Guided Missile

Introduction

Historically, the term "missile" refers to any object or projectile that is forcibly thrown, launched, or propelled at a target.

Nowadays its almost exclusively used to refer to the guided metal poles with flame shooting out the back that get launched from military planes, boats, and various land vehicles.

Design

The Problem to Solve

A missile is a closed system that needs to accomplish one task, and should be designed as so. Starting with the planning.

Before building anything, you should first think about what your missile will be trying to accomplish. A short range air to air and a sea skimming AShM are both missiles, but they share very little things in common. You should be always designing your missile for the target.

Design Constraints

Once you know what your missile needs to do, you can use that to define the set of design goals and constraints to follow during the design process.

Goals and constraints may include but are not limited to:

• Range
• Speed
• Maneuverability
• Launch platform

These are all things that will affect your final design, and should be set before building.

Segments & Parts

Guidance

Here is the single most important part of the guide

A positive signal to your fins should cause your missile to PITCH UP and YAW RIGHT

This is the same format as the output from the missile output of the missile radar and will make sure your math the same as what everyone else is doing if you're doing GPS.

Radar

A majority of missiles simply use the missile output from the 1x1 missile radar, this has many advantages such as having built-in proportional navigation (an algorithm that makes your missile intercept the target rather than chase it) and no radar noise. Making it a good choice for moving targets.

This also has the disadvantage of being able to be affected or disabled by chaff

Laser

Similarly to radar, the missile laser receiver block has a missile output with built-in PN guidance. And also doesn't really have any countermeasures if they don't know your laser frequency.

The main disadvantage of laser guidance is that you have to keep a laser pointed at the target in the first place.

Other

More advanced missiles almost always also include some form of GPS guidance to be able to fly towards targets that are either not in range or not in view. GPS guidance will be discussed later on in the GPS guidance section.

Maneuvering

Fins

The simplest way of manoeuvering is using built in fins in the solid booster fuel cylinders, as the composite node can be directly controlled by the missile output of the radar

The rule of thumb is the center of stability should always be behind your center of mass, you can roughly find the center of stability by either:

• Averaging the position of your fins, accounting for the fin factors
• Dropping your missile from a high height (it should fall forwards)

This ensures that the missile does not become unstable and/or spin during guidance, as a missile that is too unstable will almost always overcompensate for its deviation to target and start oscillating, wasting energy and reducing the final accuracy

This also means that there will always be a tradeoff in hitting more accurately and turning harder, which can later be pushed further with more advanced control systems.

Payload

Warhead

There are 4 warheads, small, medium, large, and EMP

• Small warheads damage everything in a 2.5m (10 block) radius
• Medium warheads damage everything in a 3.25 (13 block) radius
• Large warheads damage everything within a 3.5m (14 block) radius
• EMPs make vehicles within 500 meters unpowered for a minute

Each warhead also has a limit for the heaviest vehicle they can outright delete.

Compression Warhead

Autocannon drums filled with Bertha HE rounds are often used as an extremely potent and compact payload for striking heavier targets. They can be made by opening up the XML file of a drum and changing ammo type and damage to property_ammo_type="14" property_ammo_damage="1".

These need some sort of mechanism to be set off as they don't detonate on impact as easily as regular warheads. This is often done with a machine gun pointed at the drum or a small warhead with the "Destroy Vehicle" option disabled.

Kinetic

If your missile is heavy enough and moving at a high enough speed, it will also deal impact damage that scales with the how heavy and how fast it is

With a heavy and fast enough missile this can be a decent way to take out ships and structures as the damage radius is often large enough to damage internals

Fuzing

The simplest way to fuze a missile is by impact Fuzing, exploding when the missile impacts something. The warheads themselves include this function with the impact threashold setting included in the warhead. Some heavier missiles can also take enough damage to set off their compression warhead when hitting the ground, in which case no further systems are required.

Against maneuverable targets another option is Proximity Fuzing, where you use information from a Radar or Player Sensor to activate a warhead without directly hitting the target, meaning you can damage the target even if your missile closely misses

Propulsion

Anything that produces thrust can be used as propulsion for a missile.

You can even propel one off a steam turbine and propeller if you want to.

Although the sensible approach usually is to use a solid rocket booster, as they can be activated by one input and are very simple to set up.

Attachment

Almost all missiles are attached by Hardpoints, as they include battery charge and can be easily set up, attached and launched

Usually the hardpoint is placed somewhere near the middle of the missile pointing to the side, but it can also be mounted on the back for more compact mounting as the footprint of the missile will be a true 1x1

Missiles can also be stacked and launched out of the same place with the use of a linear track that guides them as they launch

GPS Guidance

The (relatively) Easy Way

The easy way?

This method of GPS guidance is considered the relatively easy way, as you don't need to use vectors and euler rotation (they scare me)

Instead this simpler method only uses the bearing and pitch of the missile for guidance

Pros:

• The maths is relatively simpler
• It works well for roll controlled things like drones and cruise missiles

Cons:

• Controls may be twitchy or inaccurate in some situations (vertical climb or dive)
• Requires the missile to have roll control

The Hard Way

The hard way?

The other way of doing GPS guidance is to use vectors, this will be harder to set up initially as it requires converting global offsets to targets to the local offset. But to most people after the initial setup it is more intuitive to program behaviors.

Troubleshooting

Launch your missile and watch it fly

My missile falls off the hardpoint:

• Launching with the release node instead of launch node on the hardpoint connector
• Booster not connected to launched node on hardpoint
• Booster not attached properly/on the wrong grid (common with smokeless motors)

My missile doesn't go towards the target at all:

• Incorrect radar settings, make sure it is set to static with a reasonable FOV
• Radar isn't being activated on launch, connected the active node of the radar to the hardpoint
• Missile fins aren't connected, connect the missile output composite node of the radar to your fins
• Screwed up balancing, make sure you have fins in front and behind your missile's center of mass

My missile doesn't go in the right direction:

• Fins are rotated incorrectly, refer to the guidance section
• Fins are connected to the radar output instead of missile output

My missile goes towards the target but loses control:

• Authority and stability issue, it is highly recommended to disconnect all fins from the radar and connect them one by one starting from the very front one, usually you will not need to link every fin to the radar

My missile spins out immediately:

• Asymmetric center of mass, check the center of mass of your missile in the editor
• Center of lift way too forward, missile need passive stability to fly properly, add more rear fins or remove some front fins

My missile explodes immediately:

• Increase the impact threshold of your warhead