Aridged retention interface is necessary to secure planetary sample tubes within a caching system for use in future sample return missions. The assumed retention interface requirements are as follows: the interface shall maintain sample integrity at large deceleration landing loads; the interface shall minimize weight and complexity; and any required actuation for sample tube retention shall be performed by an external source (such as a robotic end-effector).
A tapered collet similar to a milling machine’s tool holder was designed with a threaded profile on its outer tapered diameter. When the collet is threaded into a corresponding non-tapered threaded hole, the collet collapses inward, applying a radial force on the sample tube within. The sample is retained within the collet by both friction force and any captured features designed into the sample tube’s OML (outer mold line). Ratcheting teeth on the collet ensure that it remains locked in place once a preloading torque is applied.
The collets are pre-threaded into the sample cache at a zero preload state during assembly, test, and launch operations (ALTO). After sample acquisition, the sample tubes are inserted in the collet cache via a robotic end-effector. The end effector then torques the collet to the desired preload, reacting the resulting force via standoffs located on the cache to act as moment reaction features.
The threaded tapered collet combines the mechanical advantages of a traditional collet and a tapered pipe thread to produce a lightweight, simple, and robust latching system. The desired sample tube preload can be tailored to specific applications, and allows each sample to be individually secured.