It's a paper option. So the airline pays a negotiated payment as sort of a down payment on a purchase option at a set price per airframe.
Boom says, I'll sell you X-number of airframes for $150m. United says, I'll give you Y-dollars to secure a rolling option for X-number of airframes at $150m if you can deliver by 2035.
Because Boom has nothing to sell but hope to investors right now, the options are probably extremely cheap. They might be willing to take a loss on the first orders just to secure the funding now and have the orders in the pocket.
It's good for the airline because it gets their name in the paper with the word supersonic next to it and it locked down a price. Even if Boom later decides to price it at $200m per airframe later, the airline has a contracted option at X-number for $150m. It gives Boom a relatively small amount of money up front, and they can tell investors they have pre-orders.
Win-win. Usually. Airlines do it seed technology they want and will use for a relatively very small amount of money up front. They are gambling with their spare change knowing the preorder helps get Boom to the finish line and locks down what is usually a bargain price for purchasing.
If they buy options or a rolling option from Airbus, it's going to be much more expensive, because Airbus is selling a well-defined purchase date or product. From a start up, it's just seed money and a locked in price.
