Why the across the board LFO engine ISP nerfs?

[panzer1b]

Well as the title says, while i dont actually mind, why nerf all the engines that use LFO, for example the 909 now gets under 350 isp.

The game had already turned into nuke for 90% of anything, i fail to see why youd use anything but nukes (or ions for super light stuff) now?

Before even interplanetary missions could be done with conventional engines without bringing insane amounts of fuel, now it seems that the game has turned into a nuke/jets for everything except stuff like Tylo landers where the nukes dont quite give enough TWR to make a safe landing.

Guess its the age of nuclear travel, where conventional engines (outside of career) are at best used to lift stuff into orbit.

[X-SR71]

And nukes don't even need Oxidizer anymore!

Space planes with LF only, jet engines for lift off and nukes for interplanetary is the way to go!

[NovaSilisko]

From my understanding, the aero redo lowers the delta-v requirement to reach orbit, so stuff has been nerfed a bit to compensate.

[Coga19000]

For one, the new aerodynamics model greatly reduces drag losses, and I think it increased sea level ISP all around, so I guess it was an attempt to balance things around. My experience with FAR tells me that the new model shaves off 1km of Delta-v on Kerbin launches, which have to be compensated for.

Secondly, 1.0 adds a Kethane-like resource system for fuel harvesting, which when properly used can also make decreased ISP more of a hindrance than an actual problem.

There might actually be more reasons, but those are the ones I could document by the current previews.

EDIT: Partially ninja'd.

[Renegrade]

Well as the title says, while i dont actually mind, why nerf all the engines that use LFO, for example the 909 now gets under 350 isp.

ISP is linear. Being under 350 doesn't suddenly make it invalid. I've done LOOONG range interplanetary on OLD skippers and mainsails.

Given that LV-Ns are no longer LF/O engines, they are actually less effective than before.

And nukes don't even need Oxidizer anymore!

Space planes with LF only, jet engines for lift off and nukes for interplanetary is the way to go!

Note that LF tanks are now heavier than their LF/O compatriots in general (8:1 ratio vs 9:1). That's giving them a 6% (ln(9) vs ln(8)) across-the-board reduction in efficiency. Also jets are using proper fuel flow now allegedly (I haven't studied this in detail yet but a quick glance at a TurboJet tells me they're about 4.7x worse as their old pre-fix ACTUAL ISP peaked at around 37,500), so you'll need to carry more. The jet engines are also heavier and have limited effective ranges it seems (although more thrust at peak than before).

[Coga19000]

The jet engines are also heavier and have limited effective ranges it seems (although more thrust at peak than before).

I'm not sure how you reached this conclusion, but it could also be the reason. The whole jet engine setup is also more complex, and generally heavier -especially if the Engine Precooler is required for hypertensive

hypersonic flight.

[Basilo1146]

Wouldn't the efficiency for the NERVA's be exactly the same if it was only calculated based on mass before, and better if they somehow screwed up and only measured it based on mass of LF before the update? Anyways, I really don't get the vacuum nerf to ISP. I would have thought that an atmo nerf and the new thrust calculation would be more than enough.

[NathanKell]

The problem with nerfinig atmo Isp only, as people who use KIDS with that option and "thrust scales with Isp" on can attest, is that you need to nerf atmo Isp to like 1/2 what Vac Isp is (at least) to try to make up the difference. Then your engines double in thrust (or more) between the ground and 20km up. If you want a taste of what that would be like, try only using LV-909s and Poodles on your rockets, no other engines.

[GoSlash27]

Well as the title says, while i dont actually mind, why nerf all the engines that use LFO, for example the 909 now gets under 350 isp.

The game had already turned into nuke for 90% of anything, i fail to see why youd use anything but nukes (or ions for super light stuff) now?

Before even interplanetary missions could be done with conventional engines without bringing insane amounts of fuel, now it seems that the game has turned into a nuke/jets for everything except stuff like Tylo landers where the nukes dont quite give enough TWR to make a safe landing.

Guess its the age of nuclear travel, where conventional engines (outside of career) are at best used to lift stuff into orbit.

I'll be doing an extensive analysis of the readjusted engines over the course of this week. It's definitely too early to say which engine is best for which situation.

Having said that, the nuke was rarely the "best" engine to use in .90 from the standpoint of mass efficiency or cost in .90.

Best,

-Slashy

Edited April 27, 2015 by GoSlash27

[Hcube]

i feel like the nuke was one of the engines that most needed a nerf (you guessed right il also thinking about the 48-7S ) but that it got buffed instead : it has the same vac ISP while every other engine had it lowered. Nerf all but one and you will buff the one ! W.H.Y ?

[NathanKell]

Perhaps because 2.25 tons is the same mass as 3 tons and no gimbal is the same as gimbal?

[Brotoro]

i feel like the nuke was one of the engines that most needed a nerf (you guessed right il also thinking about the 48-7S ) but that it got buffed instead : it has the same vac ISP while every other engine had it lowered. Nerf all but one and you will buff the one ! W.H.Y ?

Buffed? It got a mass increase and had its gimbal removed. How is that a buff?

[GoSlash27]

Perhaps because 2.25 tons is the same mass as 3 tons and no gimbal is the same as gimbal?

^This. The mass penalty will be a big hit for the nuke. In most cases, the 48-7S made a better interplanetary engine than the nuke due to the nuke's sheer mass. That will not have improved any.

Best,

-Slashy

[Wayland]

Not a fan of the NERVA getting excessively nerfed.

Getting rid of the gimbal was one thing. Increasing the mass is another.

Not sure what I think about the efficiency change based on fuel. If anything getting rid of the need for a seperate tank for LOX would increase storage efficiency in real life.

[smjjames]

The problem with nerfinig atmo Isp only, as people who use KIDS with that option and "thrust scales with Isp" on can attest, is that you need to nerf atmo Isp to like 1/2 what Vac Isp is (at least) to try to make up the difference. Then your engines double in thrust (or more) between the ground and 20km up. If you want a taste of what that would be like, try only using LV-909s and Poodles on your rockets, no other engines.

What is KIDS?

[Tarheel1999]

What is KIDS?

A KSP mod that altered how ISP/Thrust was handled.

https://www.google.com/webhp?hl=en#hl=en&q=KSP+KIDS

[moogoob]

The NERV has one big issue now - overheating. On small craft, the whole craft gets hot enough to start blowing up attached batteries on a simple 850m/s munar burn. Need parts as heat sinks (more mass!) to compensate. So yeah, they've been nerfed pretty good.

[AtmaStorm]

I vaguely recall something about engine Isps being as good as they were because of the soup, but that was a long time ago before the mun was added. I feel as though the squad monkey came in, slapped me in the face and hooted 'SOUPS GONE' when I see the poodle has lost 40 seconds of Isp, or the terrier losing 45. The aerospike has been rendered practically useless.

[Giggleplex777]

The main problem I have with the nerf is the performance of engines designed to operate in the vacuum. The performance of my spacecraft in orbit have been significantly compromised. That really sucks.

Edited April 28, 2015 by Giggleplex777

[AtmaStorm]

The main problem I have with the nerf is the performance of engines designed to operate in the vacuum. The performance of my spacecraft in orbit has been significantly compromised. That really sucks.

100% with you on this. Nerf the engines that you'd use for atmospheric stuff in some way, okay, but leave my Terrier and poodle alone.

[Brotoro]

The main problem I have with the nerf is the performance of engines designed to operate in the vacuum. The performance of my spacecraft in orbit has been significantly compromised. That really sucks.

Giggleplex777 is correct.

[oversoul]

For one, the new aerodynamics model greatly reduces drag losses, and I think it increased sea level ISP all around, so I guess it was an attempt to balance things around. My experience with FAR tells me that the new model shaves off 1km of Delta-v on Kerbin launches, which have to be compensated for.

I disagree; 0.90 took about 4500dV to orbit, and FAR made it less as you state.

But I just tried to attain orbit with a 3800dV craft and failed. Had enough to barely get the APO to 70km; the remaining 150dV was nowhere near enough to complete a circularization burn.

So after my initial attempts, it feels like it's as expensive or more expensive than 0.90 stock aerodynamics to attain an 80km orbit.

[NecroBones]

The main problem I have with the nerf is the performance of engines designed to operate in the vacuum. The performance of my spacecraft in orbit has been significantly compromised. That really sucks.

EDIT: I've been corrected. Ignore:

I'm finding the vacuum-engine nerf to be really perplexing, particularly when looking at the thrust numbers. I thought the poodle was pretty under-utilized as it was, and now it has a quarter of its former thrust. The 48-7S only lost half its thrust (no change in mass), while the 909 lost about 70% of its thrust (also no change in mass). Considering the 48-7S was the one usually heralded as having the most over-powered TWR, I'd say it's strange that it was nerfed less in TWR than the others.

Most of the "lifter" engines were tweaked by around 6-30%, thrust-wise, though the "Mammoth" quad engine gained 546 thrust, plus 5.25 tons. Meanwhile the KR-2L lost about 60% of its thrust, while gaining 2 tons.

So to me, it looks like the devs aimed for similar "difficulty" to orbit as before, while making sure we get much longer burn times for orbital maneuvers, and more tricky lander design constraints.

As an amusing aside, I remember them buffing up the ion engine recently, for the sake of fun. Guess what? Thrust went from 2, down to 0.048, a 97.6% reduction.

Edited April 28, 2015 by NecroBones

[Renegrade]

I'm finding the vacuum-engine nerf to be really perplexing, particularly when looking at the thrust numbers. I thought the poodle was pretty under-utilized as it was, and now it has a quarter of its former thrust.

Um it was 2t / 220kn before, now it's 1.75t / 220kn. It effectively gained TWR (although not absolute thrust, but it certainly didn't lose any).

As an amusing aside, I remember them buffing up the ion engine recently, for the sake of fun. Guess what? Thrust went from 2, down to 0.048, a 97.6% reduction.

OH.. you're looking at the wrong numbers. It was buffed again, but only by a tiny amount (2kn to 2.016kn).

You want to look at Max Thrust (Vac) for vacuum numbers

But I just tried to attain orbit with a 3800dV craft and failed. Had enough to barely get the APO to 70km; the remaining 150dV was nowhere near enough to complete a circularization burn.

I just launched a mun orbiter craft; 3431 vacuum delta-v on the pad. Got to orbit with only about 264 missing, and I kinda botched the ascent (not badly, but I was off profile significantly). I'm in a 70x87 clumsy orbit (due to the botchery). 3,695 expended. I could probably bring that down to 3500 or thereabouts with a correct ascent profile and maybe optimizing my aerodynamics a bit (craft has a few external greebles that I might be able to ditch)

Edited April 28, 2015 by Renegrade

[NecroBones]

Um it was 2t / 220kn before, now it's 1.75t / 220kn. It effectively gained TWR (although not absolute thrust, but it certainly didn't lose any).

OH.. you're looking at the wrong numbers. It was buffed again, but only by a tiny amount (2kn to 2.016kn).

You want to look at Max Thrust (Vac) for vacuum numbers

You know what, I'm looking at the config files (not the in-game display), and I think they changed how it works. "Max Thrust" is no longer actually max thrust, aka vacuum thrust. They must be applying an ISP curve multiplier. Ugh. This is going to make fixing the mods real fun.