 While some types are rare, others, such as space shuttle covers, were carried in large numbers, and are thus relatively common, costing less than US$50.Perhaps the most common item of astrophilately is the "STS-8 flight cover".In cooperation with the USPS, the shuttle flight STS-8 carried several hundred thousand covers, franked with $9.35 express mail stamps, which were then sold to the public after the shuttle's return.