Possible additional engine configurations

[JacobB094]

From my deep dive on Delta, I caught a few missing engine variants which could be of some use. Most of those variants are largely incremental, but I found that when dealing with such a wimpy stage as Able, even a slight change in performance has a measurable impact. All these would only require config work.

AJ10-40 - An uprated AJ10-37, otherwise similar to the engine from Vanguard, but with more thrust and Isp. AJ10-101 - Uprated, but heavier, stainless steel variant of AJ-10-37, used on Able 2, which flew on both Thor and Atlas. RL-10C-2 - C-level performance with a nozzle from the B-2. It would be the most capable RL-10 variant in the mod, this one actually flew as an engine upgrade for Delta IV. ETS RL-10 from Centaur E - ETS Centaur E is a weird animal, almost as much propellant as a Centaur III, but dry mass more akin to a stretched Centaur D, and no word on how it would be insulated. It's oddly similar to some "growth Centaur" proposals from Atlas, but there seems to be no direct OTL equivalent to its variant of RL-10. Actual LR-79 NA11 - The current low tech LR-79 performs like the NA9 and should be designated as such. The real NA11, an intermediate model between NA9 and NA13, would not be amiss.

Some of that could possibly go into Pafftek as optional configurations.

[Rodg88]

Not sure there's much point in such minor updates in engine performance for the cost of even more engine switches. AJ10s are already not realistic in terms of TWR for game purposes, the 37-40-42-101 are all so close together (RO doesn't even have a 40), have hard to find actual stats, and tank masses are already not that fine tuned for realism. And afaik the RL10 C-2 would be identical in performance to B-2 too, with switch space being at a premium on the RL10.

[JacobB094]

It seems that I got rusty with my rocket research skills. Not only is it not quite clear what RL-10C-2 actually is (however, the one on Delta is apparently a rather straightforward upgrade of B-2 called RL-10C-2-1), one paper I found I actually gave it [i]lower[/i] Isp than B-2. I guess it's not much of an upgrade.

I think I'll leave untangling the full Able saga to Pappystein. All I could find out was that the -37 was flown exclusively on Vanguard and that -4x series and the -101A were used on Thor, and they had higher thrust compared to the original. The -40 itself was only on suborbital Thor-Able launches. Later, they made the orbital Thor-Baker by adding a 3rd stage, which was renamed Thor-Able I, using the -41 engine, for Pioneer 1 and 2. Next was Thor-Able II (I wonder if anyone ever called it Charlie), and that is what flew on Atlas-Able. It seems it could use both the -42 variant and the stainless steel -101A.

I picked the -40 because it's a thrust upgrade from -37 (by how much, I have yet to find out from a reliable source), and I would expect other 4x engines to differ little. The -101A may or may not be the exact same engine as -142 and the first (no letter) -118, but I'm pretty sure they were all stainless steel. They would be heavier, but allow higher specific impulse and thrust due to allowing higher chamber pressure. Gameplay wise, I wanted some way to differentiate Able I and II somehow. Personally, I find those early, wimpy upper stages fascinating.

Also worth noting here is the reason why Delta was such a step forward. Able did not have 3-axis control after engine cutoff. Delta fixed that, and was able to actually insert into a designated orbit, instead of just any random orbit, depending on where the stage was pointing at cutoff.

[Pappystein]

@JacobB094 are you able to provide your AJ10 sources?

You are correct; Thor-Able II is Charlie. But that was NASA, not USAF's name (same with Thor-Able I being Baker/Bravo.) USAF was the ordering commission, so Able is the only name for all three stages, even though they differ significantly. Yes, that means NASA ordered early thin tank Deltas that are still Able under USAF contract, and when the USAF launched a few of them, they were referred to as Able! Worse individual Able stages differ significantly from one another in the same "group." It is also why you do not see much on the RL10B-3 (XLR-119) because the USAF canceled it before NASA could even order it as RL10B-3. Like the USAF, NASA assigned its own designations. UNLIKE the USAF, there are no rules for NASA designations, which leads to a lot of fun. As a guy who stalks designation-systems.net this is very frustrating to me.

Also, something to take into account. Most of the Early AJ10s were hand-built on a mission-by-mission case, not an "as-produced" product. That is why there are FAR more "flight-proven" variants than there are stages. So tying a particular engine as the "sole" engine for a stage is very very problematic. Something I struggle to explain to myself... let alone others. In today's "mass produce" society, it seems wasteful to build on a case-by-case basis.

EG, there WERE Able stages with cold gas thrusters (not Able I or II but straight able)

At one point, I tried to track down all the AJ10 variants that flew on Able/AbleStar/Bravo/Charlie/Delta... I think I ended up with an engine count of 27? And the vast bulk of them were incremental "alterations" that didn't really change performance in a KSP way.

If we had a re-textured AJ10 model with the combustion chamber being of a "higher polish" to represent stainless steel, I would think one of the various early stainless steel engine variants would be cool, and "shiny" both in fact and in the Firefly reference...

Now, to the specifics that you mentioned. This is off the top of my head here as I do not have all my sources (and the sources I have are also not the greatest.)

-40 didn't make orbit because the thrust chamber couldn't stand up to the full-duration burn. This was WHY they experimented with Stainless steel combustion chambers. The latter -41, -42 and -101 are competing engines this way. The 41 has a thicker combustion chamber wall and stronger throat vs the 40. Other than burn duration time, there is no difference in performance between the two. -42 is a re-engineered -41 to improve the manufacturing process, as I remember.

Yes, the Stainless engines were stronger/better, but it was determined quickly that they cost significantly more, and it was not worthwhile. Remember, working with Stainless steel was a pretty new thing, technologically at the time. NOTE: this will change in the late 1960s as thrust increases in the AJ10, and eventually, most AJ10s have a stainless combustion chamber.

I will end here. NASA is in the time frame we are talking about. It was a loose coalition of research institutes. NOT a homogeneous organization (it is still set this way today for good or bad.) This leads to problems because the one thing NASA never got right (still today, this is true) is keeping the PR people supplied with correct information and preventing them from "dumbing it down" with incorrect information. IE if you see a NASA press kit as a source, read it... and toss it aside until hard NASA documents back it up.

Hope this is helpful Jacob. I will say I love these things you are finding for the BDB Crew and I to look over! Keep it up!

[JacobB094]

Unfortunately, I can't quite find the sources (sometimes even entire sites, and Wayback machine is hard to search) I used when I first looked into the AJ10s. I'm still looking for NASA papers on these. I did figure it was the NASA/USAF thing muddling it up. That they custom-built the engine for every mission is not a surprise, every space vehicle of the era was more or less a custom job. In fact, cranking rocket engines out on an assembly line is the new idea.

A secondary reason I wanted the -101A was that I was hoping to convince someone to make a nifty stainless steel PBR finish for it. :) For what it's worth, variants that are the same for KSP purposes can be "combined" in B9 PS. Though that would still require a document showing, at the very least, thrust, dry mass and Isp of the engines, or at least some values (like propellant flow rates) which could be used to derive those three.

[Pappystein]

https://web.archive.org/web/20180405050445/http://www.spacelaunchreport.com/library.html#lvdata

https://web.archive.org/web/20180307144433/www.alternatewars.com/BBOW/Space_Engines/

Two of the now defunct sites :D

You can find a lot of information on Nasaspaceflight's Level 2 forums, but that requires a subscription. That is where I garnered most of the info I mentioned above (I no longer have my L2 membership; it was from memory.) Sadly on hunt for a job right now and living on savings so have to be frugal.

[JacobB094]

Yeah, my favorites from back in the day. With that I found some approximate figures: AJ10-37: Isp 261, ~7300lbf (matches up with one currently in) AJ10-4?: Isp 271, ~7500lbf I don't know how good they are, since I still don't have any primary source, but if true, we're looking at 3% boost in thrust and a whoopin' 10s of specific impulse between Vanguard and Thor versions. The aluminum chamber was, supposedly, 20lbm lighter than the steel version, and the 7650lbf thrust Ed Kyle quotes as the top of the range for Able might have been for the -101A. Assuming the same mass flow rate, that would give it 276s, but it's probably a little high.

That said, I'm reading Hunley's "The Development of Propulsion Technology for U.S. Space-launch Vehicles: 1926 – 1991", and from what he writes, I wonder if any of those numbers are worth anything. Supposedly, even before Vanguard first flew, they raised the engine performance "above spec", except the spec quoted earlier in the chapter is 278s and 7500lbf, more efficient than most websites credit those engines with. The book paints a picture of the Aerojet engineers essentially bumbling about, tweaking the design and trying to find "something that works". So now I wonder whether anyone ever had a good idea of what the exact stats on each engine were. The ones on the internet might very well be a combination of results of working backwards from trajectory analysis of flown rockets, atmospheric tests adjusted with unknown assumptions to get vacuum values, and designers' wishful thinking (also known as "design specifications"). Even when they do give an exact value, they never give actual error bars for it. There are people out there who think "7300" counts as "about 7500".

I wouldn't put them in a scientific paper, but for a KSP mod, the values above look playable. The equivalent changes would shift payload of those launchers significantly, and BDB tweaks the exact numbers anyway to work with a smaller sized system better.

[Pappystein]

And now here is the rub. SquareQubed law Scale factor and rounding make those the same overall performance in KSP.

You are talking about something that is 32.4kn and 33.3kn. Which basically means they are 8.2 and 8.3kn. Not an appreciable difference. The problem with these smaller stages is they fall victim to Square Qubed much more harshly than, say a S-IVC does.

And yes, even in the book Ignition! it is implied that the hardware engineers were poking at things. That is why you get E-1 and F-1 explosions at Rocketdyne, "But it worked on LR79!"

[JacobB094]

Thrust is not the only thing we're looking at, though. Both specific impulse and dry mass will have an effect, Thor-Able can carry about 70kg. 20lbm is 9kg, so if that's in the engine, you'll now have closer to 60kg of payload. Besides, BDB does not follow normal scaling here, it's already tweaked to make differences more pronounced. I think we can have some tweaks to scaling so that the mutual relations between variants' performance are preserved.

Speaking of LR-79, there appears to be one more variant that I thought would be redundant... LR-79 NA11. What we currently have has identical performance to S-3D, and only differs visually, which would indicate it is actually LR-79 NA9. The NA11 would have 250s of Isp, and slightly improved thrust, between NA9 and NA13. It wasn't used a lot, mostly on some Thor-Agena variants, Deltas prior to D, and on Thor-Ablestar, but I'd prefer to get the numbering straight. I thought our NA11 is the NA11, and that S-3D configuration could represent the NA9, but upon closer inspection, it appears there was a mixup (also, why does the S-3D config not subtract the start tanks' mass and cost?).