TPF-I SWG Report - Exoplanet Exploration Program - NASA

C HAPTER 6
Figure 6-8: The Formation Control Testbed (FCT). Shown here are the two robots of the FCT, with
Jason Keim. Each robot carries cannisters of compressed air that allow them to float off a polished metal
floor. The floor is flat to within 2 one-thousandths of an inch (~50 μm) and spans a much larger area than
shown here. The robots carry a platform (shown tilted for each robot) that is supported on a spherical ball
bearing, also driven with compressed air so that the support of the platform is entirely frictionless. The
robots serve as the hardware interface and testing ground for flight software developed for space
applications in formation flying. The robots have completed their functional testing in cooperative mode
and should achieve their major milestone of range and bearing control in mid 2007. The Principal
Investigator of the Formation Control Testbed is Daniel Scharf.
The robots are being tested within a celestarium that had been used previously to calibrate star trackers
used by spacecraft. The spherical ceiling of the interior building has an array of artificial stars on it that
the robot cameras can use to derive absolute position information down to the level necessary to reach the
testbed's performance milestone.
The FCT was planned as a ground-based laboratory consisting of three test robots in its fully deployed
configuration. Much like in the distributed simulation under FAST, the FCT demonstrates formation
acquisition, TPF-like formation maneuvering, and collision-free operations using the formation
algorithms developed in the FAST. A high level of flight relevance was designed into the FCT avionics
architecture, with on-board flight-like capabilities: (a) wireless communication emulating inter-spacecraft
and spacecraft to ground communication; (b) on-board sensing and actuation using star tracker, gyros,
thrusters, and reaction wheels for attitude and translation control; and (c) PowerPC flight control
146