What propels the sun through the air in the flat earth theory? And what makes it move in a circle? If you throw a rock through the air, it doesn't move in a circle.
Uhm, the firmament is a globe that rotates in a circle around the earth, and the heavenly bodies are in the firmament. And yet you believe (from faith in the scientists) that some magical force causes the planets to circle around the sun.
None of the Globers actually believe in the firmament described by Sacred Scripture, all the Church Fathers, and even St. Thomas Aquinas (who is often cited by Globers in favor of ball earth).
Where's the firmament? Where are the waters (H2O) above said firmament? No, the firmament is not just "space", as Sungenis said. Sacred Scripture clearly describes its properties. It's solid enough to prevent waters from flooding the earth. Nor are these waters above the firmament metaphorical waters, since the account of the Flood explains that gates in the firmament were opened to allow these waters (that contributed to Flood waters) fall down onto the earth.