I’m a little more reticent these days to blog about half-baked technology ideas (for fear of being compared to our friend Gaetano), but I figured I’d toss this one out as food for thought. A couple of posts ago, I talked about the “Thrust Augmented Nozzle” concept. Now, even Aerojet will be the first to admit that this isn’t some sort of panacea–it makes sense for some applications, but might not for others. Right now they’re trying to find customers for the concept–potentially people who have an existing engine that could benefit from thrust augmentation. However, I realized that one engine that could become very interesting via thrust augmentation is already sitting in Aerojet’s very shop as it were–the AJ26-60 (formerly known as the NK-43).
The NK-33/NK-43 are high performance LOX/Kerosene engines. They run at substantially lower pressures than the RD-18x/RD17x engines used on Atlas V and Zenit, they’ve been upgraded/Americanized with modern controls, are supposedly designed for reuse and restartability, and generally are pretty good engines. Several of the orbital RLV companies from the late 90’s were planning on using these workhorse engines, and for good reason. Aerojet acquired a large number of these and modernized them as part of the Kistler K-1 project. According to Antonio Elias of Orbital Sciences, Aerojet has 60 NK-33s (though he didn’t say how many -43s) in stock and owns the rights to domestically produce them once they run out.
The NK-43 is a variant of the NK-33 designed for use on upper stages. It has an Isp of almost 350s in vacuum (due to its large expansion ratio), which is pretty good for a LOX/Kero engine (most of the RD 17x/18x engines only have vacuum Isps of around 330s due to being designed for lower altitude use). Normally the NK-43 wouldn’t work as a first stage engine due to having too low of an exit pressure. But what if Aerojet modified their own engine for thrust augmentation? Now I don’t have access to their models, so I couldn’t say exactly how much thrust augmentation would be necessary to make the NK-43 useable at sea level, but my BOTE estimates put it in the range of 2-4x. At 2x augmentation, you’re talking about the same thrust as the RD-180 engine used on the Atlas V. In a lighter system. With a better vacuum Isp. Made in the USA (or at least currently in-stock in large quantities in the USA). With 4x augmentation, it would actually be an F-1A class engine, large enough to be used (in a single engine configuration) for something as big as Atlas V Phase 2…
It’s an interesting thought and a potential solution to the concerns that currently exist about having one of the main launchers we use for US military satellites depending on engines from a no-longer-so-friendly foreign nation. Not to mention even in the lower augmentation levels, it would still likely boost the overall performance of the Atlas V launch vehicle by a decent amount. And do so with engines that run at only a little over half the chamber pressure (which means less strain on the pumps/preburners). Oh, and there’s also the possibility that you could just dial up the augmentation for extra thrust instead of using SRBs…
Anyhow, just a random thought.
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