Did the Mun get a boost to its surface gravity?

[SkyRender]

Something I noticed in my latest game is that a lander which I designed in 0.90 that could reliably land and return to Munar orbit with 8 to 12% fuel margins now gets closer to 0.5% fuel margins. I used KER to check, and the dV values are the same between the two (~1500dV), so I have to wonder what the culprit is here. It could be the engine power nerf (it's a Rockomax 48-7S, which took a massive hit in thrust), but I'm wondering if anyone else has had issues like this.

[KerikBalm]

Engines were nerfed, the Mun's gravity did not change.

Lower thrust means more losses to gravity drag.

Others have lower Isp, which also means less dV.

[SkyRender]

That's the thing, though: the losses due to gravity on an airless body should be minimal with an efficient landing sequence, even with lower TWR. Indeed, the best fuel margins I managed were around 2% with that lander in 1.0, slowing down horizontally at periapsis and only having to fight gravity for 1.5km. That doesn't really add up, particularly since a similar level of fuel use with the previous version of that engine handled over 5km vertical speed killed. The ISP was not changed for the engine at all, as I noted with the dV rating for the craft being identical between the two versions. A TWR drop from ~5 to ~2.5 should not result in a 15% increase in dV required to land. That pretty much just leaves the Mun's gravity as the culprit.

[Streetwind]

I'm pretty sure the 48-7S got a hefty hit to Isp as well... 300s now instead of 350s.

Better check the stats in the VAB - Kerbal Engineer may simply be calculating it wrong.

[LostOblivion]

It's probably the engine still. It takes longer to retro-burn, so you'll lose dV to g-drag. Also, perhaps you landed at a lower grounds than before?

[Rfmeijboom]

The ISP of the 48-7S has been reduced from 350s to 300s in vacuum.

Maybe the KER readout still assumed the old engine parameters? I don't know if KER has already been updated to work with 1.0

[Guest]

The Mun hasn't changed:

[SkyRender]

Turns out KER was calculating it wrong! The dV of the craft is actually closer to 1300m/s now, which it correctly reports in-flight. For whatever reason, it was giving the wrong number in the VAB. That's one mystery solved.

[WanderingKid]

KER lied to you.

0.90.0 48-7S: Thrust 30, ISP (ASL) 300 - 350 (VAC)

1.00.0 48-7s: Thrust 16.2 ASL, 18 VAC, ISP (ASL) 270 - 300 (VAC)

That's why you're using up more fuel.

EDIT: Super ninja'd while I brought up both editions to do a direct comparison

[KerikBalm]

That's the thing, though: the losses due to gravity on an airless body should be minimal with an efficient landing sequence, even with lower TWR.

No... tell that to a Tylo lander with only a 2.0 TWR.

On a body with air, an efficient ascent has gravity loss = aerodynamic loss (for going straight up).

So... yes, gravity loss will be more.

On a body without air, gravity loss, assuming an optimal landing profile, is *directly* related to the TWR.

But in this case, I think the ~15% Isp nerf is the culprit

[SRV Ron]

As others have stated, the 48-7 took a major rebalancing hit. KER has been updated for 1.0 so the stats should reflect that info.

[GoSlash27]

^ Turns out KER works fine and checks out empirically.

The problem is the engines have been nerfed. Lower Isp means they burn more fuel for the same DV and lower thrust means that you have more gravity losses during circularization.

There have been no changes to the bodies themselves.

Best,

-Slashy