The Not-So-Big Dig
With the equivalent power of an electric can opener, engineers try to do more than scratch the Martian surface.
- By Tom Harpole
- Air & Space magazine, November 2006
Planetary geologist James Dohm doesn’t mean to disparage when he says Idaho Falls is a lot like Mars. A large, gentle man who has spent 19 years at the University of Arizona mapping the red planet, Dohm sees exceptional possibilities in this city of 50,000 people on the west side of the Teton Range.
Idaho Falls straddles the Snake River headwaters a couple hours’ drive southwest of Yellowstone Park, where the Rockies smooth out into central Idaho’s sage-studded flatlands. But what makes it special, Dohm says, is what lies beneath—a layer of basalt that is similar to much of the crust of Mars. Basalt—a dark-colored, fine-grained igneous rock rich in iron and magnesium—is one of the barriers that planetary scientists will have to penetrate to get beneath the Martian surface. NASA is preparing now for drilling operations to better understand the planet’s evolution and perhaps answer one of its biggest mysteries: Did life ever exist there?
“Basalt is one of the hardest rocks on Earth,” Dohm says. “If we’re going to bore a hole in Mars, we need to get good at drilling into basalt.” Doing so with small but sturdy tools that haven’t quite been invented is the challenge.
As with the Earth, the surface of Mars is blanketed with regolith—loose sand, dust, rocks, and minerals deposited atop bedrock by meteors and spread by wind and erosion. Add to that eons of solar radiation bombarding the planet and you can be almost certain that no life remains on the surface. The logical step, for Dohm and other scientists, is to drill.
But deciding when, where, and how deep to drill will drive site selection discussions in the Mars exploration community for the next few years, just as such concerns kept Apollo-era scientists busy deciding where on the moon NASA astronauts should land and go prospecting.
On Mars, “there’s evidence of internal heat sources,” Dohm explains. In theory, that heat could sustain underground life. Data from orbiting spacecraft strongly suggest the presence of both hydrothermal and volcanic-driven heat flowing to the surface. “We are looking at a dynamic planet,” he says.
To go after the secrets beneath Mars, scientists can drill either into rock or ice. Drilling in rock may help them understand the geologic record of Mars, while drilling in ice could provide clues into the biological past. Since there won’t be astronauts along at first, making the drill autonomous is one of the biggest hurdles NASA faces.
So far, the space agency has had limited experience in extraterrestrial drilling. The Apollo astronauts hammered, raked, scooped, or drilled for the 842 pounds of moonrocks they brought home. The drilling, in particular, was difficult, as Apollo 15 astronauts David Scott and James Irwin, who landed on the moon in July 1971, can attest.
In boring a hole at Hadley Rille, Scott ran into trouble when the battery-powered drill jammed at about 5.5 feet. He gave up trying to wrestle it out of the lunar rock. The next day, he and Irwin manhandled the drill and its core sample out of the hole.
The problem was a key flaw in the drill’s design: Its threads were not carrying the cuttings to the surface. Instead, the cuttings were getting clogged in the hole, binding the drill stem. (Nevertheless, later X-ray analysis of the core showed 58 separate layers of regolith along with various pebbles and an increasing density down to the bottom of the core.) NASA fixed the problem on later flights. On Apollo 16, Charlie Duke drilled to the full eight feet in about one minute. On Apollo 17, Gene Cernan did it in just under three.
Robotic spacecraft also have used drills. The Soviets put drills on their Luna soil-sample return probe to the moon (capable of penetrating about 13 inches) and Venera spacecraft to Venus (just over an inch) in the 1960s and 1970s. The European Rosetta mission, which launched in 2004, is designed to land on a comet in 2014, drill down about eight inches and analyze the contents.
The requirements for a Mars drill are daunting. The machine must collect cuttings and cores, analyze the samples, and transmit the findings to Earth. It must weigh less than 90 pounds and run on an energy budget of less than 100 watts, drilling a roughly two-inch diameter hole to produce a one-inch core.
Earthbound miners, when boring a two-inch diameter hole for blasting basalt, commonly use 2,400-pound compressors that drive 55-pound drills. Even that is a relatively small outfit compared to the drills used for water or oil wells. No one has ever drilled autonomously on Earth; the rigs require constant human input, and they rely on brute force and extreme horsepower to penetrate the mantle. By contrast, the drills under development for Mars will have motors that operate with the equivalent power of an electric can opener.
Last February, Dohm and other scientists joined two teams of engineers from Swales Aerospace of Pasadena, California, and Maryland’s Raytheon/UTD, at the Idaho National Laboratory (INL) in Idaho Falls to test two candidate drills for Mars. The rigs’ designs were at opposite ends of current development in low-power, low-mass drills to retrieve core samples and cuttings for analysis.
Swales’ entry, which has a target depth of 65 feet, used a custom-made drill string: interconnecting pieces of pipe that make up the ever-lengthening shaft of a drill. In a drill string, the shaft is assembled in sections, which are added as the borehole deepens. To collect a core sample, the entire string is withdrawn from the hole and disassembled.
Raytheon/UTD’s rig, which had drilled through limestone to a depth of 4.5 feet in lab tests, used a tethered corer design. The core and cuttings are winched up from the bottom of the hole inside of the drill and collected at the surface. The advantage of the tethered system is that it reduces the weight of the drill because there is no drill string. That allows for greater depths to be bored with less energy.
Drilling conditions in Idaho Falls that February day were in some ways tougher than on Mars. Adjacent to an INL parking lot, the teams set up custom-made white canvas tents that flapped like sails under blue skies and wispy clouds. The tents protected the teams from both stiff winds and prying eyes. But an unusual weather pattern pushed daytime temperatures to the mid-50s, causing snowmelt to flood the ground and pour into the boreholes. The regolith kept collapsing, and anyone who stepped off the hastily laid plywood footpaths would find himself ankle deep in Idaho mud. “Quagmire” came to mind, a term that shouldn’t normally apply to Idaho in midwinter.
Both drills had uniquely designed bits to bore into ice or very hard rock, but not the soupy two-foot-thick layer of gravel, sand, and soil that formed atop the basalt bedrock.
The Swales team has been developing its Modular Planetary Drill System since 2005. “You want to have a cool acronym— we don’t,” said Argie Rumann, a senior systems engineer, in a notable attempt at humor during an intense week of field tests.
Swales brought a third-generation rig that measured 11 feet tall, four feet wide and weighed 425 pounds with its ground support equipment platform. To work on Mars, a shallow drill would need to shrink in all those dimensions by a factor of 10. The drill and retrieval system, as well as the instruments to analyze the Martian samples, would need to fit in a space of about 35 cubic feet—the size of a kitchen stove—and weigh less than 88 pounds.
Rumann, along with team leader Jose Guerrero and colleague Dominic Wu, piled dry ice and sandbags around their borehole to keep the meltwater at bay. Guerrero designed the patented bit, a donut-shaped cutting head that collects a core while the flutes spiraling up the outside deliver the cuttings into a separate collection chamber.
With the drill inching down at 50 rpm, they finally got into the basalt at a depth of 17 to 24 inches. The tent pulsated with vibrations and the drill string howled like a couple of coyotes. As drillers will tell you, there is an art to listening to the down-hole sounds of the drill string that they claim is vital to anticipating problems. Ignoring the warning sounds could result in an irretrievably stuck drill. But Mars is hundreds of millions of miles away, with a radio lag time of more than 10 minutes, so Earth monitors could not react to real-time changes in drill vibrations and sounds. Software must be programmed into the drill to stop it when sensors detect problems with torque, temperature, or other conditions.
“Developing the software to evaluate what the drill is doing and to react [to it] will take a team of programmers a year,” Guerrero said. Much easier is miniaturizing the drill and its scientific instruments. That, he says, “is just a matter of money. The more we spend, the easier it is to get lower weight.”
The Raytheon/UTD tethered core drill turned out to have its own problems. Jennifer Farrand and Matt Tucker, a couple of young, serious engineers, brought the drill from Maryland after 18 months of development. Their drill has an assembly that anchors itself to the sides of the hole and exerts force on the bit from down-hole instead of from the surface.
But on that unseasonable February day, the saturated Idaho regolith collapsed and captured their bit. The ground then refroze during the night. That forced Farrand and Tucker to rent an electric impact drill and bore by hand a series of holes around their stuck core until they could dig it out. Farrand took it in stride: “These conditions may arise on Mars if drill bit friction thaws ice beneath the surface. The refreezing could capture the bit permanently.” She smiled, “We’re always learning.”
The Raytheon/UTD drill is similar to a NASA/Baker Hughes Mars drill rig that Jeffrey George and his team at the Johnson Space Center tested in the Canadian arctic in May 2006. George’s team spent two weeks on Ellesmere Island testing their seven-foot-tall by 1.75-inch-diameter drill in what the scientists considered ideal weather.
“It averaged 18 below Celsius (–3 Fahrenheit) and we found new ways to break and get stuck, and new failure modes and we spent a lot of time in the weather station, working on the drill. We finally drilled through ice and sandstone to two meters. We could drill about five inches in the sandstone in 20 minutes using 50 watts,” George said upon his return to Houston in mid-May. The NASA/BH drill has three motors – one to anchor the bottomhole assembly, another to apply down pressure, and the third to provide torque. As with the Raytheon/UTD rig, the drill winches up the cores and cuttings through the drill stem to be collected and analyzed on the surface.
“An interesting aspect of the core samples we got was that with all the concern about contaminating them with pieces of the bit, we now know that the interior of the core is intact and uncontaminated,” George said. “We trust that would be true on the moon or Mars” (see “Unwelcome Visitors,” left).
After seeking the most extreme Earth environments in which to test the drill, a return to the moon may provide the best opportunity to test Mars-bound rigs. The moon would provide “fantastic field-test opportunities,” says Suparna Mukherjee, technical lead for the Subsurface Access Base Technologies office at NASA’s Jet Propulsion Lab in Pasadena, California. When Mukherjee talks about inventing hardware for Mars, she occasionally arches her eyebrows and utters a contralto “cool.” She explains the meaning of Technology Readiness Levels 1, 2, and 3.
“TRL 1 is the draw-it-on-napkins level,” she says. “It’s physics and dreaming of possibilities.” TRL 2 finds scientists prowling hardware stores for off-the-shelf parts that become components for prototype systems. “The drills we tested in Idaho were TRL 3. We’ve gone from idea to hardware to proof-of-concept through field experimentation,” says Mukherjee. “You get hooked on the challenge.”
The most mature TRL 3 machines can drill through hard rock with less than 80 watts and bring samples to the surface. The next few hurdles for Mukherjee and the half-dozen other groups developing extraterrestrial drills is to miniaturize the rigs and get them to run autonomously. The drills also have to deliver samples to on-site instruments for analysis. “The mechanical engineering, with the various teams approaching problems from different angles, will be accomplished,” Mukherjee says, confidently.
Scientists from NASA’s Ames Research Center this summer ventured to the Canadian arctic to see whether artificial intelligence could control a Mars prototype drill. The Drilling Automation for the Mars Exploration (DAME) project bored into the Haughton Crater on Devon Island in Canada’s Nunavut Territory in late July to see if synthethic brainpower could keep the rig drilling for hours at a time without human interaction. The drill, built by Honeybee Robotics, ran on its own for a cumulative total of 43 hours, with the longest shift at 4.5 hours, and bored down 10.5 feet. Operating on 100 watts of power, the drill’s software also correctly responded to five of six known major fault modes. The experiment will help in designing drills for Mars, where robots will probably be able to “talk” with controllers on Earth only once or twice a day.
In a briefing at the Idaho National Laboratory last February, Arthur Lonne Lane, principal scientist of JPL’s Astrobiological Group, brought up several ancillary issues that NASA faces before sending drills to Mars. Data from the European Space Agency’s Mars Express orbiter has shown NASA places where it does —and doesn’t—want to drill.
Scientists would love, for example, to drill at the polar ice caps, where radar surveys by Mars Express indicate that water may be found just three feet down. But engineering hurdles prevent that, for now. NASA’s next rover, the Mars Science Laboratory, scheduled to be launched in 2009, will carry equipment to bore into rocks. But the spacecraft is restricted to landing 60 degrees north or south of the equator, partly because the frozen ground at the poles could hinder the heavy rover’s movement.
Lane speaks eagerly about the possibility of studying Martian biology, while acknowledging the frustration of looking at the planet. Mars, he says, is in many places covered with a kind of “organic crud.” The deepest any spacecraft has penetrated that crud is about 10 centimeters—just under four inches—when a wheel on NASA’s Opportunity lander was purposefully spun to make a trench in February 2004. The rover then pointed spectrometers into the trench to analyze heat signatures and minerals, and found spherical, glass-like pebbles the size of BBs.
The rewards of drilling on Mars are uncertain and nearly impossible to calculate. Boreholes on Earth—whether for oil, gas, or something else—are expected to pay off right away in new resources or scientific information. It costs about $20 a foot to drill a six-inch diameter water well on Earth. Drilling a two-inch diameter hole on Mars that just might turn up fossilized life? Priceless.