SPIDER (balloon)

SPIDER (balloon)
Name	SPIDER
Mission type	High-altitude balloon-borne telescope
Operator	NASA / Columbia University
Launch mass	~2,000 kg
Payload	Cryogenic receiver, bolometric detectors, sunshield
Launch	2015, 2018
Orbit	Stratospheric balloon
Instruments	Polarimeter, cryostat
Goals	Measure polarization of the Cosmic microwave background

SPIDER (balloon) is a stratospheric, long-duration balloon-borne polarimeter designed to map the polarization of the Cosmic microwave background over large angular scales. Developed by a collaboration led by Caltech, Princeton University, and Columbia University, SPIDER targets the B-mode polarization signature predicted by models of cosmic inflation and gravitational lensing by large-scale structure. The instrument marries cryogenic bolometers, refracting telescopes, and a wide-field gondola to operate above most of the Earth's atmosphere for multi-week flights from Antarctic and mid-latitude launch sites.

Overview

SPIDER was conceived to complement satellite missions such as Planck (spacecraft), ground-based projects like the BICEP2 collaboration, POLARBEAR, and Atacama Cosmology Telescope, and sub-orbital experiments including EBEX and SPTpol. Its balloon platform aims to reduce atmospheric contamination that limits ground observatories at microwave frequencies while offering larger sky coverage than many interferometers. The collaboration includes institutions such as Jet Propulsion Laboratory, University of Chicago, University of California, Berkeley, and Imperial College London, integrating expertise from teams involved in WMAP and COBE.

Design and Instrumentation

The SPIDER payload employs multiple monochromatic refracting telescopes coupled to polarization-sensitive transition-edge sensor bolometers cooled in a large helium-based cryostat. Detectors are read out with multiplexing electronics developed in concert with groups at NIST and University of Minnesota. A rotating half-wave plate provides polarization modulation, similar to techniques used by PIPER and MAXIMA. The gondola architecture draws on heritage from BOOMERanG and BLAST, incorporating star cameras, gyroscopes, and a reaction wheel for pointing control, and an on-board telemetry suite compatible with Iridium and line-of-sight links used by CSBF launches.

Thermal management includes multi-stage refrigeration and vapor-cooled shields derived from designs used on Herschel Space Observatory sub-systems and cryogenic work at Princeton University. The optical chain uses anti-reflection coatings and nylon or polyethylene filters comparable to those in ACTPol and BICEP3, while the focal plane employs antenna-coupled or feedhorn-coupled detectors similar to developments at JPL and SRON.

Scientific Objectives and Results

SPIDER's primary science goal is to detect or constrain primordial B-mode polarization from tensor perturbations generated during inflation (cosmology), parameterized by the tensor-to-scalar ratio r, and to characterize polarized foregrounds such as thermal dust emission traced by Planck (spacecraft) and synchrotron emission studied by WMAP. Secondary objectives include measurements of gravitational lensing B-modes, constraints on cosmic birefringence tested in analyses related to Parity (physics), and cross-correlation studies with surveys like SDSS and DES.

Early flights produced polarization maps that improved upper limits on r at degree angular scales and refined models of polarized dust consistent with analyses by Planck Collaboration and the BICEP2/Keck Array joint papers. SPIDER data contributed to foreground separation techniques employed in joint likelihoods with Keck Array and informed design choices for future satellite concepts proposed to NASA and ESA.

Flights and Mission History

SPIDER's initial engineering flights followed qualification campaigns at Wallops Flight Facility and integration tests with balloon operations run by the Columbia Scientific Balloon Facility. Major long-duration flights launched from McMurdo Station and Antarctic facilities in the austral summer, with campaign coordination involving National Science Foundation (United States) logistics and Antarctic Treaty-system approvals. Flight timelines intersected with campaigns by BOOMERANG and BICEP series instruments, enabling shared calibrators and cross-checks.

Notable flights in the mid-2010s achieved multi-week duration and mapped several percent of the southern sky at frequencies chosen to balance sensitivity to CMB and foregrounds. Instrument upgrades across campaigns—detector count increases, improved filters, and enhanced pointing—paralleled developments made by SPT and ACT teams. Some flights faced typical balloon challenges: stratospheric winds, cryogen boil-off, and recovery operations managed jointly with CSBF and national Antarctic programs.

Data Analysis and Calibration

SPIDER analysis pipelines integrate map-making, time-ordered data filtering, and power-spectrum estimation using techniques developed by the Polarbear collaboration, BICEP/Keck, and Planck teams. Calibration uses celestial sources such as the Crab Nebula (Tau A), planets like Jupiter (planet), and the microwave dipole measured by COBE and WMAP to set polarization angles and gain. Foreground modeling leverages ancillary datasets from Planck (spacecraft), IRAS, and radio surveys conducted by facilities like the VLA and ATCA.

End-to-end simulations employ software tools common to CMB analyses, cross-checked with null tests and jackknife splits as done in joint analyses with Keck Array and BICEP2. Absolute calibration, beam characterization, and transfer functions are derived from in-flight star camera attitude solutions and pre-flight beam-mapping campaigns at sites used by NASA and university partners.

Collaborations and Funding

SPIDER is a multi-institutional collaboration with principal investigators and participating groups at Caltech, Columbia University, Princeton University, University of Toronto, and international partners such as University of Oxford and University of British Columbia. Funding and logistical support have come from agencies and organizations including NASA, the National Science Foundation (United States), institutional grants from participating universities, and instrumentation contributions from national labs like JPL and NIST.

The project has engaged with community consortia and working groups involved in the planning of future CMB missions and ground-based observatories, interacting with panels under NAS decadal surveys and collaborative networks that include teams from European Space Agency-related projects. Ongoing data releases and legacy products aim to support cosmology research by teams involved in surveys such as DESI and the Vera C. Rubin Observatory.

Category:Balloon-borne telescopes