Main brassboard Michelson interferometer components have been recently developed for the future flight phase
implementations of SIM Lite mission. These brassboard components include two fine steering mirrors, pathlength
modulation and cyclic averaging optics and astrometric beam combiner assembly. Field-independent performance tests
will be performed in a vacuum chamber using two siderostats in retro-reflecting positions and a white light stimulus. The
brightness and color dependence of the angle and fringe tracking performance will be measured. The performance of
filtering algorithms will be tested in a simulated spacecraft attitude control system perturbation. To demonstrate
capability of a dim star observation, the angle and fringe tracking CCD sensors are cooled to -110 C using a cold diode
heat pipe system. The new feed-forward control (angle and path-length) algorithms for the dim star observation will be
tested as well. In this paper, we will report the recent progress toward the integration and performance tests of the
The Guide-2 telescope (G2T) is an important subsystem of the new SIM Lite Astrometric Observatory. In this paper we present system identification experiments, design and implementation of the G2T stellar pointing loop that achieves milliarcsecond resolution of spacecraft attitude. Special emphasis was placed on characterization and modeling of PZT hysteresis since this nonlinearity plays an important part in the control loop performance. Power spectral densities of the star image centroids were use to evaluate the pointing loop performance with and with out the presence of simulated ACS disturbances injected via a fast steering mirror (FSM).
The SIM Lite Astrometric Observatory is to perform narrow angle astrometry to search for Earth-like planets, and global
astrometry for a broad astrophysics program, for example, mapping the distribution of dark matter in the Galaxy. The
new SIM Lite consists of two Michelson interferometers and one star tracking telescope. The main six-meter baseline
science interferometer observes a target star and a set of reference stars. The four-meter baseline interferometer (guide-1)
monitors the attitude of the instrument in the direction of a target star. The Guide-2 telescope (G2T) tracks a bright star
to monitor the attitude of the instrument in the other two orthogonal directions. A testbed has been built to demonstrate
star-tracking capability of the G2T concept using a new interferometric angle metrology system. In the presence of
simulated 0.2 arcsecond level of expected spacecraft attitude control system perturbations, the measured star-tracking
capability of the G2T testbed system is less than 43 micro-arcsecond during single narrow angle observation.
This paper reviews recent progress with technology being developed for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. TPF-I is in the early phase of its development. The science requirements of the mission are described along with the current design of the interferometer. The goals of the nulling and formation-flying testbeds are reviewed. Progress with TPF-I technology milestones are highlighted.
The interferometric version of the Terrestrial Planet Finder (TPF-I) has the potential to find and characterize earth-sized
planets in the habitable zones of over 250 nearby stars and to search for life using biomarkers in the atmospheres of any
planets found. The scientific case for such a mission continues to be strengthened by on-going progress in the detection
of planets via indirect means. This paper summarizes the status of TPF-I, illustrative scientific requirements for the
mission, and its enabling technologies.
The StarLight mission is designed to validate the technologies of formation flying and stellar interferometry in space. The mission consists of two spacecraft in an earth-trailing orbit that formation-fly over relative ranges of 40 to 600m to an accuracy of 10 cm. The relative range and bearing of the spacecraft is sensed by a novel RF sensor, the Autonomous Formation Flyer sensor, which provides 2cm and 1mrad range and bearing knowledge between the spacecraft. The spacecraft each host instrument payloads for a Michelson interferometer that exploit the moving spacecraft to generate variable observing baselines between 30 and 125m. The StarLight preliminary design has shown that a formation-flying interferometer involves significant coupling between the major system elements - spacecraft, formation-flying control, formation-flying sensor, and the interferometer instrument. Mission requirements drive innovative approaches for long-range heterodyne metrology, optical design, glint suppression, formation estimation and control, spacecraft design, and mission operation. Experimental results are described for new technology development areas.
This paper discusses the problem of designing a control system for an interferometer delay line which contains coarse-vernier loops. The vernier loop compensator has nonlinear dynamics and includes a local feedback path containing a deadzone. This accomplishes two objectives: global stability and good transient response to large signals. In addition, by ensuring global stability in the vernier loop, the gain of the coarse loop may be increased thus providing greater disturbance rejection in the overall loop.