85 research outputs found
Sub-Microarcsecond Astrometry with SIM-Lite: A Testbed-based Performance Assessment
SIM-Lite is an astrometric interferometer being designed for
sub-microarcsecond astrometry, with a wide range of applications from searches
for Earth-analogs to determining the distribution of dark matter. SIM-Lite
measurements can be limited by random and systematic errors, as well as
astrophysical noise. In this paper we focus on instrument systematic errors and
report results from SIM-Lite's interferometer testbed. We find that, for
narrow-angle astrometry such as used for planet finding, the end-of-mission
noise floor for SIM-Lite is below 0.035 uas.Comment: 5 pages, 5 figure
Heterodyne Interferometer Angle Metrology
A compact, high-resolution angle measurement instrument has been developed that is based on a heterodyne interferometer. The common-path heterodyne interferometer metrology is used to measure displacements of a reflective target surface. In the interferometer setup, an optical mask is used to sample the measurement laser beam reflecting back from a target surface. Angular rotations, around two orthogonal axes in a plane perpendicular to the measurement- beam propagation direction, are determined simultaneously from the relative displacement measurement of the target surface. The device is used in a tracking telescope system where pitch and yaw measurements of a flat mirror were simultaneously performed with a sensitivity of 0.1 nrad, per second, and a measuring range of 0.15 mrad at a working distance of an order of a meter. The nonlinearity of the device is also measured less than one percent over the measurement range
Optical Design Trade Study for the Wide Field Infrared Survey Telescope [WFIRST]
The Wide Field Infrared Survey Telescope (WFIRST) mission concept was ranked first in new space astrophysics mission by the Astro2010 Decadal Survey incorporating the Joint Dark Energy Mission (JDEM)-Omega payload concept and multiple science white papers. This mission is based on a space telescope at L2 studying exoplanets [via gravitational microlensing], probing dark energy, and surveying the near infrared sky. Since the release of NWNH, the WFIRST project has been working with the WFIRST science definition team (SDT) to refine mission and payload concepts. We present the driving requirements. The current interim reference mission point design, based on the use of a 1.3m unobscured aperture three mirror anastigmat form, with focal imaging and slitless spectroscopy science channels, is consistent with the requirements, requires no technology development, and out performs the JDEM-Omega design
An experimental testbed for NEAT to demonstrate micro-pixel accuracy
NEAT is an astrometric mission proposed to ESA with the objectives of
detecting Earth-like exoplanets in the habitable zone of nearby solar-type
stars. In NEAT, one fundamental aspect is the capability to measure stellar
centroids at the precision of 5e-6 pixel. Current state-of-the-art methods for
centroid estimation have reached a precision of about 4e-5 pixel at Nyquist
sampling. Simulations showed that a precision of 2 micro-pixels can be reached,
if intra and inter pixel quantum efficiency variations are calibrated and
corrected for by a metrology system. The European part of the NEAT consortium
is designing and building a testbed in vacuum in order to achieve 5e-6 pixel
precision for the centroid estimation. The goal is to provide a proof of
concept for the precision requirement of the NEAT spacecraft. In this paper we
give the basic relations and trade-offs that come into play for the design of a
centroid testbed and its metrology system. We detail the different conditions
necessary to reach the targeted precision, present the characteristics of our
current design and describe the present status of the demonstration.Comment: SPIE proceeding
Two-Stage Passive Vibration Isolator
The design and testing of a structural system were implemented to hold the optics of the planned Space Interferometry Mission (SIM) at positions and orientations characterized by vibrational translation and rotation errors of no more than a few nanometers or a few milliarcseconds, respectively. Much of the effort was devoted to a test bed for verifying the predicted behavior of a vibration- isolation structural subsystem working together with an active control system for positioning and orienting the SIM optics. There was considerable emphasis on the vibration-isolation subsystem, which was passive and comprised two stages. The main sources of vibration were six reaction wheels in an assembly denoted the "backpack." The first vibration-isolation stage consisted of hexapod isolator mounts - one for each reaction wheel - characterized by a natural vibration frequency of 10 Hz. The second stage was a set of three beams, disposed between the backpack and the structure that held the SIM optics, that were flexured such that they transmitted only bending loads, with a natural vibrational frequency and damping of about 5 Hz and 4 percent, respectively. Preliminary test results were presented and characterized as demonstrating the effectiveness of the two-stage vibration-isolation design
NEAT: a space born astrometric mission for the detection and characterization of nearby habitable planetary systems
The NEAT (Nearby Earth Astrometric Telescope) mission is a proposal submitted
to ESA for its 2010 call for M-size mission within the Cosmic Vision 2015-2025
plan. The main scientific goal of the NEAT mission is to detect and
characterize planetary systems in an exhaustive way down to 1 Earth mass in the
habitable zone and further away, around nearby stars for F, G, and K spectral
types. This survey would provide the actual planetary masses, the full
characterization of the orbits including their inclination, for all the
components of the planetary system down to that mass limit. NEAT will continue
the work performed by Hipparcos and Gaia by reaching a precision that is
improved by two orders of magnitude on pointed targets.Comment: 17 pages, in SPIE 2012 symposium in "Space Telescopes and
Instrumentation 2012: Optical, Infrared, and Millimeter Wave" SPIE Conference
8442, 1
Finite-source and finite-lens effects in astrometric microlensing
The aim of this paper is to study the astrometric trajectory of microlensing
events with an extended lens and/or source. We consider not only a dark lens
but also a luminous lens as well. We find that the discontinuous finite-lens
trajectories given by Takahashi (2003) will become continuous in the
finite-source regime. The point lens (source) approximation alone gives an
under (over)estimation of the astrometric signal when the size of the lens and
source are not negligible. While the finiteness of the source is revealed when
the lens transits the surface of the source, the finite-lens signal is most
prominent when the lens is very close to the source. Astrometric microlensing
towards the Galactic bulge, Small Magellanic Cloud and M31 are discussed, which
indicate that the finite-lens effect is beyond the detection limit of current
instruments. Nevertheless, it is possible to distinguish between self-lensing
and halo lensing through a (non-)detection of the astrometric ellipse. We also
consider the case where the lens is luminous itself, as has been observed where
a lensing event was followed up with the Hubble Space Telescope. We show that
the astrometric signal will be reduced in a luminous-lens scenario. The
physical properties of the event, such as the lens-source flux ratio, the size
of the lens and source nevertheless can be derived by fitting the astrometric
trajectory.Comment: 12 pages, 12 figures, 1 table, published in MNRA
First experimental results of very high accuracy centroiding measurements for the neat astrometric mission
NEAT is an astrometric mission proposed to ESA with the objectives of
detecting Earth-like exoplanets in the habitable zone of nearby solar-type
stars. NEAT requires the capability to measure stellar centroids at the
precision of 5e-6 pixel. Current state-of-the-art methods for centroid
estimation have reached a precision of about 2e-5 pixel at two times Nyquist
sampling, this was shown at the JPL by the VESTA experiment. A metrology system
was used to calibrate intra and inter pixel quantum efficiency variations in
order to correct pixelation errors. The European part of the NEAT consortium is
building a testbed in vacuum in order to achieve 5e-6 pixel precision for the
centroid estimation. The goal is to provide a proof of concept for the
precision requirement of the NEAT spacecraft. In this paper we present the
metrology and the pseudo stellar sources sub-systems, we present a performance
model and an error budget of the experiment and we report the present status of
the demonstration. Finally we also present our first results: the experiment
had its first light in July 2013 and a first set of data was taken in air. The
analysis of this first set of data showed that we can already measure the pixel
positions with an accuracy of about 1e-4 pixel.Comment: SPIE conference proceeding
The Micro-Arcsecond Metrology Testbed
The Micro-Arcsecond Metrology (MAM) testbed is a ground-based system of optical and electronic equipment for testing components, systems, and engineering concepts for the Space Interferometer Mission (SIM) and similar future missions, in which optical interferometers will be operated in outer space. In addition, the MAM testbed is of interest in its own right as a highly precise metrological system. The designs of the SIM interferometer and the MAM testbed reflect a requirement to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer with sufficient spatial resolution to generate astrometric data with angular resolution at the microarcsecond level. The internal path is to be measured by use of a small metrological laser beam of 1,319-nm wavelength, whereas the position of the starlight fringe is to be estimated by use of a charge-coupled-device (CCD) image detector sampling a large concentric annular beam. For the SIM to succeed, the optical path length determined from the interferometer fringes must be tracked by the metrological subsystem to within tens of picometers, through all operational motions of an interferometer delay line and siderostats. The purpose of the experiments performed on the MAM testbed is to demonstrate this agreement in a large-scale simulation that includes a substantial portion of the system in the planned configuration for operation in outer space. A major challenge in this endeavor is to align the metrological beam with the starlight beam in order to maintain consistency between the metrological and starlight subsystems at the system level. The MAM testbed includes an optical interferometer with a white light source, all major optical components of a stellar interferometer, and heterodyne metrological sensors. The aforementioned subsystems are installed in a large vacuum chamber in order to suppress atmospheric and thermal disturbances. The MAM is divided into two distinct subsystems: the test article (TA), which is the interferometer proper, and the inverse interferometer pseudo-star (IIPS), which synthesizes the light coming from a distant target star by providing spatially coherent wavefronts out of two mirrors, separated by the MAM baseline, that feed directly into two siderostats that are parts of the TA. The two feed mirrors of the IIPS are articulated (in translation and tilt) in order to simulate stars located at different orientations in space, while still illuminating the TA siderostats. The spectrum of the simulated starlight of the IIPS corresponds to that of a blackbody at a temperature of about 3,100 K
- …