My metric for success is simply making more money than they spent.
Supersonic planes are already proven technology. We made the Concorde and the Tu-144 in the 70s, and have plenty of supersonic military planes in active service. The assumption was simply that you can't make a profit by selling them as civil aviation planes. That's the assumption Boom is challenging, and to be proven correct they have to turn a profit. And not just an operating profit by selling planes for more than they cost to make but make back the research and development costs as well
Concorde at least made more money than it cost to operate (and maintain).
The TU-144 made 102 commercial flights, with 55 of those carrying passengers -- the others I assume were cargo.
Not 102 flights per day or month -- 102 flights TOTAL between the first commercial flight in December 1975 and retirement from passenger service in 1978 and from all commercial service in 1983.
With 16 built, that's an average of 6 flights each in their lifetime.
SpaceX has Falcon 9 rocket boosters with 4x as many hypersonic flights on them.
Of course you can exclude them, to determine whether the aircraft themselves are a viable commercial proposition for the people who bought them (the airlines) -- which they were, just as other aircraft such as the A380 today are. The people who bought A380s are happy, and will be using them for decades. Emirates would still like to buy more (and may end up buying used ones from less successful airlines)
The fact that the aircraft manufacturer spent far too much on development relative to the sales they made is of course important to the manufacturer -- or at least to whoever is financing the manufacturer, but that is a DIFFERENT question. In fact more than one question.
There is the question of whether the price they were sold to airlines for was greater or less than the incremental cost to build one aircraft. If the price was greater than the cost then there was some hope for a successful program, and they simply overspent on development and/or didn't sell enough copies.
If they were sold to airlines for less than the marginal cost then it's just an all-around manufacturing screwup that could never be solved by any amount of sales.
Flying fish that are increasingly not sustainably harvested on insanely fuel in-efficient supersonic planes is exactly humanity deserves to go extinct.
Hence why everyone thinks supersonic passenger planes are a bad idea. Lots of profitable military supersonic planes, but every existing example of a civilian supersonic plane is only justified as a Cold War dick-measuring contest.
> And make every government purchase ever, successful?
yes. From the POV of the supplier, every gov't contract is going to be profitable.
That's why the military industrial complex is so big, and profitable. It's why some people go into politics to extend it. Esp. in america.
> How do you measure the profitability of military aircraft?
what you truly meant is how to do you measure the value obtained from a purchase of a military aircraft. And scholars have studied this for centuries and not arrived at a true answer.
Supersonic planes are already proven technology. We made the Concorde and the Tu-144 in the 70s, and have plenty of supersonic military planes in active service. The assumption was simply that you can't make a profit by selling them as civil aviation planes. That's the assumption Boom is challenging, and to be proven correct they have to turn a profit. And not just an operating profit by selling planes for more than they cost to make but make back the research and development costs as well