A Small-Scale Tether Management System for Under-Ice Ocean Profiling

Under-ice ocean and lake environments on Earth are locations of scientific interest for oceanography, biology, and climatology. These settings can also inform the operations and technology for missions to other planetary bodies in our solar system. However, accessing the oceans and lakes under ice is difficult, in particular for maintaining safe communication to the surface. Exploration systems can require significant cable architecture for communications and mechanical support. Issues in cable management can result in tangling or stresses that can cause tether failure. This is particularly important in the case of fiber optic tethers, used for high bandwidth communication, which are sensitive to fractures under both radial and linear stresses. Furthermore, subglacial oceans and lakes on Earth can be covered in as much as 4km of ice; maintaining a large hole in the ice is difficult but required to spool tether from the surface using commercially available tether management systems. An on-board tether management system can minimize issues in tethered vehicle deployments by mitigating issues with spooling tether from the surface, such as refreezing or snagging of the tether within the ice, particularly in deeper subglacial deployments. Through-ice deployments either on Earth or ocean worlds such as Europa tightly constrain the size and mass of the probe to fit within a small borehole diameter, yet tether management systems of this stringent form factor do not currently exist. Thus, a small-scale on-board tether management system that is designed in concert with tether and probe designs is enabling for many styles of sub-ice exploration and data gathering. This paper presents the design, development, and benchtop testing of a custom tether management system, for use on-board a vehicle with a 15 cm outer diameter. This system packs 335 m of tether in small form factor, utilizes a tension management system to reduce load on drum in case of snags or impulses, and been tested to accommodate up to 182 lb load on the tether.