MORE ABOUT THE ROVER...

In spacecraft design, system mass is an ever-present consideration. A mass savings directly translates into lower costs and enhanced operability from the launch all the way through the lifetime of the spacecraft. In addition, any reduction in system complexity carries with it increased reliability. These two concepts are intimately related and equally important to the design process.

As the range and scope of Mars exploration missions increases, there is a need for greatly enhanced mobility while on the surface. This will be possible with a large rover capable of traversing significant obstacles without incident. From a navigation standpoint, operations personnel plotting a course can effectively disregard any obstacle smaller than the rover's safe maximum size, simplifying planning and execution of a traverse. In addition, a larger rover can simply cover more ground in a given amount of time, allowing expansion of the mission scope.

The Rover:
The JPL Experimental Rover (XRVR) is the first full-size rocker-bogie suspended rover prototype. The first-generation prototype (roll-out Nov. 2000) is the size of a small car and has a mass of approximately 500 kg. The major design driver is the requirement that it be able to negotiate a 1-m vertical obstacle. Initially a mobility subsystem testbed, it will evolve into a fully autonomous vehicle over the next three years. This design will be the basis for the 2007 Mars exploration mission as well as for the subsequent sample return mission.

The Project:
After validation of system scaling and mobility prediction methods, refinements will commence towards the goal of optimizing the design. One of the major areas in need of development is the steering subsystem. The first-generation XRVR has a simple manual steering system requiring physical input from the user to turn each wheel individually and lock it into place. The first refinement to this system needs to remove the user from the process by providing actuation to each wheel. On the successful 1997 Sojourner rover and the upcoming 2003 dual-rover missions this was done by installing a steering actuator (a gear-reduced electric motor) for each of the corner wheels. While this is an effective and reliable system, it adds a significant amount of mass to the rover. It may be possible to design the mobility subsystem so that the drive actuators can double as steering actuators, either directly or through the kinematic design of the subsystem. This would serve to reduce both mass and complexity in an area key to the overall effectiveness of the rover.