OrbitalMissile

MomentumMissile adds the following properties:

Name	Description
Speed	This property behaves differently for orbital missiles. It defines a speed in units per second (negative to go clockwise). If you want to define speed in how long it takes to orbit once, use OrbitalPeriod instead.
Range	The distance at which the OrbitalMissile orbits from the origin. The speed of the missile after a range adjustment is determined by whether it was set via Speed or OrbitalPeriod.
OrbitalPeriod	The amount of time it takes to make one rotation in seconds. Use negative values to go clockwise. This can be used instead ofSpeed, and will ensure a consistent orbital period through Range adjustments.
InitialAngle	The initial angle in degrees at which this missile is created. If left at null, will use a random angle.

The orbital missile will orbit the target at the desired range. Unlike other missiles, it cannot impact the target.

Below is a slightly more advanced example of an orbital missile. This missile completes an orbit once every 4 seconds at a range of 600, and collides with enemy units in a 150 radius. Targets hit are stored in a list and removed from TargetsHit after 1 second, allowing them to be collided with again via OnCollision.

using System.Collections.Generic;
using WCSharp.Missiles;
using WCSharp.Utils.Extensions;
using static War3Api.Common;

public class Orbital : OrbitalMissile
{
	private class UnitHit
	{
		public float Age { get; set; }
		public unit Unit { get; }

		public UnitHit(unit unit)
		{
			Unit = unit;
		}
	}

	private readonly List<UnitHit> targetsHitCooldown = new List<UnitHit>();

	public Orbital(unit caster, unit target) : base(caster, target)
	{
		TargetImpactZ = 50;
		EffectScale = 1.0f;
		EffectString = @"Abilities\Weapons\GlaiveMissile\GlaiveMissile.mdl";
		CollisionRadius = 150;
		Range = 600;
		OrbitalPeriod = 4.0f;
		Interval = PeriodicEvents.SYSTEM_INTERVAL;
	}

	public override void OnCollision(unit unit)
	{
		if (IsUnitEnemy(unit, CastingPlayer))
		{
			UnitDamageTarget(Caster, Target, 100, true, false, ATTACK_TYPE_CHAOS, DAMAGE_TYPE_UNKNOWN, WEAPON_TYPE_WHOKNOWS);
			this.targetsHitCooldown.Add(new UnitHit(unit));
		}
	}

	public override void OnPeriodic()
	{
		this.targetsHitCooldown.IterateWithRemoval(cooldown =>
		{

			cooldown.Age += PeriodicEvents.SYSTEM_INTERVAL;
			if (cooldown.Age >= 1)
			{
				TargetsHit.Remove(cooldown.Unit);
				return false;
			}

			return true;
		});
	}
}

Please see Utils for an explanation regarding the IterateWithRemoval method.