TPF-I SWG Report - Exoplanet Exploration Program - NASA

T E C H N O L O G Y R OADMAP FOR TPF-I
Figure 6-9. Inter-robot position error, showing performance slightly outside the range
requirements. Ongoing upgrades to the robot thrusters should bring the performance within
requirements.
computer on a compact peripheral communications interconnect (PCI) local bus under a vxWorks
Realtime operating system. The on-board formation control software for the FCT is being developed by
the Formation Algorithm and Simulation Testbed (FAST). To emulate the real spacecraft dynamics, the
FCT was designed for realistic spacecraft-like dynamical behavior, mobility, and agility using linear and
spherical air-bearings. With such 6-degrees-of-freedom dynamical motion and functional similarity to the
TPF spacecraft, the FCT provides direct emulation of both individual spacecraft and formation behavior
under autonomous on-board control. These architectural, functional, and dynamical similarities between
the FCT and TPF-I provide a direct path of development to the TPF flight system.
The requirements for the FCT have been listed in detail in Table 6-4. The layout of the FCT emulates the
distribution of the formation-flying telescopes, which is limited to a plane to minimize stray light from
adjacent spacecraft. The vertical air bearing has a range of ±25 cm, and the pitch and roll axes of each
robot’s motion is limited to ±30°, which is a physical limitation due to the spherical air bearings.
The FCT is designed to demonstrate an end-to-end system level formation flying control capability
(functional and performance requirements) scaleable to flight, within a ground-test environment. The
ground-operating environment for the FCT provides a more severe disturbance environment compared to
the conditions in space. The net linear disturbance force due to solar pressure of ~6 µN/m 2 (at 1 AU) for
the TPF-I spacecraft (assuming a 5.7-m radius sunshade with a surface area of 102 m 2 ) is around 0.6 mN,
comparable to the robot linear drift force of ~0.26N due to maximum residual floor slope of 80 µrad.
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