4 ms·

Has anybody even demonstrated a mach-9 air-breathing vehicle of any kind that has gone this distance? Afaik, the only things that go this fast are ICBM warheads

Has anybody even demonstrated a mach-9 air-breathing vehicle of any kind that has gone this distance? Afaik, the only things that go this fast are ICBM warheads and gliders. The only thing that comes close would be the X-15, but that was powered by rocket motors and was essentially fully rebuilt after each flight. The X-51 did a short flight on SCRAMJET power, but I doubt that would scale up to a passenger vehicle.

loloquwowndueo 3y ago
Not air breathing. From TFA: Stargazer will take off with conventional jet engines, but then transition to rockets once it reaches altitude.
- wkat4242 3y ago
  To be fair, at the attitude this will fly there won't be enough air for it to breathe anyway.
  - wkat4242 3y ago
    ^ should have said altitude :) Too late to edit the post
- yabones 3y ago
  Yeah, very true, I missed that the first time I opened the page. Honestly that makes this idea even more insane. Jet engines are hundreds or thousands of times more fuel efficient than rocket engines, can run for days at a time, and most importantly doesn't have to carry its oxidizer onboard. Rocket engines (rather, large ones) run for minutes at a time and have to carry all fuel and oxygen - to run a rocket for an hour, you'd need an absolutely absurd fuel tank the size of a building. The guys who designed this are obviously smart, much smarter than me, but it's clear that they've taken some 'creative liberties' to design the concept. My suspicion is that the real product here is the rotational-detonation-engine, the entire "hypersonic passenger vehicle" is just a flashy sales pitch to drive investment & hype towards the development of a genuinely innovative engine that otherwise wouldn't have this amount of funding poured into it.
H8crilA 3y ago
The fastest "real aircraft" was the SR-71, and it was already ridiculously expensive to keep it running at just above Mach 3. The program was cancelled due to costs, too expensive for what it was providing in the age of cheaper and better satellites. We (as in humans) couldn't even keep the expensive Concorde going, and the Concorde was delivered free of charge to British Airways and Air France. This project is just a wild dream.
- micah94 3y ago
  It's ridiculous what they had to do to even approach Mach 3. I read the SR-71 would leak fuel during take off and flight. It was intentionally loosely held together. When it went supersonic the metal would basically melt shut. Would like to know how the Stargazer folks have addressed this. Have they built it out of one solid piece of metal like a UFO?
hajile 3y ago
Scramjets don't even become operational until mach 5. How would they get this plane off the ground in the first place? The logical answer is a combined-cycle engine, but there are slim pickings here. The X-43 used a combined-cycle rocket/scramjet, but had to be dropped from a B-52. It did hit around Mach 9.6 though The Chimera engine is a turbojet/ramjet engine under active development (it or something similar is likely going to power the NGAD), but it most likely won't go faster than Mach 5-6. They aren't considering a couple important realities though. First, the US government isn't letting advanced engines get put into civilian airplanes. There's just too great a risk of them falling into Chinese or Russian hands and giving their fighter programs a massive leap forward. Second, physics aren't in their favor. A large passenger plane means lots of air resistance and lots of weight. Getting all that moving at Mach 2 in the Concorde was a huge task on its own. Moving up to Mach 9 increases the number of issues exponentially. It takes decades to get this working with a tiny plane (eg, all the NASA experiments). The time to scale that up would be even more. Third, there is ZERO economic possibilities here. The total SR-71+A-12 development costs have been estimated at around $16.5B dollars not to mention $200k per hour to fly. Let's say this company makes 100 of these planes at a similar cost (despite them being much more exotic and larger than the SR-71). The planes will cost $165M each and probably only hold less than 30 passengers/crew. If they are selling 25 tickets and flying that 1-hour flight at $200k/hr, tickets would cost $8,000 just to cover operating expenses. If they expect 20,000 flight hours per plane, that's an additional $8,250 per ticket. I'd guess minimum ticket price would be about $25,000 using these numbers. But in reality, there's not a market for 100 of these planes. The R&D costs would probably be much higher and the cost per flight hour would certainly be massively higher too. It's all snake oil.
entropicgravity 3y ago
Starship will be able to do about the same but with more passengers and spending a small percentage of the trip in the atmosphere.

loloquwowndueo 3y ago

Not air breathing. From TFA: Stargazer will take off with conventional jet engines, but then transition to rockets once it reaches altitude.

wkat4242 3y ago
To be fair, at the attitude this will fly there won't be enough air for it to breathe anyway.
- wkat4242 3y ago
  ^ should have said altitude :) Too late to edit the post
yabones 3y ago
Yeah, very true, I missed that the first time I opened the page. Honestly that makes this idea even more insane. Jet engines are hundreds or thousands of times more fuel efficient than rocket engines, can run for days at a time, and most importantly doesn't have to carry its oxidizer onboard. Rocket engines (rather, large ones) run for minutes at a time and have to carry all fuel and oxygen - to run a rocket for an hour, you'd need an absolutely absurd fuel tank the size of a building. The guys who designed this are obviously smart, much smarter than me, but it's clear that they've taken some 'creative liberties' to design the concept. My suspicion is that the real product here is the rotational-detonation-engine, the entire "hypersonic passenger vehicle" is just a flashy sales pitch to drive investment & hype towards the development of a genuinely innovative engine that otherwise wouldn't have this amount of funding poured into it.

H8crilA 3y ago

The fastest "real aircraft" was the SR-71, and it was already ridiculously expensive to keep it running at just above Mach 3. The program was cancelled due to costs, too expensive for what it was providing in the age of cheaper and better satellites. We (as in humans) couldn't even keep the expensive Concorde going, and the Concorde was delivered free of charge to British Airways and Air France. This project is just a wild dream.

micah94 3y ago
It's ridiculous what they had to do to even approach Mach 3. I read the SR-71 would leak fuel during take off and flight. It was intentionally loosely held together. When it went supersonic the metal would basically melt shut. Would like to know how the Stargazer folks have addressed this. Have they built it out of one solid piece of metal like a UFO?

hajile 3y ago

Scramjets don't even become operational until mach 5. How would they get this plane off the ground in the first place? The logical answer is a combined-cycle engine, but there are slim pickings here. The X-43 used a combined-cycle rocket/scramjet, but had to be dropped from a B-52. It did hit around Mach 9.6 though The Chimera engine is a turbojet/ramjet engine under active development (it or something similar is likely going to power the NGAD), but it most likely won't go faster than Mach 5-6. They aren't considering a couple important realities though. First, the US government isn't letting advanced engines get put into civilian airplanes. There's just too great a risk of them falling into Chinese or Russian hands and giving their fighter programs a massive leap forward. Second, physics aren't in their favor. A large passenger plane means lots of air resistance and lots of weight. Getting all that moving at Mach 2 in the Concorde was a huge task on its own. Moving up to Mach 9 increases the number of issues exponentially. It takes decades to get this working with a tiny plane (eg, all the NASA experiments). The time to scale that up would be even more. Third, there is ZERO economic possibilities here. The total SR-71+A-12 development costs have been estimated at around $16.5B dollars not to mention $200k per hour to fly. Let's say this company makes 100 of these planes at a similar cost (despite them being much more exotic and larger than the SR-71). The planes will cost $165M each and probably only hold less than 30 passengers/crew. If they are selling 25 tickets and flying that 1-hour flight at $200k/hr, tickets would cost $8,000 just to cover operating expenses. If they expect 20,000 flight hours per plane, that's an additional $8,250 per ticket. I'd guess minimum ticket price would be about $25,000 using these numbers. But in reality, there's not a market for 100 of these planes. The R&D costs would probably be much higher and the cost per flight hour would certainly be massively higher too. It's all snake oil.

entropicgravity 3y ago

Starship will be able to do about the same but with more passengers and spending a small percentage of the trip in the atmosphere.