physics

United States national missile defense

United States national missile defense is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand United States national missile defense rather than just read about it. In short: National missile defense (NMD) refers to the nationwide antimissile program the United States has had under development since the 1990s. After the renaming in 2002, the term now refers to the entire program, not just the ground-based interceptors and associated facilities.

Key takeaways

United States national missile defense belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect United States national missile defense to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of United States national missile defense from memory before moving on to harder problems.

Reference excerpt

National missile defense (NMD) refers to the nationwide antimissile program the United States has had under development since the 1990s. After the renaming in 2002, the term now refers to the entire program, not just the ground-based interceptors and associated facilities.

Other elements that could potentially be integrated into NMD include anti-ballistic missiles, or sea-based, space-based, laser, and high altitude missile systems. The NMD program is limited in scope and designed to counter a relatively small ICBM attack from a less sophisticated adversary. Unlike the earlier Strategic Defense Initiative program, it is not designed to be a robust shield against a large attack from a technically sophisticated adversary.

Definitions

The term "national missile defense" has several meanings:

(Most common, but now deprecated:) U.S. National Missile Defense, the limited ground-based nationwide antimissile system in development since the 1990s. In 2002 this system was renamed to Ground-Based Midcourse Defense (GMD), to differentiate it from other missile defense programs, such as space-based, sea-based, laser, robotic, or high-altitude intercept programs. As of 2006, the GMD system is operational with limited capability. GMD is designed to intercept a small number of nuclear-armed ICBMs in the mid-course phase, using Ground-based interceptor missiles (GBIs) launched from within the United States in Alaska and California. GMD uses non-nuclear GBIs with a kinetic warhead. Other components of the national missile defense are listed below. Any national ICBM defense by any country, past or present. The U.S. Sentinel program was a planned national missile defense during the 1960s, but was never deployed. Elements of Sentinel were actually deployed briefly as the Safeguard Program, although it wasn't national in scope. The Russian A-135 anti-ballistic missile system is currently operational only around the city of Moscow, the national capital, and is far from being national in scope in Russia. Any national missile defense (against any missile type) by any country. Israel currently has a national missile defense against short and medium-range missiles using their Arrow missile system. See trajectory phase for the types of anti-ballistic missiles, the advantages and the disadvantages of each implementation type. The role of defense against nuclear missiles has been a heated military and political topic for several decades. (See also nuclear strategy, Missile Defense Agency, and anti-ballistic missile.) But missile defense against a known ballistic missile trajectory has to be rethought in the face of a maneuverable threat (such as a hypersonic glide vehicle, which still has yet to be realized and proven, as of 2018). See Hypersonic flight § Hypersonic weapons development, and Hypersonic glide phase interceptor (GPI) (2021).

History of national missile defense systems When the United States Air Force was split from the United States Army in 1947, the Army retained the role of ground based air defenses that would evolve into National missile defense. The Army retained the lead role in this area until the success of the Aegis system shifted the focus to the United States Navy in the 21st century.

Nike-Zeus

In the 1950s, a series of anti-aircraft missiles were developed as part of Project Nike. The latest in the series, Nike-Zeus, offered extremely long-range interception and very high performance. In the late 1950s, the program investigated the use of Nike-Zeus missiles as interceptors against Soviet ICBMs. A Nike warhead would be detonated at high altitudes (over 100 km, or 60 statute miles) above the polar regions in the near vicinity of an incoming Soviet missile. The problem of how to quickly identify and track incoming missiles proved intractable, especially in light of easily envisioned countermeasures such as decoys and chaff. At the same time, the need for a high-performance anti-aircraft weapon was also seriously eroded by the obvious evolution of the Soviet nuclear force to one based almost entirely on ICBMs. The Nike-Zeus project was canceled in 1961.

Project Defender The Nike-Zeus use of nuclear warheads was necessary given the available missile technology. However, it had significant technical limitations such as blinding defensive radars to subsequent missiles. Also, exploding nuclear warheads over friendly territory (albeit in space) was not ideal. In the 1960s Project Defender and the Ballistic Missile Boost Intercept (BAMBI) concept replaced land-launched Nike missiles with missiles to be launched from satellite platforms orbiting directly above the USSR. Instead of nuclear warheads, the BAMBI missiles would deploy huge wire meshes designed to disable Soviet ICBMs in their early launch phase (the "boost phase"). No solution to the problem of how to protect the proposed satellite platforms against attack was found, however, and the program was canceled in 1968.

Sentinel Program

In 1967, U.S. Defense Secretary Robert McNamara announced the Sentinel Program, providing a defense against attack for most of the continental United States. The system consisted of a long range Spartan missile, the short range Sprint missile, and associated radar and computer system. However, U.S. military and political strategists recognized several problems with the system:

Deployment of even a limited defensive ABM system might invite a preemptive nuclear attack before it could be implemented Deploying ABM systems would likely invite another expensive arms race for defensive systems, in addition to maintaining existing offensive expenditures Then-current technology did not permit a thorough defense against a sophisticated attack Defended coverage area was very limited due to the short range of the missiles used Use of nuclear warheads on antimissile interceptors would degrade capability of defensive radar, thus possibly rendering defense ineffective after the first few interceptions Political and public concern about detonating defensive nuclear warheads over friendly territory An ICBM defense could jeopardize the Mutual Assured Destruction concept, thus being a destabilizing influence

Safeguard Program

… excerpt ends here. Continue reading the full article.

Illustrations

The logo of the Missile Defense division of the U.S. National Guard, part of the modern American missile defense system

Worked examples

Example 1 — a first encounter with United States national missile defense

Start with the simplest possible case. Write down what United States national missile defense claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to United States national missile defense before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about United States national missile defense ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of United States national missile defense

In research: United States national missile defense appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses United States national missile defense in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: United States national missile defense is common in secondary-school and first-year university syllabi. It links to neighbouring topics Missile Defense Agency, Missile defense, Nuclear warfare, so understanding it makes those chapters shorter.
In everyday life: Look for United States national missile defense outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “United States national missile defense” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study United States national missile defense in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what United States national missile defense means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain United States national missile defense out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is United States national missile defense in simple terms?

Why does United States national missile defense matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study United States national missile defense?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on United States national missile defense.