Decoupler weights

[technion]

Hey guys,

I'm looking to try something different. By "different", I mean "come up with an actual use for those hydraulic manifolds".

In this scenario, I have a stage that fires these manifolds basically as a replacement separatron, and has these science modules land on parachute.

It seems to work, but it begs the question: These things are heavy. I can deal with that while landing. I cannot deal with that after firing them and trying to ascent from the surface of Eve. Do these still have a weight on the center rocket after being used?

PS: Please let me know if you have any issues with the below image. It's running on an experimental SSL server.

[MockKnizzle]

The behavior of the other radial decouplers would suggest that the mass of the decoupler is concentrated in the part that falls off.

[Kasuha]

Do these still have a weight on the center rocket after being used?

As far as I know, all radial decouplers' mass stays with the decoupled part. The best thing to do is, of course, to make an experiment. Get a tank and a probe core, put them on launchpad, check mass. Stick multiple manifolds on it in VAB, put it on launchpad again, check mass. Then decouple them and check the mass again.

[Red Iron Crown]

I see you're using KER, so you don't even need to bring your experiment to the launchpad as Kasuha suggests. Build a simple core stage and note its mass. Add decouplers and tanks attached to them and see if the mass given for your core stage changes.

IME, the mass stays with the decoupled stage, but it's better to experiment for yourself.

[technion]

To answer everyone's question, yep, it's like you all suggested.

I've done some tests and it seems to not affect the weight.

Now, if only I could add an XL parachute without losing > 1500 DV

[cantab]

I've seen many people design their Eve landers to jettison parachutes before the ascent.

Also, if you don't know already: Tweak the lander can's monopropellant to zero if you don't need it. Saves you 60 kilos, which isn't much but if you're marginal on delta-V then every little helps.

[Taki117]

Why do you have decouplers on your SAS units? They don't appear to be attached to anything.

[technion]

I've seen many people design their Eve landers to jettison parachutes before the ascent.

Also, if you don't know already: Tweak the lander can's monopropellant to zero if you don't need it. Saves you 60 kilos, which isn't much but if you're marginal on delta-V then every little helps.

No I did not ever know that.. damn.. that's a fantastic idea.

Why do you have decouplers on your SAS units? They don't appear to be attached to anything.

There seems to be a huge amount of SAS required for the launch because A) I am playing with FAR and I cannot bring fins without having them explode due to DRE. By the time we hit around 30km and lose the bottom aerospikes and tanks, we can afford to decouple all that weight.

Over all, this was one of those ideas that looks great on Kerbin, but fails on Eve. With the massively increased gravity over there, these manifolds were useless and the parts flew straight down into the waiting rocket below.

Edited June 7, 2014 by technion

[technion]

I've seen many people design their Eve landers to jettison parachutes before the ascent.

This is basically why I'm happy to use the inefficient SRBs. They are basically just a surface to mount parachutes on, and it's easier to let them offset that weight than try to decouple an empty surface.

[Taki117]

...

There seems to be a huge amount of SAS required for the launch because A) I am playing with FAR and I cannot bring fins without having them explode due to DRE. By the time we hit around 30km and lose the bottom aerospikes and tanks, we can afford to decouple all that weight.

....

I meant that the top of the decouplers don't appear attached to anything, meaning that they are dead weight.