Although there are a large number of known exoplanets, there is little data on their global atmospheric properties. Phase-resolved spectroscopy of transiting planets – continuous spectroscopic observation of planets during their full orbits – probes varied depths and longitudes in the atmospheres thus measuring their three-dimensional thermal and chemical structure and contributing to our understanding of their global circulation. Planets with characteristics suitable for atmospheric characterization have orbits of several days, so phase curve observations are highly resource intensive, especially for shared use facilities. The Exoplanet Climate Infrared TElescope (EXCITE) is a balloon-borne near-infrared spectrometer designed to observe from 1 to 5 μm to perform phaseresolved spectroscopy of hot Jupiters. Flying from a long duration balloon (LDB) platform, EXCITE will have the stability to continuously stare at targets for days at a time and the sensitivity to produce data of the quality and quantity needed to significantly advance our understanding of exoplanet atmospheres. We describe the EXCITE design and show results of analytic and numerical calculations of the instrument sensitivity. We show that an instrument like EXCITE will produce a wealth of quality data, both complementing and serving as a critical bridge between current and future space-based near infrared spectroscopic instruments.
QUBIC, the QU Bolometric Interferometer for Cosmology, is a novel forthcoming instrument to measure the B-mode polarization anisotropy of the Cosmic Microwave Background. The detection of the B-mode signal will be extremely challenging; QUBIC has been designed to address this with a novel approach, namely bolometric interferometry. The receiver cryostat is exceptionally large and cools complex optical and detector stages to 40 K, 4 K, 1 K and 350 mK using two pulse tube coolers, a novel 4He sorption cooler and a double-stage 3He/4He sorption cooler. We discuss the thermal and mechanical design of the cryostat, modelling and thermal analysis, and laboratory cryogenic testing.
QUBIC (the Q and U Bolometric Interferometer for Cosmology) is a ground-based experiment which seeks to improve the current constraints on the amplitude of primordial gravitational waves. It exploits the unique technique, among Cosmic Microwave Background experiments, of bolometric interferometry, combining together the sensitivity of bolometric detectors with the control of systematic effects typical of interferometers. QUBIC will perform sky observations in polarization, in two frequency bands centered at 150 and 220 GHz, with two kilo-pixel focal plane arrays of NbSi Transition-Edge Sensors (TES) cooled down to 350 mK. A subset of the QUBIC instrument, the so called QUBIC Technological Demonstrator (TD), with a reduced number of detectors with respect to the full instrument, will be deployed and commissioned before the end of 2018.
The voltage-biased TES are read out with Time Domain Multiplexing and an unprecedented multiplexing (MUX) factor equal to 128. This MUX factor is reached with two-stage multiplexing: a traditional one exploiting Superconducting QUantum Interference Devices (SQUIDs) at 1K and a novel SiGe Application-Specific Integrated Circuit (ASIC) at 60 K. The former provides a MUX factor of 32, while the latter provides a further 4. Each TES array is composed of 256 detectors and read out with four modules of 32 SQUIDs and two ASICs. A custom software synchronizes and manages the readout and detector operation, while the TES are sampled at 780 Hz (100kHz/128 MUX rate).
In this work we present the experimental characterization of the QUBIC TES arrays and their multiplexing readout chain, including time constant, critical temperature, and noise properties.
QUBIC, the Q & U Bolometric Interferometer for Cosmology, is a novel ground-based instrument that has been designed to measure the extremely faint B-mode polarisation anisotropy of the cosmic microwave background at intermediate angular scales (multipoles of 𝑙 = 30 − 200). Primordial B-modes are a key prediction of Inflation as they can only be produced by gravitational waves in the very early universe. To achieve this goal, QUBIC will use bolometric interferometry, a technique that combines the sensitivity of an imager with the systematic error control of an interferometer. It will directly observe the sky through an array of 400 back-to-back entry horns whose signals will be superimposed using a quasi-optical beam combiner. The resulting interference fringes will be imaged at 150 and 220 GHz on two focal planes, each tiled with NbSi Transition Edge Sensors, cooled to 320 mK and read out with time-domain multiplexing. A dichroic filter placed between the optical combiner and the focal planes will select the two frequency bands. A very large receiver cryostat will cool the optical and detector stages to 40 K, 4 K, 1 K and 320 mK using two pulse tube coolers, a novel 4He sorption cooler and a double-stage 3He/4He sorption cooler. Polarisation modulation and selection will be achieved using a cold stepped half-wave plate (HWP) and polariser, respectively, in front of the sky-facing horns. A key feature of QUBIC’s ability to control systematic effects is its ‘self-calibration’ mode where fringe patterns from individual equivalent baselines can be compared. When observing, however, all the horns will be open simultaneously and we will recover a synthetic image of the sky in the I, Q and U Stokes’ parameters. The synthesised beam pattern has a central peak of approximately 0.5 degrees in width, with secondary peaks further out that are damped by the 13-degree primary beam of the horns. This is Module 1 of QUBIC which will be installed in Argentina, near the city of San Antonio de los Cobres, at the Alto Chorrillos site (4869 m a.s.l.), Salta Province. Simulations have shown that this first module could constrain the tensor-to-scalar ratio down to σ(r) = 0.01 after a two-year survey. We aim to add further modules in the future to increase the angular sensitivity and resolution of the instrument. The QUBIC project is proceeding through a sequence of steps. After an initial successful characterisation of the detection chain, a technological demonstrator is being assembled to validate the full instrument design and to test it electrically, thermally and optically.
The technical demonstrator is a scaled-down version of Module 1 in terms of the number of detectors, input horns and pulse tubes and a reduction in the diameter of the combiner mirrors and filters, but is otherwise similar. The demonstrator will be upgraded to the full module in 2019. In this paper we give an overview of the QUBIC project and instrument.
QUBIC, the Q & U Bolometric Interferometer for Cosmology, is a novel ground-based instrument that aims to measure the extremely faint B-mode polarisation anisotropy of the cosmic microwave background at intermediate angular scales (multipoles of 𝑙 = 30 − 200). Primordial B-modes are a key prediction of Inflation as they can only be produced by gravitational waves in the very early universe. To achieve this goal, QUBIC will use bolometric interferometry, a technique that combines the sensitivity of an imager with the immunity to systematic effects of an interferometer. It will directly observe the sky through an array of back-to-back entry horns whose beams will be superimposed using a cooled quasioptical beam combiner. Images of the resulting interference fringes will be formed on two focal planes, each tiled with transition-edge sensors, cooled down to 320 mK. A dichroic filter placed between the optical combiner and the focal planes will select two frequency bands (centred at 150 GHz and 220 GHz), one frequency per focal plane. Polarization modulation will be achieved using a cold stepped half-wave plate (HWP) and polariser in front of the sky-facing horns.
The full QUBIC instrument is described elsewhere1,2,3,4; in this paper we will concentrate in particular on simulations of the optical combiner (an off-axis Gregorian imager) and the feedhorn array. We model the optical performance of both the QUBIC full module and a scaled-down technological demonstrator which will be used to validate the full instrument design. Optical modelling is carried out using full vector physical optics with a combination of commercial and in-house software. In the high-frequency channel we must be careful to consider the higher-order modes that can be transmitted by the horn array. The instrument window function is used as a measure of performance and we investigate the effect of, for example, alignment and manufacturing tolerances, truncation by optical components and off-axis aberrations. We also report on laboratory tests carried on the QUBIC technological demonstrator in advance of deployment to the observing site in Argentina.
Remnant radiation from the early universe, known as the Cosmic Microwave Background (CMB), has been redshifted and cooled, and today has a blackbody spectrum peaking at millimetre wavelengths. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument is designed to map the very faint polaristion structure in the CMB. QUBIC is based on the novel concept of bolometric interferometry in conjunction with synthetic imaging. It will have a large array of input feedhorns, which creates a large number of interferometric baselines.
The beam from each feedhorn is passed through an optical combiner, with an off-axis compensated Gregorian design, to allow the generation of the synthetic image. The optical-combiner will operate in two frequency bands (150 and 220 GHz with 25% and 18.2 % bandwidth respectively) while cryogenically cooled TES bolometers provide the sensitivity required at the image plane.
The QUBIC Technical Demonstrator (TD), a proof of technology instrument that contains 64 input feed-horns, is currently being built and will be installed in the Alto Chorrillos region of Argentina. The plan is then for the full QUBIC instrument (400 feed-horns) to be deployed in Argentina and obtain cosmologically significant results.
In this paper we will examine the output of the manufactered feed-horns in comparison to the nominal design. We will show the results of optical modelling that has been performed in anticipation of alignment and calibration of the TD in Paris, in particular testing the validity of real laboratory environments. We show the output of large calibrator sources (50 ° full width haf max Gaussian beams) and the importance of accurate mirror definitions when modelling large beams. Finally we describe the tolerance on errors of the position and orientation of mirrors in the optical combiner.
Big Bang cosmologies predict that the cosmic microwave background (CMB) contains faint temperature and polarisation
anisotropies imprinted in the early universe. ESA's PLANCK satellite has already measured the temperature
anisotropies1 in exquisite detail; the next ambitious step is to map the primordial polarisation signatures which are
several orders of magnitude lower. Polarisation E-modes have been measured2 but the even-fainter primordial B-modes
have so far eluded detection. Their magnitude is unknown but it is clear that a sensitive telescope with exceptional
control over systematic errors will be required.
QUBIC3 is a ground-based European experiment that aims to exploit the novel concept of bolometric interferometry in
order to measure B-mode polarisation anisotropies in the CMB. Beams from an aperture array of corrugated horns will
be combined to form a synthesised image of the sky Stokes parameters on two focal planes: one at 150 GHz the other at
220 GHz. In this paper we describe recent optical modelling of the QUBIC beam combiner, concentrating on modelling
the instrument point-spread-function and its operation in the 220-GHz band. We show the effects of optical aberrations
and truncation as successive components are added to the beam path. In the case of QUBIC, the aberrations introduced
by off-axis mirrors are the dominant contributor. As the frequency of operation is increased, the aperture horns allow up to five hybrid modes to propagate and we illustrate how the beam pattern changes across the 25% bandwidth. Finally we
describe modifications to the QUBIC optical design to be used in a technical demonstrator, currently being manufactured
for testing in 2016.
EBEX is a balloon-borne telescope designed to measure the polarization of the cosmic microwave background radiation. During its eleven day science flight in the Austral Summer of 2012, it operated 955 spider-web transition edge sensor (TES) bolometers separated into bands at 150, 250 and 410 GHz. This is the first time that an array of TES bolometers has been used on a balloon platform to conduct science observations. Polarization sensitivity was provided by a wire grid and continuously rotating half-wave plate. The balloon implementation of the bolometer array and readout electronics presented unique development requirements. Here we present an outline of the readout system, the remote tuning of the bolometers and Superconducting QUantum Interference Device (SQUID) amplifiers, and preliminary current noise of the bolometer array and readout system.
KEYWORDS: Bolometers, Digital signal processing, Analog electronics, Cryogenics, Electronics, Control systems, Physics, Sensors, Telescopes, Signal processing
We present the second generation BLASTbus electronics. The primary purposes of this system are detector readout, attitude control, and cryogenic housekeeping, for balloon-borne telescopes. Readout of neutron transmutation doped germanium (NTD-Ge) bolometers requires low noise and parallel acquisition of hundreds of analog signals. Controlling a telescope's attitude requires the capability to interface to a wide variety of sensors and motors, and to use them together in a fast, closed loop. To achieve these different goals, the BLASTbus system employs a flexible motherboard-daughterboard architecture. The programmable motherboard features a digital signal processor (DSP) and field-programmable gate array (FPGA), as well as slots for three daughterboards. The daughterboards provide the interface to the outside world, with versions for analog to digital conversion, and optoisolated digital input/output. With the versatility afforded by this design, the BLASTbus also finds uses in cryogenic, thermometry, and power systems. For accurate timing control to tie everything together, the system operates in a fully synchronous manner. BLASTbus electronics have been successfully deployed to the South Pole, and own on stratospheric balloons.
An attitude determination system for balloon-borne experiments is presented. The system provides pointing information in azimuth and elevation for instruments flying on stratospheric balloons over Antarctica. In-flight attitude is given by the real-time combination of readings from star cameras, a magnetometer, sun sensors, GPS, gyroscopes, tilt sensors and an elevation encoder. Post-flight attitude reconstruction is determined from star camera solutions, interpolated by the gyroscopes using an extended Kalman Filter. The multi-sensor system was employed by the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol), an experiment that measures polarized thermal emission from interstellar dust clouds. A similar system was designed for the upcoming flight of Spider, a Cosmic Microwave Background polarization experiment. The pointing requirements for these experiments are discussed, as well as the challenges in designing attitude reconstruction systems for high altitude balloon flights. In the 2010 and 2012 BLASTPol flights from McMurdo Station, Antarctica, the system demonstrated an accuracy of < 5’ rms in-flight, and < 5” rms post-flight.
We present the thermal model of the Balloon-borne Large-Aperture Submillimeter Telescope for Polarimetry (BLASTPol). This instrument was successfully own in two circumpolar flights from McMurdo, Antarctica in 2010 and 2012. During these two flights, BLASTPol obtained unprecedented information about the magnetic field in molecular clouds through the measurement of the polarized thermal emission of interstellar dust grains. The thermal design of the experiment addresses the stability and control of the payload necessary for this kind of measurement. We describe the thermal modeling of the payload including the sun-shielding strategy. We present the in-flight thermal performance of the instrument and compare the predictions of the model with the temperatures registered during the flight. We describe the difficulties of modeling the thermal behavior of the balloon-borne platform and establish landmarks that can be used in the design of future balloon-borne instruments.
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) is a suborbital mapping experiment, designed to study the role played by magnetic fields in the star formation process. BLASTPol observes polarized light using a total power instrument, photolithographic polarizing grids, and an achromatic half-wave plate to modulate the polarization signal. During its second flight from Antarctica in December 2012, BLASTPol made degree scale maps of linearly polarized dust emission from molecular clouds in three wavebands, centered at 250, 350, and 500 μm. The instrumental performance was an improvement over the 2010 BLASTPol ight, with decreased systematics resulting in a higher number of confirmed polarization vectors. The resultant dataset allows BLASTPol to trace magnetic fields in star-forming regions at scales ranging from cores to entire molecular cloud complexes.
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) is a suborbital mapping
experiment designed to study the role played by magnetic fields in the star formation process. BLASTPol uses
a total power instrument and an achromatic half-wave plate to modulate the polarization signal. During its first flight from Antarctica in December 2010, BLASTPol made degree scale maps of linearly polarized dust emission
from molecular clouds in three wavebands centered at 250, 350, and 500 μm. This unprecedented dataset in terms
of sky coverage, with sub-arcminute resolution, allows BLASTPol to trace magnetic fields in star-forming regions
at scales ranging from cores to entire molecular cloud complexes. A second long-duration flight is scheduled for
December 2012.
We present the design and measured performance of the superconducting magnetic bearing (SMB) that was used successfully as the rotation mechanism in the half-wave plate polarimeter of the E and B Experiment (EBEX) during its North American test flight. EBEX is a NASA-supported balloon-borne experiment that is designed to measure the polarization of the cosmic microwave background. In this implementation the half-wave plate is mounted to the rotor of an SMB that is operating at the sink temperature of 4 K. We demonstrate robust, remote operation on a balloon-borne payload, with angular encoding accuracy of 0.01°. We find rotational speed variation to be 0.2% RMS. We measure vibrational modes and find them to be consistent with a simple SMB model. We search for but do not find magnetic field interference in the detectors and readout. We set an upper limit of 3% of the receiver noise level after 5 minutes of integration on such interference. At 2 Hz rotation we measure a power dissipation of 56 mW. If this power dissipation is reduced, such an SMB implementation is a candidate for low-noise space applications because of the absence of stick-slip friction and low wear.
We present the hardware and software systems implementing autonomous operation, distributed real-time monitoring,
and control for the EBEX instrument. EBEX is a NASA-funded balloon-borne microwave polarimeter
designed for a 14 day Antarctic flight that circumnavigates the pole.
To meet its science goals the EBEX instrument autonomously executes several tasks in parallel: it collects
attitude data and maintains pointing control in order to adhere to an observing schedule; tunes and operates
up to 1920 TES bolometers and 120 SQUID amplifiers controlled by as many as 30 embedded computers;
coordinates and dispatches jobs across an onboard computer network to manage this detector readout system;
logs over 3 GiB/hour of science and housekeeping data to an onboard disk storage array; responds to a variety
of commands and exogenous events; and downlinks multiple heterogeneous data streams representing a selected
subset of the total logged data. Most of the systems implementing these functions have been tested during a
recent engineering flight of the payload, and have proven to meet the target requirements.
The EBEX ground segment couples uplink and downlink hardware to a client-server software stack, enabling
real-time monitoring and command responsibility to be distributed across the public internet or other standard
computer networks. Using the emerging dirfile standard as a uniform intermediate data format, a variety of
front end programs provide access to different components and views of the downlinked data products. This
distributed architecture was demonstrated operating across multiple widely dispersed sites prior to and during
the EBEX engineering flight.
Britt Reichborn-Kjennerud, Asad Aboobaker, Peter Ade, François Aubin, Carlo Baccigalupi, Chaoyun Bao, Julian Borrill, Christopher Cantalupo, Daniel Chapman, Joy Didier, Matt Dobbs, Julien Grain, William Grainger, Shaul Hanany, Seth Hillbrand, Johannes Hubmayr, Andrew Jaffe, Bradley Johnson, Terry Jones, Theodore Kisner, Jeff Klein, Andrei Korotkov, Sam Leach, Adrian Lee, Lorne Levinson, Michele Limon, Kevin MacDermid, Tomotake Matsumura, Xiaofan Meng, Amber Miller, Michael Milligan, Enzo Pascale, Daniel Polsgrove, Nicolas Ponthieu, Kate Raach, Ilan Sagiv, Graeme Smecher, Federico Stivoli, Radek Stompor, Huan Tran, Matthieu Tristram, Gregory Tucker, Yury Vinokurov, Amit Yadav, Matias Zaldarriaga, Kyle Zilic
EBEX is a NASA-funded balloon-borne experiment designed to measure the polarization of the cosmic microwave
background (CMB). Observations will be made using 1432 transition edge sensor (TES) bolometric detectors
read out with frequency multiplexed SQuIDs. EBEX will observe in three frequency bands centered at 150, 250,
and 410 GHz, with 768, 384, and 280 detectors in each band, respectively. This broad frequency coverage is
designed to provide valuable information about polarized foreground signals from dust. The polarized sky signals
will be modulated with an achromatic half wave plate (AHWP) rotating on a superconducting magnetic bearing
(SMB) and analyzed with a fixed wire grid polarizer. EBEX will observe a patch covering ~1% of the sky with 8'
resolution, allowing for observation of the angular power spectrum from l = 20 to 1000. This will allow EBEX to
search for both the primordial B-mode signal predicted by inflation and the anticipated lensing B-mode signal.
Calculations to predict EBEX constraints on r using expected noise levels show that, for a likelihood centered
around zero and with negligible foregrounds, 99% of the area falls below r = 0.035. This value increases by a
factor of 1.6 after a process of foreground subtraction. This estimate does not include systematic uncertainties.
An engineering flight was launched in June, 2009, from Ft. Sumner, NM, and the long duration science flight
in Antarctica is planned for 2011. These proceedings describe the EBEX instrument and the North American
engineering flight.
François Aubin, Asad Aboobaker, Peter Ade, Carlo Baccigalupi, Chaoyun Bao, Julian Borrill, Christopher Cantalupo, Daniel Chapman, Joy Didier, Matt Dobbs, Will Grainger, Shaul Hanany, Johannes Hubmayr, Peter Hyland, Seth Hillbrand, Andrew Jaffe, Bradley Johnson, Terry Jones, Theodore Kisner, Jeff Klein, Andrei Korotkov, Sam Leach, Adrian Lee, Michele Limon, Kevin MacDermid, Tomotake Matsumura, Xiaofan Meng, Amber Miller, Michael Milligan, Daniel Polsgrove, Nicolas Ponthieu, Kate Raach, Britt Reichborn-Kjennerud, Ilan Sagiv, Graeme Smecher, Huan Tran, Gregory Tucker, Yury Vinokurov, Amit Yadav, Matias Zaldarriaga, Kyle Zilic
EBEX (the E and B EXperiment) is a balloon-borne telescope designed to measure the polarisation of the
cosmic microwave background radiation. During a two week long duration science flight over Antarctica, EBEX
will operate 768, 384 and 280 spider-web transition edge sensor (TES) bolometers at 150, 250 and 410 GHz,
respectively. The 10-hour EBEX engineering flight in June 2009 over New Mexico and Arizona provided the first
usage of both a large array of TES bolometers and a Superconducting QUantum Interference Device (SQUID)
based multiplexed readout in a space-like environment. This successful demonstration increases the technology
readiness level of these bolometers and the associated readout system for future space missions. A total of 82,
49 and 82 TES detectors were operated during the engineering flight at 150, 250 and 410 GHz. The sensors
were read out with a new SQUID-based digital frequency domain multiplexed readout system that was designed
to meet the low power consumption and robust autonomous operation requirements presented by a balloon
experiment. Here we describe the system and the remote, automated tuning of the bolometers and SQUIDs. We
compare results from tuning at float to ground, and discuss bolometer performance during flight.
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLAST-Pol) is a suborbital mapping
experiment designed to study the role played by magnetic fields in the star formation process. BLAST-Pol is
the reconstructed BLAST telescope, with the addition of linear polarization capability. Using a 1.8m Cassegrain
telescope, BLAST-Pol images the sky onto a focal plane that consists of 280 bolometric detectors in three arrays,
observing simultaneously at 250, 350, and 500μm. The diffraction-limited optical system provides a resolution of
30"at 250μm. The polarimeter consists of photolithographic polarizing grids mounted in front of each bolometer/
detector array. A rotating 4K achromatic half-wave plate provides additional polarization modulation. With
its unprecedented mapping speed and resolution, BLAST-Pol will produce three-color polarization maps for a
large number of molecular clouds. The instrument provides a much needed bridge in spatial coverage between larger-scale, coarse resolution surveys and narrow field of view, and high resolution observations of substructure
within molecular cloud cores. The first science flight will be from McMurdo Station, Antarctica in December
2010.
The E and B Experiment, EBEX, is a Cosmic Microwave Background polarization experiment designed to detect
or set upper limits on the signature of primordial gravity waves. Primordial gravity waves are predicted to be
produced by inflation, and a measurement of the power spectrum of these gravity waves is a measurement of
the energy scale of inflation. EBEX has sufficient sensitivity to detect or set an upper limit at 95% confidence
on the energy scale of inflation of < 1.4 × 1016 GeV. This article reviews our strategy for achieving our science
goals and discusses the implementation of the instrument.
We report on the design and tests of a prototype of the Millimeter-wave Bolometric Interferometer (MBI). MBI
is designed to make sensitive measurements of the polarization of the cosmic microwave background (CMB). It
combines the differencing capabilities of an interferometer with the high sensitivity of bolometers at millimeter
wavelengths. The prototype, which we call MBI-4, views the sky directly through four corrugated horn antennas.
MBI ultimately will have ~ 1000 antennas. These antennas have low sidelobes and nearly symmetric beam
patterns, so spurious instrumental polarization from reflective optics is avoided. The MBI-4 optical band is
defined by filters with a central frequency of 90 GHz. The set of baselines, determined by placement of the four
antennas, results in sensitivity to CMB polarization fluctuations over the multipole range ℓ = 150 - 270. The
signals are combined with a Fizeau beam combiner and interference fringes are detected by an array of spider-web
bolometers. In order to separate the visibility signals from the total power detected by each bolometer, the
phase of the signal from each antenna is modulated by a ferrite-based waveguide phase shifter. Initial tests and
observations have been made at Pine Bluff Observatory (PBO) outside Madison, WI.
The Millimeter-Wave Bolometric Interferometer (MBI) is a ground-based instrument designed to measure the
polarization anisotropies of the Cosmic Microwave Background (CMB) and contains a number of quasi-optical
components, including a complex back-to-back system of corrugated feed-horn antennas. In this paper we use MBI as
an example to demonstrate the existing modeling techniques and as a focus to develop extended modeling capabilities.
The software we use to model this system targets the millimeter and sub-millimeter region of the electromagnetic
spectrum and has been extended to efficiently model the performance of back-to-back corrugated horns embedded in
larger optical systems. This allows the calculation of the coupling of radiation from the sky to the detector array through
a back-to-back horn feed system.
The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a sub-orbital experiment designed to study the process of star formation in local galaxies (including the Milky Way) and in galaxies at cosmological distances. Using a 2m Cassegrain telescope, BLAST images the sky onto a focal plane, which consists of 270 bolometric detectors split between three arrays, observing simultaneously in 30% wide bands, centered at 250, 350, and 500 μm. The
diffraction-limited optical system provides a resolution of 30" at 250 μm. The pointing system enables raster-like scans with a positional accuracy of ~30", reconstructed to better than
5" rms in postflight analysis. BLAST had two successful flights, from the Arctic in 2005, and from Antarctica in 2006, which provided the first high-resolution and large-area (~0.8−200 deg2) submillimeter surveys at these wavelengths. As a pathfinder for the SPIRE instrument on Herschel, BLAST shares with the ESA satellite similar focal plane technology and scientific motivation. A third flight in 2009 will see the instrument modified to be polarization-sensitive (BLAST-pol). With its unprecedented mapping speed and resolution, BLAST-pol will provide insights into Galactic star-forming nurseries, and give the necessary link between the larger, coarse resolution surveys and the narrow, resolved observations of star-forming structures from space and ground based instruments being commissioned in the next 5 years.
The Millimeter-Wave Bolometric Interferometer (MBI) is designed for sensitive measurements of the polarization of the cosmic microwave background (CMB). MBI combines the differencing capabilities of an interferometer with the high sensitivity of bolometers at millimeter wavelengths. It views the sky directly through corrugated horn antennas with low sidelobes and nearly symmetric beam patterns to avoid spurious instrumental polarization from reflective optics. The design of the first version of the instrument with four 7-degree-FOV corrugated horns (MBI-4) is discussed. The MBI-4 optical band is defined by filters with a central frequency of 90 GHz. The set of baselines determined by the antenna separation makes the instrument sensitive to CMB polarization fluctuations over the multipole range l=150-270. In MBI-4, the signals from antennas are combined with a Fizeau beam combiner and interference fringes are detected by an array of spider-web bolometers with NTD germanium thermistors. In order to separate the visibility signals from the total power detected by each bolometer, the phase of the signal from each antenna is modulated by a ferrite-based waveguide phase shifter. Observations are planned from the Pine Bluff Observatory outside Madison, WI.
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