Still getting ready to break the sound barrier

"How fast will Baumgarter need to go to beat the speed of sound?
Sound travels at different speeds through the atmosphere (as well as through
different mediums), depending on atmospheric density and temperature. For
example, at sea level, in average conditions of about 15 degrees C (59 degrees
F), sound travels at around 1,223 kph (760 mph). But at higher altitudes, where
the air is colder, sound travels more slowly."

Thanks to Ken.