Earlier quoted context omitted.
Boom were previously targeted a cruising speed of Mach 2.2, I wonder why they lowered it to Mach 1.7 with the latest design update. Might be related selecting an engine. The previous version of the design had a fantasy engine that didn't exist (I think the specs came from a military engine that they couldn't use due to export restrictions), but now they are working with Rolls-Royce, and appear to have actually select…
Supersonic heat also. Concorde was in Aluminum and at 2.1 mach it was at the very limit of what could be done in aluminum. Which required a very "tight" design, engineering marvel in fact. Go faster and one have to go for titanium, which is much more difficult to work with and manufacture.
I heard they put enough fuel in it to take off and get up to temperature and then refueled it in the air for safety reasons.