28 research outputs found
A high-resolution pointing system for fast scanning platforms: The EBEX example
The E and B experiment (EBEX) is a balloon-borne telescope designed to
measure the polarization of the cosmic microwave background with 8' resolution
employing a gondola scanning with speeds of order degree per second. In January
2013, EBEX completed 11 days of observations in a flight over Antarctica
covering 6000 square degrees of the sky. The payload is equipped with
two redundant star cameras and two sets of three orthogonal gyroscopes to
reconstruct the telescope attitude. The EBEX science goals require the pointing
to be reconstructed to approximately 10" in the map domain, and in-flight
attitude control requires the real time pointing to be accurate to
0.5 . The high velocity scan strategy of EBEX coupled to its float
altitude only permits the star cameras to take images at scan turnarounds,
every 40 seconds, and thus requires the development of a pointing system
with low noise gyroscopes and carefully controlled systematic errors. Here we
report on the design of the pointing system and on a simulation pipeline
developed to understand and minimize the effects of systematic errors. The
performance of the system is evaluated using the 2012/2013 flight data, and we
show that we achieve a pointing error with RMS=25" on 40 seconds azimuth
throws, corresponding to an error of 4.6" in the map domain.Comment: 14 pages, Proceedings of the 2015 IEEE Aerospace Conferenc
Modeling and characterization of the SPIDER half-wave plate
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
On-sky performance of new 90 GHz detectors for the Cosmology Large Angular Scale Surveyor (CLASS)
The Cosmology Large Angular Scale Surveyor (CLASS) is a
polarization-sensitive telescope array located at an altitude of 5,200 m in the
Chilean Atacama Desert and designed to measure the polarized Cosmic Microwave
Background (CMB) over large angular scales. The CLASS array is currently
observing with three telescopes covering four frequency bands: one at 40 GHz
(Q); one at 90 GHz (W1); and one dichroic system at 150/220 GHz (HF). During
the austral winter of 2022, we upgraded the first 90 GHz telescope (W1) by
replacing four of the seven focal plane modules. These new modules contain
detector wafers with an updated design, aimed at improving the optical
efficiency and detector stability. We present a description of the design
changes and measurements of on-sky optical efficiencies derived from
observations of Jupiter.Comment: 5 pages, 3 figures, to appear in the IEEE Transactions on Applied
Superconductivity. arXiv admin note: text overlap with arXiv:2208.0500
The Cosmology Large Angular Scale Surveyor Receiver Design
The Cosmology Large Angular Scale Surveyor consists of four instruments
performing a CMB polarization survey. Currently, the 40 GHz and first 90 GHz
instruments are deployed and observing, with the second 90 GHz and a
multichroic 150/220 GHz instrument to follow. The receiver is a central
component of each instrument's design and functionality. This paper describes
the CLASS receiver design, using the first 90 GHz receiver as a primary
reference. Cryogenic cooling and filters maintain a cold, low-noise environment
for the detectors. We have achieved receiver detector temperatures below 50 mK
in the 40 GHz instrument for 85% of the initial 1.5 years of operation, and
observed in-band efficiency that is consistent with pre-deployment estimates.
At 90 GHz, less than 26% of in-band power is lost to the filters and lenses in
the receiver, allowing for high optical efficiency. We discuss the mounting
scheme for the filters and lenses, the alignment of the cold optics and
detectors, stray light control, and magnetic shielding.Comment: Fixed formatting of abstract; 20 Pages, 11 Figures, SPIE Conference
Proceeding