Is pax SST on the verge of making a comeback?
 

If they can succeed with a supersonic biz jet, then it's a possibility for pax airliners. An SST renaissance depends on both noise reduction and regulatory cooperation, as the video pointed out. The new technology (developed by private and government research) looks to be pretty good, but public opinion and politics will get a vote too before it's all said and done.

But for high-end biz jets it just has to be safe, reliable, and slightly cheaper to acquire and operate than the space shuttle.

An airliner will have higher economic hurdles... the vast majority of people who can afford to spend tens of thousands of dollars to save a few hours already fly private anyway. But if they can get operating costs and ticket prices down to a reasonable level, then of course there would be opportunity... maybe even lure some premium pax back from private aviation.

Also climate optics carry a lot more weight for regulators and operators of very public and visible airline aircraft. Easier to get away with gas guzzling for a few private jets (especially since the climate elite will own or fly on them anyway).

Boom is biting off a big chunk IMO, but if the other two pave the regulatory path with bizjets that could set them up for future growth (with low-boom modifications).

I doubt it. Going faster burns more fuel. Even if you make up time, you are still burning a lot more fuel to do it and therefore your costs end up being a lot higher, even if you can get more flights in. You'd have to be breaking some rules of physics and aerodynamics to make this a thing in my opinion. Ultimately efficiency and revenue vs. operating costs is what businesses look for. Private jets can cater to what select people want. Airlines have to cater to the masses.

There is some cake & eat it too effect with higher altitudes... thinner air so less drag. So increased fuel burn in a supersonic jet is typically offset by reduced drag available at higher cruise altitudes.

You need more speed to generate lift up high so faster plane can fly higher, but the upper speed limit is determined by aerodynamic design (mach tuck for subsonic airliners) and/or aerodynamic heating for supersonic jets. If you go really fast, engine inlet flow becomes another problem, but this isn't that.

As for economics, I mostly agree about airliners but there might be a big enough niche market of people willing to pay first-class like fares to cross the pond in the time it takes to read the WSJ. Especially if SST bizjets pave the way. Also worth noting that DoD has moved the technology ball down range quite a bit (for their own purposes of course). Supercruise, reduced noise signature and reduced fuel burn are all valuable to the mil, and representative aircraft are in operational service today.

IIRC, the Concorde had roughly similar specific range at best subsonic and supersonic speeds. LRC, subsonic, was something like .90-.95 at F#90-F350. Of course, supersonic, it was M2 in a block in the mid-50s

True, but you have to get there first too, as in climb and tanker that fuel to where you can use it most efficiently, which makes the plane horribly inefficient in other realms. SR-71 taking off so it could immediately refuel. A lot more has to be designed into the plane to mitigate the heat generated, etc. None of these are insurmountable if your goal is just to go supersonic and carry passengers. But to do it efficiently so it makes money...I have yet to be convinced.

I view Passenger SSTs in the same bucket as Electrical powered airliners.

The companies in these spaces seem to excel in getting press via social and mainstream media. They have all kinds of snazzy computer renderings. Their time-horizons seem to always be around "five years to carrying passengers."

They are also woefully short on any kind of corporate pedigree for bringing aircraft to market. Beyond that, they always claim to be "this close" to making things work, yet they have very little actual no-kidding flying hardware to show for it.

I dunno. Maybe these companies will have some sort of breakthrough, and I'm just an old curmudgeonly non-believer. But when companies like Gulfstream have poured all kinds of R&D into SSTs over the years, but not pulled the trigger on a production aircraft, I think that tells you something.

Ten years from now, I don't think Aerion or Boom will have produced a single certified passenger aircraft.

At this point I think there will be a biz SST, assuming one of them can build a business case for supersonic only over water. Relying on changing regulations for over-land is a bit iffy, although NASA doing the research certainly lends credibility... THEY apparently think it's worth pursuing.

Maybe.

Hell, remember the "light business jet" trainwreck? Startups left and right thought they'd be selling ~1 million dollar VLJs with Epic seeming to lead the charge at the time. I can't even begin to count how many startups and proposals there were fighting for this vision and expecting to sell thousands of jets. When you looked at it from the outside, it was total insanity. There was no way in hell that market demand would allow for all of these companies to simultaneously be selling all these very small jets.

So yeah, there might be a supersonic business jet, but that economic model is pretty damn precarious and it seems more like the things that dreams are made of, rather than a solid business plan. In other words, I wouldn't expect more than throw-away investment in it and would not count on it surviving, but if it does, that would be pretty neat. Then it has the possibility to spur on competition, but that would be pretty far down the road IMO. Airliners? They hedge on the bottom line and profitability. Not going to see that for a long time unless we have some sort of physics/engine break-through. I agree with the bit about electric airliners too. There might be some electric applications on aviation, but moving people longer distances en-mass requires energy that electricity just won't provide for a long time, long enough that it doesn't make any sense to be making up pie-in-the-sky schemes at that level. Maybe ~300 miles for a climb-to-alt and glide back, and that would still be pretty far off in the future. As problematic as hydrogen is, it will still work better in that application than batteries.

There are I think enough billionaires in the world to create a niche for SST biz jet. Even more so if they achieve the big break-through: regulatory relief for supersonic over land.

Agree about batteries and H2. Batteries can barely work for a small, very shot-range commuter hop, and somebody will do it for the optics if nothing else (actually they're already doing in Vancouver IIRC).

H2 might ultimately be useful for shorter-range narrowbody ops, but specific volume (energy density) is horrible and that's for the denser liquid H2. Reasonably pressurized gaseous H2 is half of liquid H2. But that's a lot of infrastructure and clean-sheet airplane designs for a limited operational niche. Off-hand SAF sesms like a better option, lots of different ways to make and once you have it, it's pretty much a drop-in to existing storage and delivery systems, and also aircraft systems and engines. If it's not as perfectly carbon-neutral as H2, might have to plant some trees or even do carbon capture.