Monday, September 24, 2018

The Mars Drilling Project

I was absolutely mesmerized by the discussion between Jim Gavin and Chris McKay on Planetary Radio's August 1st, 2018 episode. The discussion revolves around the discovery of liquid water 1.5km below the South Polar Ice Cap on Mars, in the Planum Australe region. You can listen to the episode here.

I have decided to take a stab at developing a drilling technique to reach the 1.5km depth on Mars. I plan to develop prototypes at home so I can continue to learn more about this engineering challenge. I think the best approach is to first build a full scale Curiosity/Mars 2020 rover (scaled-up Sawppy rover?) to use as a test bed, and take ideas from various portable drill rigs to design a rig that can be used to robotically drill on Mars.

Disclaimer: Please note that I am not representing my employer or college. For now this is a personal project.

PURPOSE

To investigate the feasibility and challenges posed by taking liquid water samples from 1500m under the Mars South Polar Ice Cap. 

REQUIREMENTS
  • Drill to a depth of 1500m
  • Reasonable diameter bore hole to meet science objectives (which have not been identified), 50mm to 150mm estimated
  • Bore portal stabilization
    • Apron / casing at portal to stabilize for possibly years of inserting / removing drilling/servicing equipment
  • Ice core sample retrieval and transfer to science instruments (which have not been identified)
  • Water sample retrieval and transfer to science instruments (which have not been identified)
  • Sample caching for future ice core retrieval and return to Earth on a follow up mission, ala Mars 2020

POTENTIAL STRATEGIES
  • On-site fabrication and repair options using 3d printed stainless steel, robotic arms and actuators, and 3D printing of useful non-mechanical items using local substrate
  • Remote sensing - conventional mast may not be the best approach
  • Small "service" rover to support the main rover
  • Small bore-bots that can drive up and down the bore to inspect the bore, remove broken cutters, drill through stones or cobbles that would destroy a cutter, remove chips and shavings, etc. 

KEY CONCEPTS

The concept of robotically fabricating repair parts and tools on site should be core to the concept of this mission. We should plan for these failures and make as many drilling system components as easy as possible to fabricate, disassemble, and assemble to give ourselves the best chance of recovery from a technical or mechanical challenge during drilling or sample retrieval operations.

Casing requirements need to be immediately investigated and discussed as the scope of the drilling hardware can't truly be defined without understanding the bore requirements. We need to understand if the bore will be self supporting and stable, if it will have a consistent enough straightness, and if the bore "quality" will be sufficient to get to these depths without casing.

Another very important concept to consider is that the the orbiter teams will be reviewing existing radar data and scheduling instrument time to find other subsurface bodies of water. The final landing site may not be Planum Australe, and therefore we can't rule out drilling through frozen soil. A robust design that can accommodate both ice and permafrost drilling should be assumed until other landing sites can be ruled out. A future scope statement will need to address this.

Atmospheric pressure on Mars, even at a depth of 1.5km in the south pole region (which is still 1.5km above the mean elevation), is below the triple point for pure water. This means when drilling
into pure water ice there is zero risk of generating liquid that can re-freeze; only vaporized water will result, but of course the vapor can still deposit on drilling equipment. That said, the liquid water at a depth of 1.5km is expected to be completely saturated with salts. For this reason it is very important to know the chemistry of the ice we will be drilling so we can adjust feed rates to prevent the accumulation of liquid water around the drilling equipment in the bore hole. Periodic sampling of the evacuated drillings will be necessary to determine the appropriate feedrate and drilling speed. Core analysis can be done more thoroughly and separately in an onboard laboratory, but a method for quickly categorizing the chemistry of shavings will be very important to keep from freezing a drill head in place. There is an option to keep this simple by exposing samples to heat and observing the results with an optical instrument. Everything in this paragraph cannot be replicated on earth without operating in a vacuum cold chamber, so "practice" feeds and speeds will need to be substantially lower than may be possible on Mars, but we may want to stay away from these Mars maximum speeds for power requirement reasons. 

NEXT STEPS
  • Build a full scale functional but "approximate" Curiosity rover
  • While rover fab is being accomplished, continue to narrow down drill rig requirements
  • Define the scope of the drilling requirements
  • Aggregate known data about Planum Australe and the polar ice. We need detailed information about any soil that may be present in the ice.
    • Note: this ice deposit is referred to as the South Pole Layered Deposit (SPLD).

Update 2/15/19: Follow up study about factors keeping the deep water liquid (proposes volcanic activity):


Please feel free to comment here. An open and vibrant discussion will be key to doing this project properly.

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