science

USA-50

USA-50 is a science 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 USA-50 rather than just read about it. In short: USA-50, also known as GPS II-6 and GPS SVN-18, was an American navigation satellite which formed part of the Global Positioning System. It was the sixth of nine Block II GPS satellites to be launched, which were the first operational GPS satellites to fly.

Key takeaways

USA-50 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect USA-50 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of USA-50 from memory before moving on to harder problems.

Reference excerpt

USA-50, also known as GPS II-6 and GPS SVN-18, was an American navigation satellite which formed part of the Global Positioning System. It was the sixth of nine Block II GPS satellites to be launched, which were the first operational GPS satellites to fly.

Background It was part of the 21-satellite Global Positioning System (GPS) Block II series that provides precise position data (accurate to within 16 m) to military and civilian users worldwide. Its signals could be received on devices as small as a telephone. The GPS II satellites, built by Rockwell International for the Air Force Space Systems Division, each have a 7.5-year design life. The Air Force intends to launch a GPS II every 2 to 3 months until the constellation of 21 operational satellite and 3 spares is aloft. The GPS Block II join 7 operational Block 1 satellites.

Launch USA-50 was launched at 22:55:01 UTC on 24 January 1990, atop a Delta II launch vehicle, flight number D191, flying in the 6925-9.5 configuration. The launch took place from Launch Complex 17A (LC-17A) at the Cape Canaveral Air Force Station (CCAFS), and placed USA-50 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.

Mission On 25 February 1990, USA-50 was in an orbit with a perigee of 20,087 km (12,481 mi), an apogee of 20,275 km (12,598 mi), a period of 717.92 minutes, and 54.6° of inclination to the equator. The satellite had a mass of 840 kg (1,850 lb), and generated 710 watts of power. It had a design life of 7.5 years, and was retired from service on 18 August 2000.

References

Worked examples

Example 1 — a first encounter with USA-50

Start with the simplest possible case. Write down what USA-50 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 USA-50 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 USA-50 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 USA-50

In research: USA-50 appears in science 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 USA-50 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: USA-50 is common in secondary-school and first-year university syllabi. It links to neighbouring topics GPS satellites, Spacecraft launched in 1990, USA satellites, so understanding it makes those chapters shorter.
In everyday life: Look for USA-50 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 USA-50 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what USA-50 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 USA-50 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is USA-50 in simple terms?

Why does USA-50 matter?

Because it connects several science 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 USA-50?

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 USA-50.