physics

PAVE PAWS

PAVE PAWS 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 PAVE PAWS rather than just read about it. In short: PAVE PAWS (PAVE Phased Array Warning System) is a complex Cold War early warning radar and computer system developed in 1980 to "detect and characterize a sea-launched ballistic missile attack against the United States". The first solid-state phased array deployed used a pair of Raytheon AN/FPS-115 phased array radar sets at each site to cover an azimuth angle of 240 degrees.

Key takeaways

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

Reference excerpt

PAVE PAWS (PAVE Phased Array Warning System) is a complex Cold War early warning radar and computer system developed in 1980 to "detect and characterize a sea-launched ballistic missile attack against the United States". The first solid-state phased array deployed used a pair of Raytheon AN/FPS-115 phased array radar sets at each site to cover an azimuth angle of 240 degrees. In accordance with the Joint Electronics Type Designation System, the "AN/FPS-115" designation represents the 115th design of an Army-Navy fixed radar(pulsed) electronic device for searching. Two sites were deployed in 1980 at the periphery of the contiguous United States, then two more in 1987–95 as part of the United States Space Surveillance Network. One system was sold to Taiwan and is still in service.

Mission

The radar was built in the Cold War to give early warning of a nuclear attack, to allow time for US bombers to get off the ground and land-based US missiles to be launched, to decrease the chance that a preemptive strike could destroy US strategic nuclear forces. The deployment of submarine launched ballistic missiles (SLBMs) by the Soviet Union by the 1970s, significantly decreased the warning time available between the detection of an incoming enemy missile and its reaching its target, because SLBMs can be launched closer to the US than the previous ICBMs, which have a long flight path from the Soviet Union to the continental US. Thus there was a need for a radar system with faster reaction time than existing radars. PAVE PAWS later acquired a second mission of tracking satellites and other objects in Earth orbit as part of the United States Space Surveillance Network. A notable feature of the system is its phased array antenna technology, it was one of the first large phased array radars. A phased array was used because a conventional mechanically-rotated radar antenna cannot turn fast enough to track multiple ballistic missiles. A nuclear strike on the US would consist of hundreds of ICBMs and SLBMs incoming simultaneously. The beam of the phased array radar is steered electronically without moving the fixed antenna, so it can be pointed in a different direction in milliseconds, allowing it to track many incoming missiles at the same time.

Description The AN/FPS-115 radar consists of two phased arrays of antenna elements mounted on two sloping sides of the 105 ft high transmitter building, which are oriented 120° apart in azimuth. The beam from each array can be deflected up to 60° from the array's central boresight axis, allowing each array to cover an azimuth angle of 120°, thus the entire radar can cover an azimuth of 240°. The building sides are sloped at an angle of 20°, and the beam can be directed at any elevation angle between 3° and 85°. The beam is kept at least 100 ft above the ground over public-accessible land to avoid the possibility of exposing the public to significant electromagnetic fields. Each array is a circle 72.5 ft (22.1 m) in diameter consisting of 2,677 crossed dipole antenna elements, of which 1,792 are powered and serve as both transmitting and receiving antennas, with the rest functioning as receiving antennas. Due to the phenomenon of interference the radio waves from the separate elements combine in front of the antenna to form a beam. The array has a gain of 38.6 dB, and the width of the beam is only 2.2°. The drive current for each antenna element passes through a device called a phase shifter, controlled by the central computer. By changing the relative timing (phase) of the current pulses supplied to each antenna element the computer can instantly steer the beam to a different direction. The radar operates in the UHF band between 420 - 450 MHz, which is shared with the 70 centimeter amateur band (just below the UHF television broadcast band), that is a wavelength of 71–67 cm, with circular polarization. It is an active array (AESA); each of the 1,792 transmitting elements has its own solid-state transmitter/receiver module, and radiates a peak power of 320 W, so the peak power of each array is 580 kW. It operates in a repeating 54 millisecond cycle in which it transmits a series of pulses, then listens for echoes. Its duty cycle (fraction of time spent transmitting) is never greater than 25% (so the average power of the beam never exceeds 25% of 580 kW, or 145 kW) and is usually around 18%. It is reported to have a range of about 3,000 nautical miles (3,500 statute miles, 5,600 km); at that range it can detect an object the size of a small car, and smaller objects at closer ranges. The functioning of the radar is completely automatic, controlled by four computers. The software divides the beam time between "surveillance" and "tracking" functions, switching the beam back and forth rapidly between different tasks. In the surveillance mode, which normally consumes about 11% of the duty cycle, the radar repeatedly scans the horizon across its full 240° azimuth in a pattern between 3° and 10° elevation, creating a "surveillance fence" to immediately detect missiles as they rise above the horizon into the radar's field of view. In the tracking mode, which normally consumes the other 7% of the 18% duty cycle, the radar beam follows already-detected objects to determine their trajectory, calculating their launch and target points.

Background

Fixed-reflector radars with mechanically-scanned beams such as the 1955 GE AN/FPS-17 Fixed Ground Radar and 1961 RCA AN/FPS-50 Radar Set were deployed for missile tracking, and the USAF tests of modified AN/FPS-35 mechanical radars at Virginia and Pennsylvania SAGE radar stations had "marginal ability" to detect Cape Canaveral missiles in summer 1962. A Falling Leaves mechanical radar in New Jersey built for BMEWS successfully tracked a missile during the October 1962 Cuban Missile Crisis, and "an AN/FPS-85 long-range phased array (Passive electronically scanned array) radar was constructed at Eglin AFB" Site C-6, Florida beginning on 29 October 1962 (the Bendix Radio Division FPS-85 contract had been signed 2 April 1962). Early military phased array radars were also deployed for testing: Bendix AN/FPS-46 Electronically Steerable Array Radar (ESAR) at Towson, MD (powered up in November 1960), White Sands' Multi-function Array Radar (1963), and the Kwajalein Missile Site Radar (1967).

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with PAVE PAWS

Start with the simplest possible case. Write down what PAVE PAWS 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 PAVE PAWS 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 PAVE PAWS 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 PAVE PAWS

In research: PAVE PAWS 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 PAVE PAWS 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: PAVE PAWS is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1978 establishments in the United States, Computer systems of the United States Air Force, Historic American Engineering Record in California, so understanding it makes those chapters shorter.
In everyday life: Look for PAVE PAWS 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.

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How to study PAVE PAWS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PAVE PAWS 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 PAVE PAWS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PAVE PAWS in simple terms?

Why does PAVE PAWS 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 PAVE PAWS?

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 PAVE PAWS.