SPIDER (balloon experiment)

SPIDER (balloon experiment)
Name	SPIDER
Purpose	Observations of the cosmic microwave background polarization
Operator	Caltech, Princeton, Columbia, NASA
Launch site	McMurdo Station
First flight	2015

SPIDER (balloon experiment)

SPIDER is a long-duration, stratospheric balloon-borne instrument designed to measure the polarization of the cosmic microwave background (CMB) across large angular scales. Developed by a consortium led by researchers at Caltech, Princeton University, and Columbia University, SPIDER flew from McMurdo Station in Antarctica to exploit the polar night for extended, stable observations. The project integrates cryogenic detector arrays, precision pointing systems, and microwave optics to probe inflationary signatures and Galactic foregrounds.

Overview

SPIDER was conceived as a follow-up to ground-based efforts such as BICEP2, Keck Array, and POLARBEAR, and as a complementary platform to satellite missions like WMAP and Planck. Its design emphasizes the ability to map degree-scale polarization across wide sky fractions while reducing atmospheric contamination inherent to South Pole and mid-latitude facilities. The science drivers intersect with theoretical work from researchers affiliated with Princeton University, Harvard University, and MIT on inflationary cosmology, and with observational programs at institutions including Caltech, University of Chicago, and Stanford University.

Instrumentation and Design

SPIDER's payload integrates multiple refracting telescopes housed within a shared cryostat developed by engineers at Jet Propulsion Laboratory and NASA Goddard Space Flight Center. Each telescope uses anti-reflection coated polyethylene lenses and a rotating half-wave plate developed with inputs from teams at University of Oxford and University of Cambridge. The focal planes employ superconducting transition-edge sensor (TES) bolometers multiplexed via SQUID readouts produced in collaboration with groups at NIST and University of Colorado Boulder. Pointing and attitude control combine a star camera from Ball Aerospace, gyroscopes influenced by designs at Honeywell, and GPS units similar to hardware used by NOAA ballooning programs. Thermal control and cryogenics leverage expertise from Columbia University and Caltech cryogenics groups to maintain sub-Kelvin operation for the detector arrays during long-duration Antarctic flights.

Scientific Goals and Observations

SPIDER targets the measurement of CMB B-mode polarization produced by primordial gravitational waves predicted by inflationary models formulated by theorists at Princeton University, Institute for Advanced Study, and Stanford University. It also measures lensing B-modes related to large-scale structure work associated with Harvard-Smithsonian Center for Astrophysics and Carnegie Mellon University, and characterizes polarized foregrounds from Galactic dust and synchrotron emission studied by groups at University of California, Berkeley, Max Planck Institute for Astrophysics, and University of Manchester. The experiment observes multiple frequency bands chosen in consultation with teams from NASA and European Space Agency to optimize separation of cosmological signals from emission traced by surveys such as IRAS and instruments like Herschel Space Observatory.

Flights and Operations

SPIDER conducted long-duration balloon flights from McMurdo Station under logistics coordinated with United States Antarctic Program and National Science Foundation support. The first science flight in 2015 followed test flights and integration campaigns at facilities used by Columbia Scientific Balloon Facility and collaborators from University of Toronto and University of British Columbia. Flight operations included daily uplink commands with assistance from teams at JPL and downlinked telemetry compatible with infrastructure used by NOAA and NASA Ames Research Center. Recovery operations involved coordination with New Zealand and Antarctic logistics providers linked to Scott Base and McMurdo Station.

Data Analysis and Results

Data reduction pipelines for SPIDER were developed in collaboration with analysis groups at Princeton University, Caltech, University of Chicago, and Stanford University, using map-making algorithms related to those applied in Planck and BICEP/Keck analyses. Foreground separation employed component-separation techniques informed by work at Max Planck Institute for Radio Astronomy and University of California, Santa Barbara. Early SPIDER results placed constraints on the tensor-to-scalar ratio r, complementing limits from Planck Collaboration and ground-based experiments such as Atacama Cosmology Telescope and South Pole Telescope. The collaboration also produced polarized dust maps relevant to interstellar medium studies led by researchers at University of Colorado Boulder and Caltech.

Collaborations and Funding

SPIDER is a collaboration among institutions including Caltech, Princeton University, Columbia University, University of Toronto, Cardiff University, and Case Western Reserve University, with technical contributions from Jet Propulsion Laboratory, NIST, and Ball Aerospace. Funding and logistical support have been provided by NASA, the National Science Foundation, and institutional grants from participating universities and research councils such as the Royal Society and national agencies analogous to NSERC. International partners and academic groups have contributed expertise in detector fabrication, cryogenics, optics, and data analysis.

Category:Cosmic microwave background experiments Category:Balloon-borne experiments Category:Astronomical instrumentation