Is the S3 KS-25x4 Engine Cluster worth using?

[THX1138]

I've never used the S3 KS-25x4 Engine Cluster because it costs 32 400 credits for which I could buy 18 S1 SRB-KD25ks at 1 800 credits each. Am I making the right choice? The problem I'm having is that my payload is virtually unlaunchable due to the performance of my computer with the high part-count. It runs fine once I've shed the first two stages but I can't correct the lean if it runs like that. I'm sure that launching separate parts and assembling them in orbit is much more expensive and very time consuming.

Will some future update give me bigger SRBs? I have 2 000 science points but nothing to spend them on.

[Technical Ben]

What kind of craft? I find the Clusters more stable and great TWR and liquid fuel more manageable than solids. But that's only for massive craft. The KD25ks should be better for smaller launches.

[UmbralRaptor]

The quad KS-25 is a bit expensive for the performance that it offers, but if you're throwing around payloads of that size (presumably at least 25 tonnes, and possible several hundred) I'm not sure money is *that* much of an issue.

As far as efficiency goes, have you considered a KR-2L core with KD25ks or LFBs to help lift it?

[THX1138]

But the KR-2L only provides a bit less than four KD25ks worth of thrust even though it costs over 11 times as much. This is before taking into account the cost of fuel and mass but I don't know how to do that without setting up a spreadsheet. I'm still inclined to say that, at least in atmosphere, the KD25ks come out on top in terms of cost per unit of delta v.

Edited January 4, 2015 by THX1138

[Laie]

Most of the time, a KR-2L on top of a bundle of 7 pencil boosters will do just as well if not better.

The quad cluster has one important advantage, namely, its high impact tolerance. Recovering that engine and the tanks on top of it requires only a very small number of parachutes, provided you can bring it down on the dry. Unfortunately, utilizing this nearly requires an SSTO... but if you're the kind of person who likes to overbuild his lifter in order to recover all of it, this engine makes the job a lot easier.

[magnemoe]

Most of the time, a KR-2L on top of a bundle of 7 pencil boosters will do just as well if not better.

The quad cluster has one important advantage, namely, its high impact tolerance. Recovering that engine and the tanks on top of it requires only a very small number of parachutes, provided you can bring it down on the dry. Unfortunately, utilizing this nearly requires an SSTO... but if you're the kind of person who likes to overbuild his lifter in order to recover all of it, this engine makes the job a lot easier.

My solution is to add 4-8 large srb, core with cargo has an twr around one and return.

My default heavy lifter

[THX1138]

What? Eight SRBs aren't going to lift anything I'd call heavy. I've got to move a class E asteroid out of the solar system. That's heavy (the rocket, not the asteroid although obviously the asteroid is also massive).

[gbleck]

Hell I built one that landed back at the pad without chutes. The mass fraction was low but it was 100% recoverable so cost is not an issue. Haven't tried it with the new destructo pad though. A blown landing could be kind of expensive if you nuke the pad. Should dust that design off and try it again tonight.

[juanml82]

SRBs are great if your computer can handle the part count, until the SRB ring happens to have a 0.1 kn of torque and you end up flipping up (and wasting fuel from your upper stages) during ascend.

A KS-25x4 as the center column of an asparagus with KR-1x2 as the outer ring can lift a lot of weight - that can be supplemented by an SRB first stage but keep in mind you might end up tilting to one side. And if your payload is heavy enough, you are going to need the additional thrust the KS-25x4 once you're in your heavy lifter final stages.

So it really depends on the mass you want to put in orbit. Once your payload is above 100T, the KS-25x4 makes a lot of sense.

[Dr-Drunk]

I'd say the bigger engines are mostly there to compact your rockets down some instead of having stacks upon stacks of asperagus stages allround. Sure the engine costs allot but if you can recover it the cost isn't nearly as bad. Every single one of my launchers, including all the heavy payload ones, come equiped with probe cores and parachutes so I can de-orbit and recover them.

With larger rockets that have to drop allot of stages this is ofcourse allot harder to do unless you use something like StageRecovery.

[Tsevion]

The main place I've found the KS-25x4 to be useful is on Eve... it has rather good atmospheric performance, and a good TWR. The ISP of the KD25k's makes them burn out far too fast on Eve (And on Jool, but not very many people do a "surface" return from there... so it's not a big concern).

On Kerbin, for TWR and ISP efficiency the KR-2L tends to be better as you spend so much less time in full pressure conditions, and for cost the KD25k tends to be more effective. So it really only tends to be advantageous in minimizing part count.