During the December tests, Auto-Gopher-2 drilled a 7.5-meter borehole, which engineers also used to perform operational readiness tests for WATSON. WATSON can use its gripping shoes to "inch-worm" on the sides of the borehole, which is important in order to precisely position the spectrometer for fine-scale borehole scanning. This is more precise than relying solely on the drill tether, which rotates and stretches, says Kris Zacny, the director of Honeybee's exploration technologies group. He said another advantage of inch-worming is to save time by taking multiple "bites" when drilling until the auger fills up with sampled cuttings, which greatly saves time when working in a hole that is hundreds of meters deep.

"We spent a lot of time doing drill automation," Zacny said. "It can work on its own in the hole. This approach is ideal for a hole on Mars." Scientists recently discovered a possible subsurface lake near Mars' south pole, estimated to be 1.5 kilometers beneath the surface.

Zacny and Bhartia said the California trials were a success, and pave the way for an upcoming trip to Greenland. In June 2019, the team plans to take WATSON to the highest point on the Greenland ice sheet: a collection of research stations known as the Summit. There, engineers will lower WATSON into an existing 80-meter-deep borehole, and command it to drill up to an additional 20 meters while scanning the ice for biosignatures and living organisms.

Auto-Gopher-2 was funded by the NASA Maturation of Instruments for Solar System Exploration (MatISSE) Program, and WATSON was funded by the NASA Planetary Science and Technology Through Analog Research Solicitation (PSTAR) program.

Here are some specifics on each drill:

Auto-Gopher-2

Drill length: 3.3 meters

Tether length: 120 meters

Mass: 70 kilograms

Power consumption: less than 500 Watts

Percussive system: JPL-designed piezoelectric hammer

WATSON