There are numerous pictures of grapple fixtures and LEE available. I can appreciate how the wire snare works to snare the center pin of the grapple. But I’m foggy on how the location cam/arm assemblies are captured and locked, or how loads are transmitted.

Any good drawings or animations?

  • $\begingroup$ This is not a duplicate question. The previous posting describes how the wires snare the center post for alignment, but does not indicate what interacts with the location cam/arm assemblies to provide load-bearing connection. The LEE appears to function on a bayonet principle. I can identify the bayonet component on the grapple, but not the LEE $\endgroup$
    – Woody
    Nov 12, 2021 at 1:21
  • $\begingroup$ I reopened the question because I'm not a big fan of wielding the dupe-hammer and the OP protested, but IMHBCO it's answered here space.stackexchange.com/a/14989/6944 $\endgroup$ Nov 12, 2021 at 1:52
  • $\begingroup$ I was wrong about “bayonet principle”. There is no rotational locking. There are 3 stages of increasing rigidity: 1) Snaring of the center pin on the grapple and snare traction on the pin-end knob with mating of cam arm shoulders 2) Engagement of castellated rings by the rigidize subassembly and 3) Engagement of the four Latch Assemblies. Apparently the stage of engagement depends on what is being grabbed. The most basic grapple fixture has no castellated ring or Latch Assembly points. Big beefy bits have all 3 features. Description and drawings: ntrs.nasa.gov/citations/19950020841 $\endgroup$
    – Woody
    Nov 12, 2021 at 2:54
  • $\begingroup$ that's the same document linked in my answer and the schematic in my answer is excerpted from it. Your comment is a decent summary of my answer, except the "rigidize subassembly" (whatever that is) doesn't engage the curvilinear coupling. That's just on the end of the end effector and has nothing to do with the carriage. $\endgroup$ Nov 12, 2021 at 3:02
  • $\begingroup$ Figure 2 page 10 gives a nice view of the Rigidize Assembly. Its ballscrew retracts the snares. So it is the Ridgidize Assembly which pulls the snared center pin into the LEE. If the grapple is a “Plain Jane” model (without Curvilinear Coupling), this motion engages the cam arm shoulders in the cam cutouts, and that’s it. If the grapple has a Curvilinear Coupling, the motion of the Rigidize Assembly mates the Curvilinear Couplings at the same time. If the LEE has couplers, these engage and then the Rigidize Assembly relaxes tension on the snares since they no longer need to be tensioned. $\endgroup$
    – Woody
    Nov 12, 2021 at 4:19

1 Answer 1


Engaging with the Latching End Effector (LEE) involves several stages:

  1. Initial manual alignment using a camera on the LEE and a target on the object’s grapple.
  2. Capture using a 3-wire wire snare
  3. Final alignment by drawing the grapple into the LEE using traction on the snare.
  4. Coupling. Details depend on the variant of Grapple Fixture and LEE (Flight releasable FLGF or Latchable LGF)

The basic capture and alignment can be illustrated by the simplest variant, the FRGF and the associated CANADARM 1 LEE:

enter image description here enter image description here

The LEE is manipulated under video control to place the pin inside the space formed by the three snare wires. Motorized carriers move the snares to close around the pin shaft. The snares are then moved axially by a screw mechanism within the LEE housing, exerting traction on the pin knob and drawing the LEE and grapple together. The shoulders of the cam arms engage with the cam cutouts, correcting any residual misalignment. Secure coupling of LEE and Grapple is dependent on maintaining tension on the 3 snare wires by the tensioning screw.

Later variants added power and electrical connections, as well as locking couplers. As well, a gear-like curvilinear coupling ring reduces backlash.

enter image description here

The newer design is backwards compatible and capable of handling more massive objects. The curvilinear coupling is passive, in that it is engaged by the same action which engages the cam arm shoulders in the cam cutouts. The four couplers are engaged by motor. At that point, tension is released on the snare system. Secure coupling is not reliant on the snare wires, but on the multiply redundant locking couplers.

Detailed description: https://ntrs.nasa.gov/citations/19950020841

  • 1
    $\begingroup$ ...Nice pictures! $\endgroup$ Nov 12, 2021 at 6:19
  • 2
    $\begingroup$ Reading your post again, I realize you were right: mine is a duplicate post. I just didn't understand your post because I had no idea what I was looking at. A case of 'the eye sees what the mind knows." In my case, the mind knows nothing.... $\endgroup$
    – Woody
    Nov 12, 2021 at 7:14
  • 1
    $\begingroup$ It's admirable of you to say so and I'm glad that you learned about a system that's near and dear to my heart. I can't close it again, the system won't let me since I already did it once. I think if you vote to close it as a dupe, it will close. If not you can ask in meta or ping a moderator. $\endgroup$ Nov 12, 2021 at 12:17

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