The current coring bit and percussive drilling style works very well for strong rocks; however, when coring into weak, crumbling rock, the core tends to break apart and simply fall out of the bit. These rocks, powder, and other debris can have useful information that is lost when they fall out of the bit after the core has been made, as there is no retention feature in place. A retention mechanism for coring into weak rocks was developed.

The passive close-off feature consists of tabs that create a double or triple door that only opens one way, allowing rocks and regolith to enter, but not fall out. The tabs hug the inside of the tube and overlap slightly so that the rocks and regolith collected could not fall out.
One way to approach the solution is to create a system of one-way valves that allows material to enter the tube, but not exit. By creating a system of one-way doors, the material that is being collected can easily be pushed further up the tube and be retained there, while new material then has more space to fill up in the lower parts of the tube that have recently been vacated.

From this concept, the tab structure was developed. The tabs effectively create a double (or triple) door that only opens one way. This allows both rocks and regolith to enter, but not fall out. The tabs were made of copper shim, and were pre-bent to hug the inside of the tube when folded up, out of the way of new rock. Four wires, in two pairs, were bonded to each copper tab and then fed through a small hole in the side of the tube and bent to create a hinge that allowed the tabs to rotate up and down easily. The tabs overlapped slightly so that the rocks and regolith collected could not fall back out the middle of the tabs, even if they were slightly misaligned.

This design is very simple and the tab pieces are inexpensive and easy to duplicate for production purposes. The implementation is also very straightforward as these tabs are attached to a sample tube that can be removed from a coring bit, thus not affecting the overall method of core drilling. This design allows for full retention of the material.

This work has applications for all current and future coring activities. There have been designs that can capture regolith or rock, but this is one of the first designs that can effectively capture both. Both of these sample form factors are important for the proposed science.

This work was done by Margaret A. Scholtz, Celena Staff, and Charles M. Dandino of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49663