Comments on: Random Thought: Thrust Augmented AJ26-60?

By: Charles F. Radley

Charles F. Radley — Sat, 22 Dec 2007 00:42:00 +0000

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.

By: Jon Goff

Jon Goff — Tue, 04 Dec 2007 15:58:00 +0000

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

By: Tom Cuddihy

Tom Cuddihy — Tue, 04 Dec 2007 15:45:00 +0000

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?

By: Iain McClatchie

Iain McClatchie — Fri, 30 Nov 2007 23:39:00 +0000

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.

By: Jon Goff

Jon Goff — Fri, 30 Nov 2007 21:02:00 +0000

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

By: Anonymous

Anonymous — Fri, 30 Nov 2007 20:47:00 +0000

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.

By: Jon Goff

Jon Goff — Fri, 30 Nov 2007 17:04:00 +0000

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

By: meiza

meiza — Fri, 30 Nov 2007 15:53:00 +0000

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.