Musings on a scratch built MIRV in RockSim

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Well-Known Member
Apr 11, 2017
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So I have been playing with RockSim and the idea of a scratch built MIRV... designed to fly on a D12 booster and 4x A83 sustainers...

The idea is that the Sustainers will have oblique nose cones - maybe all pointed in, maybe all pointed out - testing would tell what's most interesting to watch..

Both Stages with all four Independent Re-entry Vehicles (IRVs)

Just the IRVs

Just the booster

Aft view of the whole thing

Aft view of just the sustainers

Aft view of just the Booster

The whole thing in 3d..

It is a little hard to model a cloverleaf moulded shroud / transition - There would be two of them - one internal for the Booster Ejection Charge splitting into the GAP staging sustainers, one external at the top of the interstage coupler..

RockSim file attached...
View attachment MIRV -

Thoughts / suggestions welcome...
picture 3 of 7: I think you captured the idea of coincident c.g./c.p of the booster alone for a good tumble recovery, not sure if that is with a spent engine casing or an unburned engine in your sim, the propellant weight may shift that a little.

Venting... might have to make some holes, but you know that already. Can you keep the transition attached to the sustainers? Think about it. if you have a little empty space in there, you can put a short streamer for the booster, just for visibility on the ground to help find it.

Boat-tail. Just because I like them.

High-temp BBQ paint for the booster/sustainer manifold. May be easier to paint parts of that interior prior to assembly.
Potential issues:
With two fins, your sustainers are unstable. It is possible to fix this with a third asymmetric fin.
Does it matter? Maybe, maybe not. If all goes as planned (haunting music begins here) and the rocket as a unit flies straight and high on the D12, and with your dinky A8-3 sustainer engines (kidding aside, good choice, won't go far, big nozzle promotes high prob of successful black powder staging) even though sustainers are unstable they won't go far, so if staging is way up there as expected no biggie. If things DON,T go as well, you STILL may be better off even if they go catywampus as really unstable small rockets that are underpowered tend to just skywrite in twisty circles and don't get up much velocity or kinetic energy to do much damage.

After staging, is the BOOSTER still stable? If your central dowel/flying launch lug is long enough and heavy enough you may get a ballistic re-entry, dowel side down, which won't be good for a second flight of your booster dowel and might be suboptimal with whatever animal or vegetable or mineral it impacts upon. Even if you succeed in tumble recovery, it is a bit rough with the weight of a D engine, big fins, and a dowel

Can you add a recovery system to your sustainer? 3DogNight used horizontal spin, which in my opinion only works with ring fin rockets for reasons which quickly become evident when you imagine the impact of a rocket falling horizontally, rapidly spinning on its axis and hitting terra firma. Your sustainer engine burnout energy is being used to ignite upper stages, so not much if any to spare for ejecting a streamer. Could put streamer pods on sustainers, could cluster the booster with a small short delay engine to fire a chute or streamer 2 or 3 seconds after burnout (A10-3T would probably fire between 2 to 3 seconds post D12-0 burnthrough.

I will be curious to see how you pull this off. I found it a real challenge.
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By definition you are gap staging. A simple paper punch hole. Just in the tubing below where the butt end of the engine is located should easily be enough to vent the ejection gas enough to let the hot plasma get up to the nozzle to ignite the upper stages.

Smearing some Epoxy, maybe JB weld over the midportion of the trifold where are your three upper stage engines meet above the single D 12 should help with the burning problem