level sensor measures tipping angle. Simple retractable IR sensors extend down near the slab working area to monitor energy flux and temperature, and a steerable low-resolution camera with two degrees of freedom (vertical and horizontal rotation) is installed between the two main dish mirrors to check slab placement as construction proceeds. Tires are made of soft woven basalt fibers (see sec. 4.2.2), and the vehicle is driven by four low-power electric motors fore and aft geared to steerable front and rear wheel pairs. Energy requirements for mobility and onboard computing are expected to be modest, so a few square meters of exterior solar cell paneling augmented by a rechargeable fuel cell should suffice.
5C.4 Mass and Information Estimates
A 5.4 m spherical dish made of aluminum 1-cm thick will have , mass of about 620 kg, or 1240 kg for a pair. Similarly , the total for both planar mirrors is 440 kg. Assuming 2×10-2 kg computer/kg serviced (Freitas, 1980), each robot computer is about 50 kg. Camera, sensors, and navigational equipment add another estimated 50 kg. Solar panels and fuel cells may total 100 kg. The aluminum vehicle frame should be able to support its own weight (1700 kg) on Earth, so in low lunar gravity only 280 kg are required to obtain equivalent support. Each tire and drive assembly is about 40 kg, a total of 240 kg for all six wheels.
