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Missile navigation question


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There's no active terrain avoidance capability - the missile doesn't know where terrain is, and doesn't need to. You just need the target at or below the horizon and the missile won't hit ground, unless there is intervening terrain. In that case, you can't guide the missile anyway, so there's no point in complicating missile autopilots with terrain.

 

There are also logistical problems with getting and then uploading the correct terrain maps into a missile. It's probably a pretty big hassle, and it is unnecessary. If you have an active missile with datalink that you can shoot over a ridge and have it find a target in a valley beyond that, you can do that by shaping the initial trajectory - HUMRAAM was supposed to have such a capability (with targeting data provided from off-board sources).

 

For the most part, making your SAMs have the best coverage with respect to terrain etc is a siting issue.

 

Just to clarify what I'm getting at, about AAM applications of such a terrain avoidance capability (in whatever way or technique it is implemented).

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I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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CLOS missiles are often just as affected by terrain avoidance problems. In fact, any missile that employs lead (that includes CLOS, which uses cross-range-error to feed lead bias into guidance command) can be affected by it...

 

But I suppose the guidance computer can keep track of ground horizon level and if the predicted intercept point (PIP) at time-to-go is on or below the horizon altitude, switch the guidance to pure-pursuit; then switch back to PN/lead once target is above horizon again. Ofcourse, this is rather primitive way of doing things, and uneven terrain can present problems (since horizon reference is from command/launcher's POV).

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meh... even in the SA-2 simulator you can select the type of trajectory that the SAM follows depending on target type.

 

...and altitude.

 

IIRC the "K" (half-lead elevated by constant) guidance mode sets the missile on an intercept trajectory without letting the intercept point being below the target altitude.

 

I think that goes a long way to prevent missiles diving into the ground.

 

In addition to that, as previously mentioned...

The big boys are there to watch the high altitudes, then force targets into the WEZ of its little bros.

Problems setting up switches on the HOTAS Warthog or similar?

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I checked how Tor missiles navigate in DCSW and they do fly PN trajectory now, happily flying to the ground if you make a steep dive. I think the CLOS is better choice if only one can be had until improvements are made to allow different trajectories for different types of target.

DCS Finland: Suomalainen DCS yhteisö -- Finnish DCS community

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I think the CLOS is better choice if only one can be had until improvements are made to allow different trajectories for different types of target.

CLOS really isn't going to solve the 'dive to the ground' problem you're mentioning.

 

Against high flying target it flies CLOS trajectory and against low altitude target it flies at a set altitude and then dives to the target when sufficiently close.

I've watched the video. That is not CLOS trajectory, nor is it PN trajectory. That's simply command-guided trajectory forming maneuver being directed by Tor's missile guidance computer, to align the missile onto intercept path.

 

You can think of it similar to AIM-120 and Hellfire "lofting" upward for long range shot; or PAC-3 doing "dog leg" maneuver during mid-course stage. Neither PN nor CLOS is going to help the Tor missile clear the terrain on a low-altitude target, so the guidance computer performs trajectory shaping maneuver to get the missile onto an intercept route.

 

I think you're confusing trajectory shaping maneuver with CLOS guidance. I'm also not sure where you're getting the notion that CLOS is superior to PN -- realistically speaking, CLOS is not necessarily any better than PN. In many respects, it performs worse than PN and loads more acceleration demand on the interceptor. CLOS is generally popular for short-range command guided SAMs due to the sake of simplicity in implementation than COLOS setup.

 

Moreover, because CLOS' acceleration command is derived from CRE (cross range error) from guidance radar's point of view, rather than the actual LOS rate, it becomes increasingly inaccurate as the engagement distance becomes longer. PN is more effective in this instance.

 

Bottom line is that, neither PN nor CLOS has much to do with terrain avoidance problem. Any missile that leads a target is going to have a problem. Terrain avoidance is more of a command/navigation issue, rather than actual guidance issue, imo.


Edited by blahdy
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Bottom line is that, neither PN nor CLOS has much to do with terrain avoidance problem. Any missile that leads a target is going to have a problem. Terrain avoidance is more of a command/navigation issue, rather than actual guidance issue, imo.

 

What I can't understand is where the onerous complication is in simply giving a real command system (back at the launcher) a digital terrain model for the area of operations, so that the commands it gives doesn't do something stupid like waste a viable missile that could have gotten a hit.

 

This seems to me to be a quite simple and obvious software solution to the whole problem of complex terrain.

 

After that all you need to do is shape the trajectory to best conserve energy and maximise intercept options. And the DTM helps here, because it also allows the guidance system to predict the most probable path the target will take, given through the ground is not one of the options.

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CLOS really isn't going to solve the 'dive to the ground' problem you're mentioning.

 

I've watched the video. That is not CLOS trajectory, nor is it PN trajectory. That's simply command-guided trajectory forming maneuver being directed by Tor's missile guidance computer, to align the missile onto intercept path.

 

You can think of it similar to AIM-120 and Hellfire "lofting" upward for long range shot; or PAC-3 doing "dog leg" maneuver during mid-course stage. Neither PN nor CLOS is going to help the Tor missile clear the terrain on a low-altitude target, so the guidance computer performs trajectory shaping maneuver to get the missile onto an intercept route.

 

I think you're confusing trajectory shaping maneuver with CLOS guidance. I'm also not sure where you're getting the notion that CLOS is superior to PN -- realistically speaking, CLOS is not necessarily any better than PN. In many respects, it performs worse than PN and loads more acceleration demand on the interceptor. CLOS is generally popular for short-range command guided SAMs due to the sake of simplicity in implementation than COLOS setup.

 

Moreover, because CLOS' acceleration command is derived from CRE (cross range error) from guidance radar's point of view, rather than the actual LOS rate, it becomes increasingly inaccurate as the engagement distance becomes longer. PN is more effective in this instance.

 

Bottom line is that, neither PN nor CLOS has much to do with terrain avoidance problem. Any missile that leads a target is going to have a problem. Terrain avoidance is more of a command/navigation issue, rather than actual guidance issue, imo.

 

CLOS missile keeps itself in a line between target and launcher. Thats what the missiles did seem to do in the video while engaging high flying targets. Unless the target dives into the ground the missile will also stay above the ground. While errors in the flight path might make it fly into the ground if it has to fly at low altitude, it will do so lot less likely than missile with PN trajectory.

 

The low flying target wasn't engaged with pure CLOS trajectory but I didn't say it was. Also against the high flying target the missile initially flew a terrain following trajectory (or something like that, can't say for sure based on a video) until the target elevation angle rose above the missiles elevation angle and it switched to CLOS.

 

As long as the tracking and guidance sensors are in the launcher the accuracy is reduced with range regardless of the trajectory used. If the sensors are in the missile the tracking accuracy increases as the missile gets closer to the target. Tracking accuracy has nothing to do with trajectory.

 

I didn't say CLOS is superior, only that it would be better choice. What I meant with that is that it would be more effective against player who tries to do all kinds of tricks to evade the missiles while still being deadly against AI. It was a personal opinion based on considering the pros and cons of PN and CLOS trajectories.

DCS Finland: Suomalainen DCS yhteisö -- Finnish DCS community

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SF Squadron

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It's a complication, just like that. There are simpler and better ways of dealing with the problem, starting with SAM site siting and more or less ending with trajectory shaping and fuzing.

 

What I can't understand is where the onerous complication is in simply giving a real command system (back at the launcher) a digital terrain model for the area of operations, so that the commands it gives doesn't do something stupid like waste a viable missile that could have gotten a hit.

[sIGPIC][/sIGPIC]

Reminder: SAM = Speed Bump :D

I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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CLOS missile keeps itself in a line between target and launcher. Thats what the missiles did seem to do in the video while engaging high flying targets.

 

Sure, it does keep it in the LOS (offset by a guidance gain K), as otherwise it wouldn't be able to track the missile anyway. You won't see a CLOS missile flying on a perfect beam line between launcher and the target though. :pilotfly:

 

Unless the target dives into the ground the missile will also stay above the ground.
If the target dives into the ground, missile should dive with the target, as long as it stays in the LOS. You probably remember the "half-lead, elevated by constant" fix on SA-2 to 'mitigate' (but not eliminate) this problem. :-P

 

I didn't say CLOS is superior, only that it would be better choice. What I meant with that is that it would be more effective against player who tries to do all kinds of tricks to evade the missiles while still being deadly against AI. It was a personal opinion based on considering the pros and cons of PN and CLOS trajectories.

Apologies if it sounded like I was putting words in your mouth, bad choice of words there.

 

But anyway IMO, the simplest way to solve this in game would be to just use two-step PN with variable navigation constant, rather than switching to CLOS.

 

If the target track is aircraft, simply reduce constant (half-lead / pure-pursuit style) until missile approaches lesser than 1km, then switch to PN as it is in terminal flight stage. PAC-2 in RL is observed flying pure-pursuit style path during mid-course, until it goes lead during TVM/terminal stage.

 

Switching to pure-pursuit style trajectory during mid-flight phase is the simplest way to mitigate terrain clearance problems xD

 

If the target track is PGM or CM (i.e. HARM), just go full constant right off the start.


Edited by blahdy
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