The National Aeronautics and Space Administration (NASA) was developing new surface vehicles to support long range lunar exploration and the development of a lunar outpost. These vehicles will be heavier and will travel greater distances than the Lunar Roving Vehicle (LRV) developed for the Apollo program in the late 1960s. Consequently, new tires will be required to support up to ten times the weight and last for up to one hundred times the travel distance as compared to those used on the Apollo LRV, thereby requiring operational characteristics similar to passenger vehicles used on earth. However, conventional rubber pneumatic tires cannot function acceptably on the moon.
For example, rubber properties vary significantly between the cold temperatures experienced in shadow (down to 40 K) and the hot temperatures in sunlight (up to 400 K). Further, rubber degrades when exposed to direct solar radiation, without atmospheric protection. Finally, an air-filled tire is not permissible for manned lunar vehicles because of the possibility of a flat tire. To overcome these limitations, a tire design was developed for the Apollo LRV and was successfully used on Apollo missions 15, 16, and 17. This tire was woven from music wire, which was robust to lunar temperature variations and solar radiation, operated in vacuum, and did not require air for load support. This structure further functioned to contour to the lunar terrain, which facilitated traction and reduced vibration transfer to the Apollo LRV.
Because of the new weight and distance requirements for lunar vehicles, a tire with greater strength and durability would be desirable.
One conventional wheel and non-pneumatic tire assembly has a variable diameter which, in addition to changing its diameter, may also change its width, thereby increasing the area of the wheel that engages the ground. Thus, this non-pneumatic tire may be adjusted to increase a vehicle's performance according to the terrain over which it is traveling. This tire has arching members with first and second ends connecting a wheel hub. The arching members extend outwardly in an arc between the first and second ends. The arching members form a plurality of flexible hoops spaced circumferentially around the hub and extending radially outward from the hub.
More specifically, the conventional non-pneumatic tire forms a cage composed of thirty-eight equally spaced radially extending hoops that arch between axially outer rims of a hub. The hoops are made of helical steel springs filled by wires cut to a desired length and threaded through the center of the springs. The conventional hub may be expanded/contracted axially for varying the diameter of the tire.
The original wire mesh design of the Apollo LRV tire was found to not be readily scaleable. Specifically, the increase in wire diameter to create a tire that supported ten times the load of the original design created two significant limitations: 1) the ability to contour to the terrain was lost, thus limiting traction and ability to isolate vibration; and 2) the increased wire stresses limited functional life. A tire in accordance with the present invention overcomes these limitations, making the tire an innovative technological advance for Moon, Earth, and other planetary surfaces.