[1.0] Vacuum Isp Restoration

[taniwha]

Vacuum Isp Restoration (VIspR: visper) is a Module Manager* config for restoring the vacuum Isp of most rocket engines. To keep things sane, the sea level Isp of is altered as well to keep the ratio between vacuum and sea level Isp the same.

* Module Manager not included.

Download: VIspR 1.0 (GNU General Public License)

What VIspR does not do:

• It does not necessarily restore the atmospheric Isp of engines.
  
• It most certainly does not restore the variable fuel consumption/fixed thrust from prior to KSP 1.0.
  
• It does not touch the new RT-5 (Flea) SRB.
  
• It does not touch any rocket that improved in 1.0 (sepratron, the "micro" engine (ant?)).
  
• It does not seem to make launching any easier.
  

Your orbital designs are safe. Your launchers are toast.

In my brief testing, it made the launch of a vehicle that was ok getting into orbit more difficult. The vehicle's TWR of the core is very low and thus needs the SRBs to get going. Without VIspR, the core would burn off enough fuel to have a usable TWR when the SRBs burn out. With VIspR, even at full throttle, the core has not burned off enough fuel to have a good TWR when the SRBs burn out. The rocket flipped its way to 16km, stabilized then limped its way to 26km where the core was dropped for the next stage. It then struggled to (60 degree pitch) to maintain altitude while accelerating and lost 80% of its heatshield ablator on the way up. It did get to orbit, though.

[shoe7ess]

If this makes launching seemingly harder based on your description/testing, what are the pros besides restoring Vac ISP. Also, how does restoring the vacuum ISP of each part make launchers unstable? Is it the shift between thrust isp that results from the restored ISPs clashing with the new ones that you didn't change?

[smjjames]

I'm a bit confused, does this make launchers harder than stock or were you saying that a good one in 0.90 isn't so good now?

[taniwha]

It was actually a rocket designed for 1.0 that proved to be a little more difficult with VIspR. The rocket was quite marginal: TWR just barely over 1 for the lower-stage core, about 0.5 for the upper (orbital insertion) stage.

I believe the reason it flipped was due to it having gone not as high before staging.

It is the (sometimes severely) reduced sea-level thrust that "hurts" (from an "I'm used to building this way" point of view) launcher designs even with old vacuum Isps. The new vacuum Isps means you need a larger orbital stage to do the same tasks which makes for an even larger launcher, but then you need to deal with reduced atmospheric thrust and thus need more engines which makes for bigger launchers...

[AtmaStorm]

This owns and you own for making it.

I hope they unnerf Vaccum Isp in the next patch, the Atmospheric Isp and Thrust reduction works well.

[smjjames]

So, basically this makes the vacuum ISPs back to what they were? I'll definetly give this a look. Feels like I need to put more tanks on to achieve similar levels of deltaV as I had before in vacuum.

I wonder about other mods engines though.

[smjjames]

*bump*

I saw in one of NecroBones thread that SQUAD reversed the change to how "MaxThrust" works in 1.0.1, so... how is this one affected?

[taniwha]

Well, VIspR was done is such a way that it is very specific to 1.0.0's engines, so if the Isps have changed at all, then VIspR will break (but I still have the script so regenerating will be easy).

- - - Updated - - -

smjjames: I just had a chat with NathanKell and it seems that the only engine that might be affected is the aerospike. That "reversal" is instead of specifying the atmospheric max thrust, engine configs now specify the vacuum max thrust (this has no effect on VIspR). Still, I will verify that VIspR does as it should and update appropriately.

[AtmaStorm]

I've put together a config for KWRocketry here.

[smjjames]

Is this still being maintained? Might not really need it though, I dunno.

[taniwha]

I'll probably update it when I get my hands on 1.0.4, but I've been busy with other stuff.