astronomy

Teledesic

Teledesic 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 Teledesic rather than just read about it. In short: Teledesic was a company founded in the 1990s to build a commercial broadband satellite internet constellation. Using low-Earth-orbiting satellites small antennas could be used to provide uplinks of as much as 100 Mbit/s and downlinks of up to 720 Mbit/s.

Key takeaways

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

Reference excerpt

Teledesic was a company founded in the 1990s to build a commercial broadband satellite internet constellation. Using low-Earth-orbiting satellites small antennas could be used to provide uplinks of as much as 100 Mbit/s and downlinks of up to 720 Mbit/s. The original 1994 proposal was extremely ambitious, costing over 9 billion USD and originally planning 840 active satellites with in-orbit spares at an altitude of 700 km (430 mi). In 1997, the plan was scaled back to 288 active satellites at 1400 km (900 miles). Teledesic Corporation changed its name to Teledesic, LLC by pro forma assignment of its license, granted on 26 January 1998. The commercial failure of the similar Iridium and Globalstar ventures (composed of 66 and 48 operational satellites respectively) and other systems, along with bankruptcy protection filings, were primary factors in halting the project, and Teledesic officially suspended its satellite construction work on 1 October 2002.

Description Announced in March 1994 as a satellite constellation with 840 satellites and initial $5 million investments from Bill Gates and Craig McCaw, the Teledesic system would have provided "fiber-optic like" links to customers around the world. The system was to act as a network operator and support communications ranging from high-quality voice channels to broadband channels supporting video-conferencing, interactive multimedia, and real-time two-way data flow. Teledesic was notable for gaining early funding from Gates; McCaw, founder of McCaw Cellular Communications; and Saudi prince Alwaleed bin Talal. The system would have used Ka band to send and receive signals from users. Each satellite would have acted as a node in a large-scale packet-switching network. The service was planned to begin in 2002 with a total cost of the project estimated at US$9 billion. The satellites were three-axis stabilized with a faceted antenna on the bottom and a large articulated solar panel on top, weighing around 800 kg (1,800 lb) at launch (1,100 kg (2,400 lb) with a "dispenser/tug", intended to transport the satellite to its final orbit). The spacecraft was designed to be compatible with over 20 different launch vehicles to permit launch option flexibility. The satellites were to be launched into a 700 km (430 mi) circular, near-polar (98.2°) Sun-synchronous orbit. The initial rollout was to include 12 orbit planes with 24 spacecraft in each plane. The antenna footprint for each satellite was to be about 700 km2 (270 sq mi). Teledesic planned 288 satellites in 12 LEO orbits, each at an altitude of 1,315 km (817 mi). Many were immediately skeptical of the proposal. Describing Teledesic as absurd, Howard Anderson of the Yankee Group said that it was "a third-world solution at a first-world price. The developed world doesn't need it, and the underdeveloped world can't afford it". Larry Gessini of the International Communications Association was amazed by the proposal to launch 840 satellites. Andrew Seybold, consultant, doubted that Teledesic could get approval for spectrum around the world from the World Administrative Radio Conference.

BATSAT (Teledesic 1) A demonstration satellite for the Teledesic constellation, originally labeled Broadband Advanced Technologies Satellite (BATSAT), and later renamed Teledesic 1 or just T1 (COSPAR ID 1998-012B), was launched from Vandenberg Air Force Base on a Pegasus-XL launch vehicle on 26 February 1998 at 07:07:00 UTC. The satellite differed in size and design from the anticipated satellite for the final constellation, but was designed to support two-way communications at speeds up to E1 rates in the 28.6-to-29.1-GHz band. The 120 kg (265 lb) satellite was placed in a 535 km (330 mile) × 580 km (360 mile) orbit at 97.7° inclination and a period of 95.8 minutes. It was the first Ka-band satellite in orbit owned by a commercial enterprise. The satellite decayed from orbit on 9 October 2000.

References

External links Lloyd's satellite constellations - Teledesic Archived 2010-11-19 at the Wayback Machine "Teledesic home page". Archived from the original on 2001-12-17. Retrieved 2010-08-17.{{cite web}}: CS1 maint: bot: original URL status unknown (link)*

What Goes Around: Teledesic 2.0—a column by Robert X. Cringely, October 29, 2009

Illustrations

Teledesic: A typical Teledesic satellite design — A typical Teledesic satellite design

Worked examples

Example 1 — a first encounter with Teledesic

Start with the simplest possible case. Write down what Teledesic 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 Teledesic 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 Teledesic 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 Teledesic

In research: Teledesic 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 Teledesic 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: Teledesic is common in secondary-school and first-year university syllabi. It links to neighbouring topics Communications satellites in low Earth orbit, Defunct spaceflight companies, Internet technology companies of the United States, so understanding it makes those chapters shorter.
In everyday life: Look for Teledesic 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 Teledesic in 20 minutes

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

Frequently asked questions

What is Teledesic in simple terms?

Why does Teledesic 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 Teledesic?

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 Teledesic.