Tomahawk
cruise missiles frequently appear in the news because they are
the U.S. weapon of choice for a variety of quick-strike
operations. In this issue of How Stuff
Works we will look at cruise missiles so that you can
understand what they are and how they work. Then you can
explore a wide variety of links for additional information!
The Basics
A cruise
missile is basically a small, pilot-less airplane.
Cruise missiles have an 8.5-foot (2.61 meter) wingspan, are
powered by turbofan
engines and can fly 500 to 1,000 miles depending on the
configuration. A cruise missile's job in life is to deliver a
1,000 pound (450 kg) high-explosive bomb to a precise location
- the target. The missile is destroyed when the bomb explodes.
Since cruise missiles cost between $500,000 and $1,000,000
each, it's a fairly expensive way to deliver a 1,000 pound
package!
Cruise missiles come in a number of variations (see the
links section for details) and can be launched from subs,
destroyers or aircraft. When you hear about hundreds of cruise
missiles being fired at targets like Iraq, they are almost
always Tomahawk cruise missiles launched from destroyers.
Dimensions
Cruise missiles are 20 feet (6.25
meters) long and 21 inches (0.52 meters) in diameter. At
launch they include a 550 pound (250 kg) solid rocket
booster and weigh 3,200 pounds (1450 kg). The booster
falls away once it has burned its fuel. The wings, tail fins
and air inlet unfold, and the turbofan
engine takes over. This engine weighs just 145 pounds (65
kg) and produces 600 pounds of thrust burning RJ4 fuel. The
fuel load is 800 to 1,000 pounds (450 kg) of fuel at launch,
or approximately 150 gallons (600 liters). A cruise missile
has a cruising speed of 550 mph (880 km/h).
Guidance
The hallmark of
a cruise missile is its incredible accuracy. A common analogy
used when talking about cruise missiles is, "the missile can
fly 1,000 miles and hit a target the size of a single-car
garage!" Cruise missles are also very effective at evading
detection by the enemy because they fly very low to the ground
(out of the view of most radar systems). Four different
systems help guide a cruise missile accurately to its target:
- IGS - Inertial Guidance System
- Tercom - TErrain COntour Matching
- GPS - Global
Positioning System
- DSMAC - Digital Scene Matching Area Correlation
The IGS is a standard acceleration-based system that
can roughly keep track of where the missile is based on the
accelerations it detects in the missile's motion (Click
here for a nice intro article). Tercom uses an on-board
3-D database of the terrain the missile will be flying over.
The Tercom system "sees" the terrain it is flying over using
its radar
system and matches this to the 3-D map stored in memory.
The Tercom system is responsible for a cruise missile's
ability to "hug the ground" during flight. The GPS system uses
the military's network of GPS satellites and an onboard GPS
receiver to detect its position with very high accuracy.
Once it is close to the target, the missile switches to a
"terminal guidance system" to choose the point of impact. The
point of impact could be pre-programmed by the GPS or Tercom
system. The DSMAC system uses a camera and an image correlator
to find the target, and is especially useful if the target is
moving. A cruise missile can also be equipped with thermal
imaging or illumination sensors (as used in smart bombs).
Additional HSW
articles
If you are a fan of How Stuff
Works you may have noticed that cruise missiles use a
number of different technologies that are discussed in detail
in other HSW articles. Here is a list of those articles:
Links
General
Launch systems
Other
