the loader bucket, reinforced so that the bucket can be placed in a locked, elevated position and the robot driven as a dozer; and has three attachments aft which are removed during normal work, including a precision grading blade with surface contour sensors, a simple tow bar, and a somewhat more versatile towing platform.
A loader equipped in this fashion should be able to perform all six basic LMF functions enumerated above. According to Nichols, in a pinch the mining robots should also be able to act as a primitive crane, as a more versatile variable blade pitch bulldozer, as a "reach down" dozer able to cut below the depth accessible to most dozers, and as a backdragger to smooth loose dirt. Finally, it should also be possible for two loaders to join face to face to lift large boulders which neither could conveniently lift alone.
5D.3 Mining Robot Design Specifics
The team considered various specific aspects of LMF mining robot design, including machine mass, power consumption, sensor configuration, and computational and information requirements. The results and conclusions are presented below.
Robot mass and power estimates. According to Carrier (1979), haulers may be much less massive on the Moon than on Earth since the lower gravity enables the same physical structure to carry more payload mass because the force per unit mass is less. In loaders, the vehicle mass is used as a counterbalance to prevent the machine from tipping over when fully loaded, so the mass relations for these machines change little from Earth in the lunar environment. Usual terrestrial practice is to multiply the bucket load mass by a factor of 2.0 to determine a safe tipping mass (the mass of the vehicle used as a counterweight). However, lunar equipment might incorporate automatic sensing systems to prevent tipping over so a safety factor of 1.2 should be sufficient (Carrier, 1979).
If the hauling mass per trip for all mining robots is Mh, m is the rate at which lunar materials must be mined to support the LMF replication schedule, and t is the time required for a robot to complete one cycle of operation (scoop up soil, deliver to LMF, return to pit), then Mh = mt. Using a factor of 1.2, the mass of mining robots is approximately M = 1.2 Mh = 1.2 mt.
Conservatively estimating an average of 40 km travel distance per round trip to the LMF per robot (from a 20 km radius annular pit surrounding the growing seed), an average transport speed of 10 km/hr, and a typical duty cycle of 50% for actual mining work (to leave time for repairs and nonmining labors such as grading, towing, or cellaring), then the mean cycle time
- r = (40 km)(3600 sec/hr)/(50%)(10 km/hr) = 28,800 sec
