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:
Just a few thoughts from seeing this drawing:
- 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.
- 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.
- 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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