Dawn Isp and KSP Wiki

[Teilnehmer]

KSP wiki says:

Quote

As the I_sp given in seconds needs to be multiplied with a slightly higher acceleration (9.82 m/s²) than g₀ (= 9.81 m/s²) the actual I_sp in m/s is higher and therefore the xenon and electrical consumption is lower. To get the actual consumption the mass flow can be calculated using the specific impulse and thrust:

What does that mean? Why 9.82? Aren’t I_sp (in m/s) and I_spg₀ (in seconds) strictly connected with each other with the factor g₀ = 9.81 m/s² by definition?

Edited January 13, 2016 by Teilnehmer

[Temstar]

g₀ = 9.82 m/s² was experimentally determined in KSP, based on the quoted Isp in seconds figure.

[Snark]

Yeesh.  Went and read that wiki section, and it's clear as mud.  The writing is very unclear.  I can't tell what the author is trying to say-- is it that "there's a bug in the numbers for this engine so you have to use 9.82 instead of 9.81"?  Is it that "all Isp numbers in KSP for all engines are actually using 9.82, not 9.81 as you might think"?  Something else?

In any case, I really don't think it matters-- we're talking about a tenth of one percent, here.  If you've got a mission where that tenth of a percent matters, then you're cutting things way too close. 

 

[NathanKell]

As of 1.0 that's wrong, it's 9.80665 now. Yet another holdover from the pre-1.0 era on the wiki...

Same with RCS.

[Snark]

1 minute ago, NathanKell said:

As of 1.0 that's wrong, it's 9.80665 now. Yet another holdover from the pre-1.0 era on the wiki...

Was wondering about that.  Just a few lines above it, the same wiki says, "...it is possible to build an airplane powed solely on this engine...", which is clearly badly wrong for post-1.0, now that the thrust is microscopic in air.  You'd be lucky just to budge an airplane on its landing gear on the runway, let alone actually power it in flight. 

[NathanKell]

Yeah, that one's even more out of date. :]

[Teilnehmer]

16 minutes ago, NathanKell said:

As of 1.0 that's wrong, it's 9.80665 now.

Thanks for the precise figure!