TPF-I SWG Report - Exoplanet Exploration Program - NASA

TPF-I F L I G H T B ASELINE D ESIGN
5 TPF-I Flight Baseline Design
5.1 Introduction
In this chapter we describe the design and performance capability of the nominal formation-flying
interferometer (FFI) architecture. This is the stretched X-array configuration. Prior to the trade study
described in the previous chapter, the baseline design was the linear dual chopped Bracewell
configuration. The X-array 2:1 was the highest ranked in the trade study, but it was superseded by the
stretched X-array, with its ability to eliminate instability noise.
The array geometry is summarized in the next section, followed by a description of the spacecraft design
in Section 5.3 and the optics in Section 5.4. The sensitivity to planets is shown in Section 5.5 with the
inner and outer working angles, and Section 5.6 shows the stars that can be surveyed for planets. The
spectroscopic sensitivity is given in Section 5.7, followed by the imaging capabilities in Section 5.8.
5.2 Array Geometry
Figure 5-1 shows the stretched X-array geometry. All spacecraft lie in a plane normal to the direction of
the incoming starlight. The beams are then routed to the central combiner spacecraft in a single hop. The
aspect ratio is 6:1.This is still a dual chopped Bracewell design; the nulling baselines (π phase difference)
are along the short dimension of the array, and the imaging baselines form the long sides and diagonals.
The phases are inverted to switch between the two chop states. The collector spacecraft are identical, and
have apertures with a diameter of 3.8 m, consistent with packaging into the shroud of a Boeing Delta IV
0
±π/2
±π
±3π/2
Figure 5-1. The stretched X-array configuration. Blue circles represent collector spacecraft, and the
yellow circle is the central combiner spacecraft. Numerical values represent the relative phasing of
each collector as implemented in the beam combiner
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