Falcon III H (R)

The vehicle SpaceX lost the other day has been described as a Falcon IX R with three engines. It is a bit intriguing to speculate on the purpose of three engines as opposed to the nine of the full up stage, or the one of the Grasshopper I.

The first and most likely thought is that more than one and less than nine are needed for the test flight profile. So three are required to do the job, but there is no financial sense in tying up, and possibly losing, six additional engines that are not required for this particular test program. The problem with that explanation for us in the peanut gallery is that it is boring and gives us nothing to speculate about.

An explanation that I find more fun and interesting is that there might be a financial and technical case for a three engine Falcon. A shortening of the stack for the lighter vehicle would produce a lower profile for a possible reusable version. Landing on a barge at sea would be with a vehicle with far less bending moments that a full Falcon IX stage. It seems possible that such a vehicle could land (barge) in a much heavier sea state than the larger vehicle. If that is a actual possibility, then Falcon III boosters could be attached to a Falcon IX stack with very low costs per mission if the mini boosters could be reused quickly and often.

Even a first take on such an arrangement yields some suggestive possibilities. A 66% increase in take off thrust would allow as much as 66% more take off mass and slightly more than that increase in payload with the additional staging event. With cross-feed, the Falcon III stages would drop off at under a minute and a half, barely supersonic, and fairly close to the launch site for a quick booster RTLS. The fully fueled Falcon IX would be in near vacuum conditions by that time with the considerable gain in Isp compared to a ground launch. A payload gain of over 2/3 for minimal cost could not be ignored if technically feasible.

For flights where the basic Falcon IX has enough performance to do the primary mission, but not enough for any recovery options, the Falcon III boosters could up the propellant reserve to allow core stage recovery. Small, quick turn around boosters enabling the recovery of a core for certain missions would be a nearly slam dunk decision if technically feasible.

For some Falcon IX missions, a Falcon III heavy could possibly deliver a bit more payload with the same number of engines. The engines being one of the major expense items could make not requiring more of them a sound business decision if the staging events become safe and routine enough. The extra payload would come from the same nine engines powering the stack for the first couple of minute as the normal Falcon IX, after which the two boosters drop off with the consequent dead mass reduction for the remaining stage. The remaining Falcon III would have the same velocity and remaining propellant as the base Falcon IX at this point, but would be boosting 1/3 of the engine and tank mass along with the upper stage and payload.

Last thought is on the difficulty of RTLS of stages entering from far down range. A barge landing is often mentioned, virtually always coupled with the words “good sea state” in some manner. This means that barge recovery is permanently dependent on ┬áthe sea not being too rough. ┬áSome missions could be delayed by days or weeks to let the waves subside from a previous storm. Some whole seasons could be off limits if the recovery is sensitive enough.

The helicopter recovery I suggested a couple of years back might bear revisiting for lighter stages. The major objection to snagging a Falcon IX core in the air with a helicopter and flying it back to launch site was the excessive weight of the stage. A Falcon III stage might be air recoverable in a way the the Falcon IX stage could not be.

 

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13 Responses to Falcon III H (R)

  1. Jim Van Zandt says:

    I can remember when spacecraft docking simulations were popular. Landing on a barge would be a much more challenging simulation problem. I suggest the big issues are: how far in the future, and how accurately, can the barge predict its motion, and what mechanical arrangements are made to transition away from supporting the launch vehicle by rocket (i.e., the equivalent of the tail hook and arresting cables for an aircraft carrier landing). I suspect that vertical motion won’t be much problem, but horizontal motion and especially rolling will be bigger concerns. A barge could of course use active roll stabilization (as on some cruise ships).

  2. born01930 says:

    I had thought a barge with an active tower would be the way to go. You could have a capture ring rather than legs to save weight…the barge has an infinite cooling source available. For the first stage you don’t have to be too far downrange so the weather conditions for launch should be similar downrange. With both roll dampening on the barge and an active capture tower seas of up to 6′ should be manageable.

  3. ken anthony says:

    Absolutely brilliant John. If they aren’t thinking this, let’s hope they read and consider.

  4. Regardless of whether they intend to fly Falcon 3s as boosters, the fact that they were firing three engines in a linear arrangement by default makes the loss more explainable. Any aerodynamic loading orthogonal or perpendicular to the linear array of engines is going to be problematic if they do not have the TVC clearance to accommodate that and provide control authority. Clearly the outboard engines are already squeezed for space.

  5. Egad says:

    A purpose-built (or purpose-modified) self-propelled semisubmersible platform for down-range recovery would remove much of the sea-state problem. The fly in the ointment there is that, AFAIK, such things aren’t cheap to buy, operate and maintain.

    See http://www.mossww.com/technologies/baredeck.php for an example. Also look in the Google Earth image of 3/16/2004 at 25.96785 N, 97.36089 W to see it in an early stage of fitting out, without much superstructure on the bare deck.

  6. Dick Eagleson says:

    Even with a non-stabilized conventional barge a very considerable amount of both horizontal and vertical movement could be dynamically compensated for by making the actual landing platform a hydraulically-driven Stewart table of the kind used in airline and military flight simulators.

  7. john hare says:

    Ken,
    I don’t know if it is a good idea without knowing more about SpaceX that I am likely to ever learn. Falcon 9 stages may end up being so cheap and fast to turn around as to make the idea absurd. I would also want to see a serious study into both the technical and financial realities of the concept. The likelihood of major flaws that I missed in a quick blog post approaches unity.

    If it hasn’t been thought of though, it’s past time for another staff reduction. A company with that many employees missing thinking up something this basic, even if unworkable, would have some serious internal problems. Thousands of possibilities exist at the concept stage for every one that is worth further work. And dozens to hundreds that seem worth further work will reduce to a handful worth final development.

    Like the idea of putting a Falcon 3 with capsule between two Falcon 9 as boosters. 21 Merlins at take off until the boosters drop off when the 3 takes the Dragon 2 to orbit with reserve fuel for extensive maneuvering to multiple destinations, or even TMI/TLI if desired.

  8. David Janes says:

    Falcon III Heavy – 3x Falcon III, with fuel crossfed to center stage?

    Perhaps the reason SpaceX is interested in Brownsville is so they could land on a repurposed oil rig somewhere in the Gulf of Mexico? Link below is to Google Map of GoM showing ocean depth.

    https://www.google.ca/maps/place/Brownsville,+TX,+USA/@26.5312736,-94.0149157,1593561m/data=!3m1!1e3!4m2!3m1!1s0x866f7f6bc3fc6519:0xb1df1a694856522c

  9. Peterh says:

    Word has come out that the loss of the Falcon9r test vehical was related to lack of redundancy and a sensor failure, that a 9 engine vehicle with the same single sensor failure could keep going.

  10. Paul451 says:

    John,

    A barge landing is often mentioned, virtually always coupled with the words “good sea state” in some manner. This means that barge recovery is permanently dependent on the sea not being too rough.

    There are “jack-up barges” which have legs that jack down to the sea floor and lift the barge-platform to working height, and well above the sea-swell. They are inherently stable once grounded (assuming the sea floor is suitable.) That drastically increases the sea conditions under which you could launch. (Any sea-state in which a jack-up barge couldn’t operate, just 200-300km down-range from a launch site, is going to be too stormy to launch anyway.)

    Here’s one with legs down, installing an offshore wind-turbine: http://media.jackupbarge.com/media/855×855/77-JB-117_FF55962.jpg?id=11033&vlag=en&bestandID=77

    And another with legs up, under way: http://worldmaritimenews.com/wp-content/uploads/2013/03/GMS-Jack-Up-Barge-Keloa-Joins-ADMA-OPCO%E2%80%99s-Fleet.jpg

    They seem to come in any size platform with any length legs. So I would thing you could find something suitable to land the F9R (or F3HRs).

    And, conveniently, you can then jack back down to sea-level (but still supported by the legs), and transfer the stage over to a strongback on a recovery ship which lowers it back to horizontal for the trip back to dock. That way the barge itself doesn’t have to come all the way back to dock, just steam straight for the next recovery position for the next launch trajectory. And I suspect proper streamlined ships are faster back to dock than wide, flat, top-heavy barges.

    born01930,
    Re: Capture system.
    Any capture system is vastly more complex, finicky, and prone to accidents than a flat landing pad. Tiny errors in position, variations in contact forces, imperfect hitches and you smash both the landing stage and the capture-tower. Your own analogy of an aircraft carrier trap is a perfect example, vastly harder than a simple runway landing, even with experienced pilots who constantly drill on carrier procedures. Intuitively, you think a grab would be safer/easier (passing off much of the work to ground systems), but it almost never is.

    An analogy I’ve used before when this idea comes up, is to grab a normal kitchen chair, place it legs down on the kitchen table. Try to get all four feet to touch at the same time, and to “kiss” the table with virtually no force (in spite of coming in as quickly as possible.)

    Got it? Good. Now flip another chair upside down, and try to “land” your chair on feet-to-feet on the upside down chair. It doesn’t matter if the chair falls off after you let go, assume the “capture-chair” takes care of that. You are just trying to hit the window for the capture mechanism to work. Don’t forget that all four feet must touch at the same time, and the landing force can’t exceed the limits of the capture mechanism. See not only how much harder it is, but how much slower you have to move. (That slowness is extra fuel burn, extra time to be blown off course, etc.)

    Now imagine that with a cross wind, with chaotic feedback between the exhaust plume and the ground (and the capture tower itself) back onto the lander, with extremely limited fuel. And, again, any failure in any step kills not only the lander, but destroys the entire capture system.

    Four legs. Rocket engine. Big concrete pad. Bam! Done.

  11. Neil says:

    Peterh. Not quite. The normal F9v1.1 has triple sensors for redundancy and the voting would have overcome the failed sensor. The test vehicle, like F9v1.0 had only a single sensor.
    Cheers

  12. Paul451 says:

    [Reposting a prior comment, can't get out of moderation.]

    John,
    “A barge landing is often mentioned, virtually always coupled with the words “good sea state” in some manner. This means that barge recovery is permanently dependent on the sea not being too rough.”

    There are “jack-up barges” which have legs that jack down to the sea floor and lift the barge-platform to working height, and well above the sea-swell. They are inherently stable once grounded (assuming the sea floor is suitable.) That drastically increases the sea conditions under which you could launch. (Any sea-state in which a jack-up barge couldn’t operate, just 200-300km down-range from a launch site, is going to be too stormy to launch anyway.)

    [links to images deleted, presumably the cause of the mod trap.]

    born01930,
    Re: Capture system.
    Any capture system is vastly more complex, finicky, and prone to accidents than a flat landing pad. Tiny errors in position, variations in contact forces, imperfect hitches and you smash both the landing stage and the capture-tower. Your own analogy of an aircraft carrier trap is a perfect example, vastly harder than a simple runway landing, even with experienced pilots who constantly drill on carrier procedures. Intuitively, you think a grab would be safer/easier (passing off much of the work to ground systems), but it almost never is.

    Four legs. Rocket engine. Big concrete pad. Bam! Done.

  13. Paul451 says:

    {laughs} As soon as I posted that, Jon cleared my first message.

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