RedWaterExtraction of Water from Mars’ Ice Deposits
[image] concept design by Jetportal Spaceformcraft
In the past decade orbital measure-ments revealed that a third of the Martian surface con-tains shallow ground ice. MRO’s SHARAD sounder has revealed the presence of ice-rich materials in sev-eral non-polar terrains, including debris-covered glaci-ers and ground ices extending down to latitudes of 37° . These deposits are up to several 100 m thick and many appear to consist of nearly pure water ice. The ability of the radar to resolve shallow layering is lim-ited to ~20 m .Thus, to reach ice and extract water, a system would need to penetrate through at most 20 m of regolith. The discoveries of nearly pure ice deposits in mid latitudes on Mars enable implementing two proven terrestrial technologies: Coiled Tubing (CT) for drilling and Rodriquez Well (RodWell) for water ex-traction.
CT rigs use a continuous length of tubing (metal or composite) that is flexible enough to be wound on a reel and rigid enough to withstand drilling forces and torques. The tube is pushed downhole using so-called injectors (for example, a set of actuated rollers that pinch the tube and advance it downward). The end of the tube has a Bottom Hole Assembly (BHA) – a motor and a drill bit for drilling into the subsurface. To re-move drill cuttings, compressed air (or other drilling fluid) is pumped down the tube. A hole is drilled by advancing coiled tubing deeper into the subsurface while blowing cuttings out of the way. A commercial CT rig, such as RoXplorer, weighs 15 tons and drills to 500 m at 1 m/min in hard rock.
RodWell is a technology where a hole is drilled in ice, which is melted and pumped to the surface. It has been developed and tested in Antarctica in the 1960s and used at the South Pole station since 2002.
The RedWater system combines the two technologies into one. It uses the CT approach to create a drill hole. Once the hole is made, the coiled tubing is left in the hole and used as conduit for water extraction. The BHA con-tains a rotary-percussive drill subsystem (similar to the one used in Honeybee Robotics Deep Drill ), a downhole pump, and heaters. The tube houses an insu-lated and heated hose as well as wires for downhole motors and heaters. During drilling, compressed gas is sent downhole through the hose [4, 5, 6]. The gas es-capes through the annular space between the tube and borehole wall and removes cuttings that can be collect-ed and analyzed for science. Upon reaching an ice layer, the drill continues for another ~3 m and then stops advancing forward, but the bit continues to spin. Heat-ers are turned on to melt the surrounding ice. Once ice starts to melt, the peristaltic pump starts pumping a fraction of the melted water up the same hose that was used for the compressed gas, and into a storage tank on the surface via a three-way heated valve, which switch-es between the gas tank and the water tank. The re-maining water passes through a downhole heater and is pumped into the rotating bit for water jetting. This con-tinuous stirring and the injection of hot water speeds up the melting process. After melting a section of ice, the CT is reactivated to drill further into the underlying ice and the melting process continues.
Since atmospheric pressures and temperatures in the Martian northern plains extends above water’s tri-ple point, liquid water can exist at the surface. Howev-er, it is unstable and will boil off very quickly. For this reason, it is desirable to seal off the hole. This can be achieved via active means (e.g., a packer can expand in the hole and seal off the annular space between the tube and the borehole) or passive means (e.g., water vapor would re-condense on the cold borehole wall and seal it; this in fact has been observed). In the latter case, the tube would have to be heated to free itself up before continuing further down, when needed.
M. Hecht, Haystack Observatory, Massachusetts Institute of Technology
N. E. Putzig, Planetary Science Institute
D. Sabahi, NASA JPL -retired
P. van Susante, Michigan Technological University
Jetportal Spaceformcraft provided concept development, design modeling and visualization.