DeltaV formula for the decouplers/separators!

[Ferdoni]

Hi fellow Kerbonauts!

So I wanted to know what the effect of decouplers and sepatrons had on the deltaV and because I couldn't find any useful information on the internet I decided to do my own investigation. I launched a rocket with the  TR-2C Stack Separator(15 ejection force), TR-18D Stack Separator(250 ejection force) and the TR-XL Stack Separator(600 ejection force) with the Stayputnik(0.05t) a test object to shoot away. The results were respectively 4, 50 and 116 ms. Wich I destilled to the formula of (ejection force/mass)/100. 

the resulting calculations are:

(15/0.05)/100 = 4

(250/0.05)/100 = 50

(600/0.05)/100 = 120

there is a discrepancy of 4ms with the  TR-XL Stack Separator but I see this as insignificant. Please be welcome to add more valuable information on this matter if you want.

I hope this helps you to design all kinds of inspirational space craft!

 

Greetings,

Ferdoni

[Choctofliatrio2.0]

Interesting!

Decoupler force is really only a factor on light upper stages. When you get to stages even around 1.5 tons, the DeltaV force is minimal. 

[Dman979]

3 minutes ago, Choctofliatrio2.0 said:

Interesting!

Yes, it is!

3 minutes ago, Choctofliatrio2.0 said:

Decoupler force is really only a factor on light upper stages. When you get to stages even around 1.5 tons, the DeltaV force is minimal. 

No, it's also a major factor when you're trying to plot a good intercept from far away. I've used decouplers to get an atmospheric Periapsis from inside the Mun's SOI when I'm out of fuel.

Edited March 3, 2016 by Dman979

[Snowstorm]

3 minutes ago, Dman979 said:

Yes, it is!

No, it's also a major factor when you're trying to plot a good intercept from far away. I've used decouplers to get an atmospheric Periapsis from inside the Mun's SOI when I'm out of fuel.

That's clever, and absolutely true.  The same happened to me, but instead my trajectory went out of the atmosphere  

[Red Iron Crown]

The wiki helpfully lists the impulse from each decoupler, though the units are a bit odd being kgF*s. A kgF*s is equivalent to ~9.81N*s. From this you can take the mass M (in kg) of the stage and impulse J (in kgF*s) of the decoupler to get the dV applied, like so:

ΔV = 9.81 * J / M

[Ferdoni]

7 hours ago, Red Iron Crown said:

The wiki helpfully lists the impulse from each decoupler, though the units are a bit odd being kgF*s. A kgF*s is equivalent to ~9.81N*s. From this you can take the mass M (in kg) of the stage and impulse J (in kgF*s) of the decoupler to get the dV applied, like so:

ΔV = 9.81 * J / M

Yes! I knew but I wanted to look just at the simple numbers to see what the results were but your formula seems more accurate. I think its the difference between 9,81 and 100 wich is when you equal it only 1,9%