SpaceX and Reusability

While I’m waiting for the FEA solver to paint me some pretty pictures for a part I’m working on, I figured I’d write a quick blog post. Yesterday I wrote a little about SpaceX’s Falcon IX announcement, and I asked if anyone had any details about how SpaceX intends to recover its upper stage for the Falcon V and IX vehicles. I had been confused about this because I had just asked them last month if they intended to reuse the upper stage of Falcon V, and they said that they weren’t intending to, but now they’re saying that they are.

Earlier today, I received some information about how SpaceX intends to go about recovering their upper stage. Apparently, if this source is right, SpaceX is looking into having the upper stage reenter with the engine nosecone facing forward. Apparently they’ve done some analysis that shows that the upper stage should be stable in this configuration, and the upper stage nozzle will have a high temperature extension that should supposedly be able to take the heat. The source I had expressed a bit of healthy skepticism about if this would work, but was at least interested in seeing how the attempt actually goes. It is a kind of weird approach, but one that isn’t obviously stupid. If they can insure that the vehicle is aerodynamically stable in this configuration (possibly by adding some sort of flaps to drag the center of pressure back), it might just work. The shock wave would be far away from most of the vehicle, with only the bottom ring of the nozzle being very close to most of the heating. A brief search on Matweb shows that some of the refractory metals have at least semi-decent thermoconductivities, ranging from as low as Stainless Steel for some all the way up to almost as good as Aluminum for others–Not bad. That means that with the right metal, that very high temperature zone at the tip of the nozzle can transfer some heat via conduction to the rest of the nozzle, which can then radiate a lot of that away, due to its high temperature capabilities…….as I said, not obviously stupid at all.

I think that the approach that SpaceX is taking for developing first stage recovery systems for the Falcon family of vehicles may also be indicative of how they will go about the development of their upper stage recovery systems. Falcon I is almost as much a test vehicle as it is an operational vehicle. They took their best guess at a design that they think can withstand a water-based recovery, and soon they’ll flight test the concept. Any issues that come up, any components that just don’t cut it, will likely be modified and tweaked, possibly with some changes in conceptual design. Then they’ll try it again, until they eventually have a decent system. During this time, they’ll also be building up experience with recovery, getting economic data on how cost-effective it is (and where they can improve the process to make it more cost effective), and building up a store of knowledge that should allow them to do a better job the first time with Falcon V and IX first stage recovery.

I imagine they’ll probably go about the upper stage recovery development the same way. They’ve probably taken a decent amount of time to try and design the system as well as they can for recovery, then they’ll fly it. If it comes even close to working, they’ll keep tweaking and iterating till they have a workable, recoverable upper stage. They may need to change recovery concepts at some point if the nozzle-first approach doesn’t work, but I have decent confidence that if it is possible to recover and reuse an upper stage like theirs, that they’ll eventually find a way to do it, and make it economical. It’ll take time, and it probably won’t work very well right off the block, but I think from the approach we’ve been seeing them take, we can have good confidence that they will get it right eventually.

[Update: It just occured to me that if they wanted to do so, they could probably get some preliminary data on this kind of recovery method using Falcon I. Falcon I also has a radiatively cooled nozzle, so maybe they could just instrument/RocketCam the heck out of the thing, and take some data. After all, their first 2-3 Falcon I payloads only use up an tiny portion of their vehicle’s launch capacity.]

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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.
Jonathan Goff

About Jonathan Goff

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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4 Responses to SpaceX and Reusability

  1. Iain McClatchie says:

    They could cool the nozzle and shock area by bleeding gas into it. For instance, they could start up just one of the gas generators (but not the turbopump) on one engine and run it at partial throttle. The propellant is already settled and there should be some remaining pressure in the tank, which can operate in blowdown at this point.

    As for stability, isn’t the whole tank section of the stage effectively a big flap? I thought most of the weight of an empty stage was down in the engine section.

  2. Jon Goff says:

    Iain,
    They could cool the nozzle and shock area by bleeding gas into it.

    That’s not a bad idea at all. In fact that’s more or less the approach that a lot of the aerospike type reentry designs in the past have assumed for engine cooling.

    For instance, they could start up just one of the gas generators (but not the turbopump) on one engine and run it at partial throttle. The propellant is already settled and there should be some remaining pressure in the tank, which can operate in blowdown at this point.

    Not sure if this would actually work though. The turbine has a separate outlet….though I guess if you were making a turbine bypass system anyway for such cooling, that would do the trick.

    As for stability, isn’t the whole tank section of the stage effectively a big flap? I thought most of the weight of an empty stage was down in the engine section.

    I hadn’t thought of that. Might just be doable after all without a huge amount of extra systems….it’s crazy enough it might just work, eh?
    ~Jon

  3. Iain McClatchie says:

    Re: aerospikes. Do you mean gas cooling during ascent, or reentry?

    Re: separate turbine outlet. Yes, I’m assuming that the turbine exhaust, once stopped by the shock, just flushes throughout the engine area. If you can maintain a bubble of gas at the same pressure as the dynamic pressure (and that’s pretty low when the heating is at its worst, as I understand it), the gas takes the conductive heating from the shock and the nozzles just see radiative heat. If the turbine exhaust is nice and sooty, the nozzles may not even see much of that.

    A blunt shock is still going to transmit some fraction, 1%?, 5%? of the heat into the reentry vehicle. I don’t think you can dump the heat radiatively when you are in the midst of an even hotter plasma sheath. You definitely don’t want to use the engine as a heat sink — it’s been designed to be as light as possible. So use the turbine exhaust as a kind of ablative coolant. As it expands to plasma temperatures and low external pressures it will expand a lot, so you can maintain pressure even in the face of a lot of volumetric leakage with a smallish flow of fuel.

    One question though: if you run the gas generator but don’t load the turbine with flow, is there any lightweight way to keep the turbine from going too fast?

  4. Randy Campbell says:

    Ambivalent said:
    >Re: aerospikes. Do you mean gas
    >cooling during ascent, or reentry?

    Actually I think he was talking about the aerospike engine studies, where your ‘areospike’ instead of being a ‘hard’ structure, (such as has been flown) is an ‘extension’ using turbopump turbine exhaust gas’ to make the ‘extension’ section of the spike.
    During reentry cryo fuel, (usually LH2) was fed through channels in the base of the ‘plug’ (1/3rd length of the full aerospike) to help cooling and then ‘bleed’ out the combustion chambers and over-board.
    (Phil Bono is my Heeerooo :o)

    Randy

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