Calculating Delta V by hand

[starplayer]

Hi guys. I'm using the data from the KSP calculator, using a simple stage with just one liquid fuel ttank and one engine.

So, to calculate the Delta V by the Rocket equation, it is DeltaV = Ve * ln(m0/m1), where Ve is the effective exhaust velocity, m0 is the inicial mass, and m1 is the mass after burnout.

Ve = Specific Impulse / g at surface according to wikipedia.

Using the data from the calculator, Ve=5541 * 9.81=54366 m/s and

Delta V = 54366 * ln(4500/2300) = 36488 m/s,

which is obviously wrong. Can somebody tell me where's the error?

[Entroper]

I think Ve is just 5 541, not 5 541*g.

EDIT: Ve for a liquid engine is 5 682 m/s, according to my earlier calculations on the wiki: http://kerbalspaceprogram.com/~kerbalsp/wiki/index.php?title=Parts

Specific Impulse can be given in terms of mass (Newton-seconds per kilogram, equivalent to meters per second) or in terms of weight (Newton-seconds per Newton, or just seconds). On the wiki, I listed it in terms of mass, so you don't need to multiply by g.

[starplayer]

I've been reading more, and in this article http://en.wikipedia.org/wiki/Specific_impulse , in the Examples part, you can see that the specific impulse for the listed liquid engine is only 450, with an exhaust velocity of 4400, which comes from 450*9.81. The specific impulse shouldn't be equal to the exhaust velocity. The Kerbal liquid engine's specific impulse that is in the wiki, 5682 s, is greater than that of a Ion thruster, that can't be right. I think the liquid's engine specific impulse is only 5682/9.81

[Entroper]

See this section of the Wikipedia article for clarity: http://en.wikipedia.org/wiki/Specific_impulse#Specific_impulse_as_a_speed_.28effective_exhaust_velocity.29 I also have a note in the KSP wiki article explaining this.

[starplayer]

Oh right, thanks a lot, that thing slipped me. =)

However, the specific impulse in the KSP calculator is in seconds, I'll message the creator of the calculator. Thanks again