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
(Page 3 of 4)
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.