We know that we can learn a lot from the rocks on Mars, but since we can't zoom up there and take samples, it's important that the Rovers have the right gear to get the job done. On the Athena payload, the RAT-- the Rock Abrasion Tool-- stands in for the field geologist's rock hammer. Since much of the Martian rock has been weathered by wind, the RAT was designed to cut through the surface and expose fresh layers underneath. Philip Chu, our latest Way Cool Scientist, has been working at the JPL (Jet Propulsion Laboratory) in Pasadena, California, since January 2004, and has been in close contact with the RAT from the very beginning.
The RAT, a robotically-controlled instrument, is carried by the Rover's mechanical arm, and once positioned on the rock, it cuts a shallow cylindrical hole. Since power on the Mars Rover is a precious resource, the RAT is designed to use a minimal amount of power while cutting into rock. For this reason, the RAT can sometimes take up to three hours to cut a hole only 5 millimeters deep. This sounds like a lot of time and effort for such a tiny hole, but the tool doesn't have to go very deep to reach layers that reveal important information about the mineralogical content of the Martian landscape. The RAT shaves away at the rock one paper-thin slice at a time.
The RAT's small brush helps to remove dust and other fine particles from a hole while it's grinding. And, when it's finished, the brush sweeps the surface clean to produce a clean shot of the rock, so that MER (Mars Exploration Rover) scientists can observe the subtleties of color and texture.
Phil was interested in science and engineering at an early age. When he was a kid, he attended Saturday morning workshops at the local air museum in his neighborhood. He participated in hands-on aerospace related projects, like building small helium balloon blimps and model airplanes. He also created model rockets that he and his friends would launch at the local airfield. These activities introduced Phil to many of the methods of thinking that he uses today while working as a mechanical engineer.
Phil went to school at Cornell University and received both his Bachelor's and Master's degrees in Mechanical Engineering. While at Cornell, he worked with a team of students to build a replica of the Mars Exploration Rover that is now on exhibition at the Smithsonian Air and Space Museum. It's a full-scale model constructed out of everyday materials, complete with scientific instruments. He was also involved in designing and building a calibration target for two of the Athena science instruments that are now sitting on the surface of Mars.
Now Phil works for Honeybee Robotics, a small company in lower Manhattan in New York City that constructs robots, flight subsystems, and other machines created both for earthly and planetary aims. Honeybee Robotics was contracted by NASA to design, develop, and operate the RAT for the 2003 MER Mission.
During mission operations, he functions as a RAT Payload Uplink and Downlink Lead. Phil is responsible for making sure that the RAT is used properly and safely. One of Phil's most important duties is to decide whether any given rock has the right texture for "RAT-ing." "The surface roughness of the rock is a big deal to us," says Phil. Since the RAT usually only cuts a small hole (roughly, the thickness of a couple Ritz crackers), it's important to expose as much fresh rock as possible. "The smoother the surface, the better," he says. Size is also critical--if a rock isn't big enough or if it's awkwardly shaped, it might roll around while the RAT is attempting to do its job. "If the rover approaches a rock, and we say that it's not 'RAT-able,'" explains Phil, "we can tell the scientists and engineers that we will not be 'RAT-ing' that rock."
Phil also uploads and downloads information to and from the RAT. When uploading commands (telling the Rover what to do), his primary goal is to get the Rover to cut deeply and efficiently. While the RAT is carrying out commands, it generates data. Phil reviews the data to make sure that the tool is in good condition after cutting, and consults with MER scientists regarding the depth of the cut. While the RAT is operating, data often arrives every second or so. If they run the RAT for three hours, which that they often do, you can imagine how much data there is to go through!
The RAT has helped scientists answer big questions about Mars. One of the first RAT targets in Eagle Crater exposed fresh rock, revealing evidence of water in the planet's history.
Phil enjoys being a member of a generation of explorers. Much like the pioneers who charted territory on Earth, Phil and his colleagues are making new discoveries every day. "Iíve heard that images of the RAT holes that I helped to create will be in history books for the next 100 years," says Phil. "Thatís just mind blowing." The team working on the MER mission will have a lasting impact on generations to come.