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TPF-I SWG Report - Exoplanet Exploration Program - NASA

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C HAPTER 4<br />

Channel SNR<br />

10.0<br />

Channel SNR<br />

1.38 / rotn<br />

# rotations<br />

53<br />

Planet signal rms<br />

Random noise<br />

Systematic noise<br />

0.091 /s 0.042 /s 0.051 /s<br />

Local Zodi leak Stellar size leak Null floor leak<br />

photon noise photon noise photon noise<br />

0.027 /s 0.033 /s 0.006 /s<br />

Planet signal rms Local Zodi leak Stellar size leak<br />

Null floor leak<br />

Null stability<br />

0.091 /s<br />

2.3E-08<br />

71 /s<br />

1.8E-05<br />

106 /s<br />

2.6E-05<br />

3 /s<br />

7.5E-07<br />

at planet harmonics<br />

1.3E-08<br />

Amp-phase error<br />

ΔA Δφ / rad<br />

0.13% 0.0011<br />

Dynamic<br />

Control systems<br />

Fringe track<br />

Metrology<br />

Tip/tilt<br />

Shear<br />

Disturbances<br />

Beamtrain<br />

Static<br />

Coatings<br />

Reflectivity<br />

Alignment<br />

Beam combiner<br />

π phase sh<br />

Figure 4-5. Simplified <strong>TPF</strong>-I error budget for the signal-to-noise ratio (SNR) required for ozone<br />

detection at 10-μm wavelength.<br />

4.2 Performance Models<br />

The two key performance models are described in this section: the Interferometer Performance<br />

Model (IPM) for predicting the SNR on a specified target; and the Star Count Model for<br />

estimating the number of targets that can be surveyed over the duration of the mission.<br />

4.2.1 Interferometer Performance Model<br />

The <strong>TPF</strong> Interferometer Performance Model (IPM) is maintained as a series of Excel spreadsheets and is<br />

used both to estimate the performance of different architectures, and to derive the requirements for the<br />

baseline design. The spreadsheet performance model is run as a bottom-up calculation; that is, the overall<br />

performance is calculated based on the specified low-level inputs (as opposed to a top-down suballocation<br />

approach). The inputs can be adjusted and balanced until the desired output performance is obtained, at<br />

which point the input values assumed become the requirements on the instrument.<br />

64

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