TPF-I SWG Report - Exoplanet Exploration Program - NASA

C HAPTER 4
based on SNR 1.01.xls
30.00
25.00
All (1014)
50 days
100 days
200 days
> 200 days
Distance / pc
20.00
15.00
10.00
5.00
0.00
7
12
13
9
35
6
4
1
0 50 100 150 200 250 300 350
MHZ semi-major angle / mas
8
10
19
29 candidates require < 100 days
Figure 4-27. Candidate stars available for a 36-m SCI mission. Stars in the maroon area are excluded by the
IWA criterion. Stars in the blue and maroon areas are excluded by the confusion criterion. The stars are colorcoded
according to the integration time needed to detect ozone with an SNR = 5 (see legend). The small numbers
indicate the integration times for specific nearby examples. The large numbers show the number of observable
targets in each integration bin. The dashed line encloses (almost) the region containing the 29 observable stars
with characterization times of less than 100 days. See Section 5.9 for an introduction to this representation of the
target stars.
For a planet orbit that just meets both the IWA and angular resolution criteria, only 1/16 th of the orbit is
available on average for orbit determination (planet lies inside IWA 50% of the time; planet is confused
50% of the time; and star is observable 25% of the time due to ±45 degree solar shading constraint).
Figure 4-27 shows how the application of the three criteria results in 29 candidate target stars for the
Configuration B phasing (Fig. 4-24). For Configuration A, the smaller IWA pushes the red zone well to
the left, but the poor angular resolution increases the confusion and extends the blue zone out to beyond
200 mas, greatly reducing the number of candidate targets. Figure 4-28 illustrates how the performance
capability degrades rapidly as the length of the structure is reduced below 36 m.
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