Stratolaunch as Falcon9 Competition

The roll out of the Stratolaunch aircraft started a considerable amount of criticism on the sources that I read. Basically it has the same problem as the White Knight, superb aircraft with no viable rocket to mate up with. I wonder though if that is the reality.

The Stratolaunch aircraft is supposed to have a lift capacity of 500,000 pounds under that center wing. It would seem to be ideal for the three barrel launch vehicle that Gary Hudson was suggesting a few years back for air launch. Visualize a Falcon 1 heavy slung under that wing with all three Merlins the vacuum variant.  That’s just to create a visual. Now realizing that Musk isn’t involved, I go to the vehicle that I believe could exist somewhere Real Soon Now.

Paul Allen apparently went through three different big name booster companies before settling on the Pegasus. Except the Pegasus doesn’t make sense for such an aircraft. It would seem possible that somewhere there is a very quiet development effort going on. I can think of a few companies capable of developing the vehicle I am going to suggest without feeling the need to Branson about it.

When launching from over 34,000 feet, more than 3/4 of the back pressure losses from sea level are gone. This means you can have a higher expansion ratio nozzle, or lower chamber pressures, or some optimum combination of both. With lower pressure engines that still have good performance possible, pumps become simpler to develop, or even unnecessary with pressure fed by modern materials. Simpler is cheaper. Three barrels with one engine each with all large expansion ratio nozzles. Probably methane and LOX for the self pressurization aspects even at the cost of higher residual pressurant  mass than with helium. Very much an operational cost conscious design.

I start with a GLOW of 500,000 pound as maximum for the aircraft. Suggesting an exhaust velocity 3,300 m/s throughout the flight. 8,000 m/s from drop to orbit. Stage  mass of 8% at cut off.  Total mass ratio of 11.3. Mass ratio to outer stages drop 2.72. Mass ratio of core stage to orbit 4.15. Cross feed from outer stages to core until they burn out.

These are the numbers I came up with starting at the drop from the carrier aircraft in pounds.

GLOW                                           500,000

weight outer stages                     343,543

propellant outer stages               316,060

weight core stage at sep             156,456

propellant core stage                  118,798

mass in orbit                                  37,557

stage mass                                     12,516

payload mass                                25,140

It should be obvious that these peanut gallery numbers are speculation that I put together with a TI 30 at lunchtime. Real vehicles won’t hit these exact numbers as they are just what I got out of a calculator. You would need to round up or down or change the assumptions as you feel necessary to get something realistic. Look at he last number though, over 11 metric tons of LEO payload from three low pressure engines, two of which can be recovered after separation just as the Falcon9 first stage is recovered now. Actually simpler as the Stratolaunch will be from up range so that the outer boosters RTB (Return To Base) without needing a boost back burn. The Falcon9 is rated for more payload than this, but before shouting too loud, I suggest going back and looking at the actual loads orbited and find that every one of them to date is well under what I have speculated here.

Cost could beat the Falcon9 depending on assumptions. An aircraft to maintain instead of a launch pad. Two simple engines and small stages to refurbish before next flight against nine engines and a larger stage. An expended core stage comparable to the Falcon9 upper stage though simpler by design.

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johnhare

johnhare

I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.
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7 Responses to Stratolaunch as Falcon9 Competition

  1. Dave Salt says:

    I think your numbers look reasonable for a first rough cut, John, but there’s more to this than just performance. I suspect that even if you wrote-off the Stratolaunch development costs, the maintenance and operation costs of such a beast are likely to be significantly higher than a 747 (e.g. ~$10k/flight-cycle and ~$25k/flight-hour, respectively) , if only because there’s 50% more jet engines to support.

    My feeling is that the best way to utilize the benefits of an air-launch system is via a fully reusable launcher, which can better take advantage of the benefits you mention by trading them off against the increased mass margins needed to enable very high levels of re-usability. This is because the effective reduction in delta-v (~800m/s) to reach orbit that air-launch provides helps you stay within the flatter part of the rocket equation’s exponential growth curve.

    I think this may also be the main reason why air-launch using expendable rockets has never been commercially successful.

  2. johnhare John hare says:

    Changing assumptions to 3,600 m/s exhaust velocity Dry mass 10% first stage and 15% second dry, I get about 18,000 pounds payload. Shaky numbers at lunch.

  3. johnhare John hare says:

    Changed for RLV

  4. Paul451 says:

    John,

    “The Falcon9 is rated for more payload than this, but before shouting too loud, I suggest going back and looking at the actual loads orbited and find that every one of them to date is well under [11 tonnes]”

    Most of the F9 launches are GEO payloads or high-inclination ISS deliveries. Neither of which allows you to directly compare maximum LEO capabilities. The payload of your proposal would also be proportionately decreased for such payloads.

  5. johnhare john hare says:

    Paul,
    Good point for many of the launches. I was just struck by the difference in nominal capacity and reported payloads.

  6. matterbeam says:

    Can something like the Falcon booster even handle the stresses of being carried horizontally?

  7. johnhare john hare says:

    There would be a mass penalty. Whatever company built it would have to design for those stresses. The three barrels I suggest are each more Falcon1 or Falcon upper stage type vehicles substantially shorter than the Falcon9.

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