As cosmological measurements increase in precision, foregrounds are increasingly problematic. One foreground that's possible to reduce is Earth's atmosphere. I will talk about experiments that use stratospheric balloons to achieve higher sensitivity and lower systematic errors than are possible on the ground, and at much lower cost than in space.
1. Spider observes the Cosmic Microwave Background (CMB), looking for the faint "B-mode" polarization signature imprinted by primordial gravitational waves. This signal provides a window to the physics of the very early universe, which seeded all the structure we see today.
2. SuperBIT is a 0.5m optical telescope, which uses the balloon platform to achieve diffraction-limited wide-field imaging at wavelengths from 300-1000 nm. SuperBIT will make gravitational lensing measurements of the dark matter in hundreds of galaxy clusters. It will also demonstrate capabilities valuable to future missions.
3. Finally, Taurus is a planned experiment to expand on Spider's capabilities and measure CMB "E-mode" polarization on the largest scales. This lets us check standard cosmology, and enables neutrino mass measurements.
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