As of 1.0.2, do you think the engines are balanced?

[NathanKell]

Heh, asmi ninja's me as is right and proper. Please, please, all you people claiming ~realism~, go ahead and find and post what a Merlin 1D Vacuum engine's sea level Isp is.

Next, I suggest you look up actual numbers on real life, tested aerospike engines. See what sea level vs vacuum Isp those get. Don't go with your gut. Don't go with what KSP has made you think is correct. Go with real.

[zarakon]

Actually it wouldn't work at all. I'll leave it up to you to research why.

Well, here's one being test fired in what I'm guessing is not vacuum..

But I'm guessing with the full vacuum engine bell on there, the exhaust would be unstable due to overexpansion

Edited May 21, 2015 by zarakon

[ArcFurnace]

I actually couldn't find numbers for Merlin 1D-Vacuum sea level ISP anywhere, presumably because nobody bothered to calculate them (as it would never be used). I did find this webpage, which states that while the Merlin 1D has a chamber pressure of 97 bar (9.7 MPa) and an expansion ratio of 16, the Merlin 1D-Vacuum has the same chamber pressure and an expansion ratio of over 117!

Even more annoyingly, I couldn't find equations that would let me take the chamber pressure and expansion ratio and calculate the exhaust pressure at the nozzle, but I bet it's a lot lower than 1 atm, which would indeed make it effectively unusable at sea level due to massive thrust loss and/or flow instability due to gross overexpansion.

[Levelord]

We have a community that is obsessed with making the game more difficult under the guise of realism rather than what makes the game actually realistic or intuitive. I'm beyond the point of caring anymore and find this poll completely pointless.

Just learn to play the game and adapt to the engines instead of whining and complaining all the time.

[GDJ]

I can't complain about the engines per se, but something in between the crappy wimpy one and the insane Ramjet engine might be in order.

[Hannu]

I am happy now. Only question is Eve ascent. Old Aerospike was excellent for that but now it is practically useless engine (or maybe it is suitable for spaceplanes). But I accept that there are extremely hard and also totally impossible things in the game like in real world. I think that nerfing of all engines was good thing. Interplanetary dvs was far too easy to achieve before. Now there are nice possibility to make huge ships easily (1000-5000 t launch mass) but there are no use for them because you can send anything to anywhere with small ships, you can get ore and fuel from everywhere and so on. I miss crazy and unstable 2000 t 1200 part launchers from about 0.20 era. One launch to Eve and back ships, massive fuel supply ships to Tylo surface base etc. Then joints were very flexible, there were not 3.75 m parts and it took hundreds of hours to learn to make such a monsters.

Maybe they could cut LV-N's ISP to about 600 instead of insane overheating. I know that it would not be realistic. But realistic Nerva (high ISP in all pressures, high thrust, moderate costs) in KSP scale solar system would make interplanetary transporting as routinely and cheap stuff as intercontinental flights are now in Earth. It would not be interesting in KSP like game. Real Nerva would also replace all large chemical rocket engines. Maybe politicians think the balance of real life rocket engines when they ban Nervas.

[Guest]

Maybe they could cut LV-N's ISP to about 600 instead of insane overheating.

Nah, the heat will probably come down in the next update.

[Laie]

I hope this doesn't count as necromancy yet...

If your payload requires several engines, a cluster of four aerospikes is more draggy, more expensive, and inferior to a single skipper. The aerospike is only ever a choice if you only have small nodes (e.g. Mk2 spaceplanes), not because it's good, but because the other high-powered engines are even worse.

Even in the context of Eve, there is considerable room for improvement without rendering bigger engines obsolete.

[wossname]

I was disappointed to find the ion engines were nerfed so they are unusable in Kerbin's atmosphere. Before 1.0 there was a terrific Challenge which had a huge amount of interest (get to the Insular Runway in the shortest time using only ion engines as propulsion) which I and many others enjoyed immensely.

[Prepper-Jack]

Have to agree with the suite of SRBs being broken. Besides having a poor lsp, and being largely useless outside the very start of the game, they just burn wrong. Longer doesn't mean longer burning.

[Orbital Vagabond]

I'm mostly content with the engines as they are. The one thing that truly nags me is that there is no good 1.25m engine. The first two make sense in the context of career, and once you've uncovered some higher tiers, there's pretty much no reason to revisit them ever again. Except that Mk2 planes are very dependent on 1.25m engines, and there's no really good choice available.

Am I missing something? I just can't get my mind around opening claim. I haven't played 1.x into deep career, but in previous career games, I was launching 1.25m rockets all through the game. And those 1.25 rockets need 1.25 engines... I don't get why they become "bad" when you get bigger engines for bigger rockets because you still need them for small rockets because small rockets continue to have a place, largely due to cost and the amount I need to lift. That is unless you want to use spaceplanes for launching payloads of that size, but case was already addressed in this same passage.

For example, I think the Terrier's a great engine. It's high vacuum ISP and good TWR are perfect for orbital and transfer stages, and it got a thrust buff from Beta...

And whats better for getting a 1.25m stack into orbit than a t-45?

Whats the issue?

- - - Updated - - -

SRB's are badly broken. I think they just need higher ISP, they should burn longer and give a little more delta V.

Continuing SRB, we need a bigger one. That's just missing.

I think we see the purpose of SRBs differently. SRBs are about supplemental thrust off the pad, not dV (at least not directly). Strap-on boosters improve TWR at lift-off so the LFO stages can carry more fuel, which improves the reaction mass fraction, which in turn increases dV.

[hellion13]

I'm a complete newbie when it comes to the math behind the engines. I have maybe half an idea of how it works.

I've not really felt any of the engines are wrong for the most part, I've wished for more intermediary parts though. Some of which were introduced in the last couple of updates.

You could ask for more isp here, or Newtons of thrust there, but then the risk of homogenizing the variability of the crafts between players. The way it plays now, its possible to use just about every engine in every stage, making gameplay something that can be as bare bones as an Apollo craft, to something like an interstellar colony ship with 10,000(not really) Kerbals on it.

And the fun comes from the parts not having any truly specific use outside the obvious. Its perfectly possible to have 8 mainsails powering a decent on to Eve. Getting it into space is another issue entirely. Pn the others of of the spectrum, you can stack some RCS and a few mono prop engines on the pad and make orbit, go to the Mun, orbit there for a while, and still make it back into Kerbin orbit.

[r_rolo1]

I think we see the purpose of SRBs differently. SRBs are about supplemental thrust off the pad, not dV (at least not directly). Strap-on boosters improve TWR at lift-off so the LFO stages can carry more fuel, which improves the reaction mass fraction, which in turn increases dV.

That is a VERY limiting view of what SRB rockets should be able to do, especially compared with RL, where we have a nice handful of all-SRB ( or just liquids for the last stage ) rockets in active service . like JAXA Epsilon , the Lockheed Martin Athena II, Orbital Science Minotaur IV and Minotaur-C or the European Vega , not mentioning the very old tradition of all or mostly all SRB powered navy based missiles with suborbital capacity started by the 60's Polaris ...

EDIT: In other words, for the SRB being able to do in game what they can do in RL, we should definitely have a 0,625 m SRB ( I still can't swallow very well the fact that the Flea is a 1,25 m rocket ... ) and most likely one or two 2,5m SRB as well and we should have thrust vectoring in atleast some of them. Also, while SRB look cheap in paper, a orbit capable SRB rocket is still normally more expensive than a LFO solution for most of possible payload masses due to the clunky fine tuning options we have in game and the lack of options regarding SRB parts, so that aspect is also in odds with reality

Edited May 29, 2015 by r_rolo1

[Laie]

Am I missing something? I just can't get my mind around opening claim.

The LV-909 is indeed excellent.

The Reliant used to be quite versatile, much like a scaled-down Skipper. I used it in many situations where it was by no means perfect, but good enough. These days, it has abysmal ISP. It looks as if both the LV-T30 and 45 are designed to be inferior to everything that comes later in the tech tree. Which is alright from a tech progression point of view, but there's no progression in the 1.25m department. When you're looking for a powerful 1.25m engine late in the game, you're out of luck.

[problemecium]

Well I've somehow missed the poll, but what I have to say is that they seem decently balanced against one another, but perhaps all a bit too inefficient. Real-world rockets often have specific impulses in excess of 400, and the prototype NERVAs far higher.

If the game needs a balance to make up for overpowered engines, I'd rather it be something else. Perhaps when engines run hot for too long, the little "health bar" for overheating can persist as an effect on the engine, reducing its recovery value and destroying it if it reaches 100%.

[SciMan]

I have problems with only 3 engines currently.

LV-N. I can't even look at this thing in 1.0.x without thinking "What in Jeb's name were they thinking!?!". Used to be, this engine was the go-to engine for just about anything in space. Well, it's not anymore, and that's a good thing. What's not a good thing, is that now the heat makes it useless for doing the one thing it's good for, namely long burns to get payloads out past Duna or Eve. The heat thing is poorly thought out, extremely poorly implemented, and all it ends up doing is making you add 3 wing parts and a precooler for every LV-N you want to use continuously. And the whole point of a LV-N is the high specific impulse allowing long burn-times.

Once you figure out how to get around the heat problem, all it does is force higher part counts. With single-threaded physics, that's one of the WORST things that you can force a player to do.

Aerospike. Really only useful for Eve ascent, because the low rate of change of specific impulse is the only good thing about it. I do mean the ONLY good thing about it. Even a spaceplane is better served with a LV-909 and two turboramjets insead of this abomination. It's been nerfed into the ground, time for some buffs to bring it back.

Speaking of spaceplanes, the RAPIER. If its supposed to be better than the turboramjet, then why does it have worse ISP in airbreathing mode, and have difficulty going supersonic?

It would probably work out about right if you switched the stats of the turboramjet and the air-breathing portion of the RAPIER, and then gave the closed-cycle portion of it a similar nearly-constant ISP like the Aerospike has. If it's supposed to be a spaceplane engine, it should work REALLY WELL for spaceplanes, not "kinda a little bit better than the other options". It's end of tech-tree stuff, it's okay if it's a little bit overpowered.

[problemecium]

^ Ooooooor: thrust-limit the LV-N. I find 73.5% is a good magic number. Effectively this just means the LV-N got a minor thrust nerf, but still has a "turbo boost" mode for when you need a little extra push in a pinch.

[Tankman101]

^ Ooooooor: thrust-limit the LV-N. I find 73.5% is a good magic number. Effectively this just means the LV-N got a minor thrust nerf, but still has a "turbo boost" mode for when you need a little extra push in a pinch.

Also you can design a ship with the heat in mind. Throwing a F1 engine on a civic isn't going to make the civic perform the same as the F1.

[Laie]

LV-N. I can't even look at this thing in 1.0.x without thinking "What in Jeb's name were they thinking!?!".

Aerospike. Really only useful for Eve ascent, because the low rate of change of specific impulse is the only good thing about it. I do mean the ONLY good thing about it.

Speaking of spaceplanes, the RAPIER. If its supposed to be better than the turboramjet, then why does it have worse ISP in airbreathing mode, and have difficulty going supersonic?

I think the rapier is fine. You arguably save some weight compared to rocket/jet combos and once you bring it up to speed, it totally outperforms the Turbo. The worse ISP can be justified, because dual-use.

So much has been said about the LV-N that I won't even try to add something new to it.

The aerospike can't even convince on Eve. TWR is just too damn low -- whatever you save in fuel is wasted again because the engine itself is so heavy, and bulky too. As it lacks the power to lift a tall (=aerodynamic) stack, you have to build outward, increasing drag. Mainsails and Mammoths win by virtue of their much higher thrust, ISP be damned. Not to mention that the ISP advantage is shrivelling with every meter of ascent. Pushing your way out of the lower atmosphere with raw power is more efficient than trying to be smart about it.

[NikkyD]

Engines are the thing that bugs me the most ever since KSP came out!

I love to build minimalistic rockets and there simply is NO variety in engines! For a small "to mun and back" stage if its really small its a 48-7S because of its awesome TWR or a 909 because of its ISP. Bug what if i need more thrust than the 60 of the 909 ? I COULD combine 4x48s BUT the game has no adapter, and if they implement an adapter im pretty sure it has 100kg of weight and thus make an engine with 80 thrust and the same weight but a worse ISP so i will lose dV.

Again i like small rockets. Before 1.0 i could use LV30 because i never needed gimbal, now its either lots of torque (= weight) or LV45 with gimbal. If you look at the ISP it has 320 vac which almost raises the question: why should i drop it ? Why should i stage at all ?

WHY should i stage ? Building a 3 stage rocket to LKO is a joke. All those "starter" engines have really good overall stats so you dont need to drop one atm engine to have a better vac engine because carrying a 2nd engine is a lot of weight because engines are so heavy compared real rockets.

If you build a 2.5m rocket its either Mainsail or Skipper, combining 4xlv30 or 4xlv45 is not getting anywhere near the TWR of a Skipper/MS and the ISP is roughly the same...

And if you play career... a 909 costs LESS than a small separator! There are combinations where the separator makes the whole thing expensive and the engine does not O-o.

It wouldnt be that damn hard to code something like adjustable engines. You chose more ISP in space, therefor you lose thrust (for example). Or you want just 1° of gimbal on the Lv30, sure no prob, but that will make it 10% heavier or longer etc... everyone could fine tune the engines needed. Scaleable tanks... wait THERE IS A MOD FOR THAT. F*** OFF with that mandatory mod installing if you want to play anger-free because the stock game comes with nothing but a handful of parts and a licensed gfx engine. Something like MJ should be included in the stock game but.. NO...

[KerikBalm]

What's not a good thing, is that now the heat makes it useless for doing the one thing it's good for, namely long burns to get payloads out past Duna or Eve. The heat thing is poorly thought out, extremely poorly implemented, and all it ends up doing is making you add 3 wing parts and a precooler for every LV-N you want to use continuously.

I must be the only one who doesn't have a problem with heat on these things.

Yea, they get hot, but... not hot enough to damage anything.

I perapsis kick with them a lot... I did that before heat just because its more efficient than trying to do a 15 minute burn from LKO, where your orbital period is 30 minutes...

With perapsis kicking, they cool between burns, and its simply not a problem for me. It might be different capturing at Moho... I haven't tried that yet

Aerospike. Really only useful for Eve ascent, because the low rate of change of specific impulse is the only good thing about it. I do mean the ONLY good thing about it.

Well, that's supposed to be what this thing is for...close to optimal nozzle design and thus Isp for all pressures. Gets nearly the Isp of a LV-909 in vacuum, way better atmospheric Isp.

Gets better atmospheric Isp than the LV-T30/45, with better vacuum Isp.

Would you complain that the only good thing about a LV-N is good vacuum Isp? The only good thing about a turbojet is good O2 containing atmosphere Isp?

Even a spaceplane is better served with a LV-909 and two turboramjets insead of this abomination. It's been nerfed into the ground, time for some buffs to bring it back.

It hasn't been nerfed into the ground, and a LV-909 is seriously underpowered for most spaceplanes.

TWR may be the same... but you need 3x as many attachment nodes to get the same thrust with a LV-909, whch means more drag.

The alternator is also nice. Also, you start your burn at a high altitude, but not a vacuum, given small difference in vacuum Isp, and the massive Isp difference at 1 atm, I wouldn't be surprised if the Aerospike delivers more effective ISP as you reach LKO.

Speaking of spaceplanes, the RAPIER. If its supposed to be better than the turboramjet, then why does it have worse ISP in airbreathing mode, and have difficulty going supersonic?

Because its supposed to be different, not better. Because its supposed to (and does) provide a higher top speed and altitude, at the expense of reduced fuel efficiency, and poor low speed performance.

Balance, you know, the thing this thread is about.

If the Rapier were just flat out better than the turboramjet in every way, *that* would be unbalanced.

It would probably work out about right if you switched the stats of the turboramjet and the air-breathing portion of the RAPIER, and then gave the closed-cycle portion of it a similar nearly-constant ISP like the Aerospike has. If it's supposed to be a spaceplane engine, it should work REALLY WELL for spaceplanes, not "kinda a little bit better than the other options". It's end of tech-tree stuff, it's okay if it's a little bit overpowered.

So you want the rapier to be better than any other airbreathing engine in open cycle... and equal to or better than any other rocket in close cycle....

So, you want overpowered stuff... got it.. I thought we wanted balance... my mistake.

End of tech tree does nothing for sandbox balance.

Nor for career balance after you've done landers+ fuel depots to both moons of Kerbin (or science lab+timewarp).

The balance on these engines is fine... I'm just unsure about the SRB balance.

[Jouni]

I realized I hadn't used the LV-N in 1.0 yet, so I had to check whether overheating is a real problem with them. I built something similar to my pre-1.0 interplanetary transfer stages, and added a dummy payload to it.

The ship had 6741 m/s of delta-v, and the total burn time was 40 minutes 40 seconds. At full power, the first temperature gauges showed up after a 9-minute / 1100 m/s burn. About 16 minutes / 2400 m/s later, the temperature gauges spread to the payload. 13 minutes / 2600 m/s later, overheat gauges appeared for the engines. At that point, I had a bit over 2 minutes / 600 m/s remaining. The screenshot was taken immediately after the ship ran out of fuel.

It looks like the engines heat up a bit, but you don't need any special tricks to avoid overheating.

[Temeter]

Yep. The heating system is extremly tame, you need to do something very, very wrong to kill the engines.

[Orbital Vagabond]

That is a VERY limiting view of what SRB rockets should be able to do, especially compared with RL, where we have a nice handful of all-SRB ( or just liquids for the last stage ) rockets in active service . like JAXA Epsilon , the Lockheed Martin Athena II, Orbital Science Minotaur IV and Minotaur-C or the European Vega , not mentioning the very old tradition of all or mostly all SRB powered navy based missiles with suborbital capacity started by the 60's Polaris ...

EDIT: In other words, for the SRB being able to do in game what they can do in RL, we should definitely have a 0,625 m SRB ( I still can't swallow very well the fact that the Flea is a 1,25 m rocket ... ) and most likely one or two 2,5m SRB as well and we should have thrust vectoring in atleast some of them. Also, while SRB look cheap in paper, a orbit capable SRB rocket is still normally more expensive than a LFO solution for most of possible payload masses due to the clunky fine tuning options we have in game and the lack of options regarding SRB parts, so that aspect is also in odds with reality

The only thing I can agree with in this statement is that size 0 (0.625 m) SRB would be convenient. I'd also like to see the SRBs cheaper, but I'm not sure if that's a point you're trying to make here...

The SRB-only rockets you've cited are simply not very effective orbital platforms. Except for the Athena II, they're all "small-lift launch vehicles" (<2000 kg to LEO, per NASA's guidelines), and the Athena only eeks out of that category by 65 kgs. All use at least 3 stages to get into orbit. The Athena's 4th stage uses a hypergolic engine, not a solid engine and the wiki you cited claims that stage is used for "final insertion", but I'm feeling generous and won't disqualify from the discussion, even though it's not an "all-SRB rocket". Regardless, you can build an SRB only rocket with 4 serial stages and use it to put a small payload into space. If you need me to show you how, I can make a video and walk you through it.

And SRB single stage rockets can go suborbital in KSP. Not sure how that capability apparently isn't in the game...

As far as form factors, all the rockets you cited are in the 2-3 m in diameter, similar to the diameters of the Titan GLV (3.05 m), Falcon 9 (3.5 m) and Soyuz (2.95 m). Consider that shuttle SRBs are also similarly sized (3.7 m), I can't find any IRL mention of using scaled up SRBs beyond this size, with one exception: Apparently Aerojet worked on some massive prototype SRB with a 260" diameter, but this was obviously never put into use, and only 2 prototypes were built.

Note: For clarity I would consider 5 m rockets IRL, like the Delta IV rocket and S-IVB stage to be most similar to KSP's 2.5 m rockets, and larger rockets, like the Saturn V and Proton-K, to be most similar to KSP's 3.75 m rockets.

And despite looking, I can't find any mention of any SRB engine being gimballed. I'm not saying they don't exist, but I just can't find evidence. I'd like to see it, if it exists.

In summary, I can't see how you can build a case for more/larger/vectored/improved SRBs being added to the game on the grounds of "realism" because IRL, they're aren't any cases to point to representing what you're asking for.

- - - Updated - - -

And if you play career... a 909 costs LESS than a small separator! There are combinations where the separator makes the whole thing expensive and the engine does not O-o.

I agree. This is just freaking weird. Also the fact that 3 fins on a rocket cost more than a rocket engine is baffling. I had hoped that Squad would have done a better job in their "massive 1.0 rebalance", but... /shrug.

[Jouni]

Note: For clarity I would consider 5 m rockets IRL, like the Delta IV rocket and S-IVB stage to be most similar to KSP's 2.5 m rockets, and larger rockets, like the Saturn V and Proton-K, to be most similar to KSP's 3.75 m rockets.

Rocket sizes in KSP are quite arbitrary. It's better to compare the relative performance of the engines and the roles they're used in.

The Mainsail is the most powerful single engine in the game at sea level. At ~1.4 MN, it's supposed to be the KSP equivalent of the F-1 engine. Medium-sized SRBs used in real rockets such as the Ariane 5 are about as powerful as a single F-1 engine, while the large ones used in the Space Shuttle and the SLS are about 2x more powerful. Hence a medium-sized SRB should produce 1-1.5 MN of thrust in the game, while large ones should be rated for 2.5-3 MN.