Explanation concerning RIM 156A (Full Version)

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DWReese -> Explanation concerning RIM 156A (3/17/2019 3:14:02 AM)

Here is something simple for you to look at and then try to explain for me if you would.

I have a cruiser armed with RIM-156A SAMs defending and 8 DF-21s approaching at approximately 150 miles away.

The cruiser sees the missiles and begins maneuvering to fire. It releases as soon as possible.

The RIM-156As travel at 2600 miles per hours while the DF-21s come in at 6500.

In the attached test file the missiles all seem to function normally. Just before they are supposed to hit the target, they each make a right turn, and one-by-one, they turn away. The right turn appears to occur right at, or around, the time when the RIM-156 has traveled 40 miles. All 16 never even attack. Why?

In my next message I will repeat the same scenario.


DWReese -> RE: Explanation concerning RIM 156A (3/17/2019 3:21:11 AM)

I had saved the scenario PRIOR to the attack and ran it again from the time that the missiles were detected.

Everything occurred just like before until the missiles got near.

This time, however, the RIM-156A missiles all began attacking the DF-21s.

I didn't change anything. I just allowed the game to run as soon as I hit enter.

I repeated this again, and again the missiles all missed the first time around. I ran it again, and then they all started engaging in the second.

FWIW, the RIM-161 and RIM-174 work fine, so what is it about the RIM-156 that is different?

Can someone look at these and render an opinion as to why they think this is happening? Remember, there is this file, and the file in the previous message.


Zanthra -> RE: Explanation concerning RIM 156A (3/17/2019 8:13:54 AM)

Do you have the same problems if you run in high fidelity mode at 5x or less time compression for shorter ticks. If it works that way then it's probable from one tick to the next that it is passing over the enemy missiles.

Cik -> RE: Explanation concerning RIM 156A (3/17/2019 9:09:33 AM)

it's likely they are missing in the vertical. small differences in altitude are assumed away in the terminal maneuver, but if you shoot at certain ranges the differences in climb/dive speed mean that when the interceptors "pop up" to intercept the DF- at cruising altitude they will overcompensate. when the DF- begins it's terminal dive it will outpace the diverate of the interceptor, and the interceptor can miss in the vertical by far enough that the terminal attack never happens.

this is probably caused because the sim doesn't do a perfect job of extrapolating the probable flight path of the incoming missile, it's flyout calculation is based on the DF's current position, and when that position begins to radically change during it's terminal dive the interceptor can't compensate.

this is probably what's happening if i had to guess.

DWReese -> RE: Explanation concerning RIM 156A (3/17/2019 11:49:44 AM)

As the missiles approach one another, I use the 1x1 (Real Time) mode so that I can watch it.


DWReese -> RE: Explanation concerning RIM 156A (3/17/2019 11:56:24 AM)

What's weird is that when the RIM-156s begin to turn it is pretty much right at a distance of 40 miles from their firing ship. The altitude difference is only 5000 feet.

I get the idea that the intercept logic sends it out a certain distance, and then turns on its seeker. But, the missile starts turning to either the right (as in this case) or the left, or starts looking in the center. If it turns either way, then it misses all of them. But, if it were to go straight, then it will hit them.

If this is the case, then the programming logic is set to have ALL turn to the left, or right, rather than stagger with some starting left and others to the right or center. This is why they either are all off the path or in line with the target.


Zanthra -> RE: Explanation concerning RIM 156A (3/17/2019 8:24:10 PM)

In the game speed options there is a high fidelity mode that makes ticks 0.1 seconds rather than 1 second. When I tried with that, it had no problems hitting. I think there are issues with the accuracy of the simulation closing at more than 2 nm every tick.

The specific issue I suspect is that the datalink only updates once a tick, and is not entirely accurate (I still suspect that datalink intercepts are calculated on an equirectangular map projection or something similar, basically expecting the target to follow something like arhumb line rather than a great circle route). By the time the missile gets in range of its own seeker, it has 1 or 2 ticks to maneuver, and swings to try to catch the missiles, but not enough temporal resolution to get to intercept. The simulation is not deterministic, (perhaps radar contacts are updated before intercepts are updated and sometimes the opposite, a wild guess at what might cause it), as such different attempts give different results.

DWReese -> RE: Explanation concerning RIM 156A (3/17/2019 9:06:44 PM)

Thanks for the tip.

I noticed that I did already have "High-Fidelity" checked, but I also had "No Pulse" checked as well. I unchecked "No Pulse" and I have had some success.

I'm curious as to if you tried your experiment more than once, or did you just have success one time. previously, I had success once and then would fail twice because the RIM-156As would all turn either right or left.


Zanthra -> RE: Explanation concerning RIM 156A (3/17/2019 10:36:18 PM)

Ah okay. I was looking at the second version you posted which when run without high fidelity mode the missiles still miss even though their targets are with the appropriate altitude. I ran the first scenario and it's definately related to the target altitude being too high. When the missiles get close , they start turning around, but shortly after they start turning around, another determination is made that drops their targets, once that happens, they just fly off straight.

It looks like they turn to fly towards the point where the target will be in 1 second (around 1.5nm ahead of the incoming missiles). Once it's within +- some number of seconds (I think it's 2 seconds or about 3NM out against these targets) of intercept, I think the determination is made whether to intercept the target or not, but since the targets are above the max altitude for the RIM 154A, the missiles do not intercept, instead they start turning around to continue flying to where the missile will be in 1 second.

Although after more experimentation it seems that the missiles are not using datalinks at all for guidance since the targets are well within seeker range. The reason for the problems without high fidelity mode in the second scenario is related to the timing at which the targets cross under to a valid altitude for intercept, being after the interceptors are well under 4nm from their target, meaning the missiles against the first few incoming miss their chance to intercept due to insufficient temporal resolution, this coupled with the fact that the AN/SPG-62 can only illuminate 4 targets, a reluctance to release the illumination from the first incoming missiles when the interceptors miss, and the lack of ticks in which it can change the illumination target for the remaining illuminators once missiles do start intercepting means that most of the RIM 154A pass by blind.

PS: I miscalculated the vertical speed of the incoming targets. Given that they are decending at nearly 2000 meters per second with a total velocity of 3000 meters per second, then it's possible that the RIM-156A are leading the targets by flying the shortest intercept to target rather than leading by a fixed 1 second. When calculated in 3D, the incoming target has quite a distance to decend, and the RIM-156A has quite a distance to ascend to reach that intercept, so the location it has to fly to becomes behind the interceptor at about 1-2nm. I know that during terminal phase, active radar homing missiles do not lead their targets significantly, but instead fly a straight in approach, but SARH missiles may.

DWReese -> RE: Explanation concerning RIM 156A (3/18/2019 12:13:52 AM)

From what I can see, the RIM-174 has the same characteristics, but not to the same degree.

What's puzzling is that, on occasion, they will hit, but two-thirds of the time they will turn away.

The RIM-161 seems to have no problem striking at targets outside of its attack zone. From what I gather, some special rules or liberties may be in effect for the interception of ABMs.

I don't doubt your findings, but from what I have seen, it will take lots of testing (not just a one or two time test) to nail this down. When it works properly once, then fails miserably twice more, then it drives you nuts. Is it failing because it was designed to fail two out of three times, or because of some kind of glitch. My scenario creation, and subsequent hair-pulling session, led me to this. It's hard to create a scenario when you don't know what to reasonably expect unless, of course, it is by design.


Zanthra -> RE: Explanation concerning RIM 156A (3/18/2019 1:02:53 AM)

The RIM-174 has the same 115,000 feet, or 35km max target altitude. If the target has not descended below that altitude when the RIM 156 or RIM 174 reaches it, it will not get a roll to hit. The game either does not do the calculations, or does not provide enough error margin for determining whether the target will be under the appropriate altitude when the interceptors reach it before launching them. Even if they do do that math, the DF-21D complicates this further by flying a ballistic trajectory until the release of the reentry vehicle, then starting to maneuver, it may slow it's descent substantially putting it much higher during intercept then predicted and above the critical 115,000 foot altitude.

One workaround would be to reduce the max range for the RIM-156 and RIM-174 in the weapons release authorization, which will allow the DF-21s to get lower before the intercept.

DWReese -> RE: Explanation concerning RIM 156A (3/18/2019 2:07:04 AM)

You are 100 percent correct. It is the altitude that is causing the problem. When the missiles come together, the RIM-156 (or the RIM-174) are still about 15000 feet lower than the DF-21s. By the time that they get on the same altitude, the ROM-156s have already passed the DF-21s.

So, I went to WRA and assigned the RIM-156s to fre at a distance of 100 miles (as a test) rather than the 130 mile distance. That made the difference. Firing later, meant the the missiles arrived at the same altitude level, and the RIM-156s were able to destroy the DF-21s, with some help of a second wave, of course.

Thanks for your help. It may not be perfect, but it works for me.


KnightHawk75 -> RE: Explanation concerning RIM 156A (3/18/2019 2:17:28 PM)

Some great info buried in here, just wanted to say thanks.

DWReese -> RE: Explanation concerning RIM 156A (3/18/2019 3:39:27 PM)

It is an interesting topic that rarely (if ever) gets discussed or explored. I love the way that they have included it. I believe that at some point it will become a "reality" in the sense that it would be actually used in real life. So, it's nice to explore it every now and then.

If you would like another area to explore may I suggest satellites. They really add lots to the game regarding location and identification.


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