Sirius' spacecraft Radiosat 1 through Radiosat 4 were manufactured by Space Systems/Loral. The first three of the series were orbited in 2000 by Proton K Block-DM3 launch vehicles, with the final three-satellite constellation completed on November 30, 2000. Radiosat 4, built as a ground spare for the now-decommissioned elliptical mission, was transferred to the Smithsonian Institution's National Air and Space Museum in October 2012. It is on display at the Steven F. Udvar-Hazy Center. The satellites are based on the Space Systems/Loral 1300 platform. All three satellites broadcast directly to the consumer's receiver, but due to the highly elliptical orbit only two of them broadcast at any given time.