Realism Overhaul

[rbray89]

Hi All, I know some of you have been having issues with clouds showing up on ground, so I exposed the camera cuttof values in the common.cfg. you can get the new build here:http://forum.kerbalspaceprogram.com/threads/55905-0-22-Beta-2-City-Lights-and-Clouds

I don't know exactly what values should work, but multiplying them by the same factor that the bodies have been expanded by should work.

[NathanKell]

Thanks for that! I've been running Alpha 10 with it at 10x (2000) and it seems ok. I'll upgrade to Beta 2.

[Guest]

Could you share your formula for calculating fuel volumes off total mass and the volume percentages? I know it should be trivial, but I somehow managed to screw up my own algorithm that's supposed to do this.

[NathanKell]

I'll do you one better. Here you go. Go to the MFS calc spreadsheet here:

https://docs.google.com/spreadsheet/ccc?key=0AvHneDAy4k99dHlhdktvZW1NS1lndlhNNnRwd3FEblE&usp=sharing

Save as a copy for yourself, so you can edit it.

Go to the "Volumes etc" sheet

Note the Ratio Calculator on the right. Type in the white boxes (mass ratio o:f, name of fuel, name of oxidizer, tankage [in tons]) and the ratios and volumes will be calculated for you, based on the fuels and their densities on the left.

You can even add more fuel types, between MMH and Solid, if you need to. Just make sure the name you add is the same as the name you use in the ratio calc.

EDIT: Oh yeah, and Google Docs has trouble with hyphens in names. Instead of RP-1 you have to type ="RP-1" in the cell (WITH the quotes, mind; it's a text formula).

Edited November 1, 2013 by NathanKell

[Guest]

That should save me some work. I wanted to write a calculator in Mathematica (I already wrote a simple Mass Ratio to Volume Ratio calculator), but Excel will do better.

Also, do you think you could add a burn time calculator? Mass flow is constant with MFT, so burn time should be precisely defined. It'd be good for checking the configs. My Mathematica calculator for this is rather clumsy.

Edited November 1, 2013 by Guest

[NathanKell]

MJ already does it ingame, btw, though as we discussed above the engines burn everything and don't leave residuals so the burn time will be for every gram of propellant, and thus longer than reality.

The formula's just total mass of fuel * 9.81 * Isp / thrust, though. I mean, I could add lines for thrust and Isp, I guess?

EDIT: Added. And added more info.

Edited November 1, 2013 by NathanKell

[Guest]

We could implement residuals, BTW. There's a "flameout treshold" field in the engine config. AFAIK, propellant below that threshold would simply be vented. It might be worth to mess around with it, though 10s of burn time looks like a bit long to be just that, maybe there are other factors at work. Some fuel might get consumed in the ignition, for instance, which is doable with engine ignitor mod. Also, according to Astronautix, Soyuz (I don't know about Titan) carries about 9 tons of HTP and N2, which are not contributing to propulsion, but are expanded during launch. Since they're not included in the tank's empty mass, I think I counted them as propellant mass instead. I have no idea what are they for, though, so I don't know how would I go about simulating this system.

EDIT: OK, one more question. What exactly is needed for FAR to recognize a fairing? Soyuz fairings are named "Soyuz Payload Shroud", but the spacecraft shows up as IsShielded: False for some reason. The fairing has a hole on top through which LES sticks out, could that be the cause? Anyway, I suspect that part of my TWR problems stems from this.

Edited November 1, 2013 by Guest

[asmi]

We could implement residuals, BTW. There's a "flameout treshold" field in the engine config. AFAIK, propellant below that threshold would simply be vented. It might be worth to mess around with it, though 10s of burn time looks like a bit long to be just that, maybe there are other factors at work. Some fuel might get consumed in the ignition, for instance, which is doable with engine ignitor mod. Also, according to Astronautix, Soyuz (I don't know about Titan) carries about 9 tons of HTP and N2, which are not contributing to propulsion, but are expanded during launch. Since they're not included in the tank's empty mass, I think I counted them as propellant mass instead. I have no idea what are they for, though, so I don't know how would I go about simulating this system.

AFAIK N2 is used for tanks pressurization.

[Guest]

Could be. Still unsure about HTP, though. It makes up most of those 9 tons. Does it drive the engine's turbopump or something?

[Starwaster]

Could be. Still unsure about HTP, though. It makes up most of those 9 tons. Does it drive the engine's turbopump or something?

9 tons??? HTP is denser than water isn't it? If we're talking metric tons that's ~9 cubic meters.

How sure is that 9t figure?

[Guest]

It's from Astronautix. "Comments: Gross mass includes 1190 kg of hydrogen peroxide and 280 kg of liquid nitrogen expended during ascent but not contributing to propulsion." Take this times four, for the boosters, and add 2400kg for the core. There's an additional 540kg of N2 in the core, too, it adds up to about 9 metric tons. Most of this hydrogen peroxide, which I suspect isn't used for paper cuts the crew might get during the ascent. All that is obviously needed to power something, but what?

[Starwaster]

It's from Astronautix. "Comments: Gross mass includes 1190 kg of hydrogen peroxide and 280 kg of liquid nitrogen expended during ascent but not contributing to propulsion." Take this times four, for the boosters, and add 2400kg for the core. There's an additional 540kg of N2 in the core, too, it adds up to about 9 metric tons. Most of this hydrogen peroxide, which I suspect isn't used for paper cuts the crew might get during the ascent. All that is obviously needed to power something, but what?

See the part that alarmed me was that I thought we were talking about the Soyuz itself not the launcher carrying all that HTP. In the boosters, as was speculated it's for the turbopumps. And some of it is for orbital maneuvers and re-entry. (just not 9 tons worth)

And yes, they can go EVA, open up the spigot, remove their gauntlet and treat their paper cuts....

[NathanKell]

Yeah, saw that ref on the Soyuz stats...

Re: fairings. For FAR to recognize a fairing, it needs to have Fairing in the part title.

Not sure what it could be other than residuals unless they purposefully shut off the stage early and Astronautix reports that figure. I mean, the burn time formula is pretty darn clear. :]

Oh, though KSP uses 9.82 (!!!???) m/s as its gravity constant in ModuleEngines when drawing resources, but that isn't enough off 9.806-9.81 to account for 10 seconds either.

[Guest]

I replaced all instances of "Shroud" in Soyuz fairings with "Fairing" and even added "Fairing" to the LES. Still, isShielded: false. I can't get the fairings to properly shield the Soyuz for some reason.

[asmi]

It's from Astronautix. "Comments: Gross mass includes 1190 kg of hydrogen peroxide and 280 kg of liquid nitrogen expended during ascent but not contributing to propulsion." Take this times four, for the boosters, and add 2400kg for the core. There's an additional 540kg of N2 in the core, too, it adds up to about 9 metric tons. Most of this hydrogen peroxide, which I suspect isn't used for paper cuts the crew might get during the ascent. All that is obviously needed to power something, but what?

Hydrogen peroxide is used as RCS fuel to control LV attitude during ascent. Guess what - there are no "magic torque wheels" in real life, so engineers had to resort to old good RCS attitude control system

I replaced all instances of "Shroud" in Soyuz fairings with "Fairing" and even added "Fairing" to the LES. Still, isShielded: false. I can't get the fairings to properly shield the Soyuz for some reason.

Ask ferram4 in his FAR thread - he is usually very helpful.

Edited November 2, 2013 by asmi

[Guest]

Hydrogen peroxide is used as RCS fuel to control LV attitude during ascent. Guess what - there are no "magic torque wheels" in real life, so engineers had to resort to old good RCS attitude control system

Except that AFAIK, there are no RCS thrusters on Soyuz LV. Just Vernier thrusters on the bottom, and they're fed from the main tanks. That said, it seems that this HTP is indeed used to drive the fuel pumps on Soyuz. Nowadays it's done by the engines' fuel, but this is an old design.

Edited November 2, 2013 by Guest

[p3asant]

What have you guys found out as the optimal ascend profile settings for mechjeb?

I'm having problems with mechjeb not burning up (not high enough angle) enough and leading to deorbit before orbit.

[ANWRocketMan]

Depends on your TWR, size, how much control the rocket has etc. etc. I just fly manually, it's easier to adjust to it that way.

[Guest]

Well, I'm running into this issue with Soyuz, too. It seems that it doesn't have enough TWR to actually make orbit, despite having 8km/s dV like it should. I suspect drag loses to be the culprit, because my fairing doesn't work. Still, I'd like to know some efficient ascent profiles. I'm starting the turn at 1.3km and ending it at 115km, with 45% grade, and that's not enough.

[ferram4]

Are you absolutely certain that it has a high enough TWR and enough dV? Unless you've made changes to the Bobcat Soyuz rocket, it only has 6 km/s dV, which means that it will always fall short of orbit. Drag losses will be higher with the fairing not working, but it won't be significant enough to prevent you from reaching orbit unless you're always a 100 - 200 m/s short; total drag losses shouldn't increase significantly above 200 m/s with the fairing not working, but the stability of the vehicle should become a lot worse.

[Guest]

I've plugged in real values for the Soyuz. And dV isn't the problem, TWR is. With boosters, it's fine, but after that, it's ridiculously low. While it does have over 8km/s dV, it simply can't apply it fast enough for some reason. I thought about drag, because it's the highest at low altitudes, where the rocket has the most TWR. Do you think there might be another reason for it failing? The real thing does make orbit with those figures, and that's from a non-equatorial launch site, so there's either something off in our flight model, or the ascent profile isn't good.

[ZRM]

I've plugged in real values for the Soyuz. And dV isn't the problem, TWR is. With boosters, it's fine, but after that, it's ridiculously low. While it does have over 8km/s dV, it simply can't apply it fast enough for some reason. I thought about drag, because it's the highest at low altitudes, where the rocket has the most TWR. Do you think there might be another reason for it failing? The real thing does make orbit with those figures, and that's from a non-equatorial launch site, so there's either something off in our flight model, or the ascent profile isn't good.

It could be that it's because the pressure model is wrong right now. Default Kerbin (and currently rescaled Kerbin) use a simple exponential pressure scale, known as the legacy pressure implementation. Planets can switch to using the newer system that allows you to specify pressure as a function of altitude using a curve. Nathan said he's going to try and make a curve to fit the standard atmosphere model and use that instead.

[ferram4]

@Dragon01: I just ran a launch with these figures for it:

Boosters:

Dry mass: 3.78 tonnes

Full mass: 44.5 tonnes

Liquid Fuel: 3528

Oxidizer: 4312

Thrust: 991 kN

Isp vac: 310s

Isp atm: 245s

Core:

Dry mass: 6.9 tonnes

Full mass: 105.4 tonnes

Liquid Fuel: 8586

Oxidizer: 10494

Thrust: 997 kN

Isp vac: 311s

Isp atm: 264s

Upper stage:

Dry mass: 2.35 tonnes

Full mass: 22.9 tonnes

Liquid Fuel: 2061

Oxidizer: 2519

Thrust: 298 kN

Isp vac: 330s

Isp atm: 280s

Everything else the same. The Soyuz craft was released at 300 km and 7.5 km/s; I believe the difference can be made up with my poor piloting, which meant that the upper stage spent some time burning at 45 degrees above prograde to keep the rocket at apoapsis. Is it possible that your numbers might be wrong somewhere?

@ZRM: I hope that density and pressure curves can be specified separately; density should still follow a simple exponential curve. If that isn't the case, then FAR might do weird things, since density is more important for aerodynamic considerations than absolute pressure is.

Edited November 3, 2013 by ferram4

[Guest]

Well, those are the values I'm using. The only thing different is fuel/oxidizer ratio, which I adjusted a bit. This should make no difference...

WAIT! I got it! You're launching to 300km, which means longer vertical burn, which equals longer time to Ap... Much longer, actually. I was launching to about 120km, perhaps this is the key. I need to check this, this could give me enough time to finish the burn.

[ferram4]

Yeah, after the boosters come off it's got a very lackluster TWR. Pitch over later and only start to switch from surface prograde to orbit prograde at ~1.6 km/s or so.