Thrust scaling with atmosphereic pressure, instead of Fuel Flow rate. Yay!

[PB666]

I'm not sure I understand what ramifications this will have. Will it make it harder, easier, or just change the way it works?

Harder at low atmosphere, easier at high altitude.

For example the Nuclear engine will become useless as a launch engine. For aerospike it will not make a bit of difference.

[Thanny]

While it's more realistic, it's going to ground a lot of rockets. With only a fraction of the rated thrust available at sea level, TWR at the launchpad is going to fall well below 1.0 for a huge number of designs.

[Brotoro]

And now will Eve's surface atmospheric pressure be a real killer?

[Nathair]

While it's more realistic, it's going to ground a lot of rockets. With only a fraction of the rated thrust available at sea level, TWR at the launchpad is going to fall well below 1.0 for a huge number of designs.

ISP will scale with pressure doesn't say how much. I think it's a bit premature to start talking about "only a fraction of the rated thrust".

[regex]

I don't think anyone really wanted the Isp to work like it does now.

Judging by the way the fuel-flow isp model was ~defended~ several months ago I'd dispute that. Either way, this is a very welcome change and good news for KSP.

While it's more realistic, it's going to ground a lot of rockets. With only a fraction of the rated thrust available at sea level, TWR at the launchpad is going to fall well below 1.0 for a huge number of designs.

So what. If they don't launch, rebuild them. This is an early access game and things like this happen. E: And this is how rockets are supposed to behave. Finally! Edited February 11, 2015 by regex

[PB666]

Will the ISP nerf be atmospheric or universal? I wouldn't be a huge fan of a universal one.

Vacuum is just a degree of atmosphere. In space 'vacuum' is basically the point in which motion stops flowing like a fluid and starts moving like isolated particles. On kerbin I would guess its right around 32K.

The ISP is a function of atmosphere function. On Kerbin it drops off at 2.6 or 1/2.6) per 5000 M. I do not know if ISP is a linear function of this, but I do know that much of the ISP gain is in the 1st 5000 M and ISP gain over 20,000 M. A miniscule fraction (like 0.1%) of ISP is gained between 36 and 70K

I would expect that thrust would increase similarly in the 0 to 5000 M.

http://wiki.kerbalspaceprogram.com/wiki/Atmosphere the scale height atmosphere constant for Kerbin is 5000

p(alt) = p(MSL) * e ^-(alt./scale height)

[GusTurbo]

This is, of course, fantastic news. This will make Eve even more of a pain And give us a great reason to use SRBs again! Oh happy day!

Not sure about mods the change the stock engines, but I can think of one for SRBs that has always had thrust controlled by Isp.

What's the advantage of SRBs under this more realistic system? For some reason I can't work it out.

[FlowerChild]

So what. If they don't launch, rebuild them. This is an early access game and things like this happen. E: And this is how rockets are supposed to behave. Finally!

More importantly though, I think that ALL existing rocket designs for stock are going to be scrapped with this release given they're implementing a new aero model and are rebalancing the entire game

I think this is the one release where people should accept that they'll essentially be starting over from scratch, and not sweat the details of it. The more "game breaking" changes Squad bundles into this release, the less chance they'll have to do that again in the future, and given they'll no longer be able to swing the "Early Access" flag whenever they make save-breaking changes post 1.0, and people will have a legitimate right to get ticked off about that kind of thing, that's rather important right now.

Edited February 11, 2015 by FlowerChild

[Tw1]

Yes!

*fist pump*

And now will Eve's surface atmospheric pressure be a real killer?

It depends on if they use the current thrust as the max, or the minimum one.

Sounds like it might be the former. Having played with KIDS for a while, this is a far kinder option.

[cantab]

Meh.

Honestly, this is trivial. It's a simple fix to a long-standing niggle and it's maybe "about time too", but really, it doesn't matter much. The current behaviour isn't unphysical in the same way the "soup" aerodynamics is - it could be recreated by having the engine control system automatically limit the maximum thrust, though there's no real reason to do so IRL.

As far as gameplay goes, well on Kerbin launches it just means TWR rises a bit faster than it used to. For Eve and Jool ascents it could really come into play, mandating a specialised engine (eg the Aerospike) for them - but is limiting vehicle design in that way really going to be a good thing?

[regex]

Honestly, this is trivial. It's a simple fix to a long-standing niggle and it's maybe "about time too", but really, it doesn't matter much.

It matters quite a bit. The less things I can point at in this game and go "because ~Squad~" the better. The less things we can all say #LOLSOKERBAL about, the better. The more things we can point at that are realistic while playing a fun game, the better.

[RobotsAndSpaceships]

I believe the official terminology is LELSOKERBAL. Get your facts straight before you start spouting your BS all over the forums Regex.

[Renegrade]

Here: http://kerbaldevteam.tumblr.com/post/110666185425/devnote-tuesday-point-sharp-end-towards-space

Superb! Also thanks for pointing that out

I believe it was first done in Arcturus Thrust Corrector, and also appears in KIDS and BTSM. I suspect there are some other mods that also do it I'm not aware of.

RealFuels does it too, plus I'm certain there's more. If there aren't more, I could always write one myself heh.

(ATC is the earliest one I've been able to find to date)

Will the ISP nerf be atmospheric or universal? I wouldn't be a huge fan of a universal one.

It would only impact craft in atmospheres, and only a bit. Fuel usage might actually go down a bit, but you'll need moar boosters if you were low on TWR to begin with.

This wasn't even part of the realism crowd. I wanted this change. I don't think anyone really wanted the Isp to work like it does now.

I think I'm not part of the realism crowd - I'm rather lax on ISRU and scale realism for instance (your 3.2x Jumbo is about the largest I can stomach with current KSP engine) - I've also wanted it in forever and a half. My view is that as long as realism isn't imposing too much performance loss, and isn't conflicting in any serious way with gameplay, it's perfectly welcome in a simu-game like this.

Judging by the way the fuel-flow isp model was ~defended~ several months ago I'd dispute that.

Vigorously, violently defended. Like the Spanish Inquisition descending on a person accused of witchcraft (which nobody expected, of course *cough*).

What's the advantage of SRBs under this more realistic system? For some reason I can't work it out.

They have a narrow specific impulse range, so a narrow thrust variance... Plus you can cheaply (space bucks wise) loft a rocket above the thick part of the atmosphere with 'em to avoid the thick air..

As far as gameplay goes, well on Kerbin launches it just means TWR rises a bit faster than it used to. For Eve and Jool ascents it could really come into play, mandating a specialised engine (eg the Aerospike) for them - but is limiting vehicle design in that way really going to be a good thing?

The limitation (if it exists, keep in mind that they might not extend it down to zero) would be a good thing - that's basically what gameplay is. Giving the aerospike some sort of purpose (aside from 'looking pointy') can't be a bad thing.. it's otherwise 1.75t of overweight, underpowered, unstackable junk right now.

Otherwise, we might as well give the T30 thrust vectoring, a short form factor, zero mass, and 800 isp across the board and delete all the other engines.

My only concern is Harv's phrasing implies that the thrust engines currently have is their minimum, which is kinda backwards mathematically..

[NathanKell]

While the mechanics behind this have been explained rather well, I think it's time we maybe had some cold hard facts. That might make it easier for some to grasp.

Now, this chart is taking the current maxThrust as the maximum thrust, so in atmosphere thrust will be lower. If, in fact, they decide to go the other way, then, well, it'll be a different chart, but the ratios will hold.

This is as of .25, IIRC.

Engine			Mass	Thrust	SL Thr.		IspSL/V
LV-1/LV-1R		0.03	4	3		220	290
24-77			0.09	20	17		250	300
48-7S			0.10	30	26		300	350
LV-909			0.50	50	38		300	390
LV-N			2.25	60	17		220	800
Mark 55 Radial		0.90	120	109		290	320
Aerospike		1.50	175	174		388	390
RAPIER (Rocket)		1.20	175	156		320	360
LV-T45			1.50	200	173		320	370
LV-T30			1.25	215	186		320	370
Poodle			2.00	220	152		270	390
Skipper			3.00	650	562		320	370
Mainsail		6.00	1500	1333		320	360
LFB KR-1x2		6.00	2000	1706		290	340
Kerbodyne KR-2L		6.50	2500	1842		280	380
S3 KS-25x4		9.75	3200	2844		320	360

EDIT: Oh, and if you've ever used ModuleRCSFX to fix stock bugs, well, this is one of the stock bugs it fixes. So you've been having corrected thrust without knowing it. :]

Edited February 11, 2015 by NathanKell

[cantab]

Expressing it as a percentage would be more intuitive. Or in terms of such and such old launch TWR > so and so new TWR. In any case, expect the numbers to be given a big shake up.

From a realism perspective, KSP engines are underpowered boat anchors as they are. (On the other hand they have unlimited ignitions, are deeply throttlable, and never ever fail, so it's not all bad.) They don't really need making worse in that respect. The poor engine TWR, combined with tanks seemingly made from thick steel, skews staging strategies - in particular, throw in massless unlimited-flow-rate fuel lines and decouplers that never fail (the infamous decoupler bug nothwithstanding) and you end up with players using asparagus everywhere.

[kujuman]

I hope the Isp curves extend past 1. having the same thrust at SL on Kerbin and SL on Eve is annoying. (this may have been fixed...but I haven't been to Eve in a LONG time.

What's the advantage of SRBs under this more realistic system? For some reason I can't work it out.

With constant fuel flow, thrust is lower deeper in the atmosphere (aka launch). This is also the time when your rocket is heaviest. Therefore, launchers will see lower TWR than we're used to. SRBs are a good way to add thrust for little cost.

[I_Killed_Jeb]

I believe the official terminology is LELSOKERBAL. Get your facts straight before you start spouting your BS all over the forums Regex.

I wish I had a downvote.

[regex]

I wish I had a downvote.

Because he took my joke (actually NathanKell's, but don't tell anyone) and made another funny? Or is it because of "LEL"?

#LOLSOCONFUSEDABOUTKERBALS

[NathanKell]

regex, you used it first, I just popularized it.

cantab: I agree with you that KSP engines and tanks are wicked heavy. On the other hand, the solar system (and Kerbin itself) is wicked small--heck, Kerbin is less than a third the size of the Moon. If you fixed dry masses and structural fractions, you'd be hard pressed ever to not SSTO--indeed, most Real Life rocket stages yield more delta V than is needed for LKO.

That said: do note that the SRBs have the correct dry masses for SRBs, and the NTR is actually quite good--and does not have to deal with the bane of real life NTRs, the (lack of) density of their propellants--which definitely tilts things in favor of the NTR and SRBs. If the ratios were kept, the RT-10 would mass 1.5t heavier (all of it extra dry mass, so a dry mass of 2.0) and the LV-N would mass 10 (!) tons.

Edited February 11, 2015 by NathanKell

[Superfluous J]

I didn't realize this change would be so drastic. If it makes it so much harder to get high (as in > 1) TWR at Kerbin's surface, I can see why they didn't want to make it until they changed the aerodynamics model. Assuming, of course, that the new model is as close to (and perhaps even more deep than) FAR as it appears it's going to be.

Launching straight up for 10km with 1.1 TWR is no fun. Moar Boosters, no matter how amusing a phrase, is also no fun after the dozenth time or so. This change would have forced one of those, it seems. Or both.

But in FAR, low TWRs aren't a big deal and are actually FUN to launch. I still personally go for 1.5 or so but I'm a bit of a madman.

The decision to both keep the horrible-terrible-broken-omgitssolol method we have now in tandem with the atmosphere we have now makes more sense to me than ever, and actually gives me more respect for Squad and their thought processes.

[I_Killed_Jeb]

Because he took my joke (actually NathanKell's, but don't tell anyone) and made another funny? Or is it because of "LEL"?

#LOLSOCONFUSEDABOUTKERBALS

Seems I may have missed sarcasm by RobotsAndSpaceships. I award myself no points and may God have mercy on my soul

[Stormweaver]

I didn't realize this change would be so drastic. If it makes it so much harder to get high (as in > 1) TWR at Kerbin's surface, I can see why they didn't want to make it until they changed the aerodynamics model. Assuming, of course, that the new model is as close to (and perhaps even more deep than) FAR as it appears it's going to be.

It isn't that bad tbh. I use BTSM pretty much exclusively - that is, nerfed engines, soupy atmosphere and far heavier payloads than stock (not to mention a distinct lack of radial decoupling) - and in the end TWR is rarely a problem, since you just build beefier things to do the lifting. You end up with larger, more impressive rockets and a fondness for solid fuel boosters that simply won't happen with stock.

With the Aero changes though, I doubt we'll see a huge difference in launchers before and after 1.0 hits. Just maybe a few more winglets.

[SorryDave]

I don't believe the change will have a big impact.

This release will totally change how the game is played, but this one change should have a small impact.

There will be all kinds of reasons to go straight up into thin atmosphere before beginning your turn. Instead of the "turning suddenly at 10k" or the "begin turning early".

One thing they are promising is a rebalance of engines, some may get nerfed, but many will probably be more useful.

I am looking forward to learning how to play all over again.

[FlowerChild]

The decision to both keep the horrible-terrible-broken-omgitssolol method we have now in tandem with the atmosphere we have now makes more sense to me than ever, and actually gives me more respect for Squad and their thought processes.

It's really not as big a deal as it may appear, even with the current aero. It makes things *slightly* harder, but not so much so that I think it would really inspire anyone to go booster crazy. For the most part it just feels better.

It isn't that bad tbh. I use BTSM pretty much exclusively - that is, nerfed engines, soupy atmosphere and far heavier payloads than stock (not to mention a distinct lack of radial decoupling) - and in the end TWR is rarely a problem, since you just build beefier things to do the lifting. You end up with larger, more impressive rockets and a fondness for solid fuel boosters that simply won't happen with stock.

With the Aero changes though, I doubt we'll see a huge difference in launchers before and after 1.0 hits. Just maybe a few more winglets.

Beat me to making the same point

[Renegrade]

I didn't realize this change would be so drastic. If it makes it so much harder to get high (as in > 1) TWR at Kerbin's surface, I can see why they didn't want to make it until they changed the aerodynamics model. Assuming, of course, that the new model is as close to (and perhaps even more deep than) FAR as it appears it's going to be.

Like Stormweaver and FlowerChild, I play lots of BTSM, which is stock aero (souposphere) + thrust correction. It's not a dramatic scary change like say cutting Isp in half would be. Given how much easier it is to get to orbit (it's a bit harder flying wise, but much easier building wise) with real aero, the net effect is still 'easier'. I also always play with a thrust corrector (KIDS, RealFuels, etc) if I'm playing non-BTSM saves.

Basically your thrust at sea level (using the current thrust as being vacuum thrust as Nathan did) will be reduced to (SeaISP/VacISP).

For example, a T-30 is 370 vac/320 SL and 215kn of thrust.

On the launchpad (actually uh.. 60m below it? what was the launchpad altitude? 60? 140? something like that), it would get (320/370)*215 thrust, or 0.8605 (86.05%) * 215 = 186kn.

That might seem scary, but sea level Isp quickly gives way to vacuum isp.

For the 320/370 engines (T30, T45, Skipper), the curve looks like this:

Alt   AirPress%  Isp
    0m 1.00000a: 320.00
  500m 0.90484a: 324.76
 1000m 0.81873a: 329.06
 2000m 0.67032a: 336.48
 4000m 0.44933a: 347.53
 6000m 0.30119a: 354.94
 8000m 0.20190a: 359.91
12000m 0.09072a: 365.46
20000m 0.01832a: 369.08
25000m 0.00674a: 369.66
40000m 0.00034a: 369.98
46500m 0.00009a: 370.00

Note for instance that at 8km altitude, the Isp is 97% of it's maximum.

So it's not really a big thing (just a bit over 13% for the 370/320 engines and less for the Mainsail for instance)..unless they've extended it to zero and you're on Eve's surface.