You could say because they are both spacecraft. However, the right answer is that they are both made of ceramics. Saucers are made of ceramic material called porcelain, and the space shuttle is covered with ceramic tiles that resist the intense heat of re-entry into the Earth’s atmosphere.
Ceramics are materials like pottery. They are made of substances such as clay that can first be shaped and then heated to high temperatures to make them rigid. This is a simple way of producing plates, cups and saucers, but ceramics have other useful features. Although brittle, they strongly resist heat, which is why ceramic tiles line furnaces as well as space shuttles. They also resist electricity, and so are used to make insulators and sparking plugs.