Spider is a balloon-borne instrument designed to map the cosmic microwave background at degree-angular scales in the presence of Galactic foregrounds. Spider has mapped a large sky area in the Southern Hemisphere using more than 2000 transition-edge sensors (TESs) during two NASA Long Duration Balloon flights above the Antarctic continent. During its first flight in January 2015, Spider was observed in the 95- and 150-GHz frequency bands, setting constraints on the B-mode signature of primordial gravitational waves. Its second flight in the 2022–2023 season added new receivers at 280 GHz, each using an array of TESs coupled to the sky through feedhorns formed from stacks of silicon wafers. These receivers are optimized to produce deep maps of polarized Galactic dust emission over a large sky area, providing a unique data set with lasting value to the field. We describe the instrument’s performance during Spider’s second flight, focusing on the performance of the 280-GHz receivers. We include details on the flight, in-band optical loading at float, and an early analysis of detector noise.
The Super-pressure Balloon-borne Imaging Telescope (SuperBIT) is a near-diffraction-limited 0.5m telescope that launched via NASA’s super-pressure balloon technology on April 16, 2023. SuperBIT achieved precise pointing control through the use of three nested frames in conjunction with an optical Fine Guidance System (FGS), resulting in an average image stability of 0.055” over 300-second exposures. The SuperBIT FGS includes a tip-tilt fast-steering mirror that corrects for jitter on a pair of focal plane star cameras. In this paper, we leverage the empirical data from SuperBIT’s successful 39-day stratospheric mission to inform the FGS design for the next-generation balloon-borne telescope. The Gigapixel Balloon-borne Imaging Telescope (GigaBIT) is designed to be a 1.35m wide-field, high resolution imaging telescope, with specifications to extend the scale and capabilities beyond those of its predecessor SuperBIT. A description and analysis of the SuperBIT FGS will be presented along with methodologies for extrapolating this data to enhance GigaBIT’s FGS design and fine pointing control algorithm. We employ a systems engineering approach to outline and formalize the design constraints and specifications for GigaBIT’s FGS. GigaBIT, building on the SuperBIT legacy, is set to enhance high-resolution astronomical imaging, marking a significant advancement in the field of balloon-borne telescopes.
Taurus is a balloon-borne cosmic microwave background (CMB) experiment optimized to map the E-mode polarization and Galactic foregrounds at the largest angular scales (𝓁 < 30) and improve measurements of the optical depth to reionization (τ). This will pave the way for improved measurements of the sum of neutrino masses in combination with high-resolution CMB data while also testing the ΛCDM model on large angular scales and providing high-frequency maps of polarized dust foregrounds to the CMB community. These measurements take advantage of the low-loading environment found in the stratosphere and are enabled by NASA’s superpressure balloon platform, which provides access to 70% of the sky with a launch from Wanaka, New Zealand. Here we describe a general overview of Taurus, with an emphasis on the instrument design. Taurus will employ more than 10,000 100mK transition edge sensor bolometers distributed across two low-frequency (150, 220GHz) and one high-frequency (280, 350GHz) dichroic receivers. The liquid helium cryostat housing the detectors and optics is supported by a lightweight gondola. The payload is designed to meet the challenges in mass, power, and thermal control posed by the super-pressure platform. The instrument and scan strategy are optimized for rigorous control of instrumental systematics, enabling high-fidelity linear polarization measurements on the largest angular scales.
The Super-pressure Balloon-borne Imaging Telescope (SuperBIT) was a diffraction limited 0.5m optical-to-near-UV telescope that was designed to study dark matter via cluster weak lensing. SuperBIT launched from Wanaka, New Zealand via NASA’s super-pressure balloon (SPB) technology on April 16, 2023 and remained in the stratosphere for 40 days. During the flight, SuperBIT obtained multi-band images for 30 science targets; data analysis to produce shear measurements for each target is ongoing. SuperBIT’s pointing system comprised three nested frames that stablized the entire telescope within 0.34 arcseconds rms, plus a back-end tip-tilt mirror that achieved focal plane image stability of 0.055 arcseconds rms during 300 second exposures. The power system reached full charge every day and never dropped below 30% at night. All components remained within their temperature limits, and actively controlled components remained within a standard deviation of ∼0.1K of their set point. In this paper we provide an overview of the flight trajectory behaviour and flight operations. The first two days of the flight were used for payload characterization and telescope alignment after which all night time was dedicated to science observations. Target scheduling was performed by an on-board “Autopilot” system which tracked available targets and prioritized completing targets over starting new targets. SuperBIT was the first balloon telescope to fly a Starlink dish to enable high-bandwidth communications with the payload. Prior to flight termination, two Data Retrieval System modules were deployed to provide a redundant data recovery method.
We describe the cryogenic system being developed for Taurus: a super-pressure balloon-borne microwave polarimeter scheduled to fly in 2027. The Taurus cryogenic system consists of a 660L liquid helium cryostat which achieves a base temperature of ≤100mK with the help of a capillary-fed superfluid tank and a closed cycle dilution refrigerator. The main tank is supported with fiberglass flexures and is encased in two layers of vapor-cooled shields which allow Taurus to make full use of the extended flight time offered by the super-pressure balloon platform. The Taurus cryostat is projected to hold for over 50 days while weighing under 1000lbs. We present the design, testing, and thermal analysis of the Taurus cryogenic systems.
The Super Pressure Balloon-borne Imaging Telescope (SuperBIT) is a diffraction limited 0.5m optical-to-near-UV telescope launched from New Zealand on NASA’s Super Pressure Balloon (SPB) on April 16, 2023 and flew for 45 nights. There were several communication links used during SuperBIT’s flight to communicate with the telescope from the ground, including Starlink, the Tracking and Data Relay Satellite System (TDRSS), Pilot, and Iridium. While Starlink bandwidth was suitable for TCP-based communications and downlinking, the other links were only capable of supporting UDP-based communications. We designed a file transfer algorithm that downlinked files while detecting missing packets in our downlink and requested them automatically, saving limited bandwidth. We also developed a similar mechanism to upload files as 200-byte commands to SuperBIT. In addition to the downlink and uplink programs, we also created an “autopilot” program to automate observations based on the location, time, and a prioritized list of targets. In this paper, we discuss the communication and observation challenges that were faced and strategies we used to overcome these challenges while operating SuperBIT.
SPIDER is a balloon-borne instrument designed to map the cosmic microwave background at degree-angular scales in the presence of Galactic foregrounds. Spider has mapped a large sky area in the Southern Hemisphere using more than 2000 transition-edge sensors (TESs) during two NASA Long Duration Balloon flights above the Antarctic continent. During its first flight in January 2015, Spider observed in the 95 GHz and 150 GHz frequency bands, setting constraints on the B-mode signature of primordial gravitational waves. Its second flight in the 2022-23 season added new receivers at 280 GHz, each using an array of TESs coupled to the sky through feedhorns formed from stacks of silicon wafers. These receivers are optimized to produce deep maps of polarized Galactic dust emission over a large sky area, providing a unique data set with lasting value to the field. In this work, we describe the instrument’s performance during SPIDER’s second flight.
The upcoming balloon-borne imaging telescope, GigaBIT, is a three-mirror anastigmat (TMA) system with a 1.35-m primary mirror designed to perform wide-field imaging with diffraction limited resolutions in the near ultraviolet (NUV) over a 0.8-deg field of view. An in-flight alignment procedure is being developed that incorporates many techniques novel to ballooning. First, coarse rigid-body adjustments are accomplished through feedback of combined laser rangefinder and retroreflector measurements between the three mirrors. Next, rigid-body adjustments are accomplished using the field-distortion estimated misalignment of each mirror. Lastly, any residual wavefront error of the entire system is compensated by a deformable primary with a set of force actuators. As every step of the procedure will be automated, significant time reduction can be achieved from hours to mere minutes, saving precious time for scientific observations. This paper details the models and simulation results involved in the steps of the procedure.
In this work we describe upgrades to the Spider balloon-borne telescope in preparation for its second flight, currently planned for December 2021. The Spider instrument is optimized to search for a primordial B-mode polarization signature in the cosmic microwave background at degree angular scales. During its first flight in 2015, Spider mapped ~10% of the sky at 95 and 150 GHz. The payload for the second Antarctic flight will incorporate three new 280 GHz receivers alongside three refurbished 95- and 150 GHz receivers from Spider's first flight. In this work we discuss the design and characterization of these new receivers, which employ over 1500 feedhorn-coupled transition-edge sensors. We describe pre-flight laboratory measurements of detector properties, and the optical performance of completed receivers. These receivers will map a wide area of the sky at 280 GHz, providing new information on polarized Galactic dust emission that will help to separate it from the cosmological signal.
The Probe of Inflation and Cosmic Origins (PICO) is a probe-class mission concept currently under study by NASA. PICO will probe the physics of the Big Bang and the energy scale of inflation, constrain the sum of neutrino masses, measure the growth of structures in the universe, and constrain its reionization history by making full sky maps of the cosmic microwave background with sensitivity 80 times higher than the Planck space mission. With bands at 21-799 GHz and arcmin resolution at the highest frequencies, PICO will make polarization maps of Galactic synchrotron and dust emission to observe the role of magnetic fields in Milky Way's evolution and star formation. We discuss PICO's optical system, focal plane, and give current best case noise estimates. The optical design is a two-reflector optimized open-Dragone design with a cold aperture stop. It gives a diffraction limited field of view (DLFOV) with throughput of 910 cm2sr at 21 GHz. The large 82 square degree DLFOV hosts 12,996 transition edge sensor bolometers distributed in 21 frequency bands and maintained at 0.1 K. We use focal plane technologies that are currently implemented on operating CMB instruments including three-color multi-chroic pixels and multiplexed readouts. To our knowledge, this is the first use of an open-Dragone design for mm-wave astrophysical observations, and the only monolithic CMB instrument to have such a broad frequency coverage. With current best case estimate polarization depth of 0.65 µKCMB-arcmin over the entire sky, PICO is the most sensitive CMB instrument designed to date.
Balloon-borne experiments present unique thermal design challenges, which are a combination of those present for both space and ground experiments. Radiation and conduction are the predominant heat transfer mechanisms with convection effects being minimal and difficult to characterize at 35-40 km. This greatly constrains the thermal design options and makes predicting flight thermal behaviour very difficult. Due to the limited power available on long duration balloon flights, efficient heater control is an important factor in minimizing power consumption. SuperBIT, or the Super-Pressure Balloon-borne Imaging Telescope, aims to study weak gravitational lensing using a 0.5m modified Dall-Kirkham telescope capable of achieving 0.02" stability1 and capturing deep exposures from visible to near UV wavelengths. To achieve the theoretical stratospheric diffraction-limited resolution of 0.25",2 mirror deformation gradients must be kept to within 20 nm. The thermal environment must be stable on time scales of an hour and the thermal gradients on the telescope must be minimized. During its 2018 test-flight, SuperBIT will implement two types of thermal parameter solvers: one for post-flight characterization and one for in-flight control. The payload has 85 thermistors as well as pyranometers and far-infrared sensors which will be used post-flight to further understand heat transfer in the stratosphere. This document describes the in-flight thermal control method, which predicts the thermal circuit of components and then auto-tunes the heater PID gains. Preliminary ground testing shows the ability to control the components to within 0.01 K.
Balloon-borne astronomy is a unique tool that allows for a level of image stability and significantly reduced atmospheric interference without the often prohibitive cost and long development time-scale that are characteristic of space-borne facility-class instruments. The Super-pressure Balloon-borne Imaging Telescope (SuperBIT) is a wide-field imager designed to provide 0.02" image stability over a 0.5 degree field-of-view for deep exposures within the visible-to-near-UV (300-900 um). As such, SuperBIT is a suitable platform for a wide range of balloon-borne observations, including solar and extrasolar planetary spectroscopy as well as resolved stellar populations and distant galaxies. We report on the overall payload design and instrumentation methodologies for SuperBIT as well as telescope and image stability results from two test flights. Prospects for the SuperBIT project are outlined with an emphasis on the development of a fully operational, three-month science flight from New Zealand in 2020.
The Probe of Inflation and Cosmic Origins (PICO) is a NASA-funded study of a Probe-class mission concept. The toplevel science objectives are to probe the physics of the Big Bang by measuring or constraining the energy scale of inflation, probe fundamental physics by measuring the number of light particles in the Universe and the sum of neutrino masses, to measure the reionization history of the Universe, and to understand the mechanisms driving the cosmic star formation history, and the physics of the galactic magnetic field. PICO would have multiple frequency bands between 21 and 799 GHz, and would survey the entire sky, producing maps of the polarization of the cosmic microwave background radiation, of galactic dust, of synchrotron radiation, and of various populations of point sources. Several instrument configurations, optical systems, cooling architectures, and detector and readout technologies have been and continue to be considered in the development of the mission concept. We will present a snapshot of the baseline mission concept currently under development.
We describe 280 GHz bolometric detector arrays that instrument the balloon-borne polarimeter spider. A primary science goal of spider is to measure the large-scale B-mode polarization of the cosmic microwave background (cmb) in search of the cosmic-inflation, gravitational-wave signature. 280 GHz channels aid this science goal by constraining the level of B-mode contamination from galactic dust emission. We present the focal plane unit design, which consists of a 16x16 array of conical, corrugated feedhorns coupled to a monolithic detector array fabricated on a 150 mm diameter silicon wafer. Detector arrays are capable of polarimetric sensing via waveguide probe-coupling to a multiplexed array of transition-edge-sensor (TES) bolometers. The spider receiver has three focal plane units at 280 GHz, which in total contains 765 spatial pixels and 1,530 polarization sensitive bolometers. By fabrication and measurement of single feedhorns, we demonstrate 14.7° FHWM Gaussian-shaped beams with <1% ellipticity in a 30% fractional bandwidth centered at 280 GHz. We present electromagnetic simulations of the detection circuit, which show 94% band-averaged, single-polarization coupling efficiency, 3% reflection and 3% radiative loss. Lastly, we demonstrate a low thermal conductance bolometer, which is well-described by a simple TES model and exhibits an electrical noise equivalent power (NEP) = 2.6 x 10-17 W/√Hz, consistent with the phonon noise prediction.
We present the results of integration and characterization of the Spider instrument after the 2013 pre-flight campaign. Spider is a balloon-borne polarimeter designed to probe the primordial gravitational wave signal in the degree-scale B-mode polarization of the cosmic microwave background. With six independent telescopes housing over 2000 detectors in the 94 GHz and 150 GHz frequency bands, Spider will map 7.5% of the sky with a depth of 11 to 14 μK•arcmin at each frequency, which is a factor of ~5 improvement over Planck. We discuss the integration of the pointing, cryogenic, electronics, and power sub-systems, as well as pre-flight characterization of the detectors and optical systems. Spider is well prepared for a December 2014 flight from Antarctica, and is expected to be limited by astrophysical foreground emission, and not instrumental sensitivity, over the survey region.
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.
We introduce the light-weight carbon fiber and aluminum gondola designed for the Spider balloon-borne telescope. Spider is designed to measure the polarization of the Cosmic Microwave Background radiation with unprecedented sensitivity and control of systematics in search of the imprint of inflation: a period of exponential expansion in the early Universe. The requirements of this balloon-borne instrument put tight constrains on the mass budget of the payload. The Spider gondola is designed to house the experiment and guarantee its operational and structural integrity during its balloon-borne flight, while using less than 10% of the total mass of the payload. We present a construction method for the gondola based on carbon fiber reinforced polymer tubes with aluminum inserts and aluminum multi-tube joints. We describe the validation of the model through Finite Element Analysis and mechanical tests.
KEYWORDS: Digital signal processing, Control systems, Servomechanisms, Telescopes, Actuators, Gyroscopes, Sensors, Electroluminescence, Computer programming, Polarization
We present the technology and control methods developed for the pointing system of the Spider experiment. Spider is a balloon-borne polarimeter designed to detect the imprint of primordial gravitational waves in the polarization of the Cosmic Microwave Background radiation. We describe the two main components of the telescope’s azimuth drive: the reaction wheel and the motorized pivot. A 13 kHz PI control loop runs on a digital signal processor, with feedback from fibre optic rate gyroscopes. This system can control azimuthal speed with < 0.02 deg/s RMS error. To control elevation, Spider uses stepper-motor-driven linear actuators to rotate the cryostat, which houses the optical instruments, relative to the outer frame. With the velocity in each axis controlled in this way, higher-level control loops on the onboard flight computers can implement the pointing and scanning observation modes required for the experiment. We have accomplished the non-trivial task of scanning a 5000 lb payload sinusoidally in azimuth at a peak acceleration of 0.8 deg/s2, and a peak speed of 6 deg/s. We can do so while reliably achieving sub-arcminute pointing control accuracy.
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.
Here we describe the design and performance of the SPIDER instrument. SPIDER is a balloon-borne cosmic
microwave background polarization imager that will map part of the sky at 90, 145, and 280 GHz with subdegree
resolution and high sensitivity. This paper discusses the general design principles of the instrument inserts,
mechanical structures, optics, focal plane architecture, thermal architecture, and magnetic shielding of the TES
sensors and SQUID multiplexer. We also describe the optical, noise, and magnetic shielding performance of the
145 GHz prototype instrument insert.
We describe the cryogenic system for SPIDER, a balloon-borne microwave polarimeter that will map 8% of the
sky with degree-scale angular resolution. The system consists of a 1284 L liquid helium cryostat and a 16 L
capillary-filled superfluid helium tank, which provide base operating temperatures of 4 K and 1.5 K, respectively.
Closed-cycle 3He adsorption refrigerators supply sub-Kelvin cooling power to multiple focal planes, which are
housed in monochromatic telescope inserts. The main helium tank is suspended inside the vacuum vessel with
thermally insulating fiberglass flexures, and shielded from thermal radiation by a combination of two vapor
cooled shields and multi-layer insulation. This system allows for an extremely low instrumental background and
a hold time in excess of 25 days. The total mass of the cryogenic system, including cryogens, is approximately
1000 kg. This enables conventional long duration balloon flights. We will discuss the design, thermal analysis,
and qualification of the cryogenic system.
We describe SPIDER, a balloon-borne instrument to map the polarization of the millimeter-wave sky with degree
angular resolution. Spider consists of six monochromatic refracting telescopes, each illuminating a focal plane
of large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting transition-edge sensors are
distributed among three observing bands centered at 90, 150, and 280 GHz. A cold half-wave plate at the
aperture of each telescope modulates the polarization of incoming light to control systematics. SPIDER's first
flight will be a 20-30-day Antarctic balloon campaign in December 2011. This flight will map ~8% of the sky to
achieve unprecedented sensitivity to the polarization signature of the gravitational wave background predicted
by inflationary cosmology. The SPIDER mission will also serve as a proving ground for these detector technologies
in preparation for a future satellite mission.
We present a method of cross-calibrating the polarization angle of a polarimeter using Bicep Galactic observations.
Bicep was a ground based experiment using an array of 49 pairs of polarization sensitive bolometers
observing from the geographic South Pole at 100 and 150 GHz. The Bicep polarimeter is calibrated to ±0.01
in cross-polarization and less than ±0.7° in absolute polarization orientation. Bicep observed the temperature
and polarization of the Galactic plane (R.A = 100° ~ 270° and Dec. = -67° ~ -48°). We show that the
statistical error in the 100 GHz Bicep Galaxy map can constrain the polarization angle offset of Wmap W band
to 0.6° ± 1.4°. The expected 1σ errors on the polarization angle cross-calibration for Planck or EPIC are 1.3°
and 0.3° at 100 and 150 GHz, respectively. We also discuss the expected improvement of the Bicep Galactic
field observations with forthcoming Bicep2 and Keck observations.
Spider is a balloon-borne array of six telescopes that will observe the Cosmic Microwave Background. The 2624
antenna-coupled bolometers in the instrument will make a polarization map of the CMB with approximately
one-half degree resolution at 145 GHz. Polarization modulation is achieved via a cryogenic sapphire half-wave
plate (HWP) skyward of the primary optic. We have measured millimeter-wave transmission spectra of the
sapphire at room and cryogenic temperatures. The spectra are consistent with our physical optics model, and
the data gives excellent measurements of the indices of A-cut sapphire. We have also taken preliminary spectra of
the integrated HWP, optical system, and detectors in the prototype Spider receiver. We calculate the variation
in response of the HWP between observing the CMB and foreground spectra, and estimate that it should not
limit the Spider constraints on inflation.
BICEP2/SPUD is the new powerful upgrade of the existing BICEP1 experiment, a bolometric receiver to study the
polarization of the cosmic microwave background radiation, which has been in operation at the South Pole since January
2006. BICEP2 will provide an improvement up to 10 times mapping speed at 150 GHz compared to BICEP1, using the
same BICEP telescope mount. SPUD, a series of compact, mechanically-cooled receivers deployed on the DASI mount
at the Pole, will provide similar mapping speed in to BICEP2 in three bands, 100, 150, and 220 GHz. The new system
will use large TES focal plane arrays to provide unprecedented sensitivity and excellent control of foreground
contamination.
Bicep is a ground-based millimeter-wave bolometric array designed to target the primordial gravity wave signature
on the B-mode polarization of the cosmic microwave background (CMB) at degree angular scales. Currently
in its third year of operation at the South Pole, Bicep is measuring the CMB polarization with unprecedented
sensitivity at 100 and 150 GHz in the cleanest available 2% of the sky, as well as deriving independent constraints
on the diffuse polarized foregrounds with select observations on and off the Galactic plane. Instrument
calibrations are discussed in the context of rigorous control of systematic errors, and the performance during the
first two years of the experiment is reviewed.
Spider is a balloon-borne experiment that will measure the polarization of the Cosmic Microwave Background
over a large fraction of a sky at ~ 1° resolution. Six monochromatic refracting millimeter-wave telescopes with
large arrays of antenna-coupled transition-edge superconducting bolometers will provide system sensitivities of
4.2 and 3.1 μKcmb√s at 100 and 150 GHz, respectively. A rotating half-wave plate will modulate the polarization
sensitivity of each telescope, controlling systematics. Bolometer arrays operating at 225 GHz and 275 GHz will
allow removal of polarized galactic foregrounds. In a 2-6 day first flight from Alice Springs, Australia in 2010,
Spider will map 50% of the sky to a depth necessary to improve our knowledge of the reionization optical depth
by a large factor.
We describe SPIDER, a novel balloon-borne experiment designed to measure the polarization of the Cosmic Microwave Background (CMB) on large angular scales. The primary goal of SPIDER is to detect the faint signature of inflationary gravitational waves in the CMB polarization. The payload consists of six telescopes, each operating in a single frequency band and cooled to 4 K by a common LN/LHe cryostat. The primary optic for each telescope is a 25 cm diameter lens cooled to 4 K. Each telescope feeds an array of antenna coupled, polarization sensitive sub-Kelvin bolometers that covers a 20 degree diameter FOV with diffraction limited resolution. The six focal planes span 70 to 300 GHz in a manner optimized to separate polarized galactic emission from CMB polarization, and together contain over 2300 detectors. Polarization modulation is achieved by rotating a cryogenic half-wave plate in front of the primary optic of each telescope. The cryogenic system is designed for 30 days of operation. Observations will be conducted during the night portions of a mid-latitude, long duration balloon flight which will circumnavigate the globe from Australia. By spinning the payload at 1 rpm with the six telescopes fixed in elevation, SPIDER will map approximately half of the sky at each frequency on each night of the flight.
We have developed a bolometric receiver that is intrinsically sensitive to linear polarization for the purpose of making measurements of the polarization of the cosmic microwave background radiation. The receiver consists of a pair of co-located silicon nitride micromesh absorbers which couple anisotropically to linearly polarized radiation through a corrugated waveguide structure. This system allows background limited, simultaneous measurement of the Stokes I and Q parameters over ~30% bandwidths at frequencies from ~60 to 600 GHz. Since both linear polarizations traverse identical optical paths from the sky to the point of detection, the susceptibility of the system to systematic effects is minimized. The amount of uncorrelated noise between the two polarization senses is limited to the quantum limit of thermal and photon shot noise, while drifts in the relative responsivity to orthogonal polarizations are limited to the effect of non-uniformity in the thin film deposition of the leads and the intrinsic thermistor
properties. Devices using NTD Ge thermistors have achieved NEPs of 2•10-17 W/√Hz with 1/f knees below 100mHz at a base temperature of 270 mK. Numerical modelling of the structures has been used to optimize the bolometer geometry and coupling to optics. Comparisons of numerical results and experimental data are made. A description of how the quantities measured by the device can be interpreted in terms of the Stokes parameters is presented. The receiver developed for the Boomerang and Planck HFI focal planes is presented in detail.
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