science

Initial Defense Communications Satellite Program

Initial Defense Communications Satellite Program 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 Initial Defense Communications Satellite Program rather than just read about it. In short: The Initial Defense Communications Satellite Program or IDCSP was the first United States Department of Defense communications satellite constellation and the first stage of the Defense Communications Satellite Program (DCSP). Launched in five groups by Titan IIIC launch vehicles to near equatorial, subsynchronous orbits between 1966 and 1968, they were intended to be experimental testbeds.

Key takeaways

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

Reference excerpt

The Initial Defense Communications Satellite Program or IDCSP was the first United States Department of Defense communications satellite constellation and the first stage of the Defense Communications Satellite Program (DCSP). Launched in five groups by Titan IIIC launch vehicles to near equatorial, subsynchronous orbits between 1966 and 1968, they were intended to be experimental testbeds. They were so successful that, by the time of the launch of the last set of eight satellites, the IDCSP was deemed operational and renamed Initial Defense Satellite Communications System or IDSCS. This system allowed real-time collection of battlefield intelligence during the Vietnam War. A total of 35 IDCSP satellites were launched, 27 successfully.

Background The Initial Defense Communications Satellite Program or IDCSP was the first stage in the Defense Communications Satellite Program (DCSP) commissioned by United States Secretary of Defense Robert McNamara in 1962. Under the DCSP, several increasingly sophisticated satellite series would test and provide long-range communications between "fixed, transportable or shipboard terminals". Development of these series would be managed by the Defense Communications Agency (DCA). This decision came on the heels of the cancellation of Project ADVENT, the first attempt at a military geosynchronous communications satellite system, begun February 1960. Originally costed at $140 million to develop, $170 million had been spent by 1962, and the estimated total cost had reached $325 million. The cheaper, "interim" IDCSP was chosen to replace ADVENT. It would use a constellation of 24-30 satellites launched into Medium Earth Orbit via ten Atlas Agena rockets for a total cost of $165 million ($60 million of which would be spent on satellites). Philco's Western Development Division was originally selected by the United States Air Force (USAF) to build the satellites. However, by 1964, the development of the much more powerful Titan IIIC booster made it possible for fewer IDCSP satellites to fulfill the same mission at a higher altitude. Four to eight could be launched on a single Titan IIIC rocket into slightly subsynchronous orbit. Once there, the satellites would be deployed one at a time over the course of three minutes from the Transtage of the Titan. The satellites would drift randomly at an average rate of 28.5° per day becoming a roughly evenly spaced belt of satellites above the Earth's equator. In this way, at least one satellite of the constellation would always be visible to an Earth station if one failed. Full coverage would be provided by at least 12 satellites. Thus, the Titan IIIC was chosen to replace the Atlas Agena as the IDCSP launch vehicle. This change did not go unchallenged; the House Committee on Government Operations denounced the move, saying that the "plan for short-range economies depending on a high-risk program may prove costly in the end". With the selection of the Titan IIIC as the IDCSP booster, the Pentagon dropped contract negotiations with Philco, preferring to develop the satellites in-house. Through early 1965 the satellites were still being designed so that they could be lofted to Medium Earth Orbit via Atlas Agena in the event that the Titan IIIC was not available. The Titan IIIC was developed in time for use, the first launch taking place just four months behind the original schedule. The satellites built by 1966, sufficient for three launches, had cost just $33 million to produce (an overage of $3 million on original estimates).

Design

Developed primarily by TRW, the IDCSP spacecraft were identical communications satellites, spin-stabilized, 26-sided polygons, 86 cm (34 in) in diameter, covered with solar panels, and had a mass of 45 kilograms (99 lb). They were specifically designed to be simple to avoid the problems faced by the earlier Courier and Advent programs: no in-orbit control mechanisms were included, nor were the satellites equipped with batteries. The satellites were equipped with an automatic radiation shut-off device to deactivate them after six years in orbit. Each satellite contained a single 3.5 Watt X-band or SHF transponder receiving at 8.025 GHz and transmitting 7.25–7.3 GHz (similar to the Lincoln Experimental Satellites procured around the same time) capable of concurrently supporting 600 voice or 6000 teletype conversations. Complementing these satellites were ground communications terminals used to transmit and receive via IDCSP satellite voice, imagery, computerized digital data, and teletype channel using Frequency-division multiplexing/Frequency Modulation (FDM/FM), Differential Phase Shift Keying (DPSK), Multiple frequency-shift keying (MFSK), and Spread Spectrum Multiple Access (SSMA) modulation techniques. The Eimac Division of Varian Associates supplied one of the two traveling wave amplifiers used by the satellite's transmitter, the other being produced by Watkins-Johnson Company. Because of the low power of the satellites' transponders, as well as its low-gain antenna, the receiving installations had to be very large.

Operational history

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Initial Defense Communications Satellite Program

Start with the simplest possible case. Write down what Initial Defense Communications Satellite Program 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 Initial Defense Communications Satellite Program 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 Initial Defense Communications Satellite Program 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 Initial Defense Communications Satellite Program

In research: Initial Defense Communications Satellite Program 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 Initial Defense Communications Satellite Program 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: Initial Defense Communications Satellite Program is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1966 in spaceflight, 1967 in spaceflight, 1968 in spaceflight, so understanding it makes those chapters shorter.
In everyday life: Look for Initial Defense Communications Satellite Program 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 Initial Defense Communications Satellite Program in 20 minutes

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

Frequently asked questions

What is Initial Defense Communications Satellite Program in simple terms?

Why does Initial Defense Communications Satellite Program 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 Initial Defense Communications Satellite Program?

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 Initial Defense Communications Satellite Program.