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There have been air-to-air missiles using rocket-ramjet combinations: they start as a rocket, then once up to speed an inlet opens and they transition to ramjet mode (using the same chamber and nozzle). It extends range. Ramjets are best for maintaining speed rather than accelerating to speed.

EDIT: I see this was referenced above (Meteor).

My take is also a missile, but as an interceptor, not offensive purposes. North Korea has shown that they can deliver a payload to Japan if they want. If the NKs do decide to launch something at Japan, it's not going to be tipped with conventional explosives. It'll be a nuke. Hypersonic interceptor seems the more likely application is this tech to me.

judging by what we saw so far in Russia, Ukraine, and Israel, defensive missiles don't require particularly sophisticated offensive missiles to overwhelm.

I find fast missiles with AI to be pretty scary. Heck a slow drone with AI targeting chasing me is bad enough...

Well here's an economic application without nuclear tipped warheads.

https://en.wikipedia.org/wiki/Meteor_(missile)

It can be nuclear powered, so you don't have CO2 emmisions /S

You just need to add heat to the air at the point where the diameter is the lowest.

The russians are maybe using this idea for one of their new cruise missles named Burevestnik, although for them the nuclear emmisions are likely a positive side effect.

> Is a Mach-5 passenger aircraft actually the goal of this project? > Seems more likely that Japan is designing this engine for a hypersonic cruise missile program, and the passenger aircraft concept is somewhat of a cover.

Case of China's got them, and can't rely on the Orange Emperor and his heirs to have their backs.

> (not that we have ever made them commercially viable)

Concorde was commercially viable at Mach 2.2 in supercruise (although there's a common misconception that it was not).

However, its overheads were very high, and its applicability was severely limited by fears around the sonic boom (most particularly in the US, which banned supersonic flight overland, possibly largely because they wanted to kill off foreign competition).

Air breathing engines don't need the oxidizer tank, so like the 2/3 of a rocket just goes away before even touching Tsiolkovsky math. That improves payload mass fraction massively.

Also, this doesn't scale down to Mach 3-4 and under. This thing uses scramjet, or supersonic combustion ramjet. It REQUIRES intake air to be at high supersonic speeds for it to work.

Japan, Italy and UK have a program for a competing F35 design, GCAP. And Japan is focusing mainly on the engines.

Given there will at some point be the need to deliver competing cruise missiles for this platform, and after the crisis of the US not being able to keep demand with Israel's and Ukraine's orders they greenlighted SK and Japan to enter the European defense market, to answer your question yes, this is of course a defense related project.

There's been an industry request to develop native defense components on these matters within the EU following pressures and contrasts with the US (on a report to the EC for the ReArm campaign, EU's biggest playes of aerespace industry made a joint report estimating 60-80% of their components and tech are sourced from the US).

> you might as well just switch to a suborbital hop concept.

One is not exclusive to the other.

Skylon was expected to use air breathing engine up to Mach5+ and switch to rocket engine beyond it.

You can probably do the same for a suborbital airliner if you are insane enough.

90 minutes is a full low Earth orbit cycle. For a suborbital hop it should be about half of that at maximum for any 2 points on Earth.

As I understand, the problem with anything over Mach 4 (or 5), the metal begins to disintegrate. It is fine for a one way missile, but not a reusuable aircraft. Without some alien tech (see 1990s game "X-Com 2"), I cannot believe that we can build a reusuable aircraft that can reliably and safely fly for long periods over Mach 5.

Ramjets are limited in the speed they can operate because slowing the air to subsonic speed in the engine causes it to become hot, and the temperature increases rapidly with speed (the kinetic energy of an incoming air parcel is proportional to the square of the vehicle's speed, and most of that energy is being converted to heat.)

It is a safe bet that the first applications will be missiles and there won't be any passengers to worry about.

I may be wrong but I think a ramjet doesn't need Mach 5 to ignite, Mach 3 to 6 is just where it is most efficient at high altitudes.

E.g. early German experiments during WW2 based on the Lorin tube (https://en.wikipedia.org/wiki/Ren%C3%A9_Lorin) only had to get to 320 km/h to start working:

https://en.wikipedia.org/wiki/Kronach_Lorin

> Hindenburg 2.0 waiting to happen

Fortunately there's no hydrogen in that plane.

We have a lot of experience with heat shields from cosmic reentries now, though. This is probably doable.

How long of a weightlessness period does this entail?

Wait 20 years to save a few hours :)

I’d love to have a big die cast model of one, but that’s about as close as we’ll ever get to the Avro flying again.

I don’t think you’d be pushing much freight on an Arrow (though I’d love to fly one!).

An XB-70 with modern engines? Now that would be interesting.

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that headline uses a subjunctive verb mood "_could_ <verb>" and those titles are seemingly always clickbait

I don't have a good intuitive feel for that.

At 25km altitude, with 1% of normal atmosphere, maybe you're close enough to vacuum that it can get really quiet?

I think a lot of the Concorde failure is tied to its status as a British-French project. Trans-Pacific flights are much longer and there's a lot of money in PEK -> LAX than in JFK -> LHR.

Qantas wanted to offer London to Sydney, but they couldn't fly supersonic over land. Mainland China or Japan to Australia is a feasible route for high-margin, low-capacity supersonic flights.

If you could make the flight from Beijing to California take less than 5 hours that seems like a premium product many ultra wealthy people would spring for. Dubai to SFO is also a possible route.

Concord was very old technology. I am quite sure a clean sheet now

1. Would have much lower sonic booms thanks to recent research (quite a bit of it by NASA on wing geometry) and more importantly computer simulation available now

2. The engines would be far more fuel efficient

3. The flights would be able to have better efficiency in the subsonic regime as well. Just see what winglets and the like have done to fuel economy .

I fly 14 to 18 hour routes maybe 4-5 times a year on business paying 5x the economy cost and it still sucks. Breaking the flight with a connection (IMO) sucks more. My management flies such routes every month. There is a lot of revenue headroom in that fare gap for something that flies maybe 3x-4x as fast which military aircraft already do.

What will hold back the idea is conservatism among the business managers in aircraft manufactures and incumbent airlines who will "draw lessons" from a 50 year old experiment

Vastly more favorable today than it was when Concorde flew.

1) Rich people are WAY richer, and time is even more valuable 2) Businesses have some very important employees and "2 day trip" vs "3-4 day trip" is worth $50-100k 3) Larger population of people able to pay $20-30k for a flight than ever before.

The biggest practical impact is there's probably going to be a private jet version instead of just a commercial one, and there will likely be transpacific demand exceeding transatlantic. Also government/military use.

I think the SpaceX plan for point to point travel might be even more pie in the sky. Or maybe a tie.

> This is as pie-in-the-sky as it gets.

I saw the "sounding rocket" and thought: Oh, hypersonic missiles money.

Probably because there is no plan to develop a commercial plane.

  > This is as pie-in-the-sky as it gets.

It's not bad to ask these questions, but it is easy to be too dismissive. People love to tear things down, but not build them up. The two go hand in hand, but there needs to be a more measured approach. Frankly, projects can fail for many reasons. Too often it is simply bad luck. You either learn from the past or you repeat it.

[0] https://en.wikipedia.org/wiki/Globalstar

[1] https://www.cnet.com/tech/services-and-software/google-glass...

Whenever you look at supersonic or hypersonic commercial aircraft plans you should assume one of two things.

A. It's a bait and switch by a founder who wants to pivot to weapons/military aircraft but wants to be able to hire high grade talent without paying the "we're gonna kill people" premium, can pivot once a good chunk of the workforce is complacent with a paycheck. You laugh but this happens SO FUCKING MUCH.

B. It's for business jet scale operations for billionaires. There are >3000 billionaires and however many corporate aviation departments and if you can build a super/hypersonic private jet that's not horribly expensive to operate the "time savings"* for that class of person will demand they buy one.

* when I say time savings I mean dick measuring contest

Safety should probably also be considered.

“Roger ramjet he’s our man, hero of the nation!!

https://m.youtube.com/watch?v=E7SqSNQeAFM

Yes it looks a lot more cheesy now than I remember as a kid

https://youtu.be/SpEO-jIKhE8?si=89Qw1_AOXYow9PfR

But ramjets have been promised to us for years

Supposedly the SR-72 has figured this out. Just rumours at this point, but apparently they’ve cracked the hypersonic air breathing puzzle on a usefully sized aircraft.

We just didn‘t have enough billionaires back then. Today the Thiels and Musks and Bezos will be able to afford this.

Next generation of. The Type 25 HVGP just entered service few months ago. That one is just a two-stage Scud, but the Block 3 or NG or Type 35 or whatever of that could have this tech.

The world's elites have factored in global warming already. It's a cost they are happy to shift onto their descendants.

This is already a solved problem for the class of customers they are going after.

And the time wasted on transfers. I used to regularly fly from airports in NY, London, SF, Singapore, LA, Sydney, etc. I would block out the opportunities to work or rest, and the reality was that only the plane time was valuable for either. It was painful to see all the other blocks of non productive time, particularly the allowances for congestion and disruption between downtown and the airports. I would have paid thousands a flight to be able to check in/clear security at my hotel and then get driven to a holding bay at the airport, and then on to the gate, in a vehicle suitable for both work and rest.

Really? Obviously it varies by country, but there’s no customs/immigration when leaving the US, and security usually takes <5 minutes with PreCheck. Sometimes immigration takes a while on the other side, but it’s quick at airports with biometric gate systems. You still hear people talk about airport buffer time in units of hours, but I think that’s increasingly out of date.

Not necessarily for extremely long haul flights. The airport side of things takes about the same amount of time regardless. For a transpacific flight, you’re looking at maybe 3-4 hours at the airport and 10+ hours in the air. Shaving down the airport side would be nice but a faster plane could save a lot more time.

This is a solved problem in civilized countries. The time between arriving at an airport and boarding your plane in Japan is ~10 minutes, most of it walking. Because they don't spend an hour fucking around with clownshow security, and because boarding doesn't take forever, as people don't try to stuff ten pieces of carry-on luggage into five overhead bin spaces.

Customs always takes time, though, even in the happy (no extra questions, no bag searches) path.

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Do you want to know the secret to fast security lines?

Either reduce the work security does, or open more lines and hire more agents[1], until they can meet the throughput requirements. Both seem to be anathema to an American airport.

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[1] This also works to reduce lines and improve quality and cleanliness in other aspects of society. It's not that Japanese people don't produce any garbage, or dirt, it's that their public infrastructure is regularly and meticulously cleaned and maintained.

Or have their own room in first class... Maybe time trade off isn't worth it for most of the people who can afford it at that point.

Building a ramjet that is more efficient than rockets while travelling at several times the speed of sound is the easy part. The hard part is getting up to that speed first, because they give basically no thrust at low speeds. So you always need a two component engine and fuel system, with each component being useless at either launch or in-flight. Basically a similar reason why only the military uses VTOL planes. The military has no problem strapping a rocket booster on a ramjet missile.