Pointable optical system with coude optics having a short on-gimbal path length

1. A coude gimbal structure comprising:

a two-axis gimbal system including

an outer gimbal pivotable about a first rotational axis, and

an inner gimbal supported on the outer gimbal and pivotable about a second rotational axis which is perpendicular to the first rotational axis and which intersects the first rotational axis at an intersection point; and

a reflective coude optical system including

a positive-optical-power primary mirror mounted to the inner gimbal, wherein the primary mirror is directed along a third axis passing through the intersection point and lying perpendicular to the first rotational axis and perpendicular to the second rotational axis, and

an intersection flat fold mirror at the intersection point,

wherein the positive optical power primary mirror has a primary mirror aperture diameter, and

wherein a coude path length of the reflective coude optical system is about ½ of the aperture diameter of the primary mirror.

2. The gimbal structure of claim 1 , wherein the reflective coude optical system comprises:

the positive-optical-power primary mirror, a negative-optical-power secondary mirror, and a positive-optical-power tertiary mirror, the flat fold mirror, and a second flat fold mirror, and wherein

the primary mirror and the secondary mirror lie on the third axis, and wherein a beam path parallel to the third axis is reflected from the primary mirror to the secondary mirror,

the tertiary mirror lies on the second rotational axis,

the second flat fold mirror redirects the beam path reflected from the secondary mirror to the tertiary mirror, and

the flat fold mirror at the intersection point is arranged to redirect, along the first rotational axis, the beam path reflected from the tertiary mirror.

3. The gimbal structure of claim 2 , wherein the primary mirror, the secondary mirror, the tertiary mirror, and the second flat fold mirror are mounted to the inner gimbal, and the flat fold mirror is mounted to the outer gimbal.

4. The gimbal structure of claim 1 , wherein the outer gimbal includes an outer gimbal bearing having a center opening through which the beam path passes.

5. The gimbal structure of claim 1 , further including

an optical transceiver that is not mounted to either of the gimbals and intercepts the beam path.

6. A coude gimbal structure comprising:

a two-axis gimbal system including

an outer gimbal pivotable about a first rotational axis, and

an inner gimbal supported on the outer gimbal and pivotable about a second rotational axis which is perpendicular to the first rotational axis and which intersects the first rotational axis at an intersection point; and

a reflective coude optical system consisting essentially of only three powered mirrors and only two flat fold mirrors,

said only three powered mirrors comprising a positive-optical-power primary mirror mounted to the inner gimbal, wherein the primary mirror lies along a third axis passing through the intersection point and lying perpendicular to the first rotational axis and perpendicular to the second rotational axis, and

wherein said only two flat fold mirrors comprise an intersection flat fold mirror at the intersection point.

7. The gimbal structure of claim 6 , wherein the outer gimbal includes an outer gimbal bearing having a center opening through which a beam path passes.

8. The gimbal structure of claim 6 , further including

an optical transceiver that is not mounted to either of the gimbals and intercepts a beam path.

9. A coude gimbal structure comprising:

a two-axis gimbal system including

an outer gimbal pivotable about a first rotational axis, and

an inner gimbal supported on the outer gimbal and pivotable about a second rotational axis which is perpendicular to the first rotational axis and which intersects the first rotational axis at an intersection point; and

a reflective coude optical system including

a positive-optical-power primary mirror mounted to the inner gimbal, wherein the primary mirror lies along a third axis passing through the intersection point and lying perpendicular to the first rotational axis and perpendicular to the second rotational axis, and

an intersection flat fold mirror at the intersection point,

wherein the reflective coude optical system further comprises

the positive-optical-power primary mirror, a negative-optical-power secondary mirror, a positive-optical-power tertiary mirror, a first flat fold mirror, and the intersection flat fold mirror,

wherein the primary mirror and the secondary mirror lie on the third axis, and wherein a beam path parallel to the third axis is reflected from the primary mirror to the secondary mirror, and

wherein the tertiary mirror lies on the second rotational axis,

the first flat fold mirror redirects the beam path reflected from the secondary mirror to the tertiary mirror, and

the intersection flat mirror redirects along the first rotational axis the beam path reflected from the tertiary mirror.

10. The gimbal structure of claim 9 , wherein the primary mirror, the secondary mirror, the tertiary mirror, and the first flat fold mirror are mounted to the inner gimbal, and the intersection flat fold mirror is mounted to the outer gimbal.