Ballistic and Cruise Missiles.....

Hello everyone. I have a very keen interest in “all things military”, so this may seem like a very easy and dumb question, but I have never found a definite answer. After reading some other threads on similar subjects, it is clear that contributors here are very knowledgeable, so I’m sure I may at last get an answer to this!!!

OK: is the following correct??

The umbrella term ‘Cruise missile’ applies because this family of weapons (Tomahawk, etc) literally “cruise” to their target, in a (roughly) horizontal trajectory . Hence the term “cruise” applies as in, for example, Cruise Control in your family SUV. These weapons use a rocket motor (or similar), to cruise to their target.

The term ‘Ballistic missile’ applies, because this family of weapons (ICBMs, etc) ‘fall from the sky’ onto their target, following a ballistic trajectory, much like a football thrown high into the air (though guided, obviously). They are powered for launch and journey time, but not powered to hit their target by ‘cruising’ into it. Instead they use the ballistic properties of gravity to bring them onto their target(s).

Sorry for such a long post in light of such a simple question, but I need to get this basic fact correct in my head!!! Thank you!

Reported for forum change.

Yes - pretty much spot on. The only detail on which I am not clear is whether ballistic missiles ever continue to thrust on the downward part of the trajectory (this would make them harder to intercept, I expect)

Moved to General Questions.

They don’t. That’s kinda the definition of “ballistic.” :smiley:

For increased speed - no. There are enough problems with heat shields to protect warhead vitals. You have the same problems with heat and communications with space shuttles and other re-entry vehicles as with warheads. There is a point where the re-entry item can no longer communicate with external guidance systems or signals - they are on there own. There may be small thrusters for final course correction after the boost phases are over which fire on the downward portion of the trajectory.

Some advanced missiles may also dispense decoys after the boost phase to mask the true warhead.

Cruise missiles will have guidance right to final contact. There are inertial, GPS, radar, IR,TV, etc… systems governing different phases of the entire flight.

Well, yes, but the proper definition of ballistic also excludes any guidance after the cessation of thrust.

I was only wondering, out loud, if there’s such a thing as (something like) an ‘enhanced ballistic missile’ - it would still follow a typical ballistic trajectory, but with an extra push along that trajectory toward the end.

Cruise missiles generally use an air-breathing jet engine to cruise to their target, not a rocket. Ballistic missiles do use rockets for their boost phase.

Also, unlike ballistic missiles, cruise missiles generally fly at subsonic speeds. Ballistic missiles re-enter from their suborbital ballistic trajectories at many times the speed of sound, which makes them very difficult to intercept.

Yes there is:

Such as the DongFeng-21 which is the “carrier killer” ballistic missile that everyone is making a fuss about. It initially follows a ballistic path then does last minute corrections in order to be able to hit a ship on the move.

To expand on this a little, the reason cruise missiles use an air-breathing jet engine is because carrying oxygen internally for combustion would add considerable weight and size to the missile, whereas atmospheric oxygen is “free.”

Ballistic missiles have to use rockets containing their own oxygen supplies (and thus have to take into account the extra weight, size, expense, and increased potential fire danger) because they leave the atmosphere during flight, and so cannot take advantage of atmospheric oxygen.

Thank you for all your great replies!

As you are interested in all things military, it is worth noting that the the German V-1 (AKA buzzbomb) was the first widely deployed cruise missile, and the V-2 the first ballistic missile. Warheads, engines, and guidance systems have dramatically advanced, but still pretty much the same concept.

Don’t forget the MIRV, multiple somewhat close targets from on launch. Sometime in the trajectory, the “bus” carrying the warheads releases each, and either the warhead or the bus maneuvers so each warhead targets a different location. (ie.Baltimore, DC, and the naval yards…) Of course, the earlier in the trajectory this happens, the further spaced these targets can be for less impulse to reach them.

Then, the warheads may make interesting evasive maneuvers on the downward re-entry to avoid anti-missile misiles. (i.e. dodge the Patriot missiles.) Some even launch a number of duds as well to decoy the protective fire. These final maneuvers could be rocket power or aerodynamic with fins. But basically, yes, a missile is like the space shuttle or a satellite launch; it burns for a few minutes on the way up, then lets gravity do most of the work. They reach well above most of the atmospher on the way up, so air drag past the burn phase is irrelevant until the re-entry phase.

Cruise missiles are basically small computer-piloted aircraft. They guide themselves to the target hugging the ground (a hundred feet up or less?) so that it’s difficult for them to be detected by radar and if properly camoflaged, hard to see from overflying aircraft. Because subsonic technology is so much simpler and requires less fuel, they basically fly below the speed of sound.

And ballistic missiles are already practically impossible to intercept, even without needing to take any extra measures to make them more evasive. They’re just too damned fast.

Strictly speaking, this isn’t true. During the development of the Sprint ABM in the late 'Sixties and early 'Seventies, developers actually had to detune the guidance radar to prevent the missile from phsyically intercepting the target. The Sprint was designed to close on the target in the terminal phase at short ranges–below 60kft–and disable the warhead by generating a burst of fast neutrons from its “enhanced radiation” warhead, not perform a physical “hit-to-kill” (HTK) interception as current systems do.

HTK systems have been demonstrated in numerous tests, both in mid-course and terminal phases, so while difficult, it is certainly not impossible. What is more challenging is discriminating between genuine threats, decoys, and natural objects in the short period of time to perform succesful intercept, not creating greater hazard for those on the ground, and being able to cover a wide enough area to be useful. The United States deployed a successfully and extensively tested ABM system in 1975 (Sentinel), but deactivated it a few months later as it was deemed to not be worth the exhorbiant cost for protecting one Minuteman missile wing at Grand Forks, ND, especially as the silos would likely be empty holes by the time a counterforce attack could threaten the site. The more extensive “protective umbrella” envisioned by Ronald Reagan to provide general defense of the continental United States against a full-out attack was even more absurd, and only served to spur on development of faster, suppresed trajectory missiles, better penetration aids, and maneuverable reentry vehicles in order to defeat whatever provisions might be put into place.

As for the question of the o.p., the payload of ballistic missiles are, by definition, unpowered after the boost phase of flight, aside from the small trajectory adjustments provided by the post-boost vehicle (PBV) during mid-course cruising and aerodynamic maneuvering by MARVs during reentry. Cruise missiles, as have already been stated, are powered during nearly all of flight, and although they are generally launched by a first stage solid propellant boost rocket, they are then propelled to the target by a sustainer stage that is typically an air-breathing liquid engine, using aerodynamic surfaces to generate lift and maneuverability. Ballistic missiles are faster and generally have longer range for a given payload size, but cruise missiles are more compact, don’t fly high above the atmosphere, and are capable of fine controllability throughout almost the entire range of flight.