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Unlike the navigation problem of Earth operations, the precise navigation of a vehicle in a remote planetary environment
presents a challenging problem for either absolute or relative navigation. There exist no GPS/INS solutions due to a lack
of a GPS constellation, few or no accurately surveyed markers for use in terminal sensing measurements, and highly
uncertain terrain elevation maps used by a TERCOM system. These, and other, issues prompted the investigation of the
potential use of a visual navigation aid to supplement an Inertial Navigation System (INS) and radar altimeter suite of a
planetary airplane for the purpose of the identifying the potential benefit of visual measurements to the overall
navigation solution.
The mission objective used in the study, described herein, requires the precise relative navigation of the airplane over an
uncertain terrain. Unlike the previously successful employment of visual aided navigation on the MER1 landing vehicle,
the mission objectives require that the airplane traverse a precise flight pattern over the objective terrain at relatively low
altitudes for hundreds of kilometers, and is more akin to a velocity correlator application than a terminal fix problem.
The results of the investigation indicate that a good knowledge of aircraft altitude is required in order to obtain the
desired performance for velocity estimate accuracy. However, it was determined that the direction of the velocity vector
can be obtained without a high accuracy height estimate. The characterization of the dependency of velocity estimate
accuracy upon the variety of factors involved in the process is the primary focus of this report.
This report describes the approach taken in this investigation to both define the architecture of the solution for minimal
impact upon payload requirements, and the analysis of the potential gains to the overall navigation problem. Also
described as part of the problem definition are the initially assumed contribution sources of visual measurement errors
and some additional constraints which limit the choices of solutions.
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