Hold-down mechanism for a spacecraft appendage

1. An apparatus comprising:

a hold-down mechanism for a steerable spacecraft appendage, said appendage being coupled to a spacecraft structure with a positioning mechanism; the hold-down mechanism comprising:

a frame, hingedly attached, at an inboard portion, to the spacecraft structure, and detachably engaged, at an outboard portion, to a structural element of the appendage; and

a deployment spring, said deployment spring configured such that, upon release of the appendage, the deployment spring drives a rotation of the frame about a hinge axis, thereby causing the hold-down mechanism to retract from the appendage; wherein:

the frame is detachably engaged to the structural element of the appendage by a cup and cone arrangement, the cup and cone arrangement being characterized by a longitudinal axis and a separation interface, the longitudinal axis being perpendicular to a plane passing through the separation interface and the hinge axis, and

the hold-down mechanism is configured to:

support, when in a hold-down mode, the appendage at a first position substantially fixed with respect to the spacecraft, and isolate the positioning mechanism from loads imparted by the spacecraft appendage as a result of launch or other dynamic environment such that the loads are reacted by the hold-down mechanism and not the positioning mechanism;

release, upon receipt of a signal, the appendage, thereby enabling the positioning mechanism to steer the spacecraft appendage; and

retract from the appendage without regard to whether the appendage remains substantially in the first position.

2. The apparatus according to claim 1 , wherein the hold-down mechanism is configured to retract from the appendage while the appendage remains substantially in the first position.

3. The apparatus according to claim 2 , wherein the first position results in the spacecraft appendage being aligned in a nominal operating location and orientation, so that the positioning mechanism is not required to initially deploy or otherwise reorient the appendage.

4. The apparatus according to claim 1 , wherein the hold down mechanism comprises a release device configured to prevent, in a first state, relative motion of the appendage with respect to the hold-down mechanism, and, in a second state, permit relative motion of the appendage with respect to the hold-down mechanism.

5. The apparatus according to claim 4 , wherein the release device is a split-spool device.

6. The apparatus according to claim 4 , wherein the release device is a pyrotechnic device.

7. The apparatus according to claim 1 , wherein the frame comprises a convex cup configured to mate with a concave cone disposed on the structural element of the appendage.

8. The apparatus according to claim 1 , wherein the frame comprises a concave cone configured to mate with a convex cup disposed on the structural element of the appendage.

9. An apparatus comprising:

a plurality of hold-down mechanisms for a steerable spacecraft appendage, said appendage being coupled to a spacecraft structure with a positioning mechanism; each of the hold-down mechanisms comprising:

a frame, hingedly attached, at an inboard portion, to the spacecraft structure, and detachably engaged, at an outboard portion, to a structural element of the appendage; and

a deployment spring, said deployment spring configured such that, upon release of the appendage, the deployment spring drives a rotation of the frame about a hinge axis, thereby causing the hold-down mechanism to retract from the appendage;

wherein:

each frame is detachably engaged to the structural element of the appendage by a cup and cone arrangement, the cup and cone arrangement being characterized by a longitudinal axis and a separation interface, the longitudinal axis being perpendicular to a plane passing through the separation interface and the hinge axis, and

the plurality of hold-down mechanisms are configured to:

support the appendage, during a dynamic environment, at a first position substantially fixed with respect to the spacecraft, and isolate the positioning mechanism from loads imparted by the spacecraft appendage as a result of the dynamic environment such that the loads are reacted by the hold-down mechanisms and not the positioning mechanism;

release, upon receipt of a signal, the appendage, thereby enabling the positioning mechanism to steer the spacecraft appendage; and

retract from the appendage without regard to whether the appendage remains substantially in the first position.

10. The apparatus according to claim 9 , wherein the apparatus comprises three hold down mechanisms, and the structural element comprises a cruciform arrangement of a first longitudinal member and a second longitudinal member, wherein

a first end of the first longitudinal member has an interface to a first respective frame, a second end of the first longitudinal member has an interface to a second respective frame, a first end of the second longitudinal member has an interface to a third respective frame, and a second end of the second longitudinal member has an interface to the positioning mechanism.

11. The apparatus according to claim 10 , wherein each respective frame is hingedly attached about a respective hinge axis, and a projection of each hinge axis onto a common plane defines a triangle.

12. The apparatus of claim 11 , wherein the triangle is an equilateral triangle.

13. The apparatus according to claim 9 wherein the steerable spacecraft appendage comprises an antenna reflector, and the structural element comprises a reflector backup structure.

14. The apparatus according to claim 9 , wherein each hold down mechanism comprises a release device configured to prevent, in a first state, relative motion of the appendage with respect to the hold-down mechanism, and, in a second state, permit relative motion of the appendage with respect to the hold-down mechanism.

15. The apparatus according to claim 14 , wherein the release device is a split-spool device.

16. The apparatus according to claim 14 , wherein the release device is a pyrotechnic device.

17. A spacecraft appendage hold-down and release method comprising:

supporting a spacecraft appendage, with a hold-down mechanism, during a first time period, at a first position substantially fixed with respect to the spacecraft, said appendage being coupled to a spacecraft structure with a positioning mechanism, wherein supporting the spacecraft appendage includes isolating the positioning mechanism from loads imparted by the spacecraft appendage as a result of launch or other dynamic environment such that the loads are reacted by the hold-down mechanism and not the positioning mechanism;

releasing the appendage, subsequent to the first time period, thereby enabling the positioning mechanism to steer the spacecraft appendage; and

retracting the hold-down mechanism from the appendage without regard to whether the appendage remains substantially in the first position; wherein:

the hold-down mechanism comprises:

a frame, hingedly attached, at an inboard portion, to the spacecraft structure, and detachably engaged, at an outboard portion, to a structural element of the appendage; and

a deployment spring, said deployment spring configured such that, upon release of the appendage, the deployment spring drives a rotation of the frame about a hinge axis, thereby causing the hold-down mechanism to retract from the appendage; and:

the frame is detachably engaged to the structural element of the appendage by a cup and cone arrangement, the cup and cone arrangement being characterized by a longitudinal axis and a separation interface, the longitudinal axis being perpendicular to a plane passing through the separation interface and the hinge axis.

18. The method according to claim 17 , wherein the hold-down mechanism is configured to retract from the appendage while the appendage remains substantially in the first position.

19. The method according to claim 18 , wherein the first position results in the spacecraft appendage being aligned in a nominal operating location and orientation, so that the positioning mechanism is not required to initially deploy or otherwise reorient the appendage.

20. The method according to claim 17 , wherein the hold down mechanism comprises a release device configured to prevent, in a first state, relative motion of the appendage with respect to the hold-down mechanism, and, in a second state, permit relative motion of the appendage with respect to the hold-down mechanism.

21. The method according to claim 17 , wherein a dynamic environment encountered during the first time period includes at least one of a launch environment and a spacecraft dynamic test environment.