General Question Liberty Ship, calculating Mass and DV

[Hlynkacg]

I wasn't sure if I should post this here or in Addon Developement but I need somone to check my figures.

I' was browsing Atomic Rockets when on a whim I decided to plug in the values for the "Liberty Ship" decribed here into an SC3 ini file and take it for a ride.

I like the look and concept and would love to see it flying in orbiter but Unfortunatly the booster, lacking sufficient DV to reach LEO, did not perform as advertised.

What I'd need to know is whether the mistake was on my end (converting imperial units to metric) or on the orginator's?

Here's my ini file...

[CONFIG]
MESHNAME="BigFriendlyRocket"
SIZE=75
EMPTY_MASS=0.34e6
FUEL_MASS=1.1e6
MAIN_THRUST=37.38e6
ATTITUDE_THRUST=5000
ISP=3060
PMI=(10.58,11.74,2.67)
CROSS_SECTION=(360,360,45)
TRIM=0.05
COG=10.0
CAMERA=(0.0,0.0,52)
VISIBLE=0
LAUNCH_PT1=(0,-16,-65)
LAUNCH_PT2=(-14,-8,-65)
LAUNCH_PT3=(14,-8,-65)
LAND_PT1=(0,-16,-65)
LAND_PT2=(-14,-8,-65)
LAND_PT3=(14,-8,-65)

;Main Engine
[EX_MAIN_0]
OFF=(0.0,0.0,-54.0)
DIR=(0,0,-1)
LENGTH=64.0
WIDTH=8.0

 

[Loru]

Orbiter reads ISP as an exhaust velocity (in [m/s]) so change ISP to 30018

 

[Hlynkacg]

I did not know this, thank you.

I suppose this is why my Skytrain project has also been under performing, but with a low-thrust engine it wasn't nearly as noticable.

What exactly is the conversion formula for "Newtons per Kilogram/Second" to whatever Orbiter's unit is called?

 

[Loru]

Can you post some pics of that skytrain?

 

[TJohns]

Divide the real figure by yours - look familiar??

 

[martins]

...

What exactly is the conversion formula for "Newtons per Kilogram/Second" to whatever Orbiter's unit is called?

1

 

[RisingFury]

What exactly is the conversion formula for "Newtons per Kilogram/Second" to whatever Orbiter's unit is called?

Is this a joke?!

 

[Hlynkacg]

Originally Posted by Hlynkacg:
What exactly is the conversion formula for "Newtons per Kilogram/Second" to whatever Orbiter's unit is called?

1

Divide the real figure by yours - look familiar??

Yes, yes it does. :facepalm:

Can you post some pics of that skytrain?

It isn't much to look at right now, its more a "proof of concept" than anything else.

---------- Post added at 10:47 PM ---------- Previous post was at 10:45 PM ----------

Is this a joke?!

Wish it were, I forgot to multiply by 9.8.

In short I missed a step in my conversion formulae.

 

[Urwumpe]

What exactly is the conversion formula for "Newtons per Kilogram/Second" to whatever Orbiter's unit is called?

It is "Newton seconds per kg" or [math]\frac{Ns}{kg}[/math] the SI unit of specific impulse (impulse per propellant mass). Orbiter uses exactly the same, since Orbiter generally uses SI units, but you used seconds or in its complete form "lb*s/lb", the US customary unit of specific impulse. This is 9.81 times less than the SI value.