Random Thought: Thrust Augmented AJ26-60?

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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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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8 Responses to Random Thought: Thrust Augmented AJ26-60?

  1. meiza says:

    Pm Antonio 🙂
    Isn’t he Elias, not Eliason?
    Perhaps they could go with a single NK-33 after all for the Cygnus / Delta II replacement, even with a kerosene second stage.

    And where does the extra propellant flow come from? The engine might have no margins in that regard as it’s an upgrade version from the N-1 engines.

    Btw the NK-33 is the highest T/W lox-kero engine in the world. 🙂

  2. Jon Goff says:

    You’re right, it is Elias, not Eliason. As for the extra flow, there are several options, each of which has differing levels of complexity. One they could have separate high pressure tanks (at say 600-800psi or so) for the TAN propellants. Another option would be to use the existing pumps, run the main chamber at a lower pressure and the TAN propellants at a higher augmentation level (but lower pressure). The power required is proportional to pressure times volume flow, but I’m not sure if you can use the existing pump in that way. The most likely solution would be a separate pump for the TAN propellants.

    ~Jon

  3. Anonymous says:

    2 pumps?

    Hard enough to get one pump running right on a bird.

    Better to have a high pressure pump, expand the
    flow just a bit to drop the pressure for the main
    feed, and have a second tap to get high pressure
    into the TAN nozzle.

  4. Jon Goff says:

    Anonymous,
    Whether doing one big new pump or one new smaller pump (in addition to the existing pump) is easier depends on a lot of details. You might be right, but I’d have to see more data before I could really say one way or another. The two sections are operating at vastly different pressures/flow-rates (the main chamber wants much lower flow rate at much higher pressure), that it may make doing a single big pump more complicated then just having two pumps. Also, by having two pumps, you can keep all your throttling in the lower pressure pump system and have the higher pressure pump only have to run at a pretty fixed thrust level (ie you throttle by slowly turning down the TAN flow)….

    but I’m not really a turbopump guy so I couldn’t really say which would be easier or harder.

    ~Jon

  5. Iain McClatchie says:

    If you are going to augment the thrust of the NK-43 by a factor of 4, then the propellant flow will go up by a factor of ~5 (Isp is lower). At what point do you intend to shut down the augmentation? If the augmentation is burning for, say, 60 seconds after launch, you will have consumed most of the fuel that the engine is going to burn. At that point, do you really want to cart around the tanks and extra turbopump hardware?

    Wouldn’t it be easier to just drop the tanks, drop the turbopump, and, while you’re at it, drop that fancy ignitor and just light up another NK-43?

    I like the idea of no pump and high pressure drop tanks, though. That looks like it gets the most take off thrust per development dollar, by actually using the NK-43 as an ignitor for a bigger, dumber engine.

  6. Tom Cuddihy says:

    Wouldn’t this functionally be the same effect as a variable-expansion ratio engine –i.e. aerospike? I would think the additional required piping and tankage would essentially eliminate any advantage of increase thrust. If you have to do all that why not go with an aerospike engine?

  7. Jon Goff says:

    Tom,
    Wouldn’t this functionally be the same effect as a variable-expansion ratio engine –i.e. aerospike?

    Not exactly, though there is some overlap. You get at least some of the benefit due to being able to carry a high expansion ratio engine that can also work at sea level. But the key difference is that Aerospikes get less thrust at sea level than at altitude (like all non-TAN engines). Which means you have to size the aerospike for the takeoff thrust levels (which are also almost always the highest required thrust levels), and you have to throttle the engine down fairly deeply towards the end of flight to keep the thrust levels reasonable. Now throttling isn’t evil (we really haven’t had huge issues with it at MSS), but having to carry an engine around that’s several times too heavy for most of your flight isn’t so much fun.

    I would think the additional required piping and tankage would essentially eliminate any advantage of increase thrust. If you have to do all that why not go with an aerospike engine?

    Well, if you went for pressure-fed tanks, that might make the system heavier than an all-pump fed aerospike. But if you went with a low-pressure pump for the TAN propellants, it would likely be a *lot* lighter. Aerospikes are already pretty complicated plumbing-wise, so the engine itself would definitely have a much better T/W ratio (probably by a factor of 2-4x). As for the rest of the structure, plumbing, etc, it wouldn’t add that much weight unless you went with a tripropellant system, and there are ways to do a tripropellant system that don’t add much weight at all.

    There is however, no reason you can’t combine the two ideas (Aerojet also has a patent for adding thrust augmentation to plug nozzles, aerospikes, and E-D nozzles).

    ~Jon

  8. Charles F. Radley says:

    Hi Jon, looks like the masten-space.com domain name has expired.

    What’s up?

    Also tried to email you but it bounced.

    Thanks,

    Charles R.

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