MIRV with oblique nose cones on sustainers

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Apr 11, 2017
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So there has been discussions on MIRV clones, and I just so happen to have had some oblique nose cones delivered from Apogee this week:

So It got me thinking... I was pondering 4 sustainers, each with two fins side mounted at 90 degrees as follows, but with the oblique nose cones:

rocksim006.png rocksim007.png

Given this can't easily be simulated in either rocksim or OR even with normal straight parabolic nose cones, here are my two questions:

1) I assume with only two fins, we are likely to get lift forces that banana peel all four of the sustainers away from the booster in the direction between the two fins.. is this correct?

2) If I was to have the sustainers with an oblique nose cone that is angled in towards the centre line of the booster, what will this do to the flight? Will the pitch on the oblique nose cone create forces that somewhat counter the "peeling away" forces the 2 fins create if they are angled correctly?
Those are good questions. If they happen to all light at the same time, there might be a suction created between the nose cones that could keep them held together. The asymmetric fin pattern, due to both the lift and drag combined forces, will tend to rotate the sustainers away from each other when they break apart. The fins should have a longer moment arm than the nose about the c.g., so their forces would have a stronger rotating torque compared to the nose, which is smaller in surface area and has a shorter moment arm about the c.g.

Concepts to think about: a rotating torque comes from a force times the moment arm distance, here the distance from where the force is located to the c.g. of the rocket. Aerodynamic forces come from a distributed pressure over a surface area (and friction which is usually a much smaller portion than that due to pressure).
If the fins are touching, they should effectively act like one fin. Any tendency to separate should create a low pressure between them that would want to keep them together. You could increase this tendency by beveling the fins toward each other. As far as the nose goes, whichever way it points, the tube will want to go.
One idea to help get the sustainers to separate is to put slightly different nose weights in each. While not likely that each sustainer is exactly the same weight, due to variations in the engines and thrust even, if you have slightly different nose weights, than their accelerations will be different and they will launch from the booster at different speeds. The noses are close enough to each other that it should not make much difference during the booster phase when they are together.
The whole point of the original MIRV was for the sustainers to go unstable. That is what makes the flight paths "Multiply Independent" and cool for the kids. . . and big kids too!
The whole point of the original MIRV was for the sustainers to go unstable. That is what makes the flight paths "Multiply Independent" and cool for the kids. . . and big kids too!

Maybe I'll point the obliques outwards!

Best part is, I'll be able to orient the NCs on the sustainers however I want each launch, so we can play and report back... 😜