It looks like seventies science fiction television is (finally) going to meet reality with NASA planning to set up a real Moonbase Alpha by 2020. In order to meet the heavy load/long range transport requirements of life on the moon, NASA recently teamed up with Goodyear to review and redesign some 40-year-old technology in the shape of the airless tires first seen on the Lunar Rover Vehicles of Apollo missions.
In late 2006 the National Aeronautics and Space Administration (NASA) announced: "an incremental buildup would begin with four-person crews making several seven-day visits to the moon until their power supplies, rovers and living quarters are operational. The first mission would begin by 2020. These would be followed by 180-day missions to prepare for journeys to Mars."
Unlike the rovers used on the Apollo missions, the new vehicles will be large, heavy and will need to travel over 100 times the distance of the original vehicles. This left the old non-pneumatic tire design in need of a bit of an overhaul.
Reinventing the wheel
NASA asked the Goodyear Tire & Rubber Company to help. As the tires on the original Lunar Rover Vehicle (LRV) performed so well on earlier moon missions, the Goodyear-NASA team started the new design process by going back to school and examining those 81.8cm diameter, 23cm wide tires.
Historic drawings, documents, photographs and notes taken from files and interviews with Ferenc Pavlic (designer of the original Lunar Rover wheels) and Sam Romano (from the original project team) were studied by the research team to get a feel for the 40-year-old bias ply (a weave of angled wires) technology.
The mesh on the Apollo LRV tire was woven from zinc-coated piano wire, the tread formed from a series of titanium-alloy chevrons and the inner frame comprised of a partly rigid metal "bump stops" to minimize impact damage to the aluminum hub. Looking like a skeleton of a car tire, the design worked so well on the LRV because it only needed to support 60 pounds (360 pounds Earth weight) of weight over short distances.
Pavlic and Romano continued to share their knowledge and experience during the build process and even loaned the research team an original wheel for study. But despite all this background information, a complete picture on how to actually fabricate and build the replicate wheels was still not available. So the researchers resolved the outstanding issues by coming up with new designs and build processes, resulting in a dozen replicas.
Spring into action
Subsequent testing of the replicas led the researchers to the realization that using springs instead of wires and cables would allow the tires to be used on much heavier vehicles and make them much less prone to failure. "With the combined requirements of increased load and life, we needed to make a fundamental change to the original moon tire. What the Goodyear-NASA team developed is an innovative, yet simple network of interwoven springs that does the job. The tire design seems almost obvious in retrospect, as most good inventions do," revealed NASA's Vivake Asnani.
The new tires currently include some 800 load bearing springs though exactly how many springs are in a lunar vehicle tire will "depend on the desired size and load capacity of the tire. For example, the tire tested on the Chariot could carry 10 times the load of the original LRV tire. Smaller tires, however, are also possible," according to Goodyear.
Changing a tire in a spacesuit is possible but arduous. Thankfully, researchers claim that the new design should prove less susceptible to failure thanks to the unique properties of the springs. If one or two or even 20 springs suffer impact damaged it doesn't necessarily mean that the new lunar vehicles will stop roving, "Individual springs are not foreseen to be replaceable, due to the complex weave of the mesh. The tire, however, can still perform well with many damaged springs."
Extensive testing on a lunar truck simulator at Houston's Johnson Space Center has shown that the tires benefit from both stiffness and flexibility, acting as shock absorbers of sorts, allowing vehicles to travel at speed over rough terrain without much of the motion being felt in the vehicle.
The new tires are energy efficient too, Jim Benzing (Goodyear's lead innovator on the project) confirmed: "The spring design contours to the surface on which it's driven to provide traction. But all of the energy used to deform the tire is returned when the springs rebound. It doesn't generate heat like a normal tire."
Earthly uses too
The Goodyear-NASA team says that vehicles closer to home might also benefit from this project's research as tough airless, all-terrain tires could be used on "mobility critical small vehicle applications; such as fire fighting support vehicles, robotic vehicles, off road and desert vehicles, trash hauling and mining equipment. One of the advantages of this design is its flexibility. We can scale the size of the tire to meet the needs of a particular application."