  SPIDER is a balloon-borne instrument designed to map the polarization of the
millimeter-wave sky at large angular scales. SPIDER targets the B-mode
signature of primordial gravitational waves in the cosmic microwave background
(CMB), with a focus on mapping a large sky area with high fidelity at multiple
frequencies. SPIDER's first longduration balloon (LDB) flight in January 2015
deployed a total of 2400 antenna-coupled Transition Edge Sensors (TESs) at 90
GHz and 150 GHz. In this work we review the design and in-flight performance of
the SPIDER instrument, with a particular focus on the measured performance of
the detectors and instrument in a space-like loading and radiation environment.
SPIDER's second flight in December 2018 will incorporate payload upgrades and
new receivers to map the sky at 285 GHz, providing valuable information for
cleaning polarized dust emission from CMB maps.
