Drilling advances

	Vol. 225 No. 12
ROBERT E. SNYDER, EXECUTIVE ENGINEERING EDITOR

Drilling on Mars. As a project that is part of NASA's Astrobiology Technology & Instrument Development Program (ASTID), a group involving NASA Johnson Space Center (JSC); NASA Ames Research Center (ARC); Baker Hughes Inc. (BHI); McGill University; and the Lunar and Planetary Institute, is developing a low mass (»20 kg) drill that will be operated without drilling fluids and at very low power levels (»60 watts electrical) to access and retrieve samples from permafrost regions of Earth and Mars. The drill, designed and built as a joint effort by NASA and BHI takes the form of a downhole unit attached to a cable so that it can, in principle, be scaled readily to reach significant depths.

A parallel lab effort is being carried out at UC Berkeley (UCB) to characterize dry drilling under Martian conditions of pressure, temperature and atmospheric composition. Data from the UCB and JSC lab experiments as well as BHI drilling lab tests are being used as input to a drill simulation program that is being planned to provide autonomous drill control.

Observing commercial drilling team at Eureka, Ellesmere Island. Photo courtesy Brian Derkowski.

The first Arctic field test of the unit was conducted May 14 – 18, 2004 at the Eureka weather station on Ellesmere Island, within the Arctic Circle in Canada's Northwest Territories off the NW tip of Greenland, following a field expedition to Eureka in Spring 2003, that provided an introduction to the practical aspects of drilling under Arctic conditions. The field effort was organized by McGill and ARC. A conventional science drill provided by New Zealand colleagues was used to recover ground ice cores for analysis of their microbial content and to develop techniques using tracers to track the depth of penetration of contamination from the core surface into the samples' interiors.

NASA's Mars Exploration Payload Assessment Group (MEPAG) has identified science goals, objectives, investigations and priorities for future Mars exploration in a document (JPL Publication 01-7) that addresses the importance of gaining access to the subsurface. Such access is identified as a priority in determining: 1) if life exists, 2) the nature/ inventory of organic carbon in soils and ices, 3) the state, distribution and cycling of water, 4) the large-scale vertical structure and chemical/ mineralogical crust composition, and 5) distribution of accessible water in soils, regolith and groundwater systems.

Development of the technology to permit autonomous drilling to access core samples has already begun. In the case of drills that eventually must operate on Mars, more than one terrestrial environment may be considered relevant. For the drill being developed by a team at JSC, BHI, UCB and ARC, the chosen relevant environment is that of the Canadian High Arctic.

A drill bound for Mars will bear only a passing resemblance to those used on Earth for geoscience drilling. The mass available will be measured in tens of kilograms, precluding use of drilling fluids for removing cuttings and cooling the bit. There will also be severe limits on use of conventional casing. Power may be less of an issue if newly available nuclear power sources can be used; however, bit temperature considerations (from sample alteration and bit wear) will likely prevent more than a few tens of watts of electricity to be used.

Automation of the drill will be mandatory, given the time delay in communications between Mars and Earth, and the need for rapid reaction in the event of off-nominal events, e.g., bit lock-up in penetrating an ice lens if the bit is allowed to get warm enough to melt the ice. Clearly the automation of a Mars drill will be a challenge, but the team has made progress in identifying the sensors, e.g., motor currents, rpm, rate of penetration and temperatures.

The drill system under development has a number of innovations. The downhole unit (DHU) is attached to a wireline (cable) so that the depth to which it can, in principal, penetrate is not constrained by a drillstring of joined rods. Further, the wireline allows high-rate data to be returned from the downhole unit, easing the challenge of automation. The DHU anchors itself to the sides of the hole, and weight on bit is provided by a spring compressed by a motor in the unit.

The coring bit contains only the minimum amount of material needed to capture a core of about 2-cm diameter. The cuttings are carried upward by an auger and deposited in a “basket” sitting on top of the core receptacle. When sufficient core has been captured, it is snapped off and the entire unit is winched to surface where the cuttings are removed and the core extracted.

At Ellesmere Island, in May, the team of JSC-BHI and UCB used a small portable rig that had been previously used for field work in Antarctica. Samples of ground ice (estimated age 10,000 years) were recovered from depths of up to 20 m, during which time the team logged drill performance data and recorded the numerous practical problems that can arise when drilling in permafrost terrain. The team carried out experiments using fluorescent tracer beads of appropriate size (representative of bacteria) to understand contamination issues that will be faced on Mars.

One advantage is the very slow rate at which the drill will penetrate and the expectation that the drill will be fully instrumented with sensors, whereas the performance monitoring of a typical geoscience drill relies mainly on the senses of the operator. The NASA-BHI-UCB collaboration in the development of a drill capable of robotic operation on Mars has made good progress over the last year; and the team is encouraged regarding the feasibility of adding a new (vertical) dimension to the scientific exploration of Mars.