science

USA-251

USA-251 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-251 rather than just read about it. In short: USA-251, also known as GPS IIF-6, GPS SVN-67 and NAVSTAR 70, is an American navigation satellite which forms part of the Global Positioning System. It was the sixth of twelve Block IIF satellites to be launched.

Key takeaways

USA-251 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-251 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of USA-251 from memory before moving on to harder problems.

Reference excerpt

USA-251, also known as GPS IIF-6, GPS SVN-67 and NAVSTAR 70, is an American navigation satellite which forms part of the Global Positioning System. It was the sixth of twelve Block IIF satellites to be launched.

Launch Built by Boeing and launched by United Launch Alliance, USA-251 was launched at 00:03 UTC on 17 May 2014, atop a Delta IV carrier rocket, flight number D366, flying in the Medium+(4,2) configuration. The launch took place from Space Launch Complex 37B at the Cape Canaveral Air Force Station, and placed USA-251 directly into medium Earth orbit.

Orbit

As of 17 May 2014, USA-251 was in an orbit with a perigee of 20,443 kilometers (12,703 mi), an apogee of 20,474 kilometers (12,722 mi), a period of 729.22 minutes, and 55.04 degrees of inclination to the equator. It is used to broadcast the PRN 06 signal, and operates in slot 6 of plane D of the GPS constellation. The satellite has a design life of 15 years and a mass of 1,630 kilograms (3,590 lb). It is currently in service following commissioning on June 10, 2014.

References

Illustrations

Worked examples

Example 1 — a first encounter with USA-251

Start with the simplest possible case. Write down what USA-251 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-251 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-251 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-251

In research: USA-251 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-251 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-251 is common in secondary-school and first-year university syllabi. It links to neighbouring topics American spacecraft stubs, GPS satellites, Spacecraft launched by Delta IV rockets, so understanding it makes those chapters shorter.
In everyday life: Look for USA-251 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-251 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what USA-251 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-251 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is USA-251 in simple terms?

Why does USA-251 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-251?

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-251.