science

Inmarsat-4A F4

Inmarsat-4A F4 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 Inmarsat-4A F4 rather than just read about it. In short: Inmarsat-4A F4, also known as Alphasat and Inmarsat-XL, is a large geostationary communications I-4 satellite operated by United Kingdom-based Inmarsat in partnership with the European Space Agency. Launched in 2013, it is used to provide mobile communications to Africa and parts of Europe and Asia.

Key takeaways

Inmarsat-4A F4 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Inmarsat-4A F4 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Inmarsat-4A F4 from memory before moving on to harder problems.

Reference excerpt

Inmarsat-4A F4, also known as Alphasat and Inmarsat-XL, is a large geostationary communications I-4 satellite operated by United Kingdom-based Inmarsat in partnership with the European Space Agency. Launched in 2013, it is used to provide mobile communications to Africa and parts of Europe and Asia. Inmarsat-4A F4 has been constructed by EADS Astrium and Thales Alenia Space based on the Alphabus satellite bus. It was the first Alphabus spacecraft to be launched, and as such it carries several experimental communications systems in addition to its commercial payload. The spacecraft had a launch mass of 6,649 kilograms (14,659 lb), and is expected to operate for at least fifteen years. Arianespace had been contracted to launch Inmarsat-4A F4, with an Ariane 5ECA rocket, flight number VA-214, delivering it and INSAT-3D into geosynchronous transfer orbit. The rocket lifted off from ELA-3 at Kourou at 19:54:07 UTC on 25 July 2013, with Inmarsat-4A F4 separating from the rocket around 27 minutes later. The spacecraft operates in a geostationary orbit at a longitude of 25 degrees east. As of 29 October 2013, it is in an orbit with a perigee of 35,771 kilometres (22,227 mi), an apogee of 35,771 kilometres (22,227 mi) and 0.14 degrees inclination to the equator. The orbit had a semimajor axis of 42,157.20 kilometres (26,195.27 mi) and eccentricity of 0.0003552, giving it an orbital period of 1,435.75 minutes, or 23.92 hours.

European Data Relay System test The satellite was used as part of an in-orbit verification of the ESA European Data Relay System. In 2014, data from the Sentinel-1A satellite in LEO was transmitted via an optical link to the Alphasat in GEO and then relayed to a ground station using a Ka band downlink. The new system can offer speeds up to 7.2 Gbit/s in the future.

References

External links

EDRS SpaceDataHighway

Illustrations

Worked examples

Example 1 — a first encounter with Inmarsat-4A F4

Start with the simplest possible case. Write down what Inmarsat-4A F4 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 Inmarsat-4A F4 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 Inmarsat-4A F4 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 Inmarsat-4A F4

In research: Inmarsat-4A F4 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 Inmarsat-4A F4 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: Inmarsat-4A F4 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Communications satellite stubs, European spacecraft stubs, Inmarsat satellites, so understanding it makes those chapters shorter.
In everyday life: Look for Inmarsat-4A F4 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 Inmarsat-4A F4 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Inmarsat-4A F4 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 Inmarsat-4A F4 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Inmarsat-4A F4 in simple terms?

Why does Inmarsat-4A F4 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 Inmarsat-4A F4?

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 Inmarsat-4A F4.