VTVLs as RTLS Boosters

guest blogger john hare

The increasing tempo of VTVL development flights and the recent success of the Falcon 9 lead to possibilities for a different type of cooperative venture. Two companies have VTVLs testing  that are pretty much gas-n-go while SpaceX has vehicles that are quite difficult to get back. Using gas-n-go boosters to improve an expendable rocket payload might be a viable business.

Two VTVLs are built proportionate to the Falcon 9 and used as strap on boosters with propellant cross feed so that the Falcon 9 is fully fueled up when the VTVLs stage off and return to launch site for a pinpoint landing. What I propose that is different than what I have seen before is that the VTVLs separate at about a minute into the flight before transonic flight and maxQ is reached. By separating at high subsonic, the VTVL vehicles and the coop vehicle clusters never have to be designed for or subjected to the stresses of transonic and supersonic flight.

VTVL Boost

Subsonic flight is a far more forgiving and understood aerodynamic problem than the higher velocities and leads to considerably less problems, though also with less results. By staging at high altitude the Falcon’s engines are attaining near vacuum thrust and the vehicle could be considerably heavier than on a ground take off. A small tank stretch and a subsonic boost should get about 40-50% more payload to orbit. While the Falcon would be the main player, the supporting cast could improve the bottom line considerably with benefits for all.

The benefits for Falcon would be of the same order as the subsonic air launch scenarios that so many have studied. The VTVLs just do the airplane’s job. It is the emergence of the fast turnaround rocket vehicles that make it possible to virtually airlaunch in unlimited sizes.

The VTVL players would have a market for a fairly low velocity vehicle with a high dollar (compared to the suborbital field) market that doesn’t require high flight rates. It would give them early experience with a larger vehicle than would fit in their normal course of development, and a large launch assist platform in the bargain. Though the vehicles developed for Falcon assist would not go supersonic in their booster role, they would have plenty of size margin for modifications to allow them to carry relatively large VTVL upper stages to mach 3-4 and still do an RTLS maneuver for another flight or two that day.

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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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13 Responses to VTVLs as RTLS Boosters

  1. kert says:

    Pad would be horribly complex. And why fly VTVL rocket boosters, why not VTVL turbojets instead ?

  2. johnhare john hare says:

    Why would the pad be more complex than with the Falcon 9 heavy?

    You would need a boatload of turbojets to do the same job as a rocket engine. The business case for developing a new single purpose vehicle class around turbojets against using a known rocket vehicle type that will eventually be built anyway doesn’t close.

  3. khlhl says:

    why do this over elon’s plan of just recovering the whole booster with a parachute into the ocean?

  4. anom says:

    Why not use this concept to build an orbital launch vehicle placing 20-kg into LEO yourself? Why try to partner with SpaceX who has a different business model, technology, avionics, launch-pad infrastructure, and corporate culture than Armadillo or Masten?

    Armadillo and Masten both have engines in the 3,000-lb thrust class and in the 800-lb thrust class so 2 reusable VTVL strap-ons and one vacuum-optimized expendable with 9,000-lbs combined thrust on the 1st stage, 3,000-lbs thrust on the 2nd stage (i.e. the expendable vacuum-optimized version of your VTVL is the 2nd stage) and a 3rd stage with 800-lbs thrust for orbital insertion should probably get you over 20-kg to LEO.

    Army SMDC’s Nano-Launch Vehicle program will pay $1,000,000 per launch for this responsive 20-kg LEO capability so you would have a market. XCOR supposedly has customer interested in its 650-kg upper stage for their Lynx space plane, so this path to a 20-kg LEO launcher seems to make a lot more sense for Masten and Armadillo versus partnering with SpaceX or ULA.

  5. Neil H. says:

    One oddball idea I had over at the NSF forums was if, with some modification like landing struts, the Falcon 9 first stage could actually act as a VTVL lander itself, acting as a pop-up booster for the F9 second stage. Of course, payload mass would decrease substantially, so something like the F9 heavy or Raptor upper stage might be necessary.

  6. johnhare john hare says:

    It is not certain at this time that SpaceX will be able to recover the boosters in a useful manner. Recovering boosters with ships and refurbishment will almost certainly be more expensive than paying someone else to use a gas-n-go RLV for the job.

    This idea in no way prevents them from pursuing other markets. Having a market for hot dogs doesn’t prevent selling soda to wash them down.

    Neil H,
    I think this is where SpaceX is going to go eventually. This booster concept might get them enough mass margin to do exactly that without losing payload. One I threw out somewhere was that a barge could be downrange for a Falcon 9 VTVL stage landing platform.

  7. Ed Minchau says:

    Buzz Aldrin had a similar (although VTHL) idea with Starbooster.

  8. Ian Woollard says:

    The flight plan as shown is a bad idea. The optimum shape goes West during the initial ascent before burning East relatively soon before the separation, and then the stage can fall back to the launch pad.

    The reason is that drifting West slowly while climbing costs almost no delta-v, the flight plan you’ve shown has the booster going fast East, *away* from the pad, and it would have to do another burn to bring it back to base. It costs lots of delta-v.

  9. johnhare john hare says:

    I take it that you didn’t notice that was a subsonic booster that doesn’t go that far downrange?

  10. Tom D says:


    It would be good to run some spreadsheet numbers to estimate what kind of help these boosters really are and whether that is worth the trouble of the additional staging event. These boosters remind me of the “stage 0” Kistler was talking about at one time.

  11. johnhare john hare says:

    The various estimates for subsonic airlaunched rockets give a good first estimate. We are looking at 40-50% potential payload increase, or margin to improve the recovery potential of the assisted vehicle. Worth it or not is another question of course. The subsonic staging under active control should be a fairly benign event as staging goes.

    The cost of the assist vehicles compared to their value is what matters. Recuring and fixed costs should be quite low. Servicing the development debt is the big question, and that is tied directly to flight rate. Something that occured to me later was that these same VTVL assist vehicles could also work with Atlas, Delta, Taurus II, and other vehicles that might be developed with this capability in existance. Plus using the same vehicles as a pop up launch assist vehicle for much smaller rocket craft to much higher altitudes. The higher the flight rate, the lower the cost in this case.

  12. Big D says:

    It seems to me that it would make more sense to SpaceX to add such a capability as a variant of the F9H, using technology (particularly software) acquired from MSS/Armadillo (whether purchase, license, or joint venture). That keeps the core engines and systems theirs, which they would probably prefer both from a marketing/insurance standpoint, and from a technology standpoint.

    If you can get payload mass up to a good fraction of F9H with very little marginal cost increase over base F9, what additional missions or capabilities does that give you? Would Dragon be able to make use of it, or is this something more applicable to the (rarer) heavy satellite launch or (hopefully more common at some point) depot milk runs?

  13. johnhare john hare says:

    Big D,

    I think it would depend on time to market and flight rate. If the little guys can get the capability in there and available well before SpaceX could do it alone, then they might have a market. If SpaceX can get there first and do it with vehicles that can go through transonic and max Q together then you are almost certainly right. If SpaceX can do that, then they also might have another product to boost capabilities of their competition for a fee.

    This would be Clark Lindsey’s rent-a-booster with a vengence.

    For a modest improvement below the capabilities of the Falcon 9H, this might still have a niche market, especially if they could sell capabilities to other players, and get to market earlier.

    Gas-n-go instead of seawater salvage would seem to be a slam dunk business case if they could do a Falcon 9HRLV.

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