Secret Projects Forum

Secret Projects => Missile Projects => Topic started by: PMN1 on February 14, 2009, 08:12:06 am

Title: Missile guidance systems
Post by: PMN1 on February 14, 2009, 08:12:06 am
According to BSP4, 'Artemis used an early form of semi-active homing, whereby the target was to be illuminated by AI radar in the launch aircraft with the reflected signal picked up by Artemis'.

If semi-active radar was being looked at in 1943/44, why did missiles such as Sea Slug use beam riding homing?
Title: Re: Missile guidance systems
Post by: Grzesio on February 14, 2009, 02:32:34 pm
A guidance system choice depends of many factors.
For example semi-active or active guidance may not be appropriate for air-to-surface missiles with somewhat steeper trajectory, as the radar cannot 'see' the target against the background surface. For example this was the reason for equipping Roc bombs with a TV guidance instead of initially intended radar one.
In case of a surface-to-air missile as the Seaslug, the reason for not using active or semi-active radar guidance may be caused by a fairly complex way of guiding a missile towards its target. Generally it's easier to have such a missile remotely controlled (by signals or a beam) instead of self-homing (at least at the majority of its trajectory) - as in this case the missile's path can be calculated with appropriate advance, heading etc. by a fairly elaborate control system in such a way, that missile's trajectory is optimized according to given conditions of interception, allowing the missile to reach its target quickly and with minimum maneuvering.
An early self-homing missile would usually always point at its target, moving at the pursuit curve, what would usually result in relatively violent maneuvers at the final stage of its flight, what could lead to a miss. Such a missile needs also to cover a greater distance before hitting the target than a missile guided with e.g. constant bearing method etc., what means pursuit curve missile's kill range is actually smaller, even if its flight range is the same as of a constant bearing missile.


Title: Re: Missile guidance systems
Post by: RP1 on March 18, 2009, 06:40:58 pm
Further to Grzesio's comments, one should note that Artemis was more of a course corrected 5-inch rocket, rather than a missile in the modern sense.

In "British Destroyers and Frigates", Friedman mentions that the guidance range of a beam-riding missile is much greater than a semi-active homing weapon due to the limited power of the illuminator. I find this a little confusing, as the receiving SARH missile is closer to the target than the receiving director in a B-R system. Perhaps it relates to the size and sensitivity of the missiles receiver, and choice of frequency?

There is also the issue of changes in signal strength as the SARH missile closes on the target - IIRC this was a problem in the development of the BAT active homing anti-ship weapon.

Title: Re: Missile guidance systems
Post by: Grzesio on March 19, 2009, 05:56:18 am
You're right. I've once read a very interesting book of 1947 about advanced weapons development by the NDRC - there were problems with the Bat indeed - as the Navy for some unexplainable reason chosen the active homing Bat instead of the semi-active Pelican (unexplainable, because rules of engagement always required visual identification of the target). This caused a lot of problems due to very rapid increase of reflected signal strength at the final stage of the trajectory (as both the transmitter and receiver were closing to the target) leading to a miss. The problem caused serious delay in development and eventually the Bat was put into service a couple of months later than the Pelican could have been.

Well, I understand the problem of the beam riding missile in such a way:
The illuminator size and power of an active homing missile is limited by the missile size, but there are no such limits when an external illuminator is concerned.
When the actively homing missile closes to its target both the illuminator and receiver are close to the target indeed - but at the moment when the missile is launched, the onboard illuminator is equally far from the target as the external, ship mounted illuminator would be, while the latter can be much more powerful. This obviously limits ARH missile's max. range as compared to to SARH missile.
Then, there's some unavoidable loss of signal strength during the reflection by the target - while the beam riding missile always receives a direct signal. And the BR signal covers the smallest distance, only the ship-missile one. SARH needs to cover ship-target-missile distance.


Title: Re: Missile guidance systems
Post by: Weasel Pilot on June 07, 2009, 07:44:03 pm
Real problem with beam riding guidance is that the beam spreads with distance so accuracy decreases with range whereas with SARH (or active RH) accuracy improves as distance to the target decreases (or range from the launcher increases - same thing)

Dave Mason
Title: Re: Missile guidance systems
Post by: pathology_doc on May 07, 2010, 04:23:32 am
Talos, of course, had the best of both worlds - midcourse guidance on a beam with SARH terminal homing. IIRC this was used to advantage in Vietnam, bringing the missile down on the target under beam-riding guidance and then switching to SARH illumination too late for the enemy RWR to give meaningful notice before the end. The problem there of course is the size and complexity of the system (and not just the missile handling gear and the missiles), but it offered trajectory optimisation (with the bulky computers in the most optimal place - on the ship, right next to the guidance-beam projector) with reasonably precise terminal guidance, a combination you didn't otherwise get until AEGIS arrived (I can't remember to what extent SM-1 performance is optimised - if at all - through being directed by an AEGIS ship, but I'm of the understanding that the old Terrier ships which fired SM-2 ER did better to allow AEGIS to control the missiles so long as there were enough channels of fire available).

I remember reading something about Seaslug Mk2 being a SARH weapon; which might imply that it could ride the beam in the boost and approach phases, until it got close enough that returns off the homing head gave better control than ship direction, or it might not.
Title: Re: Missile guidance systems
Post by: PMN1 on May 19, 2015, 01:37:10 pm
Artemis was based on a 3" rocket, what diameter would you need to go to to have made it effective?

Title: Re: Missile guidance systems
Post by: PMN1 on April 04, 2018, 08:09:30 am
Was it planned to use Artemis with an existing AI or was a new system to be developed?