Withstanding engine backwash

[suicidejunkie]

I'm looking for design ideas on how to build a launch pad capable of withstanding a skipper's backwash without exploding.

Recently I has built one with EL to deliver a load of ore from Mun to Kerbin, and during takeoff it quite naturally torched everything behind it, leaving my base in four independent pieces.

 

I did try testing with a disposable heatshield full of ablator to take the brunt, but that only lasted one frame before exploding on the next.

At the moment, I've assembled some struts into a side stand so that the rockets will only destroy a few non-critical components and limit the repairs necessary after each launch.

 

Is there a better way to protect the base from engine wash?

[bewing]

The engine wash has a length limit. So if you make your launch clamps pretty tall (so that your rocket is a couple of orange tanks off the ground) then there should be no damage at all.

 

[Zeiss Ikon]

Another option: launch from the natural surface of whatever body you're starting on.  I've never seen a rocket plume so much as leave a mark on Kerbin, Mun, or Minmus, and certainly not on Gilly (the only bodies I've landed on so far).  Otherwise, if you want to launch from a built-up structure other than KSC's launch pad, you probably need to look for one of the mods that lets you build and launch vessels from other bodies or other places on Kerbin -- those will include the ability to make a launch pad that will (usually) stand up to reuse.

[Streetwind]

14 hours ago, suicidejunkie said:

Is there a better way to protect the base from engine wash?

The problem with engine wash is that it's based on an inversely exponential function of distance, so it grows extremely large when your engine is directly touching another part.

However, even in such a case, you would think that a launchpad should logically survive a rocket launch, right? I think you're well justified to fudge the numbers in your favor here.

Try going into the config file that defines the EPL launchpad, and changing the following numbers:

- maxTemp (literally a temperature in Kelvin, change it to something ridiculous like 20000)
- skinMaxTemp (if this value exists, delete it entirely)
- skinMassPerArea (a value between 0 and 1, use something like 0.5)
- skinInternalConductionMult (pick a large value, like a few thousands)
- thermalMassModifier (again, pick a large multiplier)

All of these can usually be found in the same block where the part's mass is declared. If a value doesn't exist, just write it in yourself.

Doing this should make the launchpad absurdly heat resistant in every imaginable way and situation, so that engine exhaust doesn't kill it anymore.

[suicidejunkie]

Bewing: I can't believe I didn't think of launch clamps.  That could work perfectly, but the tricky bit will be how to safely recycle/dispose of them on Mün after use.

Zeiss Ikon: True, switching to the survey station would probably be best.  I always worry about the deployment orientation and I'll have to keep a hose point nearby for easy hookup & fueling after construction.

Streetwind: Good to know the math behind it.  I'm currently using the spacedock for tech level & reliability, which is really designed to have things drift away on RCS power rather than burn straight for orbit.