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The LMRs' Role LMR Design Systems Outline |
LMR Design Tree 
GPS GPS stands for Global Positioning System. The basic concept behind GPS is to have a system of satellites orbiting Mars. By communicating with at least four satellites, an LMR will be able to calculate its position on the Martian surface. In order to use GPS, satellites must be launched into orbit around Mars. The type of GPS used in the mission would be based on the GPS system that is currently in use in the United States today. This system had twenty-four satellites orbiting the Earth, arranged so that there are at least four satellites within a GPS receiver's range anywhere around the world.In order to calculate an object's position in space, the GPS system must be capable of measure its distance from at least four other objects with known positions. These four distances can specify four spheres, and since four spheres intersect at exactly one point, the LMR would be able to calculate its exact position on the Martian surface. To measure the distance from the four satellites, each LMR would have a GPS receiver component attached to its chassis. The GPS receiver would send out radio waves towards the satellite, and by measuring the time it takes for the satellites to receive the signals, the LMR would be capable of calculating its distance from the satellite as the speed of radio waves in space is known. Source: http://www.howstuffworks.com/gps1.htm Unfortunately, it will not be possible to launch a sufficiently large number of satellites into Martian orbit for Mission 2004. The satellites that are launched, however, will be part of the first few communication satellites about Mars, and will open up the possibility for a future GPS system as more and more satellits are sent to support future Mars Missions. GPS-Like Surface Antenna This method is similar to GPS, but instead of having satellites orbiting the Martian surface, the humans will need to set up position points on the Martian surface. Like GPS, this method uses measured distances from four known points in space in order to calculate an objects position. Basically, the orbiting satellites of GPS are replaced with waypoints established on the Martian surface. This method will undoubtedly require some time from the humans' schedule, which is valuable time that could be used in other efforts. Also, this method does not provide any notable advantage compared to GPS with satellites.Visual Triangulation Visual triangulation allows the LMR to determine its position on the Martian surface using its vision and computer systems. With an extensive built in database, the LMRs will be capable of picking out key, clear, landmarks on the Martian surface. By taking into account the positions of the key landmarks in terms of the LMR, and comparing the data to the built in database of sites, the LMRs will be capable of determining their positions on the Martian planet to a great degree of accuracy. The computations involved in such a task would be quite daunting, however. Under normal circumstances, only the medium LMR would be responsible for determining the LMR family's position. Should the family separate, or a small LMR's communications systems fail, small built-in navigation systems would be capable of guiding the small LMRs back to the habitat. This is very complicated, however, and it may be easier to allow the small LMR to blindly backtrack its way to the habitat. A sufficiently well-designed decision making system could allow the LMR to log its motions as part of the family, and follow the same motions to return to the habitat.Despite its limitations, the visual triangulation method for navigation has been used on the Apollo Mission (Buck, S. 2000). Though human intuition was involved in locating the key landscape features required to determine position, new, more powerful, computer technology should allow autonomous vehicles to make the necessary decisions and choices involved for visual triangulation. Dead Reckoning Dead Reckoning navigation is a method of estimating the position of a vehicle by calculating from a previous position of the vehicle, the direction of travel, the speed, and time traveled. In other words figuring out where the LMR will be after a small period of time if the speed and course are held constant. This method lacks accuracy because it is based on measurements of wheel orientation and velocity, and the measurements are always subject to some error. This method of navigation is becoming obsolete due to the advent of computers, electronic and satellite navigation systems, but may figure into the medium LMRs navigation system as a backup system to compare results with the visual triangulation system. Dead reckoning may not be very easy using the small LMRs legged system, however. It may be necessary to run only the visual triangulation and backtracking systems on the small LMRs in cases where the small LMRs are separated from the LMR family. Source: Encarta Encyclopedia 2000 |
