Mission Operations

Main Site Information | Data Products | Calibrations | SIM-SIM:End-to-End Simulator

The main SIM website contains overview information about the SIM mission, including mission operations, the end to end data system, experiment planning, and a sample timeline during flight operations. Additional information about data products, calibrations, and simulations can be found on this page.

Science Data Products Descriptions

SIM data will be available in a variety of formats, from the raw data to increasingly data-processed products. The data product description gives a high-level overview of the data types, the applied calibrations, and the models that will be used as part of the calibration and validation process.

Raw Data

Telemetry (Level 0)

Time-ordered, non-duplicate data as received on the ground. No transformations of any kind applied. This data product represents the full telemetry stream with transmission artifacts removed.

Engineering Calibrated Data

Telemetry (Level 1)

Time ordered data with engineering calibrations applied, ie in engineering units and in the local inertial reference frame. Timestamps are applied.

Ancillary (Level 1)

Navigation data, spacecraft and planet ephemerides, ground-derived environmental data.

Instrument Calibrated Data

Delay data (Level 2)

Delays, baselines, and ancillary data in the local instantaneous inertial reference frame.

Visibility data (Level 2)

Visibility phases, amplitudes, baselines and ancillary data in the local instantaneous inertial reference frame.

Nulling data (Level 2)

Fringe scans, baselines, and ancillary data in the local instantaneous inertial reference frame.

Scientific data

Delays (Level 3)

Delays, baselines and ancillary data with all Special and General Relativistic signatures removed in the barycenter tangent frame. The barycenter tangent frame is the mid-mission inertial reference frame defined by the instantaneous motion of the solar system barycenter.

Astrometry (Level 4)

Inferred RA, Dec, and ancillary data for astrometric targets at the epochs of observation with all Special and General Relativistic effects removed in the barycenter tangent frame.

Images (Level 4)

Synthesized images astrometrically registered in the SIM reference frame corrected for Special and General Relativistic effects.

Nulling Images (Level 4)

Synthesized nulling images astrometrically registered in the SIM reference frame corrected for Special and General Relativistic effects.

Models

Flight System

Model describing the time-evolving state of the spacecraft plus instrument as derived from engineering data.

Solar System

General Relativistic model of the solar system describing how light propagates through the solar system potential.

Grid

Model describing the time-evolving positions of all objects in the SIM Grid in the barycenter tangent frame, with Special and General Relativistic effects removed.

Coordinate Transformation

Mechanism for transforming between the local instantaneous inertial reference frame and the barycenter tangent frame with Special and General Relativistic effects removed.

Calibrations back to top

Instrument scientists will examine calibration techniques for various types of known instrumental biases, and then determine how those methods will be used in data analysis. This work will encompass such diverse areas as the instrument, end-to-end data reduction (e.g. SIMSIM), and simulation tools such as grid simulation. Computational efficiency and development of simple, clear analysis interfaces are additional sample concerns.

A list of possible instrument calibration concerns is appended to give a sense of the issues under consideration.

Coordinate Frame Calibrations
TBD until coordinate frames are defined -- should include star tracker-to-starlight transformations and starlight-to-metrology transformations.

Optical Calibrations
Calibrate pointing on siderostat camera, guider camera, and angle tracker.
Calibration of beam combiner spectrometer, starlight throughput and detector quantum efficiency, diffraction/delay line errors, angle-dependent polarization-related and diffraction-related delay errors, and metrology optical power levels.

Mechanism Calibrations
Actuator model for siderostat mirror, Fast SteeringMirror, guider camera scanning mechanism, switchyard, delay line, delay line dither PZT, beam launcher pointing dither, siderostat bay alignment, and metrology vertex alignment.

Other Calibrations
Siderostat fiducial position measurements for absolute metrology and baseline co-parallelism corrections. Calibration of siderostat surface to corner cube vertex offset.
Calibration of siderostat gimbal axis to mirror surface offset.
Calibration of FSM rotation axis to mirror surface offset.
Calibration of multiple corner cube offsets.
Accelerometer axis calibration.
Accelerometer bias and scale factor calibration.
Three baseline system calibration on pseudostars and/or stars.

Post-Processing Calibrations
Removal of time- and angle-dependent errors.
Calibration using absolute and relative metrology data.
Removal of stellar aberration general relativity, and non-co-parallelism effects.

SIM-SIM back to top

The goal of SIM-SIM is to produce an end-to-end simulation of the total SIM system operation (see schematic below). Simulated measurements from the nominal instrument will be generated by the SIM Integrated Modeling team to include the effect of system noise and thermal response, through a generalized observation schedule, and solved for the apparent positions, proper motions, etc. of the target stars. This process will be iterated many times to investigate the effects of various types of measurement noise, observational sequences, and data reduction algorithms, to show that SIM as designed will be able to meet its science requirements.

Current plans call for a prototype software system to process simulated data from the Integrated Modeling team into a smaller data set suitable for the Science Interpretation team software, by mid-2000.

This page last updated: February 15, 2000
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