[1.2] Real Solar System v12.0 Dec 8

[jrandom]

When ever i launch rocket in space// about after 100km it starts to spin like crazy.. and i cant stop it.. even with sas and rcs it spins out of control... any ideas what is causing the problem?

My first guess is you've got parts clipping in a weird way that's causing a malfunction in the physics system, but again this is just a guess. Have an image of your vessel we could study? (And you're not running out of electricity, are you?)

[NathanKell]

Yay! Less work for me! I love less work for me!

Yeah, well, it means more work for _me_, so screw you

[jrandom]

Yeah, but you're all mathy 'n stuff, which I am jealous of, so it all balances out!

[Kimaera026]

Yay! Less work for me! I love less work for me!

yes!! less work! woo!

Yeah, well, it means more work for _me_, so screw you

you're a legend.

Edited December 1, 2013 by Kimaera026

[MAKC]

I'm considering "extending" the atmosphere to roughly ~200km ASL as currently atmospheric drag magically disappears above 104km.

How would I go about doing this in a "realistic" enough fashion? I won't bother with the entire thermosphere, nevermind the exosphere.

maxAtmosphereAltitude is obvious, but what does atmosphereScaleHeight do? I'm guessing it's related to density?

Is it possible to do this without screwing up stuff like FAR?

Edited December 1, 2013 by MAKC

[ferram4]

Atmosphere scale height is how quickly density falls off with altitude, using the formula:

density = SL_density * e^{-alt / scaleHeight}

Where:

SL_density is 1.225 kg / m³

and scaleHeight is 7.5km for Earth.

Unfortunately, the game cuts everything off when the ship is above maxAtmosphereAltitude or when e^{-alt / scaleHeight} is less than 10^-6.

If you try increasing scale height, you'll just increase the altitudes that you hit the same atmospheric densities at.

Edited December 2, 2013 by ferram4
Edit: original scale height value was for Kerbin; changed it to Earth's

[MAKC]

Atmosphere scale height is how quickly density falls off with altitude, using the formula:

density = SL_density * e^{-alt / scaleHeight}

Where:

SL_density is 1.225 kg / m³

and scaleHeight is 5km for Earth.

Unfortunately, the game cuts everything off when the ship is above maxAtmosphereAltitude or when e^{-alt / scaleHeight} is less than 10^-6.

If you try increasing scale height, you'll just increase the altitudes that you hit the same atmospheric densities at.

So if I'm not completely daft, going by what you said, all I really have to do is increase the maxAtmosphereAltitude and the atmospheric density will continue to scale where it "left off"?

[Starwaster]

When ever i launch rocket in space// about after 100km it starts to spin like crazy.. and i cant stop it.. even with sas and rcs it spins out of control... any ideas what is causing the problem?

Is this during launch? And do you have FAR? If so it sounds like a problem with your ascent profile or rocket design.

Or is this after you reach and stabilize orbit?

If the latter does it just continue to spin randomly or does it have a particular orientation it tries to reach?

[NathanKell]

KSP has two atmosphere models: legacy and pressure curve. Pressure curve uses the same floatcurve mechanic that solar panels, engine specific impulse, velocity curve, etc., use; legacy uses an exponential equation that appears to work like this:

base pressure multiplier := (e * staticPressureASL) ^ (-altitude_in_km / scaleHeight)

if base pressure multiplier < 0.000001, base pressure multiplier = 0

return base pressure multiplier * atmosphereMultiplier

This means that when the formula yields < 0.00001, even before the final multiplier is applied, the pressure function will return 0. That's why there's a cutoff. Note that maxAtmosphereAltitude does precisely zip; it's only for reference in the encyclopedia.

The scale height for Earth is about right; when I get a chance I want to switch to pressureCurve, though. For now, you can try increasing the scale height, but note that your pressure (and density, because KSP annoyingly has density in linear relationship with pressure) will then be greater at lower altitudes than it should be.

[MAKC]

Just noticed something. According to http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html, Earth's scale height is 8.5km, yet RSS sets Kerbin's to 7.5km. Is this intentional?

Ninja'd.

Thanks you guys for answering and for your work in the modding scene.

Edited December 1, 2013 by MAKC

[NathanKell]

So if I'm not completely daft, going by what you said, all I really have to do is increase the maxAtmosphereAltitude and the atmospheric density will continue to scale where it "left off"?

No, it's the exact opposite. Ferram just said if you increase scale height, you've just scaled everything, so the pressure that once was at 20km will now be at 25km, and so forth.

Re: your latest: yes, intentional. It's a closer fit to Earth's actual pressure curve.

[MAKC]

No, it's the exact opposite. Ferram just said if you increase scale height, you've just scaled everything, so the pressure that once was at 20km will now be at 25km, and so forth.

Re: your latest: yes, intentional. It's a closer fit to Earth's actual pressure curve.

Nah. I wasn't talking about scale height. I was talking about maxAtmosphereAltitude under the assumption that it actually mattered.

[Captain_Party]

How much delta-v does it cost to land on the Moon?

[jrandom]

How much delta-v does it cost to land on the Moon?

My current chart says 7300m/s from an orbit of 100km. I have not yet tried this as I'm still trying to get these darned satellites into geosynchronous orbit.

Edit: From 100km Munar orbit, not Kerbin's. Again, I just have this one chart and cannot entirely vouch for its accuracy.

Edited December 1, 2013 by jrandom

[NathanKell]

9300 Earth ascent. ~3200 TLI. ~900 LOI. ~2000 DOI and landing. ~1800 ascent. ~800 TEI.

[Starwaster]

Nah. I wasn't talking about scale height. I was talking about maxAtmosphereAltitude under the assumption that it actually mattered.

If I'm understanding Ferram correctly and if my math is correct, you could increase it to 110336 (meters). That's about the point that it would reach the other limit Ferram was talking about. (it's when either condition is reached that it stops calculating)

[Ralathon]

How much delta-v does it cost to land on the Moon?

When landing probes on the moon I tend to aim for about 16km/s. That gives me enough of an error margin to be a bit sloppy and launching the ship in a 23 degree orbit so I don't have to wait for a moon launch window.

[tomrigus]

Is this during launch? And do you have FAR? If so it sounds like a problem with your ascent profile or rocket design.

Or is this after you reach and stabilize orbit?

If the latter does it just continue to spin randomly or does it have a particular orientation it tries to reach?

My first guess is you've got parts clipping in a weird way that's causing a malfunction in the physics system, but again this is just a guess. Have an image of your vessel we could study? (And you're not running out of electricity, are you?)

I dont have electricity problems.. and my rocket builds are pretty sturdy... i have far installed.. it starts to spin out of control during ascent but when i'm out of the atmosphere. plus, FAR doesnt let me to do an early gravity turn with that vessel because it's some what big.. but the parts are very few so i dont think it's a building issue. a lot of my other vessels had that problem too. when it starts to spin.. it is trying to match the deorbit vector in the Sphere.. but it can stay stable at it , becuase it is spining way too fast.. then the G force becomes high and the whole rocket breaks apart.. i've tried to stage it to see if the problem persisted , and it does ... i think it drives the physics crazy

[Dante80]

Can you post a picture in the VAB with the center of mass and center of lift showing?

[p3asant]

I dont have electricity problems.. and my rocket builds are pretty sturdy... i have far installed.. it starts to spin out of control during ascent but when i'm out of the atmosphere. plus, FAR doesnt let me to do an early gravity turn with that vessel because it's some what big.. but the parts are very few so i dont think it's a building issue. a lot of my other vessels had that problem too. when it starts to spin.. it is trying to match the deorbit vector in the Sphere.. but it can stay stable at it , becuase it is spining way too fast.. then the G force becomes high and the whole rocket breaks apart.. i've tried to stage it to see if the problem persisted , and it does ... i think it drives the physics crazy

I found out that if the engines aren't perfectly symmetrical and in line with center of mass, this happens.

My solution was to put engines ( i was using four) one with the bottom node and then three in symmetry around the centre one instead of four in symmetry with nothing in centre.

Or then lock the gimbals with all but the centre engine.

[NathanKell]

FAR doesnt let me to do an early gravity turn with that vessel because it's some what big

When are you starting the turn? That's usually a symptom of starting it way too late. Start it when you're at less than 100m/s, which is usually 0.5-1.5km.

[regex]

Quick question: Is Kerbin in the stock game essentially where Earth would be if the system were scaled down? As in, are the relevant Kerbin values simply multiplied by 10.03 (or whatever)? I'm interested in scaling up the Kerbin system instead of playing in our solar system and, rather than bug you for all the maths, just thought I could extrapolate what would need to be done from Kerbin.

Thanks.

[Ralathon]

Quick question: Is Kerbin in the stock game essentially where Earth would be if the system were scaled down? As in, are the relevant Kerbin values simply multiplied by 10.03 (or whatever)? I'm interested in scaling up the Kerbin system instead of playing in our solar system and, rather than bug you for all the maths, just thought I could extrapolate what would need to be done from Kerbin.

Thanks.

Its not exactly in the right spot, but it is pretty close.

SMA for earth is about 150Gm while Kerbin is 13.5 Gm (unmodded). So if you multiply that by a factor of 10.5 (Or 10 if you're a lazy ******* like me) you get within 10% or so.

I´ve been playing with a system scaled by a factor 10 for some time now. It works fine, the only issue is that figuring out launch windows is a bit tricky.

[regex]

Its not exactly in the right spot, but it is pretty close.

SMA for earth is about 150Gm while Kerbin is 13.5 Gm (unmodded). So if you multiply that by a factor of 10.5 (Or 10 if you're a lazy ******* like me) you get within 10% or so.

Awesome, thank you. Is that config file available for us other lazy ****s?

I´ve been playing with a system scaled by a factor 10 for some time now. It works fine, the only issue is that figuring out launch windows is a bit tricky.

If I know what to change the new values are I can edit alexmun's planner.

[Ralathon]

Awesome, thank you. Is that config file available for us other lazy ****s?

PMed it to you. (Can't distribute it online because it adjusts PlanetFactory orbits, Don't want to get in trouble with the license police. Shhhh)