The SIM Lite Astrometric Observatory will be the first space-based Michelson interferometer operating in the visible
wavelength, with the ability to perform ultra-high precision astrometric measurements on distant celestial objects. SIM
Lite data will address in a fundamental way questions such as characterization of Earth-mass planets around nearby
stars. To accomplish these goals it is necessary to rely on a model-based systems engineering approach - much more so
than most other space missions. This paper will describe in further detail the components of this end-to-end performance
model, called "SIM-sim", and show how it has helped the systems engineering process.
This paper examines how narrow-angle (NA) processing of data from the SIM Lite optical interferometry mission can be
undertaken when realistic spacecraft and mission operational constraints are taken into account. Using end-to-end
mission simulations we show that the goal of 1 μas single measurement accuracy (SMA) is obtainable, and hence the
detection of earth-like planets is achievable with the SIM Lite mission.
This paper develops an observing and processing scheme for narrow angle astrometry using a single
baseline interferometer without the aid of "grid" stars to characterize the interferometer baseline vector in
inertial space. The basic concept derives from the recognition that over a narrow field the set of fundamental
unknown instrument parameters that arise because the interferometer baseline vector has large uncertainties
(since there are no grid star measurements) is indistinguishable from a particular set of unobservable errors in the determination of star positions within the field. Reference stars within the narrow field are used to circumvent these unobservable modes. Feasibility of the approach is demonstrated through analysis and example simulations.
The Kepler Mission is designed to characterize the frequency of Earth-sized planets in the habitable zones of solar-like stars in the solar galactic neighborhood by observing >100,000 main-sequence stars in a >100 square degree field of view (FOV) and seeking evidence of transiting planets. As part of the system engineering effort, we have developed an End-To-End Model (ETEM) of the photometer to better characterize the expected performance of the instrument and to guide us in making design trades. This model incorporates engineering information such as the point spread function, time histories of pointing offsets, operating temperature, quantization noise, the effects of shutterless readout, and read noise. Astrophysical parameters, such as a realistic distribution of stars vs. magnitude for the chosen FOV, zodiacal light, and cosmic ray events are also included. For a given set of design and operating parameters, ETEM generates pixel time series for all pixels of interest for a single CCD channel of the photometer. These time series are then processed to form light curves for the target stars and the impact of various noise sources on the combined differential photometric precision can be determined. This model is of particular value when investigating the effects of noise sources that cannot be easily subjected to direct analysis, such as residual pointing offsets, thermal drift or cosmic ray effects. This version of ETEM features extremely efficient computation times relative to the previous version while maintaining a high degree of fidelity with respect to the realism of the relevant phenomena.
In this paper we discuss the use of an innovative SIM simulator,
called SIMsim, to perform end-to-end simulations of the SIM mission.
The inputs to the simulator are a physically-based parameterization of
the major SIM error sources and the output is the mission astrometric
accuracy for various observing scenarios such as narrow-angle (NA) and
wide-angle (WA) observations. The primary role of SIMsim is to
validate the SIM astrometric error budget (AEB), but it is also being
used to study a variety of mission performance issues as well as being
a test-bed for prototype data reduction algorithms. SIMsim is giving
us confidence that the SIM AEB is a valid estimate of mission
performance. It also is illustrating where analytical formulas for
estimating certain effects breakdown and a numerical approach has to