astronomy

Horizons-2

Horizons-2 is a astronomy 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 Horizons-2 rather than just read about it. In short: Horizons-2 is a Ku band communications satellite owned by Horizons Satellite, a joint venture between SKY Perfect JSAT Group and Intelsat. Its orbital slot is located at 74° west longitude.

Key takeaways

Horizons-2 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Horizons-2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Horizons-2 from memory before moving on to harder problems.

Reference excerpt

Horizons-2 is a Ku band communications satellite owned by Horizons Satellite, a joint venture between SKY Perfect JSAT Group and Intelsat. Its orbital slot is located at 74° west longitude.

Launch Horizons-2 was launched from the Guiana Space Centre—along with the Rascom-QAF 1 spacecraft—aboard an Arianespace Ariane 5-GS. Launch occurred at 21:42 GMT on 21 December 2007.

Platform and payload Horizons-2 was built by Orbital Sciences Corporation based on its STAR-2 satellite platform, which will generate 3.5 kilowatts of payload power by means of two solar arrays, each equipped with three panels of UJT gallium arsenide cells. The solar arrays charge two lithium ion batteries with capacities of at least 3,850 watt-hours. The spacecraft is 3-axis stabilized, with a zero momentum system. Hydrazine-fuelled monopropellant thrusters are used for stationkeeping, with an IHI BT-4 bipropellant engine used for insertion into geostationary orbit. It has a design life of 15 years; however, it is fuelled for at least 16 years of operations. Its payload consists of 20 Ku-band transponders broadcasting through two 2.3-meter (7.5 ft) dual gridded shaped reflectors. It has 16 active transponders with 22-for-16 redundant 85 W TWTAs and four active transponders with 6-for-4 redundant 150 W TWTAs. The satellite will provide service to the continental United States, the Caribbean and parts of Canada.

References

Worked examples

Example 1 — a first encounter with Horizons-2

Start with the simplest possible case. Write down what Horizons-2 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, 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 Horizons-2 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 Horizons-2 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 Horizons-2

In research: Horizons-2 appears in astronomy 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 Horizons-2 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: Horizons-2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Communications satellite stubs, Communications satellites in geostationary orbit, Horizons satellites, so understanding it makes those chapters shorter.
In everyday life: Look for Horizons-2 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 Horizons-2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Horizons-2 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 Horizons-2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Horizons-2 in simple terms?

Horizons-2 is a Ku band communications satellite owned by Horizons Satellite, a joint venture between SKY Perfect JSAT Group and Intelsat. Its orbital slot is located at 74° west longitude.

Why does Horizons-2 matter?

Because it connects several astronomy 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 Horizons-2?

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 Horizons-2.