Rockets and Missiles - Physics for Game Programmers - page 344

Quite a bit of research has been performed on developing sophisticated guidance systems, but
an equal amount of research has also gone into finding ways to confuse missile guidance systems
so they lose sight of their target. Some targets may try to electronically jam a radar guidance
system. Small metal strips, called chaff , can be thrown into the air to confuse radar guidance as
well. High-temperature flares can be released by an airplane, causing a heat-seeking missile to
lock on to the flares instead of the airplane. If you are developing a sophisticated missile simu-
lation, you probably will want to include guidance system countermeasures as part of the
simulation.
To accomplish their objective, missiles have to be highly maneuverable. Most missiles
have control fins that can be rotated to change the direction of travel. The direction of the
rocket nozzle exhaust can be adjusted using what is called a thrust vector control system to
change the course of the missile as well.

Missile Specifications
In order to model a missile in a game simulation, the technical specifications of the missile
must be obtained. Fortunately, there are a lot of resources online, in topics, or in technical
papers where missile specification data can be obtained. Unfortunately, some of the informa-
tion, such as the thrust generated by the missile, can be classified information. Sometimes the
missing information can be guessed at if other information about the missile is known. For
example, if the maximum velocity of the missile is known and an estimate can be made of the
drag coefficient, the thrust generated by the engine at the maximum velocity can be estimated
by computing the drag force at the maximum velocity condition.
As an example of what missile specifications look like, Table 11-5 lists geometric and
performance specifications for two missiles, the AIM9 Sidewinder and the AGM-114 Hellfire. 7
The Sidewinder is an older air-to-air missile, whereas the Hellfire is an air-fired antitank missile.
Both missiles use a solid-propellant rocket motor. Because of their simplicity, solid-propellant
rocket engines are used to power most small-scale military missiles. The thrust for the Sidewinder
missile was unavailable from the publicly accessible sources, but could be estimated from the
maximum velocity data.

Table 11-5. Sidewinder and Hellfire Missile Specifications

Quantity AIM9 Sidewinder AGM-114 Hellfire

Missile type Air-to-air Air-to-surface

Purpose Anti-aircraft missile Antitank missile

Guidance system Infrared Laser seeking

Length ( m ) 2.87 1.63

Diameter ( m ) 0.13 0.178

Mass ( kg ) 85.5 45.5

Engine type Solid-propellant Solid-propellant

Engine thrust ( N) Classified 2220-2670

Maximum velocity ( m/s ) 850 420