Mars Rover to Earth: "Where to now?" The two Mars Explorer Rovers launched last summer which landed on the Red planet this past January will stay in touch with Earth during their 90-day missions using three different systems: a low-gain antenna (LGA), a UHF antenna, and a high-gain antenna. Identical azimuth and elevation drives steer the antennas through a hemispherical field of regard. Each axis uses a 34-Vdc RE20 brush motor from Maxon Motor, to spin an integral three-stage, 81.37:1 planetary gearbox which, in turn, drives a 1.333:1 spur-gear stage. The spur-gear stage then powers an HD Systems Size-14 SHF 50:1 harmonic drive, for a final reduction ratio of 5425:1. Harmonic drives are noted for their ability to retain out-of-box backlash specs without adjustment for the life of the device. They also pack high output torque and stiffness into a small, lightweight package -- all are important metrics for the application. Once on the Martian surface, the go-cart-sized, 185-kg rovers will travel about 100 m daily, searching for signs of ancient water.
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