5 ms·

For a moment, reading only the first paragraph, I was hopeful that the problem of accelerating from subsonic to hypersonic had been solved. Alas, further down i

For a moment, reading only the first paragraph, I was hopeful that the problem of accelerating from subsonic to hypersonic had been solved. Alas, further down it makes clear that a booster was involved. Presumably a small solid rocket that accelerates to Mach 3-5(?) prior to scramjet ignition. Fine for a weapons system but will never be useful as transportation. Is anyone aware of progress toward being able to reach these speeds without disposable boosters? The SR-71 could make Mach 3 on its own but at incredible cost in fuel and complexity.

panick21 5y ago
SpaceX Starship will do this and be fully reusable. Starship can fly long distance with a reusable booster and somewhat shorter distances without a booster. Granted, its not really 'flying' but it does reach the speed needed.
pengaru 5y ago
> The SR-71 could make Mach 3 on its own but at incredible cost in fuel and complexity. the SR-71 never struck me as "incredibly complex", the space shuttle however...
- sonofhans 5y ago
  The J58 powering the SR-71 is still one of the most complex engines ever built. The space shuttle is a simple rocket by comparison. https://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58 https://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58
  - pengaru 5y ago
    And the SR-71 is so simple the complexity falls off a cliff at the engine, hence your inclination to only care about that in comparing the two. The space shuttle is like a reusable mobile space station, airlocks and all. Occupants of the SR-71 wore space suits the entire time, there's a lot of minimalism on display in the SR-71 which is a large part of what makes it so glorious.
    - speedybird 5y ago
      You seem to be suggesting but not outright saying something that is a misconception: The SR-71 did in fact have a pressurized cockpit, which was also air conditioned as well (it had to be, because the aircraft would cook the crew otherwise.) The SR-71 was sophisticated in other ways as well; for instance in having ejection seats. In fact the first four shuttle flights (all Columbia) had ejection seats too and guess where they got those seats from? The SR-71 of course. And on those flights with ejection seats, guess what the shuttle crew wore? They wore pressure suits, like those worn by SR-71 crew! They stopped wearing those starting with STS-5, when they removed the ejection seats. However the pressure suits (though not the ejection seats) came back after the demise of the Challenger. What I am not saying: that the shuttle was simple. What I am saying: That the SR-71 was more sophisticated than you've given it credit for.
      - jacquesm 5y ago
        I think the two of you are largely in agreement, but GP rightly points out that the SR-71 was less complex than it could have been and that this is in party why it was so successful. The ability to leave stuff out in engineering exercises can lead to substantial benefits and that's worth noticing.
    - Gravityloss 5y ago
      The SR-71 was very complex. For example it had multiple heat exchangers to get rid of heat, to transfer it to the fuel before it was combusted. The titanium structure was complex to maintain. Welding needed to be done in "bubble" work stations under protective gas.
      - pengaru 5y ago
        > The titanium structure was complex to maintain. Welding needed to be done in "bubble" work stations under protective gas Operational complexity is orthogonal, and tends to be inversely proportional to simplicity in implementation... For instance they needed to refuel the thing immediately upon reaching operating temperature in flight, since it leaked like a sieve on the runway until everything expanded. Rather than try fix that somehow with more engineering, they shifted the complexity into operations. IIRC it couldn't even start its own engines cold, relying instead on hot-rod v8s setup on the runway to bootstrap the thing. More operational complexity in favor of leaving an entire subsystem out of the plane. Don't get me wrong, I'm a huge fan of the SR-71, but so much of that appreciation stems from its ruthless pursuit of its narrow operational goals, for as much what it isn't as it is. It's the polar opposite of stuff like the space shuttle or F-35 where the aggregate complexity is through the roof to accommodate a kitchen sink.
detritus 5y ago
I believe the descendant of HOTOL is intended to bridge that gap... https://www.reactionengines.co.uk/ https://www.reactionengines.co.uk/
numpad0 5y ago
Blackbird does 3.75 designed maximum on turbo-ramjet I think?
soverance 5y ago
Check out Hermeus, working on building a reusable hypersonic aircraft. The engine they're using is a proprietary TBCC engine based on the GE J85.
speedybird 5y ago
Unless you're trying to go to space, there really isn't much reason to go this fast in the first place. Even relatively modest supersonic passenger flight has proven to be a commercial failure (good luck to Boom Tech inc... you guys will need it.) If you're going to space, an SSTO with scramjets would be interesting. But I think if SpaceX's reusable Starship succeeds without that tech, it would be hard to justify the additional complexity and expense of an SSTO built with a class of engine which hardly exists at all right now.
- JumpCrisscross 5y ago
  > relatively modest supersonic passenger flight has proven to be a commercial failure Tried it once in the 70s. Didn’t work. Everyone go home.
  - wongarsu 5y ago
    We tried with the British-French Concorde, the US Boeing 2707, and the Russian Tupolev Tu-144. That's three tries (or maybe two, the Boeing version was cancelled before prototype completion). Maybe we can do better today with the lessons learnt and the advances in material science since then. There's several startups banking on that. But so far commercial supersonic flight has only worked out as prestige projects, not as commercial successes.
    - anaganisk 5y ago
      Wasn’t TU-144 just a pissing contest entry with retrofitted engines of another aircraft? And Boeing 2707 quickly scrapped? Only Concorde ever saw the light of commercial operations. It was truly limited by its technology, of that date. And post 9/11 situation sealed its fate, its had one fatality in 20 years, its already better than 747 max by that metric. There is no point in saying Supersonic is impossible, things changed a lot in last few years. Having computer monitors instead of a dedicated flight engineer with gazillion dials and Fly by wire, it can be much more optimised now. Boom just needs to make a working jet, and it would definitely revolutionise aviation again.
T-A 5y ago
https://en.wikipedia.org/wiki/SABRE_(rocket_engine) https://en.wikipedia.org/wiki/SABRE_(rocket_engine)

panick21 5y ago

SpaceX Starship will do this and be fully reusable. Starship can fly long distance with a reusable booster and somewhat shorter distances without a booster. Granted, its not really 'flying' but it does reach the speed needed.

pengaru 5y ago

> The SR-71 could make Mach 3 on its own but at incredible cost in fuel and complexity. the SR-71 never struck me as "incredibly complex", the space shuttle however...

sonofhans 5y ago
The J58 powering the SR-71 is still one of the most complex engines ever built. The space shuttle is a simple rocket by comparison. https://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58 https://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58
- pengaru 5y ago
  And the SR-71 is so simple the complexity falls off a cliff at the engine, hence your inclination to only care about that in comparing the two. The space shuttle is like a reusable mobile space station, airlocks and all. Occupants of the SR-71 wore space suits the entire time, there's a lot of minimalism on display in the SR-71 which is a large part of what makes it so glorious.
  - speedybird 5y ago
    You seem to be suggesting but not outright saying something that is a misconception: The SR-71 did in fact have a pressurized cockpit, which was also air conditioned as well (it had to be, because the aircraft would cook the crew otherwise.) The SR-71 was sophisticated in other ways as well; for instance in having ejection seats. In fact the first four shuttle flights (all Columbia) had ejection seats too and guess where they got those seats from? The SR-71 of course. And on those flights with ejection seats, guess what the shuttle crew wore? They wore pressure suits, like those worn by SR-71 crew! They stopped wearing those starting with STS-5, when they removed the ejection seats. However the pressure suits (though not the ejection seats) came back after the demise of the Challenger. What I am not saying: that the shuttle was simple. What I am saying: That the SR-71 was more sophisticated than you've given it credit for.
    - jacquesm 5y ago
      I think the two of you are largely in agreement, but GP rightly points out that the SR-71 was less complex than it could have been and that this is in party why it was so successful. The ability to leave stuff out in engineering exercises can lead to substantial benefits and that's worth noticing.
  - Gravityloss 5y ago
    The SR-71 was very complex. For example it had multiple heat exchangers to get rid of heat, to transfer it to the fuel before it was combusted. The titanium structure was complex to maintain. Welding needed to be done in "bubble" work stations under protective gas.
    - pengaru 5y ago
      > The titanium structure was complex to maintain. Welding needed to be done in "bubble" work stations under protective gas Operational complexity is orthogonal, and tends to be inversely proportional to simplicity in implementation... For instance they needed to refuel the thing immediately upon reaching operating temperature in flight, since it leaked like a sieve on the runway until everything expanded. Rather than try fix that somehow with more engineering, they shifted the complexity into operations. IIRC it couldn't even start its own engines cold, relying instead on hot-rod v8s setup on the runway to bootstrap the thing. More operational complexity in favor of leaving an entire subsystem out of the plane. Don't get me wrong, I'm a huge fan of the SR-71, but so much of that appreciation stems from its ruthless pursuit of its narrow operational goals, for as much what it isn't as it is. It's the polar opposite of stuff like the space shuttle or F-35 where the aggregate complexity is through the roof to accommodate a kitchen sink.

detritus 5y ago

I believe the descendant of HOTOL is intended to bridge that gap... https://www.reactionengines.co.uk/ https://www.reactionengines.co.uk/

numpad0 5y ago

Blackbird does 3.75 designed maximum on turbo-ramjet I think?

soverance 5y ago

Check out Hermeus, working on building a reusable hypersonic aircraft. The engine they're using is a proprietary TBCC engine based on the GE J85.

speedybird 5y ago

Unless you're trying to go to space, there really isn't much reason to go this fast in the first place. Even relatively modest supersonic passenger flight has proven to be a commercial failure (good luck to Boom Tech inc... you guys will need it.) If you're going to space, an SSTO with scramjets would be interesting. But I think if SpaceX's reusable Starship succeeds without that tech, it would be hard to justify the additional complexity and expense of an SSTO built with a class of engine which hardly exists at all right now.

JumpCrisscross 5y ago
> relatively modest supersonic passenger flight has proven to be a commercial failure Tried it once in the 70s. Didn’t work. Everyone go home.
- wongarsu 5y ago
  We tried with the British-French Concorde, the US Boeing 2707, and the Russian Tupolev Tu-144. That's three tries (or maybe two, the Boeing version was cancelled before prototype completion). Maybe we can do better today with the lessons learnt and the advances in material science since then. There's several startups banking on that. But so far commercial supersonic flight has only worked out as prestige projects, not as commercial successes.
  - anaganisk 5y ago
    Wasn’t TU-144 just a pissing contest entry with retrofitted engines of another aircraft? And Boeing 2707 quickly scrapped? Only Concorde ever saw the light of commercial operations. It was truly limited by its technology, of that date. And post 9/11 situation sealed its fate, its had one fatality in 20 years, its already better than 747 max by that metric. There is no point in saying Supersonic is impossible, things changed a lot in last few years. Having computer monitors instead of a dedicated flight engineer with gazillion dials and Fly by wire, it can be much more optimised now. Boom just needs to make a working jet, and it would definitely revolutionise aviation again.

T-A 5y ago

https://en.wikipedia.org/wiki/SABRE_(rocket_engine) https://en.wikipedia.org/wiki/SABRE_(rocket_engine)