Falcon IX Upper Stage Recovery Kremlinology

I just wanted to post a couple of short thoughts about the Falcon IX Upper Stage information that came out in the article I linked to in a blog post a few days ago. Specifically this picture from Figure 9 of the Asian Space Conference Paper (with my labels added) provides some interesting hints at how SpaceX is intending to recover the stage:

Falcon 9 Upper Stage Schematic (Courtesy SpaceX)

Just a few thoughts from seeing this drawing:

  1. It looks like they’re planning on doing a nose-first reentry with a heatshield on the nose taking the brunt of the reentry heating.  A previous rumor (which I may deserve the ignominity of having first spread) was that they were going to try and reenter tail first using the big niobium extention of the engine nozzle as a sort of radiatively cooled TPS.  I asked Elon about this back in January (the only occasion I’ve had to meet him in person), and he just laughed, and then said something about using a normal heat shield and parachutes for landing.
  2. With the main propellant tanks empty, the chunks of mass are the engines, the helium pressurant tanks inside the LOX tank, the heat shield, and those mysterious spheres in the front right behind the heat shield.  I’m not sure what those are, but my main guesses would be a) ballast, b) RCS propellants for deorbit and reentry.  There’s a long-shot third possibility as well–the heat shield might not actually be an ablative (or just an ablative) shield.  The tanks could be transpiration coolant.  But I think option “b” is the most likely.  Either way, by locating those tanks up front, it helps drag the CG forward during reentry, which makes the vehicle more aerodynamically stable.
  3. Those big black panels at the back look like they could be aerodynamic control surfaces.   By moving them outward a bit, they can possibly drag the aerodynamic center of pressure back enough to make the stage aerodynamically stable.  Alternatively, they might allow a somewhat unstable design to fly by active controls.  There are plenty of examplse of aircraft that would rip themselves to shreds in seconds if it weren’t for their computer controls (due to being very aerodynamically unstable).

All in all, the more I look at it, the more I’ve come to the conclusion that SpaceX could actually pull off recovering this stage.  It may take them a few tries, and as their first stage recovery efforts have shown, there are lots of details that need to be just right for recovery to work.  Not to mention the fact that I still think that splashing turbopump-fed rocket stages in the ocean is a great way to make reusability a pain in the neck.  But I think the fundamental recovery concept is sound, and if they can be succesful enough with their launches, they’ll be able to stick around long enough to make reusability a reality.

I wonder if they can make this work if that will down the road lead others of their competitors to move in that direction for LEO launches.  Centaur is a fairly valuable stage, and I could see a similar configuration possibly making it be reusable as well (though the LM guys would probably use Mid Air Recovery instead of splashdown).  Wouldn’t make sense at current flight rates, but if things like Bigelow’s station come into reality, you might see enough demand to start justifying more creative incremental improvements like this.

I don’t think that these recoverability methods are the end-all, be-all of space launch.  And I don’t even think that many of them are even on the same evolutionary path as the ultimate direction things need to go.  But I do think they’re a useful improvement that could help lower the cost of heavier launches while small RLVs are getting their feet.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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38 Responses to Falcon IX Upper Stage Recovery Kremlinology

  1. Tim says:

    Given that it uses balloon tanks, does an empty Centaur have the structural integrity to survive reentry and recovery? Do you keep the pressurant gasses on the way down to keep the thing strong, and are you able to stop them boiling off?

  2. corrodedNut says:

    Splashing the stage and engine with salt-water is less than ideal, but with properly placed floatation bags, is there any reason to think that the engine and turbo-pump would have to be submerged? If the stage comes nose-down, with a chute lanyard attached near the engine mount (I think I see a wedge-shaped chute box near there, with orange lid) wouldn’t it bob mostly upright?

  3. Tim,
    Pressurized stages can be amazingly strong. I bet the reentry loads are lighter than the loads it experiences during launch with a big heavy payload on one end and a rocket firing from the other. They might want to reinforce the stage a tad if they were reusing it though, just to raise the FOS enough that it isn’t as much of a maintenance pain.

    Also, pressurizing gasses are by definition already “boiled off”. They’re typically helium in this case. I *think* they can keep them pressurized after the mission. Not 100% positive, but I figure they can probably figure out a way to do it if SpaceX can prove out the concept for them.

    ~Jon

  4. CN,
    I agree that with proper flotation devices it might be easier. It’s still less ideal than a powered landing or Mid air recovery.

    ~Jon

  5. anon says:

    Anyone else think that upper stage recovery is an ideal place to develop new re-entry/landing methods? At least, if the economics of it make getting the stage back a bonus, rather than a vital part of your financial plan.

  6. another anon says:

    You know, a reusable upper stage would be pretty similar to one which could aerobrake…

  7. John Schneider says:

    Does anyone know how they plan to recover the first stage?

  8. Jon,
    Could you’re mysterious tanks have pressurant to repressurise those tanks for the rigours of reentry?
    Rob.

  9. Gordan says:

    Let’s say the green clamp-like things are what holds the heat shield in place. Is that a plausible assumption and would one really need so many of them spaced so closely?
    If they do serve this purpose, what would be the purpose of their blue-colored equivalents at the stage’s aft end? Would one want to jettison something from that section?

    What is the typical cost distribution on a stage like this between the tankage and the engine, does the engine cost the majority of the stage? If not, would it be a crazy idea to jettison the entire thrust structure and engine and recover only the tankage? It would sure help the CG during reentry.

    It’s very interesting that SpaceX didn’t show us any glimpses of an actual stage yet. ITAR-related issues, given how much stuff visibly hangs out?

  10. Anon,
    I think so. As you say though, only so long as recovery is something that improves the bottom line if it works, but doesn’t kill you if it doesn’t. If you have flexibility like that, then you can possibly afford to tinker with it over time. Especially if tinkering can be done in a way that doesn’t risk your customer’s payloads.

    ~Jon

  11. That said, I think that a small upper stage launched off of a suborbital vehicle might end up being a cheaper TPS/reentry testbed.

    ~Jon

  12. Comga says:

    Your term “Kremlinology” is amusing and apt.

    Your theory “b” seems the most logical. You know my opinion that SpaceX would not use inert ballast. There are also no tanks visible on the back end, although they could be behind the black “flaps”. What do you think would be the mass of such tanks when empty?

    This is making sense. Moreover, it may be that SpaceX is expending resources (engineer’s and machine shop time, and capacity to orbit) to evolve a reuse capability. It avoids the quantum leap needed for something like your conceptual mid-air recovery of a separable Atlas recovery module. This would be in accordance with other choices we have seen from SpaceX. Evolution happens. Leaps to the ultimate solution wind up like the X-33.

    Speaking of optimized solutions, I still think it would be better to use your friend John Hare’s toroidal tanks instead of all those spherical tanks inside the LOX tank, particularly if external but thermally coupled. (Who could resist making this kind of suggestion, despite only being informally trained in cryo thermal engineering?)

    CN’s idea that the orange in the image is the lid of a parachute box is logical, but quite a stretch from about 400 pixels with compression artifacts. 🙂

    What we probably all agree on is that we want more pictures and news!

  13. Jonathan Goff Jonathan Goff says:

    Another anon,
    You know, a reusable upper stage would be pretty similar to one which could aerobrake…

    Yes and no. They are similar in many ways, but the key difference is that if your heatshield is ablative, it’s probably not useful for too many aerobraking missions. The heat load for aerobraking is roughly similar to the heat load for reentry, but if your heat shield is sized for reentry, and can’t be replaced on orbit, it’s not very useful as an aerobrake.

    Now, if you have a transpiration cooled heat shield, and the ability to retank the water…then you’re in business.

    ~Jon

  14. Jonathan Goff Jonathan Goff says:

    John,
    Not entirely sure. The terminal phase is parachutes and water recovery, but I think they have some sort of TPS for the reentry phase. Not very clear though what the details of that are.

    ~Jon

  15. Jonathan Goff Jonathan Goff says:

    Rob,
    Could you’re mysterious tanks have pressurant to repressurise those tanks for the rigours of reentry?

    Well, I don’t know for sure either way, but I kind of doubt it. Reentry loads are probably gentler than launch loads. With a ~90klb engine on the back and a 20klb payload on the front, the tanks are actually taking quite a bit of loads during launch. It’s possible though. But since there appear to be Draco thrusters on the back end of the module, and no other sign of RCS propellant tanks, that’s still my best guess.

    ~Jon

  16. Jonathan Goff Jonathan Goff says:

    Gordon,
    Let’s say the green clamp-like things are what holds the heat shield in place. Is that a plausible assumption and would one really need so many of them spaced so closely?

    I would think those would actually be what’s holding on the payload fairing (or the Dragon capsule). They’re in the right place, and either of those would require beefier reinforcement than just the heat shield.

    If they do serve this purpose, what would be the purpose of their blue-colored equivalents at the stage’s aft end? Would one want to jettison something from that section?

    The first stage? 😉 Seriously, I think those are the connection to the interstage section.

    What is the typical cost distribution on a stage like this between the tankage and the engine, does the engine cost the majority of the stage? If not, would it be a crazy idea to jettison the entire thrust structure and engine and recover only the tankage? It would sure help the CG during reentry.

    Unfortunately, engines are typically much more expensive than the tankage. But you lose a lot of the benefit of reusing the stage if you toss either.

    It’s very interesting that SpaceX didn’t show us any glimpses of an actual stage yet. ITAR-related issues, given how much stuff visibly hangs out?

    Or maybe they don’t want to give away all their secrets already? When I asked a friend there how many limbs (and naming rights for how many children) would it cost to get a glimpse of their second stage before it left Hawthorne. Alas, the response was a laugh.

    It was worth a try though!

    ~Jon

  17. Elmar_M says:

    This is very interesting indeed.
    Unfortunately this graphik is very small as someone mentioned before. I do wonder though where the flotation devices are stored. Could that not be what these tanks are for (though the placement would be kinda bad and should probably be on the other end of the stage to keep the engine out of the water).
    I guess the same can be said for parachutes (they do need some space too).

  18. Tim says:

    Jon,
    From what I can tell, you seem to be implying that a vehicle using true balloon tanks (like a Centaur) would keep the tanks rigid with pressurant gas during reentry, even if the gases later escape. Can you clarify whether you believe this to be the case? Thanks.

    I misused the term “boil off” back there. What I was concerned about was the helium expanding due to the heat of reentry and escaping out of the engine plumbing or what have you.

    Preserving the pressurant helium presents an interesting possibility. I wonder if the density could be low enough to provide a significant amount of lighter-than-air lift during the terminal stages of the descent? If it does you’d open up a nice set of possibilities, such as reducing the weight of the terminal chute; keeping more of the stage out of the water after splashdown; or being able to use a smaller and therefore more manouverable helicopter for mid-air recovery.

  19. Mike Puckett says:

    “Tim,
    Pressurized stages can be amazingly strong.”

    Simple and cheap experiment:

    Stand on the top of a sealed can of pop.
    Then stand on one that is empty Tim, and see for yourself what Jon is talking about.

  20. Mike Puckett says:

    Jon,
    What would you say if I told you I knew of a product that was remarkably effective at protecting metal against salt corrosion, was cheap, likely not degrading of seals and considered food safe and totally environementally benign?

    My only concern is it would act as a contaminant. I am thinking this stuff could be used to flush out the working parts of an engine.

  21. anon says:

    My guesses.

    1) The blue and green items are stage release clamps.
    if you are going to use a reusable stage, mechanical separation
    is better then pyro devices.

    2) While the black flaps could be aero-devices, i highly doubt they
    would be effective until subsonic. the supersonic shock would
    leave these utterly blanked. Now they have a length of 1/6th
    the wing chord, so they could have trim effectiveness, but,
    only once you have elliptical flow running. I also doubt they are active
    controls for unstable reentry, as, the power requirements for
    that are very high, and with the engine off, you lack that kind of
    power.

    3) The forward tanks look like they are for a small RCS package,
    so that might get you enough power to hold stable, but,
    i’d want to see some thrusters on the back end as well.

    the big one is, dipping rocket engines in salt water is a bad idea.
    so, no recovery scheme is going to work. NASA can’t even
    handle the SRB casings coming back after a salt bath, and
    those are pretty simple.

  22. Brad says:

    Re: 2nd stage recovery goals

    I bet SpaceX isn’t counting on full reuse of the 2nd stage after recovery. Reuse of (or canniblizing) just the engine probably makes stage recovery worthwhile. And maybe the avionics could be salvaged too. With the new manufacturing techniques SpaceX is using, stage structure is probably the cheapest component of the Falcon rocket.

    Re: mystery nose tanks

    I suggest two other possibilities. First off, perhaps those are CG ballast tanks after all, but not for use during re-entry. Instead maybe they start empty and after spashdown fill up with seawater to stabilize the stage in a nose-down engine-up posture.

    The other possibility is maybe those tanks are pressurants for an inflatable-ballute hyper-cone heat-shield. If large enough that ballute could also eliminate the need for parachutes and also serve to cushion impact on the stage at splashdown.

    Inflatable hyper-cones are a technology of possible use to landing much larger payloads on the surface of Mars than current methods. I am aware that Mars is the ultimate goal of Elon Musk’s space ambitions. So wringing out hyper-cone technology by using it for recovery of the Falcon 9 second stage does double duty.

  23. Pingback: Transterrestrial Musings » Blog Archive » It Always Takes Longer Than You Think

  24. Gordan says:

    anon: “While the black flaps could be aero-devices, i highly doubt they
    would be effective until subsonic. the supersonic shock would
    leave these utterly blanked. ”

    What other options for stabilization would be available? Would Draco RCS thrusters be able to hold proper attitude until subsonic transition and alternatively, would spin-stabilization help in keeping it pointed the right way during reentry?

  25. Roger Strong says:

    Here’s an unlikely possibility for that mystery cluster of tanks in the nose, but perhaps one worth mentioning: A secondary payload – a small space tug.

    Used as a publicity shot camera platform for now, but with lots of potential uses in the future. Say, for taking a microgravity experiment off the Kibo’s exposed facility for a while to isolate it from vibrations on the space station. Or for retrieving lost tool bags (or astronauts).

  26. Stan Wright says:

    Just maybe…
    The forward tanks are propellant tanks for a rocket that will fire into the hypersonic flow at re-entry. This will create a supercavitating bubble, just like in the Russian Shkval torpedo. The four fins on the aft of the stage will then indeed be useful for re-entry guidance. The fins will be able to move against the envelope of the supercavitation bubble to provide control authority. The spent stage will decelerate through the atmosphere until subsonic speeds are reached. The fins will then have full utility as control surfaces. The big question still unanswered is how SpaceX plans to slow the stage for final splashdown or aerial capture. ( conventional parachute recovery is likely, as indicated before and verbally confirmed by Elon Musk )

  27. Comga says:

    Roger: Why would they put a secondary payload UNDER the heat shield?

    Gordan: I see two Draco engines pointed aft, but none pointed sideways, either radially or tangentially. Wouldn’t this be less than optimum for attitude control? Could one even do that during reentry with 90 lb thrusters?

  28. Stan Wright says:

    Notice also the annular rings on the front of the heat shield. They could serve as boundary ducts during re-entry. Compare the Shkval.

    http://www.fas.org/man/dod-101/sys/missile/row/Shkval-1.jpg

  29. Gordan says:

    Comga: I would think it needs additional sets of thrusters anyway to maintain 3-axis control in space during coast phases, which is what would be required if stage restarts are required. It wouldn’t be too much of a stretch to use the thrusters to spin up the stage, but the obvious question is would it work (spinning up a 3-axis stabilized stage) and would it actually help during reentry. Maybe it would just produce weird gyrations as the CG is too far behing CP.

  30. Josh Reiter says:

    So, what is the red diamond shaped area between the mystery tanks under the heat shield?

    Combustion chamber for an APU? When I see red, I think hot. When you look into the red area up close there looks like there is a shaft with a conical end housed in a black (compressor) area.

    Is the black pipe running along the bottom of the stage an umbilical to the payload/capsule? Or, is it part of the wiring harness that would come from the APU to the areas marked in green which all seem to be in proximity to the alleged control surfaces. An APU could provide current to powerful servo motors that adjust the attitude of the aerodynamic control surfaces. At supersonic reentry speeds the control surfaces could be fully extended to turn the stage into a shuttle cock.

  31. I wonder if what we’re looking at is the final itiration of the second stage? Based on what someone at SpaceX told me, he hinted that the upper stage design is an evolving process. Early on — to get the launch business rolling — the second stage will likely not be recovered.

  32. corrodedNut says:

    OK, here’s my smorgasboard of replies and comments:
    SpaceX has some literature showing the Dragon with similarly shaped/sized green objects, refered to as “seperation fittings”. Earlier drawings show it with six fittings, but newer renderings have eight, which seems to correspond to this image of the 2nd stage.
    The “black pipe” could be a cable trunk similar to the one that runs the length of the Falcon1 upper stage. On the F1 US it houses, among other things, the rearward and forward-facing cameras for video telemetry. There used to be two of these trunks but (as of flight 4) they’ve been consolidated.
    I don’t think we should expect a recovered F9 US for at least a few flights either, but even the first one up will have to have a RCS. I don’t think we can see all of the Draco’s on this picture, the ones that point towards “the camera” would be very difficult to see. Even if there isn’t a planned de-orbit on the first few flights, SpaceX needs to perform a upper stage-Dragon orbital rendezvous on the second COTS demo mission, which means they would likely want the RCS working properly ASAP.
    The best “publicity shot” they could hope for is video showing the gently seperated payload, floating away….into the correct orbit.
    Best of luck to them.

  33. Gordan says:

    corrodedNut: “The best “publicity shot” they could hope for is video showing the gently seperated payload, floating away….into the correct orbit.”

    Which brings me to perhaps the most important question of all: Will the first F9 carry an onboard camera? 😀

  34. corrodedNut says:

    I sure hope so, every SpaceX vehicle has so far.

  35. Gordan says:

    But every SpaceX vehicle so far was a F1 with the external, sizable cable trunk. It does appear to me there’s a real good place to put one on F9 2nd stage as easily as it was on F1. Unless that black horizontal line in the schematic represents the external cable trunk, that is.

    Anyway, I guess we can now lay the reason SpaceX didn’t show us images of the 2nd stage to rest. There *is* no 2nd stage yet! 😀

  36. corrodedNut says:

    Now that we’ve seen some actual 2nd stage hardware, what can we deduce? Refering to the earlier diagram; I was wondering what the yellowish zig zag lines around the narrow end of the expansion nozzle are? I thought it might be another regen cooled section, welded tubes, maybe, but the caption on the Merlin Vac image makes it sound like the expansion nozzle is just going to be bolted on to the end of the exhaust nozzle. Any thoughts?

  37. dorkmo says:

    i think they turned the second stage into a mars entry vehicle. the aero surfaces would steer them through the atmostphere and then when they get hot they release the cap. then when i gets really hot the front plate separates getting even closer to surface. then just before contact the plate detaches at the tanks are used for a powered landing.

    am i rite?

  38. Jonathan Goff Jonathan Goff says:

    I’m pretty sure that isn’t the point. Elon may be a Mars fan, but I’m 99.5% sure that F9 Upper stage isn’t being designed as a powered-landing mars reentry vehicle.

    ~Jon

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