The SLOPE (simulated lunar operations) facility at the NASA Glenn Research Center is a unique lab among NASA for simulating the mobility of rovers on the surface of the moon. The facility features several simulated lunar surface pits, with the largest being 60 feet by 20 feet. The tour of this facility allowed interns to handle various lunar surface soil simulants in glass jars. Some of these samples simulated how lunar soil performed under lunar vehicles, while others simulated the abrasiveness of the lunar soil, which is so fine and sharp, that it is a significant health hazard.
One of the large pits was filled with a lunar simulant composed of very small hollow aluminum beads, which is so soft, that a 3-foot threaded rod could be pushed to the bottom of the pit with hardly any effort (imagine doing that on a beach). Several designs of lunar wheels were passed around, including the design which was on the lunar rover of Apollo 15-17, while the tour guide described each design and how they performed best under a certain weight. All wheels were primarily a wire frame and hollow construction, some so intricate that they must be constructed and assembled by hand. To eliminate single point failures, the wheels cannot be punctured or deflated like a rubber car tire, as they are completely supported by their metallic wire frame shell.