Curiosity drill bit design, showing powder flow path and two sample chambers
Note the donut-shaped diaphragms separating the two chambers and the aft exterior of the bit. These diaphragms have to flex in order to allow the percussive force to transmit to the bit from the percussion assembly that the bit is coupled to. As a result, they could not have welded edges.
The Curiosity drill is a powdering drill design. It does not collect intact cores. Instead, it pulverizes the rock and collects the resultant powder in a sample chamber for processing and distribution to the instruments. It does this using rotary percussive action, similar to a hammer drill you can buy at a hardware store. The main difference is that instead of just getting rid of the powder like a home drill, Curiosity's drill was designed to collect this powder through a sample tube that extends over most of the drill bit. The powder is augured up the tube using the rotating action of the drill and collected in a two-chamber sample collection area behind the bit.
Two chambers are required in order to support the ability to drill into surfaces angled up to 20 degrees from horizontal. With a five-degree-of-freedom robotic arm, we can’t control the orientation of the drill sample exit tube. As a result, we would potentially dump sample onto the ground while drilling if we did not have the sample chambers. These sample chambers have Teflon / fiberglass / molybdenum disulfide edge seals, which turned out to be a potential source of contamination for the SAM instrument. I won’t go into the details of that issue here, but maybe in a future blog entry. This powdering bit design comes at the science cost of losing the ability to view acquired intact cores, but it simplifies the overall system by removing the need for a rock crusher to pulverize the core after collection.