4 ms·

We're not going to have Mach 5 commercial air travel for the same reason we don't have Mach 2 or 3 commercial air travel. The economics just don't work. That r

We're not going to have Mach 5 commercial air travel for the same reason we don't have Mach 2 or 3 commercial air travel. The economics just don't work. That reason is much more boring than the technical obstacles, which are formidable, fun to try to solve, and kind of beside the point. In that sense, this problem resembles a lot of software engineering. But just to keep this comment from being too depressing, here's one technical gripe: consider that liquid hydrogen is an extremely bulky fuel, even if you don't include the necessary insulation. Notice how nearly the entire volume of the satellite launcher in the diagram consists of hydrogen tank. There's not a lot of room in there for passenger lounges and drink trolleys.

twic 12y ago
> The economics just don't work. Given that you don't know how much this will cost to operate, you can't possibly know that, right? At some point, i think i read a claim that an airliner based on this technology would be able to supply Europe - Australasia trips for about the same price as a business class ticket on a conventional airliner on that route. Passengers currently buy a fair few of those tickets; some might choose to do the trip in two hours instead of twenty-four in exchange for a smaller seat and the loss of a couple of meals.
- idlewords 12y ago
  We know how much the Concorde cost to operate: a zillion shittons (metric) [http://www.concordesst.com/retire/faq_r.html http://www.concordesst.com/retire/faq_r.html] . And that was with proven technology and all the sunk costs behind them. I think that makes a sensible floor for this project, unless you are willing to argue that researching and deploying this completely new technology would somehow cost less.
- jvm 12y ago
  Is there really a tremendous amount of demand on the Australia / Europe segment? If London/NYC wasn't viable for the Concorde (probably the most popular international airline segment), I can't imagine the demand being higher on routes to Sydney. If the fixed costs of a flight are high, it will likely be even more expensive than the Concorde on trans-Atlantic routes.
  - kjjw 12y ago
    As far as I remember, stopping Concorde had more to do with poor sales after the Air France crash rather than anything inherent in cost efficency.
  - timthorn 12y ago
    Concorde reportedly made BA about £750M. I'm not sure whether that figure takes into account the development costs - but the reason that it was retired was due to Airbus withdrawing support. http://www.concordesst.com/retire/faq_r.html http://www.concordesst.com/retire/faq_r.html
    - idlewords 12y ago
      The CEO of Airbus said in the Financial Times that "The costs of operating Concorde, and in particular maintenance and support, have become such that operations are unrealistic for any operator." The reason BA booked a profit is because of massive de facto government subsidies for Concorde, for reasons of national prestige.
- maxcan 12y ago
  parasitic drag increases with the square of velocity. these engines wont change that.
  - m_mueller 12y ago
    They do. Because they can operate in much thinner air.
- bjelkeman-again 12y ago
  SpaceX is predicting $2000/kg to low earth orbit.[1] Reaction Engines are predicting an order of magnitude cheaper than current tech[2], so let's be charitable and say that this is $200/kg. (Although the Wikipedia article mentions $650/kg). Consider that a Skylon launch is for a non pressurised satellite and capable of lifting 15,000 kg, which supposedly could be for 30 passengers in a passenger module [3]. That would meant $100,000/passenger to anywhere on earth. Cheap if you want to go to orbit, less so for a trip to Japan maybe. [1] http://en.m.wikipedia.org/wiki/Falcon_Heavy#Pricing_and_development_funding http://en.m.wikipedia.org/wiki/Falcon_Heavy#Pricing_and_deve... [2] http://www.reactionengines.co.uk/space_skylon.html http://www.reactionengines.co.uk/space_skylon.html [3] http://en.m.wikipedia.org/wiki/Skylon_(spacecraft)#Specifications_.28Skylon_C2.29 http://en.m.wikipedia.org/wiki/Skylon_(spacecraft)#Specifica...
  - m_mueller 12y ago
    Why do you assume intercontinental flight will use the same configuration as the orbiter? First of all, the orbiter still needs lots of oxygen on board, even though they can save around half of it with their hybrid jet/rocket engine. Furthermore it needs heavy heatshields. Both things that are not needed (or to a much lesser extent) in an intercontinental craft. The saved weight for oxygen alone should allow you to go from 30 to 200 passengers, giving you another order of magnitude - and suddenly you're at first class ticket prices.
    - idlewords 12y ago
      You need some way to keep the passengers from being roasted alive, and you need to engineer it to commercial air safety standards (redundant systems, emergency exits, little sign that says 'no smoking'). By the end of the process you'll be pining for the days of having to just lug around a little oxygen.
teamonkey 12y ago
> Notice how nearly the entire volume of the satellite launcher in the diagram consists of hydrogen tank. There's not a lot of room in there for passenger lounges and drink trolleys. The passenger variant presumably wouldn't need as much fuel as the one designed to launch satellites into orbit.
- idlewords 12y ago
  Why not? You have to slow down and land with the full passenger load, rather than launching the payload into space[1]. And you need to engineer the vehicle to very conservative airline safety standards. [1] Although launching the passengers into space is an attractive option, given the kinds of people who could afford tickets on this thing.
  - teamonkey 12y ago
    You need a massive multi-stage rocket that is 90% fuel (+ reactant etc.) by mass to get a couple of tons of satellite into orbit 160km up; yet a fraction of that fuel mass can take a plane and hundreds of passengers thousands of kilometres at a stretch, but only 1 or 2km high. In other words, going up is hard.
m_mueller 12y ago
They claim about the same fuel expense for long distance flight as today's craft. The reason is that they fly much higher where air resistance is very low. Fuel volume is a good point though - it probably means that a commercial airliner would need to be made bigger than now in order to be cost effective? At the end of the day, if they can deliver a craft that carries ~200 people ~8 times faster to long distances than a normal airliner for a similar fuel expense as today, with a turnaround time similar to today, you'll have something that generates money ~5 times faster, which should please even the bean counters. But obviously, there are many ifs in that equation, so we just have to wait and see. I just wouldn't be too dismissive right from the start, as always with unproven but promising technology.
- virtue3 12y ago
  To go higher with tons of weight requires even more fuel. This is a _very_ common rocket science problem and is the reason why almost all space vehicles have stages that drop off. To go high, you need more fuel, to get more fuel up you need more fuel... etc etc. "we just go higher with less air resistance" is a bullshit marketing thing and not really showing the math. Engines designed to be supersonic are also _very_ shitty at subsonic speeds. Sure, cooling 1000 degree air for use in a turbo fan is great. You're not gonna get _any_ benefit doing it at ground level.
  - m_mueller 12y ago
    You don't need the fuel to go high.[1] You need it to go fast. Orbital velocity is Mach 25, not the puny Mach 5 that they talk about for transporting passengers here. [1] See Virgin Galactic's 'spacecraft'. You see lots of fuel tanks? No? That's because they only do a little 'hop' to 100km or so, not accelerating sideways.
    - idlewords 12y ago
      The fuel required to accelerate from Mach 5 in near vaccum to Mach 25 is a fraction of what you need to accelerate the vehicle + fuel combo to Mach 5 in air. Remember how the space shuttle had those massive rockets on the side, that fell off way before it was close to horizontal? You need the fuel to get high enough to go fast.

twic 12y ago

> The economics just don't work. Given that you don't know how much this will cost to operate, you can't possibly know that, right? At some point, i think i read a claim that an airliner based on this technology would be able to supply Europe - Australasia trips for about the same price as a business class ticket on a conventional airliner on that route. Passengers currently buy a fair few of those tickets; some might choose to do the trip in two hours instead of twenty-four in exchange for a smaller seat and the loss of a couple of meals.

idlewords 12y ago
We know how much the Concorde cost to operate: a zillion shittons (metric) [http://www.concordesst.com/retire/faq_r.html http://www.concordesst.com/retire/faq_r.html] . And that was with proven technology and all the sunk costs behind them. I think that makes a sensible floor for this project, unless you are willing to argue that researching and deploying this completely new technology would somehow cost less.
jvm 12y ago
Is there really a tremendous amount of demand on the Australia / Europe segment? If London/NYC wasn't viable for the Concorde (probably the most popular international airline segment), I can't imagine the demand being higher on routes to Sydney. If the fixed costs of a flight are high, it will likely be even more expensive than the Concorde on trans-Atlantic routes.
- kjjw 12y ago
  As far as I remember, stopping Concorde had more to do with poor sales after the Air France crash rather than anything inherent in cost efficency.
- timthorn 12y ago
  Concorde reportedly made BA about £750M. I'm not sure whether that figure takes into account the development costs - but the reason that it was retired was due to Airbus withdrawing support. http://www.concordesst.com/retire/faq_r.html http://www.concordesst.com/retire/faq_r.html
  - idlewords 12y ago
    The CEO of Airbus said in the Financial Times that "The costs of operating Concorde, and in particular maintenance and support, have become such that operations are unrealistic for any operator." The reason BA booked a profit is because of massive de facto government subsidies for Concorde, for reasons of national prestige.
maxcan 12y ago
parasitic drag increases with the square of velocity. these engines wont change that.
- m_mueller 12y ago
  They do. Because they can operate in much thinner air.
bjelkeman-again 12y ago
SpaceX is predicting $2000/kg to low earth orbit.[1] Reaction Engines are predicting an order of magnitude cheaper than current tech[2], so let's be charitable and say that this is $200/kg. (Although the Wikipedia article mentions $650/kg). Consider that a Skylon launch is for a non pressurised satellite and capable of lifting 15,000 kg, which supposedly could be for 30 passengers in a passenger module [3]. That would meant $100,000/passenger to anywhere on earth. Cheap if you want to go to orbit, less so for a trip to Japan maybe. [1] http://en.m.wikipedia.org/wiki/Falcon_Heavy#Pricing_and_development_funding http://en.m.wikipedia.org/wiki/Falcon_Heavy#Pricing_and_deve... [2] http://www.reactionengines.co.uk/space_skylon.html http://www.reactionengines.co.uk/space_skylon.html [3] http://en.m.wikipedia.org/wiki/Skylon_(spacecraft)#Specifications_.28Skylon_C2.29 http://en.m.wikipedia.org/wiki/Skylon_(spacecraft)#Specifica...
- m_mueller 12y ago
  Why do you assume intercontinental flight will use the same configuration as the orbiter? First of all, the orbiter still needs lots of oxygen on board, even though they can save around half of it with their hybrid jet/rocket engine. Furthermore it needs heavy heatshields. Both things that are not needed (or to a much lesser extent) in an intercontinental craft. The saved weight for oxygen alone should allow you to go from 30 to 200 passengers, giving you another order of magnitude - and suddenly you're at first class ticket prices.
  - idlewords 12y ago
    You need some way to keep the passengers from being roasted alive, and you need to engineer it to commercial air safety standards (redundant systems, emergency exits, little sign that says 'no smoking'). By the end of the process you'll be pining for the days of having to just lug around a little oxygen.

teamonkey 12y ago

> Notice how nearly the entire volume of the satellite launcher in the diagram consists of hydrogen tank. There's not a lot of room in there for passenger lounges and drink trolleys. The passenger variant presumably wouldn't need as much fuel as the one designed to launch satellites into orbit.

idlewords 12y ago
Why not? You have to slow down and land with the full passenger load, rather than launching the payload into space[1]. And you need to engineer the vehicle to very conservative airline safety standards. [1] Although launching the passengers into space is an attractive option, given the kinds of people who could afford tickets on this thing.
- teamonkey 12y ago
  You need a massive multi-stage rocket that is 90% fuel (+ reactant etc.) by mass to get a couple of tons of satellite into orbit 160km up; yet a fraction of that fuel mass can take a plane and hundreds of passengers thousands of kilometres at a stretch, but only 1 or 2km high. In other words, going up is hard.

m_mueller 12y ago

They claim about the same fuel expense for long distance flight as today's craft. The reason is that they fly much higher where air resistance is very low. Fuel volume is a good point though - it probably means that a commercial airliner would need to be made bigger than now in order to be cost effective? At the end of the day, if they can deliver a craft that carries ~200 people ~8 times faster to long distances than a normal airliner for a similar fuel expense as today, with a turnaround time similar to today, you'll have something that generates money ~5 times faster, which should please even the bean counters. But obviously, there are many ifs in that equation, so we just have to wait and see. I just wouldn't be too dismissive right from the start, as always with unproven but promising technology.

virtue3 12y ago
To go higher with tons of weight requires even more fuel. This is a _very_ common rocket science problem and is the reason why almost all space vehicles have stages that drop off. To go high, you need more fuel, to get more fuel up you need more fuel... etc etc. "we just go higher with less air resistance" is a bullshit marketing thing and not really showing the math. Engines designed to be supersonic are also _very_ shitty at subsonic speeds. Sure, cooling 1000 degree air for use in a turbo fan is great. You're not gonna get _any_ benefit doing it at ground level.
- m_mueller 12y ago
  You don't need the fuel to go high.[1] You need it to go fast. Orbital velocity is Mach 25, not the puny Mach 5 that they talk about for transporting passengers here. [1] See Virgin Galactic's 'spacecraft'. You see lots of fuel tanks? No? That's because they only do a little 'hop' to 100km or so, not accelerating sideways.
  - idlewords 12y ago
    The fuel required to accelerate from Mach 5 in near vaccum to Mach 25 is a fraction of what you need to accelerate the vehicle + fuel combo to Mach 5 in air. Remember how the space shuttle had those massive rockets on the side, that fell off way before it was close to horizontal? You need the fuel to get high enough to go fast.