (I think these are commonly hydraulic, and Falcon 9's

by zlsa 5y ago

The thrust vector control method in this case is gimbaling, and it basically means using linear actuators (I think these are commonly hydraulic, and Falcon 9's Merlin engines actually use the kerosene fuel in the TVC hydraulic system) to point the engine in a different direction: Raptor TVC test: https://www.youtube.com/watch?v=3pD5CZZfnYk https://www.youtube.com/watch?v=3pD5CZZfnYk Merlin TVC test: https://www.youtube.com/watch?v=Pigsq5rt-mY https://www.youtube.com/watch?v=Pigsq5rt-mY

bigyikes 5y ago
Are you saying that they use kerosene fuel in place of hydraulic fluid? If so, wow, you just blew my mind. Would that be to save on weight?
- perl4ever 5y ago
  Probably just as important to save on complexity.
  - zlsa 5y ago
    Yeah, critically the rocket engine turbopump already produces very high pressure kerosene and liquid oxygen; so why not tap off some kerosene there instead of building a separate hydraulic pump system?
    - bolangi 5y ago
      IOW, the best part is no part.
- sgtnoodle 5y ago
  As others have said, there's already a turbopump providing kerosene at a high pressure. Also, the hydraulics are open loop; the dumped low pressure kerosene is fed into the engine. That's a lot simpler than a closed loop system, or an open loop system with a dedicated supply of fluid. There's no risk of running out of kerosene for the actuators because as soon as you do, you can't thrust anymore either and so the actuators don't matter. They also use the kerosene to cool the engines' nozzles before it gets combusted. This keeps the nozzles from melting, and preheats the fuel so it combusts more efficiently.
hcrisp 5y ago
Besides gimballed rocket bells, it looks like they also use side venting of fuel, oxidizer, or inert gas. It's not steady, it starts and stops apparently to give an extra torque moment when rotating the body or stabilizing the upper end just prior to and after landing. https://youtu.be/Y_9FZDnCaoU https://youtu.be/Y_9FZDnCaoU
- zlsa 5y ago
  The big vents about midway up the vehicle are gaseous depressurization vents for the methane and liquid oxygen tanks; the RCS (reaction control system) that's designed to provide torque has thrusters at the nose and tail (to maximize the length of the lever arm.) https://youtu.be/6iBnXy1ag8A?t=109 https://youtu.be/6iBnXy1ag8A?t=109

by zlsa 5y ago

bigyikes 5y ago

Are you saying that they use kerosene fuel in place of hydraulic fluid? If so, wow, you just blew my mind. Would that be to save on weight?

perl4ever 5y ago
Probably just as important to save on complexity.
- zlsa 5y ago
  Yeah, critically the rocket engine turbopump already produces very high pressure kerosene and liquid oxygen; so why not tap off some kerosene there instead of building a separate hydraulic pump system?
  - bolangi 5y ago
    IOW, the best part is no part.
sgtnoodle 5y ago
As others have said, there's already a turbopump providing kerosene at a high pressure. Also, the hydraulics are open loop; the dumped low pressure kerosene is fed into the engine. That's a lot simpler than a closed loop system, or an open loop system with a dedicated supply of fluid. There's no risk of running out of kerosene for the actuators because as soon as you do, you can't thrust anymore either and so the actuators don't matter. They also use the kerosene to cool the engines' nozzles before it gets combusted. This keeps the nozzles from melting, and preheats the fuel so it combusts more efficiently.

hcrisp 5y ago

Besides gimballed rocket bells, it looks like they also use side venting of fuel, oxidizer, or inert gas. It's not steady, it starts and stops apparently to give an extra torque moment when rotating the body or stabilizing the upper end just prior to and after landing. https://youtu.be/Y_9FZDnCaoU https://youtu.be/Y_9FZDnCaoU

zlsa 5y ago
The big vents about midway up the vehicle are gaseous depressurization vents for the methane and liquid oxygen tanks; the RCS (reaction control system) that's designed to provide torque has thrusters at the nose and tail (to maximize the length of the lever arm.) https://youtu.be/6iBnXy1ag8A?t=109 https://youtu.be/6iBnXy1ag8A?t=109