These weapons are in a distinct category from cruise missiles, which are aerodynamically guided in powered flight. Unlike cruise missiles, which are restricted to the atmosphere, it is advantageous for ballistic missiles to avoid the denser parts of the atmosphere and they may travel above the atmosphere into outer space.
One modern pioneer ballistic missile was the A-4,[1] commonly known as the V-2 developed by Nazi Germany in the 1930s and 1940s under the direction of Wernher von Braun. The first successful launch of a V-2 was on October 3, 1942, and it began operation on September 6, 1944, against Paris, followed by an attack on London two days later. By the end of World War II in Europe in May 1945, more than 3,000 V-2s had been launched.[2]
An intercontinental ballistic missile trajectory consists of three parts: the powered flight portion; the free-flight portion, which constitutes most of the flight time; and the re-entry phase, where the missile re-enters the Earth's atmosphere. The flight phases for shorter-range ballistic missiles are essentially the first two phases of the ICBM, as some ballistic categories do not leave the atmosphere.[4]
Ballistic missiles can be launched from fixed sites or mobile launchers, including vehicles (e.g., transporter erector launchers), aircraft, ships, and submarines. The powered flight portion can last from a few tenths of seconds to several minutes and can consist of multiple rocket stages.[4]
When the fuel is exhausted, no more thrust is provided and the missile enters free flight. In order to cover large distances, ballistic missiles are usually launched into a high sub-orbital spaceflight; for intercontinental missiles, the highest altitude (apogee) reached during free-flight is about 4,500 kilometers (2,800 mi).[5]
The re-entry stage begins at an altitude where atmospheric drag plays a significant part in missile trajectory, and lasts until missile impact.[4] Re-entry vehicles re-enter the Earth's atmosphere at very high velocities, on the order of 6–8 kilometers per second (22,000–29,000 km/h; 13,000–18,000 mph) at ICBM ranges.[6]
Ballistic missiles vary widely in range and use, and are often divided into categories based on range. Various schemes are used by different countries to categorize the ranges of ballistic missiles:
Most current designs have intercontinental range with a notable exception of Indian operational SLBM Sagarika and K-4 as well as North Korea's currently operationally deployed KN-11[7] which might not have intercontinental range. A comparable missile would be the decommissioned China's JL-1 SLBM with a range of less than 2,500 km.
Tactical short- and medium-range missiles are often collectively referred to as tactical and theatre ballistic missiles, respectively. Long- and medium-range ballistic missiles are generally designed to deliver nuclear weapons because their payload is too limited for conventional explosives to be cost-effective in comparison to conventional bomber aircraft (though the U.S. is evaluating the idea of a conventionally armed ICBM for near-instant global air strike capability, despite the high costs).
Quasi-ballistic missiles
A quasi-ballistic missile is a category of SRBM that has a low trajectory and/or is largely ballistic but can perform maneuvers in flight or make unexpected changes in direction and range.[8] Large guided MLRS rockets with range comparable to an SRBM are sometimes categorized as quasi-ballistic missiles.[9]
Many ballistic missiles reach hypersonic speeds (i.e. Mach 5 and above) when they re-enter the atmosphere from space. However, in common military terminology, the term "hypersonic ballistic missile" is generally only given to those that can be maneuvered before hitting their target and don't follow a simple ballistic trajectory.[14][15]
Throw-weight
Throw-weight is a measure of the effective weight of ballistic missile payloads. It is measured in kilograms or tonnes. Throw-weight equals the total weight of a missile's warheads, reentry vehicles, self-contained dispensing mechanisms, penetration aids, and missile guidance systems: generally all components except for the launch rocket booster and launch fuel. Throw-weight may refer to any type of warhead, but in normal modern usage, it refers almost exclusively to nuclear or thermonuclear payloads. It was once also a consideration in the design of naval ships and the number and size of their guns.
Throw-weight was used as a criterion in classifying different types of missiles during Strategic Arms Limitation Talks between the Soviet Union and the United States.[16] The term became politically controversial during debates over the arms control accord, as critics of the treaty alleged that Soviet missiles were able to carry larger payloads and so enabled the Soviets to maintain higher throw-weight than an American force with a roughly comparable number of lower-payload missiles.[17]
The missiles with the world's heaviest payloads are the Russian SS-18 and Chinese CSS-4 and as of 2017[update], Russia was developing a new heavy-lift, liquid-propellant ICBM called the Sarmat.[6]
Throw-weight is normally calculated using an optimal ballistic trajectory from one point on the surface of the Earth to another. An optimal trajectory maximizes the total payload (throw-weight) using the available impulse of the missile. By reducing the payload weight, different trajectories can be selected, which can either increase the nominal range or decrease the total time in flight.
A depressed trajectory is non-optimal, as a lower and flatter trajectory takes less time between launch and impact but has a lower throw-weight. The primary reasons to choose a depressed trajectory are to evade anti-ballistic missile systems by reducing the time available to shoot down the attacking vehicle (especially during the vulnerable burn-phase against space-based ABM systems) or a nuclear first-strike scenario.[18] An alternate, non-military purpose for a depressed trajectory is in conjunction with the spaceplane concept with use of airbreathing jet engines, which requires the ballistic missile to remain low enough inside the atmosphere for air-breathing engines to function.
Combat use
The following ballistic missiles have been used in combat:
^Science & Global Security, 1992, Volume 3, pp.101-159 Depressed Trajectory SLBMs: A Technical Evaluation and Arms Control Possibilities [1]Archived 2013-03-18 at the Wayback Machine
Needham, Joseph (1986). Science and Civilization in China: Volume 5, Chemistry and Chemical Technology, Part 7, Military Technology; the Gunpowder Epic. Taipei: Caves Books.
Further reading
Bath, David W. Assured Destruction: Building the Ballistic Missile Culture of the U.S. Air Force (Naval Institute Press, 2020) online book review
Futter, Andrew (2013). Ballistic Missile Defence and US National Security Policy: Normalisation and Acceptance after the Cold War. Routledge. ISBN978-0-415-81732-5.
Neufeld, Jacob (1990). The Development of Ballistic Missiles in the United States Air Force, 1945–1960. Office of Air Force History, U.S. Air Force. ISBN0-912799-62-5.
