Description of the payload
The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne mission to measure the polarization of the cosmic microwave background (CMB) in search of the signature of primordial gravity waves excited by an inflationary epoch in the early universe.
It is composed by two identical telescopes cooled to 1.5 K within a large (3 meter tall, 3500-liter capacity) liquid helium bucket dewar. There are no windows between the LHe-cooled telescope and the ambient environment: PIPER uses the efflux of boiloff helium gas to prevent the atmosphere at balloon altitudes from condensing on the optics. This technique was first applied in a previous balloon-borne instrument denominated ARCADE. The unusual cryogenic design provides mapping speed a factor of 10 better than any other CMB instrument, allowing PIPER to achieve sensitivities with overnight balloon flights that would otherwise require 10-day flights from other places like Antarctica.
Each of PIPER's twin telescopes illuminates a pair of 32x40 element transition-edge superconducting detector arrays for a total of 5120 detectors. A Variable-Delay Polarization Modulator (VPM) injects a time-dependent phase delay between orthogonal linear polarizations to cleanly separate polarized from unpolarized radiation. The combination of background-limited detectors with fast polarization modulation allows PIPER to rapidly scan large areas of the sky.
Details of the balloon flight and scientific outcome
External references and bibliographical sources