TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 2
Error Budget Validation
Given the critical role of the CEB, it is necessary to validate that the budget is properly
constructed and captures all the important errors and interactions. The error budget is based on
linear sensitivity matrices, meaning that the contrast contribution caused by errors from each
source can be added directly to calculate a total error as described below. This approach allows
straightforward scaling and modification, and is chosen because of its simplicity and suitability
for sensitivity analysis. It remains to be validated through end-to-end models designed to
capture the non-linear effects arising from propagation of diffraction. The error budget is
finalized and validated before the end of Phase B through a combination of testbed results and
end-to-end system models that address each item in the error budget tree. The level and method
by which each item or set of items is to be addressed is determined by the end of Phase A.
Error Budget Structure
The TPF coronagraph contrast error budget comprises the static (initial wavefront setting at the
start of an observation) and dynamic (any changes to the wavefront during an observation) terms
that contribute to image plane contrast. Static terms include wavefront sensing and control
(WFSC), stray light, coronagraph mask imperfections, and polarization leakage. Dynamic terms
include motion of an optic or bending of an optic due to vibrations or thermal effects. Figure 2-2
shows the structure of the error budget including reserve factors, mean image plane contrast, and
the standard deviation of contrast as detailed below.
Initial work has focused on the dynamic part of the error budget. It was assumed based on
Figure 2-2. Error Budget Tree
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