Business, Economics, Political Commentary, Space

On Airbreathing Propulsion

13 Comments

Long-time readers know that I am not a fan. I believe that the benefits of airbreathing for launch vehicles are overhyped, and the technical risk too high for anyone trying to develop cost-effective space transportation in the short term (i.e., private investors), when properly designed rockets can dramatically reduced launch costs without such technical risk. That doesn’t mean, of course, that it wouldn’t be useful for the government to do focused technology development in this area, which will help with non-space applications, as NACA did to support the aviation industry throughout the first half of the last century.

That said, John Bossard, a fan of such propulsion systems, has a thoughtful essay with which I largely agree, particularly this part:

In the final analysis, the argument about whether or not airbreathers have a place in launch vehicle systems becomes secondary to how we will approach launch vehicle development. Anyone who doubts whether free-market forces can do a better job that government elites in deciding what is the correct approach for something as relatively straightforward as launch vehicle development, need look no further than the current debacle of our home-mortgage industry, or our nationalized car companies. Perhaps no better example exists than to look at our current national launch vehicle concept, a concept chosen by a elite cadre of our nation’s finest aerospace technologists, and compare the success of that program with that of launch vehicles being developed by private companies.

I would claim that if we allow it, nay, if we demand it, we can let free-market forces decide what the right approach is, and whether airbreathing propulsion has a role in launch vehicle development. We can let all-comers try their hand. Let a plethora of concepts take to the field, and let free-market forces separate the winners from the losers. Cheer your champions! Raspberry your competition! But whatever you do, support the process, be an enabler of the free enterprise and entrepreneurism, and do what you can to make the field open to whoever has the fortitude to try.

If NASA will finally start being a good customer, and purchasing transportation services instead of engineering services, the market might finally be able to sort these issues out, even if decades later than it could have.

13 thoughts on “On Airbreathing Propulsion”

  2. Well, except for the European CO2 in the air. That has an incremental price about 20 Euro per metric tonne.

    I haven’t run any numbers, but my heuristic (hand-wavy claim) is that air breathers won’t replace first stage rocket engines until the amortized, marginal lifetime savings in propellant outweighs the amortized, marginal costs of the rocket replacement.

    I expect that won’t happen until launch services approach the frequency of the airlines in the early Jet Age (1960?)

  3. ‘Twas what, 20+ years between Whittle’s turbojet and the successful incorporation of the turbojet into the 707?

  5. MG,

    I can’t help but point out that while lightweight piston engines made powered flight possible, it was the jet engine that made commercial air travel successful.

    The superior performance of the later trumped the lower price of the former. People did try to build a bigger version of what they were used to (see Spruce Goose), but scaling up standard tech proved inferior to paying the cost to develop something else.

    John’s been pointing out for while now just how immature a technology “man-rated artillery” rockets are. Don’t rule out the possibility of something better just yet.

  6. Jsuros,

    Please don’t confuse my snide (thread-hijacking) remarks about European Cap’n Trade with having little hope.

    The missile template for current launchers may or may not be the optimum solution for first stages. The “installed base” of design, manufacturing, and launch infrastructure creates a sizable intellectual investment in the status quo.

    One of the (many) exciting aspects of NewSpace is that a number of companies is attempting to re-work first stage concepts without the missile as a template. I would work for food to work with one of them. Regrettably, no takers yet.

    One of my occasional ponderings is this:

    Billions go into air-breathing turbomachinery design improvements. Can’t *any* of it insert into NewSpace, or is the barrier to such an insertion too high?

    In short, does the problem NewSpace launch companies seek to solve really require a 10 figure investment (a la “The Rocket Company”), or does it *just* require an 8 figure investment, based on (say) an old GE90 turbofan?

  7. >>SCRAMJET propulsion is the technology of the future… and always will be.<<<

    Spelling flame, there’s no r in scamjet. 🙂

  8. John’s been pointing out for while now just how immature a technology “man-rated artillery” rockets are. Don’t rule out the possibility of something better just yet.

    Of course we believe that there’s something better (if there isn’t, we’re in trouble). We just don’t think that you need airbreathing propulsion to get it.

  9. There are lots of better things than rockets. Beamed propulsion is one (4 GW nuclear power plant and lasers not included).

  11. I can’t help but point out that while lightweight piston engines made powered flight possible, it was the jet engine that made commercial air travel successful.
    You are forgetting turboprops.

  12. Rockets are a light thrust system thats easy to integrate with a airframe, adn indifferent to ambiend high drag atmosphere around it; but they force you to build a big, highdrag, kind of flimsy vehicle. Air breathers demand you stay in the air, and are heavier; but allow much smaller and likely cheaper to build and service craft.

    Can’t see eiather has a decisive edge without some mission drivers. Air breathers fit in better for suborbitals, and integrate in better with traffic in urban airspace. Rockets certainly make more sence with ELV’s. Integrating the 2 make SSTOs a hell of a lot easier since you can double the average ISP to orbit.

    Use as you prefer.

  13. I thought the big advantage of turbine engines over piston engines, at least for transport aircraft, was not performance, but rather reliability and reduced maintenance costs.

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