The Space Interferometry Mission (SIM) requires fringe measurements to the level of picometers in order to produce astrometric data at the micro-arc-second level. To be more specific, it is necessary to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer to a few hundreds of picometers. The internal path is measured with a small heterodyne metrology beam, whereas the starlight fringe position is estimated with a CCD sampling a large concentric annular beam. One major challenge for SIM is to align the metrology beam with the starlight beam to keep the consistency between these two sensors at the system level while articulating the instrument optics over the field of view. The Micro-Arcsecond Metrology testbed (MAM) developed at the Jet Propulsion Laboratory, California Institute of Technology, features an optical interferometer with a white light source, all major optical components of a stellar interferometer and heterodyne metrology sensors. The setup is installed inside a large vacuum chamber in order to mitigate the atmospheric and thermal disturbances. Wide angle astrometric observations are simulated by articulating the optics over the 15 degrees field of regard to generate multiple artificial stars. Recent data show agreement between the metrology and starlight paths to 350pm in the full wide angle field of view of SIM. This paper describes the MAM optical setup, the observation process, the current data and how the performance relates to SIM.
The New Worlds, New Horizons report released by the Astronomy and Astrophysics Decadal Survey Board in 2010
listed the Wide Field Infrared Survey Telescope (WFIRST) as the highest-priority large space mission for the coming
decade. This observatory will provide wide-field imaging and slitless spectroscopy at near infrared wavelengths. The
scientific goals are to obtain a statistical census of exoplanets using gravitational microlensing, measure the expansion
history of and the growth of structure in the Universe by multiple methods, and perform other astronomical surveys to be
selected through a guest observer program. A Science Definition Team has been established to assist NASA in the
development of a Design Reference Mission that accomplishes this diverse array of science programs with a single
observatory. In this paper we present the current WFIRST payload concept and the expected capabilities for planet
detection. The observatory, with science goals that are complimentary to the Kepler exoplanet transit mission, is
designed to complete the statistical census of planetary systems in the Galaxy, from habitable Earth-mass planets to free
floating planets, including analogs to all of the planets in our Solar System except Mercury. The exoplanet microlensing
survey will observe for 500 days spanning 5 years. This long temporal baseline will enable the determination of the
masses for most detected exoplanets down to 0.1 Earth masses.
The Space Interferometry Mission PlanetQuest Light (or SIM-Lite) is a new concept for a space borne astrometric
instrument, to be located in a solar Earth-trailing orbit. SIM-Lite utilizes technology developed over the past ten years
for the SIM mission. The instrument consists of two Michelson stellar interferometers and a precision telescope. The
first interferometer chops between the target star and a set of Reference stars. The second interferometer monitors the
attitude of the instrument in the direction of the target star. The telescope monitors the attitude of the instrument in the
other two directions.
SIM-Lite will be capable of one micro-arc-second narrow angle astrometry on magnitude 6 or brighter stars, relative to
magnitude 9 Reference stars in a two degree field. During the 5 year mission, SIM-Lite would search 65 nearby stars for
planets of masses down to one Earth mass, in the Habitable Zone, which have orbit periods of less than 3 years. SIMLite
will also perform global astrometry on a variety of astrophysics objects, reaching 4.5 micro-arc-seconds absolute
position and parallax measurements. As a pointed instrument, SIM-Lite will be capable of achieving 8 micro-arc-second
astrometric accuracy on 19th visual magnitude objects and 15 micro-arc-second astrometric accuracy on 20th visual
magnitude objects after 100 hours of integration.
This paper will describe the instrument, how it will do its astrometric measurements and the expected performance
based on the current technology.
Astrometry from space is capable of making extremely precise measurements of the positions of stars, at angular
precision of well below 1 micro-arcsecond (uas) at each visit. Hundreds of visits over a period of five years could
achieve a relative astrometric precision for the mission of below 0.05 uas; this is well below the astrometric signature
of 0.3 uas for a Sun-Earth system at a distance of 10 pc. The Sun's photometric fluctuations on time scales from days
to years are dominated by the rotation and evolution of stellar surface features (sunspots and faculae). This flux
variability is a source of astrophysical noise in astrometric as well as radial velocity (RV) measurements of the star. In
this paper we describe a dynamic starspot model that produces flux variability which is consistent with the measured
photometric power spectra of the Sun and several other stars. We use that model to predict the jitter in astrometric and
RV measurements due to starspots. We also employ empirical stellar activity models to estimate the astrometric jitter
of a much larger sample of stars. The conclusion of these simulations is that astrometric detection of planets in the
habitable zones of solar-type stars is not severely impacted by the noise due to starspots/faculae, down to well below
one Earth mass.
SIM is a space astrometric interferometer capable of better than one-microarcsecond ( as) single measurement accuracy,
providing the capability to detect stellar "wobble" resulting from planets in orbit around nearby stars. While a search for
exoplanets can be optimized in a variety of ways, a SIM five-year search optimized to detect Earth analogs (0.3 to 10
Earth masses) in the middle of the habitable zone (HZ) of nearby stars would yield the masses, without M*sin(i)
ambiguity, and three-dimensional orbital parameters for planets around ~70 stars, including those in the HZ and further
away from those same stars. With >200 known planets outside our solar system, astrophysical theorists have built
numerical models of planet formation that match the distribution of Jovian planets discovered to date and those models
predict that the number of terrestrial planets (< 10 M(+) ) would far exceed the number of more massive Jovian planets.
Even so, not every star will have an Earth analog in the middle of its HZ. This paper describes the relationship between
SIM and other planet detection methods, the SIM planet observing program, expected results, and the state of technical
readiness for the SIM mission.
SIM PlanetQuest is a space-borne Michelson interferometer with a nine meter baseline that will survey ~200 stars
within 30 parsecs for terrestrial mass planets. Ultra-precise astrometric observations will reveal the gravitational wobble
of the target star (due to a planetary companion) against an inertial frame of reference stars located within a 1.5 degree
radius. Here, we report the results of multiple Monte Carlo simulations which have modeled SIM's ability to detect and
determine the orbital parameters and masses of the terrestrial mass planets around its potential sample of target stars.
We find that SIM will detect 80% of the planets in the 60 star sample. Out of those planets SIM detects, we will be able
to estimate the masses of at least 50% of the planets to 30%. Whether SIM should observer 60 or 240 stars, will be
aided by the results of the Kepler mission which will provide statistics on the frequency of terrestrial-mass planets
around solar type stars. By determining the orbital phase of the planet, SIM will be able to assist TPF-C by telling it
when to look to ensure that the planet will be outside the TPF-C 62 mas inner working angle. Furthermore, the masses
determined by SIM will not suffer from the msini ambiguity inherent in radial velocity surveys.
The Space Interferometry Mission (SIM) requires fringe measurements to the level of picometers in order to produce astrometric data at the micro-arc-second level. To be more specific, it is necessary to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer to tens of picometers. The internal path is measured with a small heterodyne metrology beam, whereas the starlight fringe position is estimated with a CCD sampling a large concentric annular beam. One major challenge for SIM is to align the metrology beam with the starlight beam to keep the consistency between these two sensors at the system level while articulating the instrument optics over the field of regard.
The Micro-Arcsecond Metrology testbed (MAM), developed at the Jet Propulsion Laboratory, features an optical interferometer with a white light source, all major optical components of a stellar interferometer and heterodyne metrology sensors. The setup is installed inside a large vacuum chamber in order to mitigate the atmospheric and thermal disturbances. Astrometric observations are simulated by articulating the optics over the 15 degrees field of regard to generate multiple artificial stars. Recent data show agreement between the metrology and starlight paths to 20pm in the narrow angle field and to 350pm in the full wide angle field of regard of SIM. This paper describes the MAM optical setup, the observation process, the current data and how the performance relates to SIM.
One of the most critical technology requirements for the Space Interferometry Mission is that the difference in pathlength traveled by the starlight through each arm of the instrument be known with picometers of precision. SIM accomplishes this by using an internal laser metrology system to measure the optical path traveled by the starlight. The SIM technology program has previously demonstrated laser gauges with measurement accuracy below 10 picometers. The next challenge is to integrate one of these gauges into a full interferometer system and demonstrate that the system still operates at the required level. For SIM, the ultimate requirement is that the internal metrology system be able to give an accurate measure of the starlight internal path difference to about 150 picometers over its narrow-angle field, with a goal of 50 picometer accuracy. This accuracy must be maintained even as SIM's various active systems articulate the SIM optics and vary the SIM internal pathlengths.
The Microarcsecond Metrology Testbed (MAM) is a full single-baseline interferometer coupled with a precision pseudostar, intended to demonstrate the level of agreement between starlight and metrology phase measurements needed to make microarcsecond-level measurements of stellar positions. MAM has been under development for several years and is now producing picometers-level consistency that translates into microarcseconds-level performance. This paper will present an overview of the MAM Testbed, together with recent results targeting the 150 picometer performance level required by SIM.
Like all astrometric instruments, the Space Interferometry Mission (SIM) suffers from field-dependent errors requiring calibration. Diffraction effects in the delay line, polarization rotations on corner cubes, and beam walk across imperfect optics, all contribute to field-distortion that is significantly larger than is acceptable. The bulk of the systematic error is linear across the field - that is, it results in magnification and rotation errors. We show that the linear terms are inconsequential to the performance of SIM because they are inseparable from baseline length and orientation errors. One approach to calibrating the higher-order terms is to perform 'external' calibration; that is, SIM periodically makes differential measurements of a field of bright stars whose positions are not precisely known. We describe the requirements and constraints on the external calibration process and lay the groundwork for a specific procedure detailed in accompanying papers.
The Space Interferometry Mission (SIM) is a space-based
long baseline optical interferometer designed to perform precision
astrometry to an unprecedented accuracy. Highly accurate white
light fringe estimation is an important enabling technology for
the success of SIM. To accomplish this, the combined light from
the two arms of the interferometer is sent through a prism so that
fringes formed at different wavelengths are dispersed across a
number of spectral channels. The relative optical path difference
(OPD) between the two arms is modulated so that an estimate of the
phase in each of the channels can be obtained using phase shifting
interferometry (PSI) techniques. The present paper presents
several of the difficulties encountered in white light fringe
estimation for SIM, and offers a number of alternatives for
mitigating them.
An external calibration technique for SIM1,2,3 involves measurement of calibration stars whose positions must already be known to an accuracy of 2 milliarcseconds. We demonstrate a procedure that effectively 'bootstraps' calibration star positions from an ab initio catalog to the required accuracy by observing them with the uncalibrated SIM instrument.
MAM is a dedicated systems-level testbed that combines the major SIM subsystems including laser metrogy, pointing, and pathlength control. The testbed is configured as a modified Michelson interferometer for the purpose of studying the white-light fringe measurement processes. This paper will compare the performance of various algorithms using the MAM data, and will aid in our recommendation of how the SIM flight system should process the science and guide interferometer data.
This paper summarizes two different strategies envisioned for calibrating the systematic field dependent biases present in the Space Interferometry Mission (SIM) instrument. The Internal Calibration strategy is based on pre-launch measurements combined with a set of on-orbit measurements generated by a source internal to the instrument. The External Calibration strategy uses stars as an external source for generating the calibration function. Both approaches demand a significant amount of innovation given that SIM's calibration strategy requires a post-calibration error of 100 picometers over a 15 degree field of regard while the uncalibrated instrument introduces tens to hundreds of nanometers of error. The calibration strategies are discussed in the context of the wide angle astrometric mode of the instrument, although variations on both strategies have been proposed for doing narrow angle astrometry.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.