Theory vs. Practice: The ARM parts.

[Rakaydos]

How do we decide whether or not the parts are balanced? Is it going to be some mathematical mixup of Thrust/ISP/TWR? Just a couple of those factors? Just one? As SQUAD considers ARM an 'official mod' should we also require other modders to adhere to an arbitrary balance? Should we consider cost?

Many of them already do. Novepunch and KW rocketry are, aside from 3 of their engines, actually more balanced than ARM.

[LethalDose]

The Space Shuttle was able to put roughly the same mass into orbit as the Saturn V,

Can you cite a source for this? I did a quick Wikipedia search for shuttle and Saturn V payloads, which provided:

Shuttle payload to LEO: 24,400 kg

Saturn V payload to LEO: 118,000 kg

The Saturn V was able to put 5 times more mass into orbit than than the shuttle, which is no where near comparable. In fact according the to the wiki, the Saturn V could put twice as much mass into translunar injection than the shuttle could put into LEO.

Not trying to start a fight, just fact checking statements.

[m4v]

How do we decide whether or not the parts are balanced? Is it going to be some mathematical mixup of Thrust/ISP/TWR? Just a couple of those factors? Just one? As SQUAD considers ARM an 'official mod' should we also require other modders to adhere to an arbitrary balance? Should we consider cost?

How to balance the parts was already discussed and I won't rehash it, if you want to know look for the balance mod. And really, don't give me a wall of text preceded by "we should hold off serious discussion".

[UmbralRaptor]

Can you cite a source for this? I did a quick Wikipedia search for shuttle and Saturn V payloads, which provided:

Shuttle payload to LEO: 24,400 kg

Saturn V payload to LEO: 118,000 kg

The Saturn V was able to put 5 times more mass into orbit than than the shuttle, which is no where near comparable. In fact according the to the wiki, the Saturn V could put twice as much mass into translunar injection than the shuttle could put into LEO.

Not trying to start a fight, just fact checking statements.

The Shuttle orbiter vehicle itself was an extra 68,500 kg - 109,000 kg that was nonetheless lugged to LEO and back. Hence why the Shuttle-C would have been able to fairly easily get 2-3x the payload. Edited April 18, 2014 by UmbralRaptor

[Jouni]

Can you cite a source for this? I did a quick Wikipedia search for shuttle and Saturn V payloads, which provided:

Shuttle payload to LEO: 24,400 kg

Saturn V payload to LEO: 118,000 kg

I was talking about the mass fraction, not the payload fraction. According to Wikipedia, the total mass that reached orbit in the Apollo 15 mission was 141 tonnes. A fully loaded Space Shuttle weighted 109 tonnes, and it could also place the external fuel tank (dry mass 26.5 tonnes to 35 tonnes, depending on the version) into orbit.

[csiler2]

How to balance the parts was already discussed and I won't rehash it, if you want to know look for the balance mod. And really, don't give me a wall of text preceded by "we should hold off serious discussion".

Oh gee, you're right, I have no right to justify my position. I'm not unwilling to talk about rebalancing engines, but it's premature to discuss it when the supposedly unbalanced parts appear to be taking cues from the next update that will add new factors to the game. Perhaps you can explain to me why it's such a problem that the ARM engines are better?

I was talking about the mass fraction, not the payload fraction. According to Wikipedia, the total mass that reached orbit in the Apollo 15 mission was 141 tonnes. A fully loaded Space Shuttle weighted 109 tonnes, and it could also place the external fuel tank (dry mass 26.5 tonnes to 35 tonnes, depending on the version) into orbit.

In response to your posts and LethalDose's response: I ignored hypothetical shuttle arrangements and operations for the sake of simplicity. If we include the orbiter and external tank, whose only mission is to put things into orbit, then we would need to include the S-IVB and upper stages of any GTO-capable launchers as part of their payload fraction rather than the launcher.

That said, the shuttle was probably a more efficient launcher if evidence from the shuttle-derived SLS is any indication.

[rkman]

it's premature to discuss it

If you think it is premature to even discuss it, what do you make of the fact that the rebalance mod has been created and has been featured in The Daily Kerbal's Modding Mondays?

[m4v]

Oh gee, you're right, I have no right to justify my position. I'm not unwilling to talk about rebalancing engines, but it's premature to discuss it when the supposedly unbalanced parts appear to be taking cues from the next update that will add new factors to the game. Perhaps you can explain to me why it's such a problem that the ARM engines are better?.

They are a problem because I play .23.5, the current version, not some .24 version that isn't out yet and we know nothing about. And because they are unbalanced in the current version they ruin my fun now.

[G'th]

My opinion is that if you're complaining about the ARM parts being too powerful, then you're clearly not utilizing them to their potential.

ARM parts aren't meant to carry an average payload to the mun and back without staging. They're meant to lift gigantic payloads that would otherwise require large (and thus laggy, less efficient, and more prone to disaster. Also expensive if we look ahead to currency) arrays of non-ARM rockets.

You don't make bigger rockets to lift the same payloads. You make bigger rockets to lift bigger payloads.

[Klingon Admiral]

You make bigger rockets to lift bigger payloads.

Only that the ARm aprts, the LFB in particular, allows one to build a smaller rocket to lift larger payloads. In FAR, I used a LFB and nothing else for a SSTMinmus.

[m4v]

Only that the ARm aprts, the LFB in particular, allows one to build a smaller rocket to lift larger payloads. In FAR, I used a LFB and nothing else for a SSTMinmus.

And you're not paying attention to the issue we have with them. Nobody is complaining about their high thrust, but of their high TWR and Isp, they are ridiculously efficient at lifting anything.

[G'th]

Only that the ARm aprts, the LFB in particular, allows one to build a smaller rocket to lift larger payloads. In FAR, I used a LFB and nothing else for a SSTMinmus.

Yeah, and I said that. You misunderstood "bigger rockets" as "more parts". I was actually referring the power of the rockets.

The problem is that the payloads most people seem to have aren't large enough for the ARM parts to be appropriate, which leads to the idea that ARM parts are overpowered. In reality, you're basically using industrial bleach to clean up a water spill.

This problem exists mostly because Squad hasn't created enough reason to create very large payloads. Grand Tours, Jool System exploration, A.I.O space stations, and very over engineered crafts are generally the only things ARM parts are appropriate to use with. Not everyone does any of these things though, and because the few goals in the game can be achieved very efficiently with what was already in the game, people are naturally coming to the conclusion that ARM parts are overpowered, when the real problem is that the solution to difficult goals came before the difficult goals themselves were introduced.

Asteroids are the only things currently in the stock game (besides the already mentioned things) that ARM parts are really appropriate to use for (because duh), and while they are a neat goal it doesn't really make up for the fact that for the other 97% of the game, ARM parts are completely unnecessary.

It should also be noted that most people play sandbox, and honestly if you're getting overly concerned about how powerful X is in sandbox, you're kind of silly. Sandbox is there so you can use the most powerful parts and nothing else, if you so choose. Something being "overpowered" doesn't mean anything in sandbox, because there's little to no restrictions anyway.

[SpaceGremlin]

If you think it is premature to even discuss it, what do you make of the fact that the rebalance mod has been created and has been featured in The Daily Kerbal's Modding Mondays?

Lots of mods are featured in modding mondays, so what's your point? Featuring the balance mod is Squad acknowledging that not everyone agrees with the current balance situation. Remember that the Better Than Starting Manned mod was featured even though Squad deliberately made manned capsules available at the start of the tech tree?

[Dogoncrook]

And you're not paying attention to the issue we have with them. Nobody is complaining about their high thrust, but of their high TWR and Isp, they are ridiculously efficient at lifting anything.

That high twr is what makes them a horrible choice for average payloads. What compels you to ignore all the other negative attributes of using an overpowered rocket and instead insist it's now the be all end all, it clearly isn't.

[maccollo]

That high twr is what makes them a horrible choice for average payloads. What compels you to ignore all the other negative attributes of using an overpowered rocket and instead insist it's now the be all end all, it clearly isn't.

High TWR is only beneficial since we can reduce the thrust without penalty to engine performance.

Edited April 19, 2014 by maccollo

[Dogoncrook]

High TWR is only beneficial since we can reduce the thrust without penalty to engine performance.

Sure but who suffers through tweaking and nerve wracking piloting just because its more efficient technically, when they could easily just build an appropriate rocket that nearly flies itself? It isn't easier to use arm on a small payload. You have to worry about over building as much as under, especially in kerbal.

[csiler2]

They are a problem because I play .23.5, the current version, not some .24 version that isn't out yet and we know nothing about. And because they are unbalanced in the current version they ruin my fun now.

You're playing a BETA not a full release, that means some features have yet to be implemented or are only partially implemented. .23.5 and .24 were in parallel development and it makes sense to start adding the changes of .24 to .23.5. Why should the Devs release a version that's 'balanced' with the current version of a Beta when they already know it will become unbalanced when the next update comes out? That's a lot of extra work to keep the public testors happy for a couple months.

If you think it is premature to even discuss it, what do you make of the fact that the rebalance mod has been created and has been featured in The Daily Kerbal's Modding Mondays?

I think the Community Manager has decided to A) appease a subset of the KSP community that has been vocal about their distaste for the way ARM has been implemented and chose one of the very few ARM-only mods, which not only achieves A, but also promotes the 23.5 update. It's a win-win.

[Pecan]

I am now using ARM parts for payloads of 10t plus as it is so simple.

[Dogoncrook]

I am now using ARM parts for payloads of 10t plus as it is so simple.

Well it isn't easier than an appropriate sized rocket to get in orbit. And the idea that you would complaign that you've imposed a boring playstyle on yourself is a bit rich. Did you use a mainsail on everything before? (Mainsail is still overkill for 10t)

[Pecan]

Well it isn't easier than an appropriate sized rocket to get in orbit. And the idea that you would complaign that you've imposed a boring playstyle on yourself is a bit rich. Did you use a mainsail on everything before? (Mainsail is still overkill for 10t)

I'm sorry, if there is anything in that which is meant to be a discussion I don't know what it is.

"it isn't easier than an appropriate sized rocket" - it is a rocket and it is the appropriate size. It is fewer parts, lower cost, simpler to build and 20t more than the launch vehicle I used before.

"complaign" [sic] - I'm not complaining about anything, I'm stating a fact. This thread is titled "Theory vs Practice" and I am stating that my practice has changed, for the reasons above.

"imposed a boring playstyle" - no imposition, no boredom. Feel free to join in when you next design a rocket.

"use a mainsail" - I have never used a mainsail in anything apart from finding out how awful it was. I have spent many, many hours on launchers and was reasonably pleased with my previous fleet.

10t launcher is single-stage 88t and 10 parts, compared to previous 'standard' 68t which itself was under 17% payload ratio so not that interesting. Payload ratio, however, doesn't seem to be most peoples' interest and at the stage I'm only launching 10t payloads in my tutorial series simplicity is more appropriate.

This is how I am currently choosing to do things. Your complaints are?

[Dogoncrook]

I'm sorry, if there is anything in that which is meant to be a discussion I don't know what it is.

"it isn't easier than an appropriate sized rocket" - it is a rocket and it is the appropriate size. It is fewer parts, lower cost, simpler to build and 20t more than the launch vehicle I used before.

"complaign" [sic] - I'm not complaining about anything, I'm stating a fact. This thread is titled "Theory vs Practice" and I am stating that my practice has changed, for the reasons above.

"imposed a boring playstyle" - no imposition, no boredom. Feel free to join in when you next design a rocket.

"use a mainsail" - I have never used a mainsail in anything apart from finding out how awful it was. I have spent many, many hours on launchers and was reasonably pleased with my previous fleet.

10t launcher is single-stage 88t and 10 parts, compared to previous 'standard' 68t which itself was under 17% payload ratio so not that interesting. Payload ratio, however, doesn't seem to be most peoples' interest and at the stage I'm only launching 10t payloads in my tutorial series simplicity is more appropriate.

This is how I am currently choosing to do things. Your complaints are?

I made an assumption I suppose, but what was the point of your statement of fact? If you believe my comment wasn't discussing anything than what's the point of yours? And then you go right on ahead and make the same assumption (that my comment was a complaint) that you attempt to call me out for. You also contradict yourself , you say your play style has changed, apparently so much you just had to come on here and post a single sentence on it. And yet you mention that the only thing that's changed is the parts you use your play style hasn't really been altered. I couldn't care less what you do with kerbal, if your comment wasn't complaint just say so, the condescending drivel you added wasn't necessary.

[Vanamonde]

As always, guys, discuss the game and not each other's personalities, please.

[architeuthis]

It takes at least 9400 m/s of dV to get to low Earth orbit in real life, whereas in KSP it takes 4500 m/s to get to low Kerbin orbit.

This is a really good point, I personally find the ARM SLS components to be overkill for most of the missions I tend to take on, but if we want to compare the new rockets to their assumed real life analogs it is easy to see a pattern that the KSP rocket engines tend to have slightly lower isp on average and a lot less thrust. Also propellant tanks tend to have lower mass fractions than in reality. So even if Kerbal rocket performance is worse the RL, they may not have been scaled down enough to compensate for the reduced delta-v requirements. But the point of KSP isn't to be as hard as real life!

Assuming the Kerbodyne KR-2L is supposed to represent the Aerojet Rocketdyne J-2X that may potentially be used for a future cryogenic upper stage of the SLS, the Kerbodyne KS-25 is the same as the Rocketdyne RS-25 which powered the Space Shuttle as well as the the SLS core stage, and the KR-1 is the same as the Dynetics "Pyrios" advanced liquid booster (powered by two Rocketdyne F-1 engines!) which may be used for the 3rd SLS flight and forwards; and dividing by the number of engines per core, then we can make these comparisons:

[table=width: 500]

[tr]

[td]Scale factor[/td]

[td]thrust[/td]

[td]Isp vac[/td]

[td]Isp atm[/td]

[/tr]

[tr]

[td]LVN/NERVA[/td]

[td]0.18[/td]

[td]0.94[/td]

[td]0.58[/td]

[/tr]

[tr]

[td]KR-2L/J-2X[/td]

[td]1.91[/td]

[td]0.85[/td]

[td][/td]

[/tr]

[tr]

[td]KS-25x4/RS-25[/td]

[td]0.43[/td]

[td]0.80[/td]

[td]0.87[/td]

[/tr]

[tr]

[td]KR-1x2/F-1[/td]

[td]0.15[/td]

[td]1.22[/td]

[td][/td]

[/tr]

[tr]

[td]S1 SRB-KD25/Shuttle SRB[/td]

[td]0.06[/td]

[td]0.93[/td]

[td]0.97[/td]

[/tr]

[/table]

My conclusions from this are that the KR-2L is probably intended to be an upper stage engine, given its high (by KSP standards) isp, but it otherwise bucks the trend of lower thrust for KSP engines compared to their RL analogs. The KR-2L has better vacuum isp than the KS-25 even though the RL RS-25 has slightly better isp than the J-2X. Both the KR-1 and S1 SRB boosters have massively less thrust than their RL analogs, though the KR-1 has substantially better vacuum isp than the mighty F-1. Interestingly the model used for the KR-1 is smaller than the one used for the KS-25 (though the RL F-1 easily dwarfs the RS-25s used on the Space Shuttle), and they have the same isp, but the KR-1 has slightly higher thrust (per engine).

One of serious problems of engines with better ISP in vacuum is that thrust is not influenced by atmospheric pressure (atmospheric curve in KSP) but fuel consumption - low atmosphere ISP for this engine should be significantly lower but this causing engine to suck fuel at ridiculous rate.

IRL fuel flow is constant for the engine and max thrust is available only at certain pressure range (sea-level, vacuum or something in between for compromise) and thrust is lower in case of under/overexpansion of the exhaust... in short engine should consume same amount of fuel all the time it's turned on and it's thrust should change with altitude (so vacuum engines could be nearly useless on ground in extreme cases).

I agree completely.

Edited April 21, 2014 by architeuthis

[Pecan]

I made an assumption I suppose, but what was the point of your statement of fact?

The point I was making is that I've found the simplicity of build and reduced part-count using ARM parts becomes worth considering for payloads as low as 10t. With fewer, more powerful, parts I am also no longer using asparagus staging as a matter of course, which again makes builds simpler and reduces build-count. The new launch vehicles are also cheaper, in as much as cost has any relevance at the moment. Maintaining a launch TWR of 1.6 - 2 and deltaV of 4,600 - 4,800m/s the only downside is their reduced payload ratio; in this specific case down from 16.49% for a somewhat optimised asparagus build to 11.34%. As 10% rocket payload ratio is to be expected as a rule of thumb that's "acceptable", if not inspiring. Launchers for heavier payloads have better ratios.

Before the introduction of ARM parts I found 'simple' builds - such as just sticking a mainsail under everything - were so inadequate that parts had to be multiplied and supplemented (moar boosters!) just to get decent performance, obviating any benefits. Broadly, the 'practice', which has changed and which I am addressing, is that 'simple' is now, often, also right, thus I have shunned more complex builds that I would have adopted before. You are right, of course, in that I am still interested in efficiency and performance and, to that extent, my play style has not changed.

None of this is a complaint about anything. It is simply a practical observation, such as this thread was intended for. Not polemic.

Edited April 21, 2014 by Pecan

[raygundan]

How do we decide whether or not the parts are balanced?

I think this is it in a nutshell. "Balance" means about a half-dozen different things to start with. Off the top of my head, here's a few:

* Part effectiveness should be uniform enough that every part in the game sees common use

* Cost should correlate well with performance

* Tech-tree level should correlate well with performance

* Things should correlate with the real-world

* Gameplay concerns should be balanced against realism

I'm sure there's more. Some of these things can't even be true at the same time. Realism fights with gameplay and cost/tech correlations. A realistically balanced tree has overwhelming "best parts" like real life does, and nine-tenths of the things in the game would go unused. Every design would use either the one engine with the highest performance, or the one engine with the best cost/performance. The ion engine and the LV-N are great examples where gameplay tradeoffs were made against realism-- the ion is a zillion times more powerful than real life, simply because using it would require tedious, dull gameplay with hours-long burns. The LV-N is quite a bit *less* powerful than real life, because a realistic nuclear thermal rocket with high TWR and Isp would quickly replace every other engine in every design.

In short, there will *always* be something that is "imbalanced" to somebody because there is no solution that satisfies everyone's definition of balance. KSP does a pretty reasonable job of doing some of all of the above-- but there's at least one imbalanced outlier in every category. I think that's about the best you can hope for without just throwing out some definitions of "balanced."