Public Service Announcement: Dealing with New ISP Calculations!

[Renegrade]

New and scary ISP calculations are coming to KSP in 1.0! This is very dangerous, and may be used against us at any time!

Here's the procedure to prepare yourself:

When danger appears, you:

1. Duck

2. and Cover!

Err wait wrong PSA.

In order to deal with the new ISP calculations, follow THIS procedure:

1. Download K.I.D.S. by Ferram

2. Click on the "KIDS" configuration button in the KSC screen

3. Enable "Extend Curve to Zero Isp" and "Thrust Varies with Isp" in the default profile (alternatively: create a new profile with those settings set)

It looks like this:

Now you can play with the new ISP calculations, to get used to them, without exploding your entire space program in 1.0!

Note to BTSM users: The above steps are unnecessary. BTSM already has these features.

[AmpsterMan]

On eof the neat things about this though, is that burn time is the same no matter what because flow rate is the same. That means, you can guesstimate how much a fuel tank would last very easily by just counting how many their are, the capacity of the tank, the flow rate of the engine, the throttle of the engine.... oh wait, that's a lot of stuff. Nvm

Seriously though, glad to see this in place. Much more realistic and the changing flow rate in OldAero through me off once I realized real life isn't like that.

[NathanKell]

Excellent point!

[Violent Jeb]

New and scary ISP calculations are coming to KSP in 1.0!

Is this very similar to the model that is expected in 1.0?

[smjjames]

Since theres a whole lot of things different including the new aerodynamics, I'd rather get used to the new ISP stuff with the new aerodynamics, trying to get used to it while using FAR (or even the stock soupisphere) may just be confusing.

[forenci]

Curious to see how much this will impact anything in terms of launches and such. Quite fun!

[UmbralRaptor]

s/new and scary/long awaited and awesome/

[Renegrade]

Is this very similar to the model that is expected in 1.0?

It should be - the only real question is whether or not Squad did the "Extend Curve to Zero Isp" option or not.

s/new and scary/long awaited and awesome/

That's how I feel about it (long awaited and awesome), but there were plenty of people who seemed to think it was more like an atomic bomb attack than a feature... :/

[Red Iron Crown]

TL,DR: Delta-V is calculated as before. TWR must take atmospheric effects into account during calculation.

(Really hoping KER updates quickly after 1.0 drops)

[Sandworm]

How can DeltaV remain the same if ISP is varied? The deltaV will change based on how much time you spend in the lower atmo, where engines suffer a lower ISP.

I think that the biggest real change this will bring is a total end to the use of ion engines within atmosphere. Reduced thrust, rather than increased fuel consumption, will make them useless. Other than that, i think this change has more to do with making launches more difficult by reducing initial thrust. That is needed to offset the gains made by the new drag calculations.

Edited April 17, 2015 by Sandworm

[Starwhip]

How can DeltaV remain the same if ISP is varied? The deltaV will change based on how much time you spend in the lower atmo, where engines suffer a lower ISP.

I think that the biggest real change this will bring is a total end to the use of ion engines within atmosphere. Reduced thrust, rather than increased fuel consumption, will make them useless. Other than that, i think this change has more to do with making launches more difficult by reducing initial thrust. That is needed to offset the gains made by the new drag calculations.

It doesn't remain the same, the way it is calculated is the same. Delta-V = g * Isp * ln(Wet Mass/Dry Mass)

[Red Iron Crown]

How can DeltaV remain the same if ISP is varied? The deltaV will change based on how much time you spend in the lower atmo, where engines suffer a lower ISP.

Because Isp varying with atmospheric pressure is already modeled in game. All that is changing is thrust varying instead of fuel flow rate, which has zero effect on the dV of a design.

I think that the biggest real change this will bring is a total end to the use of ion engines within atmosphere. Reduced thrust, rather than increased fuel consumption, will make them useless. Other than that, i think this change has more to do with making launches more difficult by reducing initial thrust. That is needed to offset the gains made by the new drag calculations.

Depends on if they adjust ion's atmospheric Isp, currently they have the same Isp in both vacuum and atmo. We'll see, I guess.

[Renegrade]

Depends on if they adjust ion's atmospheric Isp, currently they have the same Isp in both vacuum and atmo. We'll see, I guess.

They used to have some sort of really bad atmospheric Isp (I forget what the number was), but Squad changed that so that the fuel/charge flow rates would show you the vacuum rates (as it stands, the UI shows the maximum flow rate, which is the atmospheric rate with the current engine set).

Given that fuel flow should be constant now, they could actually restore the old atmospheric Isp value..whatever it was.

[Botch]

I'm dumb and confused. What will the new model 'feel' like in terms of a typical rocket launch, say the Kerbal X? I know I could experiment with the mod but I'm interested in what people who understand this stuff have to say. So far I've got 'harder' and 'more realistic' which explains little. Harder just means use moar boosters and more realistic just sounds like a synonym for harder.

[Gnou]

Realistic just means dealing with more coherent constraint & effect.

Not necessary harder nor as we have on Earth.

[Red Iron Crown]

I'm dumb and confused. What will the new model 'feel' like in terms of a typical rocket launch, say the Kerbal X? I know I could experiment with the mod but I'm interested in what people who understand this stuff have to say. So far I've got 'harder' and 'more realistic' which explains little. Harder just means use moar boosters and more realistic just sounds like a synonym for harder.

All other things being equal, a given rocket will have less thrust at launch. So I would expect a slower liftoff and slower accumulation of speed and altitude early in the ascent.

Many part stats are changing, though, and the new aero model is another complication in knowing what to expect.

[regex]

I'm dumb and confused. What will the new model 'feel' like in terms of a typical rocket launch, say the Kerbal X?

It'll feel more like an actual rocket launch, you'll tip the rocket over slowly and follow the prograde marker to orbit. In stock, if it's anything like FAR/NEAR, you'll probably start turning at 75~80m/s, maybe less or maybe more depending on TWR. There will be no need to wait until 8~10km altitude to start turning because drag will be more realistic. Some stock craft will no doubt have to be redesigned for use under the new aerodynamic model, and you'll have to pay attention to your TWR as much as your delta-V when it comes to launchers. Interestingly, SRMs get more useful under a realistic aero/thrust model by providing initial TWR kick. Reference the Space Shuttle.

So far I've got 'harder' and 'more realistic' which explains little. Harder just means use moar boosters and more realistic just sounds like a synonym for harder.

"Realism" is not a synonym for "harder", that's a myth perpetuated by people who don't want to learn a new way of doing things or face having to play under certain constraints.

[Cdr_Zeta]

I hope they fixed the free-flight with things like the canards which can seemingly fly a plane without engines; maybe adding winglets will add lift somewhere now where it wasnt before, which in my opinion...forget that I dont add wings to my rockets anyways...this might look good for those SSTO fliers to space; too long a trip for my tastes; I will be looking at the DRAG...

Cmdr Zeta

[Kylekov]

It doesn't remain the same, the way it is calculated is the same. Delta-V = g * Isp * ln(Wet Mass/Dry Mass)

The DeltaV of your ship will stay the same but how much DeltaV it takes to get somewhere will change with the new aero right? I think that is what Sandworm is trying to say, that with the aero changes something WILL change. The way we calculate a ships DeltaV won't change so how much DeltaV is required to get somewhere has to change right?

[Red Iron Crown]

The DeltaV of your ship will stay the same but how much DeltaV it takes to get somewhere will change with the new aero right? I think that is what Sandworm is trying to say, that with the aero changes something WILL change. The way we calculate a ships DeltaV won't change so how much DeltaV is required to get somewhere has to change right?

Pardon the pun, but that's still up in the air. If the new aero reduces dV to LKO like NEAR/FAR then that will obviously affect just about everything. Moving from one body to another once in orbit will be largely unaffected dV-wise assuming the planets remain the same size and in the same orbits, though how much aerobraking can be utilized will likely be affected.

[EtherDragon]

All other things being equal, a given rocket will have less thrust at launch. So I would expect a slower liftoff and slower accumulation of speed and altitude early in the ascent.

Many part stats are changing, though, and the new aero model is another complication in knowing what to expect.

What's cool about this is that it leaves way for more intriguing rocket designs. Back when 0.24 came out, I had quite a successful run at using Air Breathing Engines as lift-off / booster stages to my rockets. Lift off was decidedly slower, but these "boosters" had fuel to spare for a long time.

And to clarify the ISP / Thrust calculation - yes rockets will have less thrust per KG of fuel (an important distinction) in thicker atmosphere. The difference will be directly proportional, so if a rocket motor has 20kn of thrust with a vacuum ISP of 400, and an atmospheric ISP of 300, it's thrust on the ground will be 15kn.

This is the main reason rockets in real life have boosters - to provide a lot of extra umph on the ground when the rocket liquid fuel motors have lower thrust. As you climb out of the atmosphere the rocket motors really pick up some steam.

Edited April 21, 2015 by EtherDragon

[panzer1b]

Pardon the pun, but that's still up in the air. If the new aero reduces dV to LKO like NEAR/FAR then that will obviously affect just about everything. Moving from one body to another once in orbit will be largely unaffected dV-wise assuming the planets remain the same size and in the same orbits, though how much aerobraking can be utilized will likely be affected.

I think its most likely going to be similar to FAR/NEAR atmo in terms of less dV to orbit, but also i think they might change ISPs here and there, and also you might have slower initial ascents when using engines not designed for atmospheric useage. Overall im not expecting any massive changes to how much fuel/engines we need to get to x location from KSC. Im guessing space dV of most engines will be similar to what it is now (except perhaps a few OP engines like the KR-2L, and 48-7s that are just too good in terms of TWR and ISP given their TWR), with possibly a few balance tweaks to improve a few bad engines, nerf some OP stuff, and make it more across the board balanced.

Anyways, im mostly excited for that xenon tank, gone are the days of 100+ zenon tank ships (heck even my super small 10t SSTO has 20 of them). I hope they dont nerf bat the ions (i like them as is, especially ion propelled motorcycles/rovers, who doesnt like efficient high speed machines that dont need to drag overweight LFO anywhere). Still, nomatter what they do, i hope the game will be just as enjoyable as it was before (worst case scenario i can always load up 0.90 if 1.0 ends up not to my liking, but i dont think thisll be an issue since squad doesnt care about 100% realism, just playability and fun moreso).

[Wahgineer]

Burt the turtle?!

And here I thought the only time I'd see him was in American Studies.

[Kylekov]

Pardon the pun, but that's still up in the air. If the new aero reduces dV to LKO like NEAR/FAR then that will obviously affect just about everything. Moving from one body to another once in orbit will be largely unaffected dV-wise assuming the planets remain the same size and in the same orbits, though how much aerobraking can be utilized will likely be affected.

Sorry should have clarified I only meant from the surface of Kerbin, not from one body to another.

[TheAdversary238]

Doesn't this also mean that Eve ascents will go from extremely difficult to nightmare mode? Atmospheric thickness there would have even more detrimental effects on surface Isp than Kerbin. Couple that with heavy gravity and even Mainsail landers are looking iffy.