In varying embodiments, the fault tolerant linear actuator of the present invention is a new and improved linear actuator with fault tolerance and positional control that may incorporate velocity summing, force summing, or a combination of the two. In one embodiment, the invention offers a velocity summing arrangement with a differential gear between two prime movers driving a cage, which then drives a linear spindle screw transmission. Other embodiments feature two prime movers driving separate linear spindle screw transmissions, one internal and one external, in a totally concentric and compact integrated module.
 The U.S. Government may own certain rights in this invention pursuant to the terms of the U.S. Department of Energy grant number DE-FG04-94EW37966. This application claims priority to U.S. Provisional Patent Application Ser. No. 60/386,661, filed Jun. 5, 2002.