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the electrical energy is converted into microwave energy

and is beamed silently and safely to an earth receiver or


The earth located rectenna, as shown in Figure 1,

reconverts the mircowave energy into electrical energy which

is then connected to the ground electrical grid for our use.

Each Solar Power Satellite is located at a 22,200 mile

geosynchronous altitude.

At this altitude it takes exactly

24 hours for the satellite to circle the earth and since the

earth rotates once every 24 hours the Solar Power Satellite

is constantly overhead.

This makes it possible, therefore,

for us to receive electrical power from the Solar Power

Satellite on a nearly continuous basis,

The only time

electrical energy is not available from the Solar Power

Satellite during the year, is during the relatively small

period of time when it is shadowed by the earth from the sun's


This period, which amounts to less than 1% of the total

operational time, occurs near local midnight when electrical

requirements will normally be minimal.

Each Solar Power Satellite can generate between 5 million

and 10 million kilowatts of electrical energy, enough to supply

the needs of most states in our nation and even to meet the

needs of an area as populous as Washington, D.C.

This system, with its many attractive features including

potentially small environmental impact, nevertheless requires

many years of development. Much work must be done in many

critical technology areas before it can become a reality.

Interestingly enough, however, the technical challenges for

the Solar Power Satellite are primarily in the engineering

areas; scientific breakthroughs do not have to be made in

order for this system to be made operational.


Grumman has been involved in studies of the solar power

system since 1970 along with increasing numbers of other private


NASA in-house and funded work have strengthened the

study results.

The independent ERDA Task Group on Satellite

Power Stations stated that "Both economic and net energy

compatibility for SPS with future inexhaustible systems (e.g.

fusion) were deemed possible if R&D targets could be met."

Early experimental work on some of the critical elements of

Solar Power Satellite has also been undertaken over the past

seven years.

For instance, experiments have been conducted

ground-to-ground to show the feasibility of receiving

substantial amounts of electrical power by the microwave beam

and the needed efficiencies for the system have been roughly


Solar array technology is progressing at a heartening rate and the very lightweight solar arrays needed for the

Solar Power Satellite appear to be within our grasp in the next

10 to 15 years.

Techniques for developing the capability for

fabricating and assembling these large space structures are beginning to be developed by imaginative engineers.

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not have the scope or the sense of urgency which should be

assigned to one of the possible solutions to our long range energy deficiency. Even when completed, the current efforts

will not bring us substantially closer to the point where

commitment to Solar Power Satellite development can be



A far more vigorous effort is needed now to provide the firm experimental data that can justify further development

steps for the Solar Power Satellite.

A coordinated ground

program followed by Shuttle sortie missions and leading to a

Power Technology Module, PTM, program should be undertaken so

that the necessary experimental work will be obtained in a

timely low cost fashion.

A clear and early goal such as that provided by the Power

Technology Module which could be operational by 1984 will pull

diverse and fragmented efforts together toward a common goal.

The total system can be deployed in only a single Shuttle flight.

Once operational, the Power Technology Module can answer in a

year's time the critical SPS technology questions.

The Power Technology Module concept is illustrated in

Figure 2.

As can be seen, there are two solar arrays which

absorb solar energy and provide between 25 and 35 kilowatts

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Some of the key features of the PTM system are illustrated

in Figure 3.

The solar arrays differ from conventional arrays

used in present day satellites in that they have been fabricated

using lightweight manufacturing techniques and have been unrolled

like window shades during the assembly process.

From the results

of its assembly and construction in space, valuable Large Space

structure lessons are learned even before the system becomes

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