Subglacial Bedrock Sampler

Lead Research Organisation: University of Glasgow
Department Name: School of Engineering

Abstract

This project will apply technologies developed by the planetary exploration community to the problem of obtaining rock samples from below the ice caps on Earth. This will open up the available area of exploration and allow the uncertainty in predictions of sea level rise to be greatly reduced.
Rock samples from beneath the Antarctic or Greenland ice caps will significantly increase our knowledge of both the underlying geology and the history of the overlying ice. Currently the under-ice geology has to be inferred from the few locations where the rock rises through the ice, as well as some gravity and magnetometer measurements taken from aircraft.
We could learn much more if we had actual samples. Rays from space age the surface of exposed rocks, and measurements of this aging can indicate how long that rock has been exposed to daylight. This method, cosmogenic dating, can be used on the samples to determine when they were last exposed to radiation, and therefore reveal how long the rock has been covered by ice. Provided samples can be obtained across a wide area, it would be possible to chart the growth and withdrawal of the ice sheets in earlier climate epochs. That knowledge helps us to understand how the ice sheets will change in the future, which is very important as we try to understand the processes of climate change and sea level rise.
Obtaining these samples is not easy. The ice is many hundreds of metres thick, and stretches across extremely remote areas. Drilling through it has been possible, using heavy drilling rigs powered from the surface, but there are still a number of very major problems.
Firstly, a drill which can cut through ice is not necessarily suited to drilling through rock, and vice versa. The teeth used to plane through ice will not penetrate rock, while rock grinding teeth can glaze over if an attempt is made to force them through ice. Furthermore a huge drilling rig, mechanically powered from the surface, cannot easily be transported across the large areas we need to sample. A smaller system, which can be transported by aeroplane, is needed.
This type of system is called a wireline drill. The drill unit is lowered into a hole by a cable, and it uses its own weight to recover a few metres' worth of ice using an auger. The drill is then winched out, emptied, and lowered back in again. Repeating this process allows the hole to be dug out, deeper and deeper, until the drill hits the rock boundary.
The problem comes when we reach the rock boundary. It is very hard to drill into the hard rock and extract the samples using the small weight of the wireline device, and so we have turned to technologies developed to drill through rock in other situations where force available to push the drill into the rock is limited.
In space, planetary rovers must drill through rock to obtain samples even though gravity is very low. That means that they cannot force their way through very easily, but yet percussive tools can still operate. We are therefore going to assess two different types of percussive drill, both of which have been suggested for Mars exploration: the cam-hammer and the ultrasonic-percussive device. They both generate high impulse forces by moving small hammer masses against a drilling bit, and they have been tested in icy conditions. Most importantly, this hammering motion does not result in large external forces that need to be supplied by the wireline. In fact, the external forces can be around 100 times smaller than the hammering forces, if the shocks are properly damped.
This project will determine if these devices can be fitted to a wireline drill, and then evaluate how well each type works before choosing one for development. That technology will then be designed into a new wireline device that could be lowered downhole to obtain rock samples, instead of just ice. And with the rock samples, we can start to ununravel the history of the ice sheets above.

Planned Impact

We believe that the scientific outcomes associated with the terrestrial subglacial samples should be considered primarily academic (even though the effects of climate change ultimately affect everyone), and so here we focus solely on the impact of the technical engineering work.
Firstly, this study will represent the first upscaling of ultrasonic-percussive tools towards to 40+ mm diameter range, which is a scale that begins to attract commercial (as opposed to domestic) drilling applications. This type of drilling, perhaps for survey purposes, is often conducted using sonic drilling techniques, whereby a solid drillstring is repeatedly struck from the surface using a rotating hammer unit. There are, however, some difficulties: resonances in the drillstring at a depth where the time-of-flight of an impulse matches the beat frequency of the hammer need careful control. Investigating the performance levels that could be obtained using downhole tools therefore has commercial value in this field, and Harkness has a contact within the UK's leading sonic drilling contractor who will be kept fully aware of our activities.
Domestic hammer drills based on the cam-hammer approach are also ubiquitous, but at least one company is currently developing an ultrasonic-percussive drill for the power tools market. This study, which intends to conduct a first direct comparison between the two approaches, would therefore have significant impact on a sector worth over $25bn per annum. [Value from placidus-tech.com].
Finally, there are also aspects of the space systems engineering community that stand to benefit from this work. The European Space Agency (ESA), for example, is working on low-footprint drill technologies with partners at Roscosmos in support of the upcoming series of Luna landers. Harkness has a strong relationship with the technology team at ESA, and will ensure that the results are fully communicated. The same is true for colleagues at the Jet Propulsion Laboratory. These research institutions also have relationships with specialised private companies, such as Honeybee Robotics, which focusses on the development of planetary drilling devices. Again, Harkness has good contacts here, and is in fact working on a joint publication with Honeybee Robotics staff. This project would support the ongoing collaboration.

Publications

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Timoney R. (2018) P-RAID: Deep Subglacial Bedrock Sampling in AGU Fall Meeting Abstracts

 
Description Acquiring rock samples from deep under an ice sheet is difficult. Fundamentally, the problem is that drilling in remote polar regions is largely dependent on equipment flown in by aircraft, which means that long, rigid drillstrings (as used in the oil industry) or large sonic drilling rigs require major logistics. Lightweight wireline drilling methods are strongly preferred for both ice and rock. To this end a highly-portable wireline ice-drill, Rapid Access Isotope Drill (RAID), has already been developed by the British Antarctic Survey. Nonetheless, attempts to obtain rock samples have yielded mixed results. The problem is that the cutters on an ice-drill operate by planing through the ice, which is not effective in rock, and yet if a specialised rock-cutter is lowered instead, meltwater can glaze the teeth and prevent progress. The higher torque, speed, and weight-on-bit requirement of rock cutters are also not suited to wireline drills. Ultimately, the unsuitability of current rock and ice cutting methods mean that a new sampler is required: one which can operate at the low weight-on-bit and torque values available downhole using portable wireline technology. This is the technology developed under the Subglacial Bedrock Sampler project.

We have been going through a process of technological development and have worked up from laboratory testing (broadly 2017) to first field deployment (broadly 2018, but actually in the field in January 2019) and an upcoming second field deployment (broadly 2019, with the intention of going south in January 2020). We have learnt how important it is to have effective autonomous control systems that can govern the behavior of the drill system, and how important it is to cold- and dry-test hardware before deploying it to a new and harsh environment.
Exploitation Route Our antarctic deployment application, which will lead to the first recovery of subglacial rock samples, is currently in review.
Sectors Environment

URL https://www.bas.ac.uk/project/p-raid/
 
Description This project demonstrated that a low-force, low-torque, low-power percussive system could deliver controlled progress into rock samples at low temperatures. This led to a further grant, ST/R00269X/1, which sought to develop a deployable drill system that could actually be deployed to antarctica in pursuit of subglacial samples. A third application, to enable a first field test, was successful, and the drill system was successfully integrated with the winch apparatus in the field, and a number of shakedown technical issues were identified. A fourth application, to enable a drill campaign with the objective of collecting subglacial samples in the 2019/20 summer season, is now in review.
First Year Of Impact 2016
Sector Environment
 
Description Impact Acceleration Account
Amount £60,000 (GBP)
Organisation University of Glasgow 
Sector Academic/University
Country United Kingdom
Start 06/2018 
End 03/2020
 
Description Mars Sample Return to Terrestrial Polar Science - Planetary drilling concepts applied to subglacial rock sampling in Antarctica
Amount £93,155 (GBP)
Funding ID ST/R00269X/1 
Organisation UK Space Agency 
Sector Public
Country United Kingdom
Start 10/2017 
End 03/2018
 
Description BAS 
Organisation British Antarctic Survey
Country United Kingdom 
Sector Academic/University 
PI Contribution Provision of the drill hardware for testing.
Collaborator Contribution Provision of the appropriate rock samples and test environment.
Impact We are working together to create a uniquely deployable and capable subglacial sampling system.
Start Year 2016