Title:
Trading Robustness Requirements in Mars Entry Trajectory Design
Trading Robustness Requirements in Mars Entry Trajectory Design
Author(s)
Lafleur, Jarret M.
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Abstract
One of the most important metrics characterizing an atmospheric entry trajectory in
preliminary design is the size of its predicted landing ellipse. Often, requirements for this
ellipse are set early in design and significantly influence both the expected scientific return
from a particular mission and the cost of development. Requirements typically specify a
certain probability level (sigma-level) for the prescribed ellipse, and frequently this latter
requirement is taken at 3sigma. However, searches for the justification of 3sigma as a robustness
requirement suggest it is an empirical rule of thumb borrowed from non-aerospace fields.
This paper presents an investigation into the sensitivity of trajectory performance to varying
robustness (sigma-level) requirements. The treatment of robustness as a distinct objective is
discussed, and an analysis framework is presented involving the manipulation of design
variables to effect trades between performance and robustness objectives. The scenario for
which this method is illustrated is the ballistic entry of an MSL-class Mars entry vehicle.
Here, the design variable is entry flight path angle, and objectives are parachute deploy
altitude performance and error ellipse robustness. Resulting plots show the sensitivities
between these objectives and trends in the entry flight path angles required to design to these
objectives. Relevance to the trajectory designer is discussed, as are potential steps for
further development and use of this type of analysis.
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Date Issued
2009-08
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