The authors of the Glenn Research Center document described in detail why a pressurized rover would one day have to be considered. Long-duration missions on the Moon and Mars would of necessity need to provide the astronauts with protection against radiation, as well as offering the advantage of operating and living in the vehicle without constantly having to wear the EVA suit. Unpressurized rovers would be ideal for single-day EVAs that would require the return to the lunar base crew module, whereas longer exploration missions would require pressurized rovers that would permit crews to venture tens or even hundreds of kilometers from the lunar base. Most of the pressurized rover designs employed a cylindrical body with spherical end bulkheads but their power systems varied from solar arrays with batteries, to the use of fuel cells, or the use of some form of RPS. Many designs recognized the need for each wheel to be individually driven. Wheels were the overwhelming choice for supporting and driving the vehicle over the Lunar or Martian surface, but track designs were also a possibility that was considered.
The authors of the GRC document recognized the severe problem that lunar dust will cause to rover mechanical systems, seals, and other equipment. The dust will also be a concern in keeping all electrical components within their thermal operating envelope. Virtually every component of the rover will have to be designed to withstand the long-term abrasive and corrosive effects of the lunar dust. There is an even greater danger crews will have to cope with on the Moon and Mars, which the GRC report succinctly described:
''The radiation exposure, with no appreciable atmosphere or magnetic field for protection, can be as high as that of interplanetary space in the solar system. Solar and cosmic radiation concerns will dominate human protection as well as electrical component protection from single-event upsets and hard failures. Degradation of optical components will also be a factor. The rovers will encounter the harsh space ionizing radiation environment: large fluxes of low-energy wind particles, smaller fluxes of high-energy galactic cosmic rays, and occasional intense particle fluxes emitted by solar flares. In addition to the ionizing radiation that reaches the lunar surface, soft x-rays and ultraviolet light are also present in significant quantities.''
There are other unknowns in the long-term presence on the Moon or Mars that can affect the durability of components. Here is where the experience gained from the Apollo Lunar Roving Vehicle and the Mars Exploration Rovers can add to the necessary body of information that will contribute to the durability and reliability of future rovers. However, it is most curious that the authors of this extensive document seemingly overlooked the only manned vehicle ever to roam the surface of the Moon. The successful Apollo Lunar Roving Vehicle represents a wealth of proven engineering that should be drawn upon for the design of the next generation Lunar Roving Vehicle. Doing so would shed light on why some sub-system design concepts were considered and later discarded, thus avoiding unnecessary trial and error. System performance evaluation of LRV surface activity should be conducted, together with post-mission analysis, in order to contribute this body of knowledge to the next LRV. There have been dramatic advances in the areas of metallurgy, plastics, electronics, mechanisms, power generation, communications and vision systems since Apollo that would vastly improve the LRV's performance and long-term reliability and enhance the safety of its crew.
Pressurized rovers have always been the preferred choice of lunar and planetary exploration planners. There is no lack of clever design and sophisticated appearance and their theoretical advantages are well known. So, too, are their primary disadvantages. For example, they are prohibitively large and heavy. It took a launch vehicle the size and power of the Saturn V to get the small and somewhat cramped Lunar Module to the surface of the Moon. The LM was the literal embodiment of form following function and the Saturn V first stage F-1 engines had to be up-rated in order to get the improved Lunar Module (with the capability to stay on the lunar surface for three days and take the LRV with it to the surface) off the ground. Future lunar modules will, of necessity, be even larger and heavier, and they will certainly take an unpressurized LRV on the early missions. The weight of each and every component that must be boosted to low-Earth orbit and then on to the Moon must be as minimal as engineering and technology can make it. Large pressurized rovers could only be assembled from modules or subassemblies launched separately, they are much too large and heavy to be launched on proposed heavy-lift launch vehicles because of the primary spacecraft and stages that would have to be launched as well. Because of these constraints, pressurized rovers will not likely be employed in the first missions that return to the Moon, but they are, in one form or another, certainly in the future of long-duration lunar and Martian exploration.
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