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We describe a low-cost, open-access, CubeSat-based calibration instrument that is designed to support ground-based and sub-orbital experiments searching for various polarization signals in the cosmic microwave background (CMB). All modern CMB polarization experiments require a robust calibration program that will allow the effects of instrument-induced signals to be mitigated during data analysis. A bright, compact and linearly polarized astrophysical source with polarization properties known to adequate precision does not exist. Therefore, we designed a space-based millimeter-wave calibration instrument, called CalSat, to serve as an open-access calibrator, and this paper describes the results of our design study. The calibration source on board CalSat is composed of five “tones” with one each at 47.1, 80.0, 140, 249 and 309GHz. The five tones we chose are well matched to (i) the observation windows in the atmospheric transmittance spectra, (ii) the spectral bands commonly used in polarimeters by the CMB community and (iii) the Amateur Satellite Service bands in the Table of Frequency Allocations used by the Federal Communications Commission. CalSat would be placed in a polar orbit allowing visibility from observatories in the Northern Hemisphere, such as Mauna Kea in Hawaii and Summit Station in Greenland, and the Southern Hemisphere, such as the Atacama Desert in Chile and the South Pole. CalSat also would be observable by balloon-borne instruments launched from a range of locations around the world. This global visibility makes CalSat the only source that can be observed by all terrestrial and sub-orbital observatories, thereby providing a universal standard that permits comparison between experiments using appreciably different measurement approaches.

The development of CubeSats and more frequent launch chances of sounding rockets are a total game changer to the space program, and it allows us to build space instruments that are technologically feasible and affordable. Therefore, it gives us a good opportunity to build a small cosmic-ray detector which has capabilities to measure the flux, direction, and even energy of cosmic rays at an altitude above the limitation of balloon experiments, and it may open a new door for building a constellation of detectors to study cosmic-ray physics. Compact Scintillator Array Detector (ComSAD) is a funded sounding rocket mission of Taiwan’s National Space Organization. In this paper, we present the concept, design, and performance of ComSAD which is also suitable for future CubeSat missions.