Seal for gimbaling and/or fixed rocket engine nozzles, and associated systems and methods

1. A rocket propulsion system, comprising:

a rocket engine having an exhaust nozzle;

a seal plate carried by the exhaust nozzle; and

a seal engaged with the seal plate, the seal including:

at least one support;

multiple pivotable first flaps, with an individual one of the first flaps carried by the at least one support and positioned to contact the seal plate;

multiple pivotable second flaps, with an individual one of the second flaps positioned to shield the individual one of the first flaps, and wherein the individual one of the first flaps and the individual one of the second flaps are pivotable about a common axis; and

at least one forcing element operatively coupled to the individual one of the first flaps or the individual one of the second flaps, or both, to apply a pivoting force to the individual one of the first flaps or the individual one of the second flaps.

2. The system of claim 1 wherein the at least one forcing element is operatively coupled to the individual one of the second flaps to bias the individual one of the second flaps into contact with the individual one of the first flaps.

3. The system of claim 1 wherein the individual one of the first flaps has a higher rigidity than the individual one of the second flaps.

4. The system of claim 1 wherein the individual one of the first flaps or the individual one of the second flaps, or both, includes a carbon-carbon material.

5. The system of claim 1 wherein the individual one of the second flaps has a higher heat resistance than the individual one of the first flaps.

6. The system of claim 1 wherein the individual one of the first flaps or the individual one of the second flaps, or both, includes a ceramic or ceramic matrix composite material.

7. The system of claim 1 wherein the at least one forcing element includes a spring coupled to the individual one of the first flaps or the individual one of the second flaps via an actuator rod.

8. The system of claim 7 wherein the spring is a first spring, and wherein the system further comprises:

a second spring coupled to the actuator rod, with the first spring positioned to bias the actuator rod in a first axial direction, and the second spring positioned to bias the actuator rod in a second direction opposite the first direction; and

a canister housing the first spring, the second spring, and the actuator rod.

9. The system of claim 1 wherein at least a portion of the seal plate engaged by the seal is spherical.

10. The system of claim 1 wherein at least a portion of the seal plate engaged by the seal is flat.

11. The system of claim 1 wherein the nozzle has a thrust axis and is gimbalable relative to the thrust axis.

12. The system of claim 1 wherein the nozzle has a thrust axis and is rotationally fixed relative to the thrust axis.

13. The system of claim 12 wherein the nozzle is axially movable along the thrust axis.

14. The system of claim 1 wherein the nozzle is:

positioned to direct thrust along a thrust axis;

axially moveable along the thrust axis;

gimbalable about a first axis transverse to the thrust axis; and

gimbalable about a second axis transverse to the thrust axis and the first axis.

15. A rocket propulsion system, comprising:

a rocket engine having a gimbalable exhaust nozzle;

a spherical seal plate carried by the exhaust nozzle; and

a seal engaged with the seal plate, the seal including:

at least one support;

multiple flap pairs arranged circumferentially around the nozzle, each one of the flap pairs including:

a first pivotable flap positioned to contact the seal plate;

a second pivotable flap positioned to shield the first pivotable flap, the first and second pivotable flaps being pivotable about a common axis wherein the first pivotable flap of one of the multiple flap pairs overlaps the second pivotable flap of a neighboring one of the multiple flap pairs;

an actuator rod coupled to the second pivotable flap;

a first spring coupled to the actuator rod to bias the second pivotable flap in a first rotary direction;

a second spring coupled to the actuator rod to bias the second pivotable flap in a second rotary direction opposite the first rotary direction; and

at least one hinge pin pivotably supporting the first and second pivotable flaps.

16. The system of claim 15 wherein the first spring, the second spring, and the actuator rod are housed, at least in part, in a cylinder, and wherein the cylinder is pivotably carried by the at least one support.

17. The system of claim 15 wherein multiple spring pairs are positioned circumferentially around the nozzle.

18. A seal for a rocket engine, comprising:

at least one support;

multiple, pivotable first flaps, each having a sealing surface, with an individual one of the first flaps coupled to a pin carried by the at least one support and rotatable about an elongated axis of the pin;

multiple, pivotable second flaps, with an individual one of the second flaps positioned to shield the individual one of the first flaps; and

at least one forcing element operatively coupled to the individual one of the first flaps or the individual one of the second flaps, or both, to apply a pivoting force to the individual one of the first flaps or the individual one of the second flaps.

19. The seal of claim 18 wherein the individual one of the second flaps is rotatable about the elongated axis of the pin.

20. The seal of claim 18 wherein the at least one forcing element includes a spring coupled to the individual one of the first flaps or the individual one of the second flaps via an actuator rod.

21. The seal of claim 20 wherein the spring is a first spring, and wherein the system further comprises:

a second spring coupled to the actuator rod, with the first spring positioned to bias the actuator rod in a first axial direction, and the second spring positioned to restrict motion of the actuator rod in a second direction opposite the first direction; and

a canister housing the first spring, the second spring, and the actuator rod.

22. A seal for a rocket engine, comprising:

at least one support:

multiple, pivotable first flaps, each having a sealing surface, with an individual one of the first flaps carried by the at least one support;

multiple, pivotable second flaps, with an individual one of the second flaps extending radially from a pivot axis in a first direction and being positioned to shield the individual one of the first flaps;

an arm coupled to the individual one of the second flaps and extending radially from the pivot axis in a second direction different than the first direction, and

at least one forcing element forcibly coupled to the arm by a pin to apply a pivoting force to at least the individual one of the second flaps at the arm, wherein the at least one forcing element and the arm are rotatable about an elongated axis of the pin.

23. The seal of claim 22 wherein the at least one forcing element includes a spring coupled to the individual one of the first flaps or the individual one of the second flaps, or both, via an actuator rod.

24. The seal of claim 23 wherein the spring is a first spring, and wherein the system further comprises:

a second spring coupled to the actuator rod, with the first spring positioned to bias the actuator rod in a first axial direction, and the second spring positioned to restrict motion of the actuator rod in a second axial direction opposite the first axial direction; and

a canister housing the first spring, the second spring, and the actuator rod.