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

[Torquemadus]

It will be interesting to see what effect this change will have on air breathing engines, such as the turbojet. Jet ISP increases somewhat after take off, but then starts to decline as altitude increases. Presumably, this means that jets will loose thrust at higher altitudes?

[regex]

It seems that this is the 'get Regex to shut the hell up by giving him what he wants' edition!

They'll never give me what I want, but it's nice to see them finally fixing their game.

[Ikaneko]

They'll never give me what I want, but it's nice to see them finally fixing their game.

I've never gotten your exact views on how development should go ahead.

Not SQUAD's views is about as far as I've gotten, but I thought this new update will tick off several of your "Points of disagreement".

You know, new lift model, isp change up, etc.

I'm with you on the DV readout thing though. Carting a rocket out to the pad just to see DV?? Farcical.

[Red Iron Crown]

I've never gotten your exact views on how development should go ahead.

Not SQUAD's views is about as far as I've gotten, but I thought this new update will tick off several of your "Points of disagreement".

You know, new lift model, isp change up, etc.

I'm with you on the DV readout thing though. Carting a rocket out to the pad just to see DV?? Farcical.

Oh man, he wrote up a proper manifesto a few months ago, you should see if you can find it with the search.

Edit: Linky. His views might have changed since then, though.

[Randazzo]

They'll never give me what I want, but it's nice to see them finally fixing their game.

You could always go play Orbiter.

[regex]

I've never gotten your exact views on how development should go ahead.

It wouldn't be "fun" anymore because one of the things I'd love to see is more realism: proper majestic planets, realistic engines and fuels, procedural parts so we can make great-looking replicas, etc... I can live without that in stock, though, considering there are some excellent mods for those things. Hopefully Squad ensures that modders can access and change the base game values because recently they've locked out some pretty important variables from realism modders (the pad weight is the biggest example, I haven't touched the code in two version, though, so I'm not entirely up-to-date).

Also, the re-introduction of The Barn is bad for the game, IMO, but adding female Kerbals is a total win.

Not SQUAD's views is about as far as I've gotten, but I thought this new update will tick off several of your "Points of disagreement".

It most certainly will, and it's looking to be a very good update for the game. I'll probably try 1.0 myself when it's out without immediately running to the mods forums and I'll be willing to let my daughter play it without worrying about her learning Bad Things.

You could always go play Orbiter.

Orbiter doesn't allow me to build my own spacecraft via VAB/SPH, KSP does. Orbiter is also Windows only while KSP runs natively(-esque?) in Linux. Trust me, I've looked into it.

Edit: Linky. His views might have changed since then, though.

Re-reading that, I feel like they're making good on some of what I consider to be the most important points. I still think axial tilt and multiple launch sites would be one of the most awesome things you could add to KSP. I don't think it's realistic to ask them to make a properly-scaled solar system, though (again, excellent mods cover that right now). Edited February 11, 2015 by regex

[LABHOUSE]

They'll never give me what I want, but it's nice to see them finally fixing their game.

They should, all of it (and then some).

Not suggesting:

Also, I think that they should keep the currently sized and everything the kerbin system has, just make it another system, far away from one identical to ours and with humans instead of kerbals (could be changed in debug menu after the player reaches kerbin ksc) that can be launched, and once the player reaches ksc on kerbin, they could do stuff there.

Edited February 11, 2015 by LABHOUSE

[rosenkranz]

While I think this is pretty cool, it's pretty minor in my book. I always wrote this off as the turbopumps being throttled to maintain a specific thrust rating rather than being fixed fuel flow. With ever more advanced pumps, who is to say they won't start doing just that in real life.

I suppose my question is this: Is there a RL situation where it might be worth while to throttle the pumps to maintain a specific thrust rather than just letting them run wide open?

[Nathair]

I suppose my question is this: Is there a RL situation where it might be worth while to throttle the pumps to maintain a specific thrust rather than just letting them run wide open?

The shuttle used to throttle back quite significantly when approaching max Q to reduce stress. (They also "cut thrust" on the SRBs at about the same point.)

[regex]

AFAIK even a deep-throttling engine wouldn't have its delta-V affected by throttling because the reaction mass required for velocity change remains the same, which is unlike the current KSP model because the fuel-flow was directly affected by atmospheric pressure regardless of how you throttled while thrust remained the same per throttle setting.

Well, you might lose delta-V to throttling because the engine's chamber pressure might be too low to sustain proper combustion (chemical rocket) and you're not using your fuel well... KSP's engines are very unrealistic in this way since even the SSME was only throttlable down to 67% IIRC. Most lifting engines run full blast or within a small range (like 95~107%, for example).

E: For me, realistic throttling is an unimportant detail for stock since half of the fun I find in the game is flying loose and manually. Sure, I respect the limits in RSS/Realism Overhaul, and proper engines work perfectly fine there, but for a small solar system full-blast throttle all the time is very imprecise IMO.

Edited February 11, 2015 by regex

[problemecium]

I'm not excited about this - I'm afraid I'm going to have to re-learn how to build efficient lift rockets all over again :\

On principle I'm in favor, but I can't say it wasn't nice having the Kerbals work out super-precise engines that always made sure to provide consistent thrust in any condition...

[regex]

I'm not excited about this - I'm afraid I'm going to have to re-learn how to build efficient lift rockets all over again :\

Oh c'mon, it'll be like playing a whole new game all over again! That's when KSP is the best!

[metl]

Okay, so here's a few observations and questions I have regarding all of this. First, in the current model, I would reduce my throttle for part of my ascent to conserve fuel. I worked under the assumption that since the engine became more fuel efficient as I ascended, I could reduce the throttle and get the same thrust. I generally eyeballed by ascent speed and assumed since I kept it steady, the thrust was steady. I'm guessing that was wrong and not at all what was really going on?

The second thing is, how does this affect Dv calculations if the thrust does not remain constant? I guess it would be steady once in a vacuum, so I guess the answer is it wouldn't?

So again, does this have any actual effect on the user's gameplay experience (beyond altering how TWR is calculated) or is this just more of an internal thing?

[Orionkermin]

I wonder if this means that the LV-N will have much more thrust in vacuum than it's current form.

[regex]

Okay, so here's a few observations and questions I have regarding all of this. First, in the current model, I would reduce my throttle for part of my ascent to conserve fuel. I worked under the assumption that since the engine became more fuel efficient as I ascended, I could reduce the throttle and get the same thrust. I generally eyeballed by ascent speed and assumed since I kept it steady, the thrust was steady. I'm guessing that was wrong and not at all what was really going on?

You can definitely throttle down to maintain a good ascent speed. in RSS I've shut down engines to do the same (because throttling is generally restricted and that's how Saturn V did it).

The second thing is, how does this affect Dv calculations if the thrust does not remain constant? I guess it would be steady once in a vacuum, so I guess the answer is it wouldn't?

Calculating your delta-V is done in the same manner as now.

So again, does this have any actual effect on the user's gameplay experience (beyond altering how TWR is calculated) or is this just more of an internal thing?

It's a realism thing. If Squad's aero overhaul results in a system like NEAR or FAR, you'll want your on-pad TWR somewhere around 1.3 and you'll start slight turning (5 degrees) at 75~80m/s, following the prograde marker until you hit the third atmosphere band, at which point you adjust your trajectory. At least, that what works for me and it varies by rocket, how much the TWR changes in flight, how staging goes, etc... Your launches should end up looking much more like a real rocket launch rather than the previous snooze-worthy climb to 8~12km.

I wonder if this means that the LV-N will have much more thrust in vacuum than it's current form.

It really depends on how they define it. If the fuel-flow is based on sea-level isp then the thrust of the LV-N will have to be set much less than now to maintain the current in-space thrust. If they base fuel-flow on vacuum isp then nothing will have to change in the engines.

[Thanny]

I'd like to add a couple points. First, the information about changing aerodynamics clearly expressed Squad's desire to not obsolete existing designs. People are not going to have to start from scratch with every rocket.

Second, I don't think many people understand the significance of the TWR drop, if the current thrust becomes max thrust, rather than initial thrust. The KR-2L probably gives the most extreme example. If you have a ship weighing about 195t powered by a single KR-2L, your current TWR is 1.3, which makes for a bit of a slow start but works quite well. If you make the current max thrust the vacuum max thrust, then your TWR with the same ship drops to 0.96, and you won't even get off the pad.

It is a big deal which will require massive changes in ship designs, which is something Squad has said they don't want to force on people. So it's very likely the changes to engines will be more extensive, so that a good chunk of existing rockets can still fly. KSP is, after, intended to be a game first and simulator second.

[kujuman]

So it's very likely the changes to engines will be more extensive, so that a good chunk of existing rockets can still fly.

Harv's expressed that he knows the most important rule of software updates several times in the past: if an update is worth it enough to break existing saves, break as many things as you can at the same time.

Several of us have lived through updates that broke our rockets and saves. When that started happening less and less in the .20s updates, I figured we'd have to endure at least one last great breaking event before 1.0. There's no compelling reason for Squad to "rebalance" in such a way as to make it so rocket A performs the same in 1.0 as it did in 0.90; in fact, such a "rebalance" would not be a rebalance at all because nothing is changing.

We're going to have to start designing rockets for the new atmo performance, adding room for upgraded engineers, rebalance on every part (including cost, big factor in career), new engine flow etc. So we're going to have to learn a whole neeeeww gaaammeee!

[LABHOUSE]

You can definitely throttle down to maintain a good ascent speed. in RSS I've shut down engines to do the same (because throttling is generally restricted and that's how Saturn V did it).

Calculating your delta-V is done in the same manner as now.

It's a realism thing. If Squad's aero overhaul results in a system like NEAR or FAR, you'll want your on-pad TWR somewhere around 1.3 and you'll start slight turning (5 degrees) at 75~80m/s, following the prograde marker until you hit the third atmosphere band, at which point you adjust your trajectory. At least, that what works for me and it varies by rocket, how much the TWR changes in flight, how staging goes, etc... Your launches should end up looking much more like a real rocket launch rather than the previous snooze-worthy climb to 8~12km.

It really depends on how they define it. If the fuel-flow is based on sea-level isp then the thrust of the LV-N will have to be set much less than now to maintain the current in-space thrust. If they base fuel-flow on vacuum isp then nothing will have to change in the engines.

So no more boring launches? No more mechjeb need?

[Van Disaster]

I'd like to add a couple points. First, the information about changing aerodynamics clearly expressed Squad's desire to not obsolete existing designs. People are not going to have to start from scratch with every rocket.

Second, I don't think many people understand the significance of the TWR drop, if the current thrust becomes max thrust, rather than initial thrust. The KR-2L probably gives the most extreme example. If you have a ship weighing about 195t powered by a single KR-2L, your current TWR is 1.3, which makes for a bit of a slow start but works quite well. If you make the current max thrust the vacuum max thrust, then your TWR with the same ship drops to 0.96, and you won't even get off the pad.

It is a big deal which will require massive changes in ship designs, which is something Squad has said they don't want to force on people. So it's very likely the changes to engines will be more extensive, so that a good chunk of existing rockets can still fly. KSP is, after, intended to be a game first and simulator second.

Yeah, that's a desire rather than a promise - I have a feeling that's going to get quietly ignored. It's also still currently a game in development so there's no real reason anyone should expect anything at all to work between versions, let alone craft performance being unchanged. Aero changes that bring real drag unrelated to mass are going to pretty much obsolete a huge pile of rocket designs as it is. What I suspect might happen is a bunch of parts get tweaked so overall performance for tank & engine combos is broadly similar if taken end-to-end which fulfills the spirit of their desire - but I also suspect the actual journey from launch to debris is going to be rather different.

Large amounts of current stock rocket designs technically work in FAR, but you would never want to actually use them...

[cantab]

I'd like to add a couple points. First, the information about changing aerodynamics clearly expressed Squad's desire to not obsolete existing designs.

Not quite. Their viewpoint expressed was rather that they wanted some way to test out the new aerodynamics, and one way was to see how the old stock planes flew in them. And that I think is just talking about the aerodynamics. The part rebalancing is another matter, that will throw the behaviour of old craft off inevitably.

[Renegrade]

Second, I don't think many people understand the significance of the TWR drop, if the current thrust becomes max thrust, rather than initial thrust. The KR-2L probably gives the most extreme example. If you have a ship weighing about 195t powered by a single KR-2L, your current TWR is 1.3, which makes for a bit of a slow start but works quite well. If you make the current max thrust the vacuum max thrust, then your TWR with the same ship drops to 0.96, and you won't even get off the pad.

Or you could wait 15 seconds, and lift off the pad. Or slap a pair of those S1 SRB-KD25k (gesundheit!) SRBs on the side, and have a 1.3 TWR again. Granted my test rocket was only 194.8 tons, not 195, but that brought the TWR back up to 1.31 on the pad again. And also gave me 400 extra delta-v and gave me something to strut sections across.

Also the new aero will mean the air is more like... air, than say.. thick jello. The usual 1.7-1.9 TWR needed to keep on movin' in stock air won't be required anymore, so you'll be fine on the pad with a 1.3-1.5. (1.3 is very low for a current stock air rocket)

[Northstar1989]

I read through as much of the thread as I could, and I never saw it pointed out that not all bell thrusters are made to perform most efficiently in vacuum.

http://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Rocket_nozzle_expansion.svg/200px-Rocket_nozzle_expansion.svg.png

Source: Wikipedia article on rocket engine Isp

I wonder if any of the engines will be made into dedicated "lifter" engines that have more efficiency/power at higher pressure than in space?

No, you don't understand the Wikipedia article. ALL, I repeat *ALL* engine nozzles have the highest ISP in vacuum. The diagram you posted relates the shape of the exhaust jet to ambient pressure- which is always zero in vacuum. Therefore ALL exhaust streams are under-expanded in vacuum. That figure is about matching exhaust pressure to ambient pressure- which means expanding it as much as possible in vacuum.

Regards,

Northstar

[NecroBones]

I read through as much of the thread as I could, and I never saw it pointed out that not all bell thrusters are made to perform most efficiently in vacuum.

http://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Rocket_nozzle_expansion.svg/200px-Rocket_nozzle_expansion.svg.png

Source: Wikipedia article on rocket engine Isp

I wonder if any of the engines will be made into dedicated "lifter" engines that have more efficiency/power at higher pressure than in space?

No, you don't understand the Wikipedia article. ALL, I repeat *ALL* engine nozzles have the highest ISP in vacuum. The diagram you posted relates the shape of the exhaust jet to ambient pressure- which is always zero in vacuum. Therefore ALL exhaust streams are under-expanded in vacuum. That figure is about matching exhaust pressure to ambient pressure- which means expanding it as much as possible in vacuum.

Regards,

Northstar

That's a good point.

As a point of clarification for other readers-- All engines are most efficient in a vacuum, however some are more optimized for low altitude atmospheric flight than others. What happens is that a bell that is optimized for lower-stage use, will have a better atmospheric ISP than one that is optimized for space, but that atmospheric ISP is still lower than the vacuum ISP.

The best way to represent this in KSP, IMHO, is for vacuum-optimized engines to have a wide ISP gap (high vacuum ISP and low sea-level ISP), whereas the atmosphere-optimized engines will have narrow ISP gap (both ISP numbers are closer to the middle).

[Northstar1989]

You can definitely throttle down to maintain a good ascent speed. in RSS I've shut down engines to do the same (because throttling is generally restricted and that's how Saturn V did it).

Calculating your delta-V is done in the same manner as now.

It's a realism thing. If Squad's aero overhaul results in a system like NEAR or FAR, you'll want your on-pad TWR somewhere around 1.3 and you'll start slight turning (5 degrees) at 75~80m/s, following the prograde marker until you hit the third atmosphere band, at which point you adjust your trajectory. At least, that what works for me and it varies by rocket, how much the TWR changes in flight, how staging goes, etc... Your launches should end up looking much more like a real rocket launch rather than the previous snooze-worthy climb to 8~12km.

I'm afraid you don't fully-understand optimal ascents Regex. The most fuel-efficient ascent is generally at Terminal Velocity, and with the new aerodynamics model (and the possibility to streamlined your designs and take advantage of the Square-Cube Law if they do it right...) your ideal launchpad TWR will go *UP*, not down.

Think of it this way- your rocket weighs just as much as ever, so you still have an incentive to get to orbit FASTER (so you experience fewer gravity-losses), but a proper streamlined design will experience less drag than before for a given velocity- meaning it is to your advantage to ascend to orbit faster than before.

In a theoretical, infinitely-tall atmosphere that had no Scale Height, a rocket with TWR = 2 (where the TWR never changed) would still eventually even out at its Terminal Velocity (which will now finally vary across designs and headings rather than being the same for a flat, low-density disk and a long, dense, streamlined cylinder!) but this is NOT the case on a real planet. The larger/taller and more streamlined your rocket, the higher its Terminal Velocity (and Ballistic Coefficient) and (in the case of larger, but not taller, rockets) the more safely it can quickly pitch over after launch without this leading to the atmosphere hugely destabilizing its flight path... (leading to a crash)

The gap between you initial velocity of 0 and Terminal Velocity will be larger the bigger/more streamlined your rocket, and your ideal TWR on the launchpad will go up further so as to close that gap more quickly... Higher TWR will also mean you can get out of the thicker atmosphere (which reduces your engine's thrust) and get into the thinner atmosphere where your Thrust is higher (and your Fuel Flow unchanged) more quickly...

Anyways, long story short- your ideal TWR (from a Delta-V perspective) on the pad will go UP, not DOWN, with the improved aerodynamics (although the ISP/Thrust fix will mean it's desirable to start with a lower TWR to maintain a controllable TWR later in the flight...)

Regards,

Northstar

[regex]

I'm afraid you don't fully-understand optimal ascents Regex.

It doesn't matter, I still get to orbit (in fact, I overbuild everything because that's just how I do). However, if you'd like to offer better practical advice on how to actually launch in KSP (like actual steps), please do.

E: Perhaps I should really be asking how what I said here

you'll want your on-pad TWR somewhere around 1.3 and you'll start slight turning (5 degrees) at 75~80m/s, following the prograde marker until you hit the third atmosphere band, at which point you adjust your trajectory. At least, that what works for me and it varies by rocket, how much the TWR changes in flight, how staging goes, etc...

is somehow incorrect given the qualifier? Can you offer a better launch sequence for new people to follow? You are entirely correct according to other people, and I see nothing wrong with what you're saying, what I am asking to see is better practical launch advice so I can give better practical launch advice. Edited February 13, 2015 by regex