Global Prosperity Through Space-Based Solar Power

The Power StarTM Concept

Prof. David HylandMech Aero – 2014

Hilton Philadelphia Airport HotelSeptember 8 -10, 2014

So new it’s scarcely noticed,So old it’s almost forgotten

Also contributed at the International Conference on SBSP, Kobe, Japan, April 2014

Background

• All previous SPS concepts• Involve gigantic, complex, articulated structures• Contain numerous, perhaps 1000s, of moving parts• Require numerous launches• Require on-orbit fabrication/construction, usually robotic• Involve serious dynamic stability issues

• Power StarTM combines very new and very old technologies to obtain:

• The simplest possible structure• No moving parts (except electrons and photons)• One launch vehicle (A one-km system can fit into several

existing vehicles)• No on-orbit construction• Inherent dynamic stability and robustness

The New

• The next slide shows the new technology.• Solar collectors and microwave transmitters can be

printed on a thin fabric.• The collectors and transmitters are combined in

modules called “collectennas”TM.

Substrate layer

Transmitter

Solar cell Solar cell

Conductive coating (ground)

Power connectors

Printed Solar Arrays Printed Patch Antennae

Solar-Microwave

Fabric

The New

The Old

• The next slide shows the Echo satellite technology.• The satellite is launched in a small container, then

inflated to form a large, hollow sphere.

The Old

Fabrication of the Power StarTM

• Solar-Microwave FabricTM is produced in oval strips• The strips are joined to make the sphere

Meridonial SectorsSpherical Balloon

Deployment

• The Power Star is folded in a small container that is launched in one launch vehicle.

• The container opens and the balloon is inflated

Packaging and Deployment

Negligible final angular velocity

The Basic Module

• The sphere is covered with collectennaTM modules arranged in a randomized pattern

• This avoids grating lobes

• Ground beacons give the desired power distribution on the ground

• Each collectennaTM module senses the ground beacon radiation, amplifies it, and transmits it in reverse time.

• This gives the best fit to the desired power distribution• Multiple beams can be formed and shaped

Rectenna Beacons

Beacon Radiation

Microwave Power

Printed microwave transmitter elements

Printed solar array elements

Random Tessellation to prevent grating

lobes

In each patch antenna:

Local microprocessor records beacon radiation waveform

Amplifies waveform and emits it back in reverse time.

Power optimally matches desired power distribution on the ground.

No moving parts!

Exterior surface

Substrate layer

TransmitterSolar cell Solar cell

transceivers

Copper grid

Power connector

Fundamental Power Shaping Concept• The next two charts illustrate the power shaping

concept as first devised for acoustics

The very same time-reversal principle has been applied to acoustics. See Scientific American, November 1999.

The Acoustic Time-Reversal Mirror

Illustration of Power Shaping

• The collectennaTM operations are simultaneous. But we illustrate one step at a time.

• The next chart shows a simulation of a flat phased array receiving radiation from two beacons on the ground.

Recording the beacon signals, then amplifying them and playing them back in reverse time occur concurrently. To simplify the explanation, we illustrate these steps separately. First, consider the beacon propagation…

On this plane we have two point sources representing the beacons

Each pixel on this line segment is a separate recorder

When the beacon radiation reaches the line segment representing the phased array, each point on the line records the wave-form that it sees.

Illustration of Power Shaping (Continued)• The next chart shows the transmission step• Two spots of concentrated power, centered on the

beacon locations are created.• If the phased array were infinitely large, the two point

sources would be matched exactly

Now turn off the beacon and let each pixel on the line segment re-transmit the wave-form it recorded - but in reverse time…

Note the converging wave fronts

Each pixel on this line segment transmits the recorded signal in reverse time

The amplitude on the ground plane has two concentrations centered on the beacons. If the transmitting array were infinite in extent, these would be point concentrations.

A Better Shape

• The next chart shows that a spherical phased array would work as well.

• A sphere gives flexibility – collect power from any direction, transmit power in any direction.

• No moving parts needed.

Nor must the phased array be flat!

Beacon radiation

Solar radiation

,S B

,S B

,S B

,S B

Interior surface printed with -wave receiver/transmitters (possibly shorter wavelengths)

, exterior surface illuminated by both sun and beacon

External solar arrays power local external transmitters

, exterior surface illuminated by sun but no beacon

External solar array

S B

S B

s power the local internal

receiver/transmitters & they transmit power to the

internal receiver/transmitters in sector ,

, exterior surface exposed to beacon, but not t

S B

S B

he sun

Exterior transmitters powered by the local interior

receiver/transmitters (that receive power from , )

, exterior surface shaded from both sun and beacon

Do nothing

S B

S B

Localized Power Distribution

Power Distribution - Summary• Each antenna transmits only if the beacon(s) radiation is

received.• Each transmitting antenna draws power from

• Solar cells in its immediate vicinity (within a few centimeters), or• Through the thickness of the “skin” from receivers on the inner surface

of the skin.

• Power transmission through the skin traverses a few centimeters or less. Each transmitter receives just a few Watts No high voltages, no large wires

• Power distribution to each antenna is local – there is no need for a complex power management system.

• Strictly local architecture means robustness against partial damage!

Dynamic Stability of Power StarTM

• The next chart shows that surface errors or damage can be compensated solely by electronic means.

• There is no control/structure interaction – The system is inherently stable

Error Compensation is purely electronic. There is no control/structure Interaction

System Dynamics Sensor measurements of array element position errors

Array element deformation/vibrat

ion

Dynamic feedback control

Actuator dynamics

Actuator commands

Actu

ato

r force

s a

nd to

rque

s

Electronic phase adjustment

Phased Array Gain

Undistorted radiation pattern

Disturbances

The Overall Concept

• The next chart shows a sketch of the overall concept• We also list the important features

~ 1 km

w

Printed microwave transmitter elements

Printed solar array elements

Random Tessellation to prevent grating lobes

Summary Sketch of the Concept

Unique features:

Its structure is extremely simple and can be fit into many launch vehicle payload envelopes.

It can gather solar power from any angle and beam power in any direction (s) without slewing or structural deformation.

It has no moving parts.

It can optimally approximate any desired field distribution on the ground.

It requires no in-space assembly or construction

It has no control/structure feedback so the system is guaranteed dynamically stable.

The operation of the phased array is adaptive so that even if severely damaged, the system can retain some level of useful performance.

Substrate layer

Transmitter

Solar cell Solar cell

transceivers

Conclusion

• Power StarTM is launched as a small seed, then grows to a mighty sphere.

• Although large, it uses the independent action of each small part.

• It uses the very new to give new life to an old but beautiful satellite design.

• (The Latin means: “Nature is greatest in the smallest things”)

Natura in Minima Maxima