National Aeronautics and Space Administration

Glenn Research Center

SLOPE Facility

A SLOPE Lab researcher explains the special challenges for lunar tire design.Tuesday, June 30, 2009, Glenn Research Center – Cleveland, OH

One of the newest laboratories at Glenn Research Center, the SLOPE Laboratory is used to test different hardware configures in a mock-up lunar setting. SLOPE stands for Simulated Lunar OPErations, but it is often lovingly referred to as “the sand box,” due to its large bin of lunar simulant. The lab is effectively a large soil tank filed with GSC-3, a lunar regolith simulant. The tank is made up of two sections, a 12 m by 6 m by 0.3 m portion used for flat surface operations, and a 7 m by 5 m by 0.3 m adjustable tilting section capable of producing slopes between 0º and 45º.

The laboratory is primarily used for lunar vehicle testing. There has been almost a forty-year gap in lunar vehicle development at NASA since the Apollo program, and thus this lab is currently being used to test and obtain data on various lunar vehicle designs. The facility is also used to test various wheel designs and materials.

Recently, this lab commissioned a team to try to recreate the wheels on the Apollo Lunar Rover. None of the actual tires from the 1970s still exist and thus, the new tires had to be recreated from photo evidence and eye-witness accounts. The tires were constructed of a wire mesh woven out of piano strings. These tires were designed to deal with the extreme temperature shifts and lack of air pressure on the lunar surface. These non-inflatable tires were also used because they cannot be punctured or become flat. Glenn developed twelve of these tires and currently uses them as a baseline for comparisons with new tire and tire tread designs.

One of the lunar vehicles designed to test the performance of different equipment on slanted lunar simulant surfaces.

Preparation of the facility for vehicle and tire testing is long and tedious. Before testing a new vehicle, the “sand” tank has to be dug up, leveled, and tilled to get a particle density similar to that of the lunar surface. A portable bevameter is used to analyze the surface strength of the terrain so experimental results can be properly analyzed and modeled.

Current work at the SLOPE Lab has involved driving techniques to explore lunar craters and other steep slopes on the moon’s surface. The facility uses the CHARIOT simulator robot developed by Carnegie Mellon to model a future lunar vehicle. The vehicle has four innovative actuators that can control wheel motion and other vehicle movements. A drawbar pull rig is used to apply a controlled pull force to examine when the vehicle begins to slip under various conditions. Using various slope angles and lunar stimulant density parameters, the SLOPE Lab hopes to determine the capabilities and limits of future lunar vehicles.

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