Photonic Propulsion System

This Photonic Propulsion System (PPS) is a system that I think could be someday an alternative to conventional rockets used to propel objects into space and to various locations once in space.  Present rocketry systems are huge in scope, and therefore require enormous amounts of fuel.  I will show you how photons can be used as fuel to achieve orbit even if the craft were to weigh as much as  2.00 X 106 kg, the approximate weight of the now retired space shuttle.

The Photonic Propulsion System would also make for a highly maneuverable craft.  It could do all that the space shuttle used to do, as well as maneuver like jet planes and even hover motionless in the atmosphere for long periods of time (possibly even for years).

Photonic Propulsion System Description

Refer to diagram I.  The parts that are labeled in the diagram are:

            A.  Cargo, passenger, and equipment deck.

            B.  Photonic Crystal Array

            C.  Flight deck.

I will first discuss the most important part of the system, the photonic crystal array.  I would ask you to refer to diagram II.  The photons used for propulsion are being stored in the photonic crystal array labeled A in the diagram.  The photonic crystal array is attached to a large parabolic shaped reflecting surface labeled F.  This parabolic surface will reflect out of the bottom of the craft, any photons that do not directly move from the photonic crystals towards the bottom of the craft.  Large ball bearings labeled E, will allow the parabolic surface to be rolled into different positions so that photons will be reflected from it in the desired direction.  This allows the craft to be maneuvered by reflecting and ejecting the photons in different directions.  The ball bearings will role on another curved surface labeled D, which will be attached to the spacecraft.

To discuss the photonic crystal array in greater detail, refer to diagram III.  An array of millions or billions of photonic crystals would be arranged into a thin structure one crystal thick when viewed in cross section (Edge View).  The top view reveals the outer surface attached to the parabolic reflecting surface and the grid like arrangement of the crystals.

A material which is a photonic crystal has local optical properties which vary to give the material some kind of desirable optical property.  In our case, the desired optical property is a response that causes photons to travel in a circular path within the crystal.  This crystal would be a properly designed silicon crystal structure that produces a synthetic magnetic field when an electric current is applied to the crystal. This synthetic field will exert a "magnetic force" upon the photons in a direction perpendicular to the direction of travel of the photons.  The photons will therefore travel in circular paths within the photonic crystal.  The radius of the circular path will depend upon the electric current applied to the crystal.

This effect is similar to the effect that a magnetic field has on the direction of movement of charged particles moving through the magnetic field.  With attempts to confine high energy plasmas in magnetic fields, the charges on the ions in the plasmas interact with each other and the motions of the ions also produces secondary magnetic fields.  These two effects disrupt the confinement of the plasma making it difficult to control or store the plasma for long periods of time.  Further, the need to maintain a vacuum also hinders the confinement of charged particles.  Photons don’t have a charge and therefore will not interact with each other or produce magnetic fields that can disrupt the storage of the photons in the photonic crystal.  Photons can travel through a medium and therefore do not require a vacuum.

Fiber optics could be used to cause photons to move in a circular path, but fiber optics is not without flaws.  These flaws cause light to be backscattered and absorbed by the fiber.  Therefore, fiber optics would not be a good candidate for storing photons until needed.  A photonic crystal constructed properly breaks the time-reversal symmetry of light.  This breaking of the time-reversal symmetry of light prevents the photons from being backscattered and absorbed by the photonic crystal.  Once the photon enters the photonic crystal, because it cannot go back, disorder and loss of photons is eliminated.  Therefore, properly constructed photonic crystals should be an excellent way of storing photons for a long period of time until they are needed to produce the thrust for a space craft.

The photonic crystal array consisting of millions or billions of photonic crystals, would have to be computer controlled so that the current of each crystal in the array would be varied as needed in order to release the correct number of photons to produce the desired thrust.  The photons would be put into the crystals before launch, or for long journeys, would be produced on board by a nuclear reactor, and then stored until needed in the crystal array.

For more information about photonic crystals, I suggest visiting these sites:

https://photonics.engr.wisc.edu/papers/nphoton.2012.Fang.pdf

http://www.gizmag.com/synthetic-magnetism-stanford-photonic-crystal/25261/

https://www.researchgate.net/publication/3422474_Molding_the_flow_of_light

https://press.princeton.edu/books/hardcover/9780691124568/photonic-crystals

Referring back to diagram I, I will now talk about the Cargo, Passenger, and Equipment Deck.  The Cargo, Passenger, and Equipment Deck is the part of the craft that would carry your pay load (satellites, passengers etc.) into orbit.  This region of the craft also would house a small nuclear reactor for generating the necessary power to operate on board systems.  The shape of the Cargo, Passenger, and Equipment Deck is such that the center of mass of the spaceship lies below the photonic crystal array.  The consequence of this design is that the photonic crystal array will pull the craft forward rather than push it forward.  This design gives greater stability for the spaceship and artificial gravity is produced whenever the craft accelerates in space.  When the craft is in a gravitational field, the center of mass of the spaceship will hang below the photonic crystal array, and therefore the craft will always hang upright from the array.  It may be necessary to have a gyroscope mounted in the craft, so that when the craft is freely moving in space without using the photonic crystal array, the craft can easily be rotated in any desired direction, so that the photonic crystal array can be fired in the proper direction to produce the desired acceleration.

Now I will talk about the Flight Deck.  The Flight Deck is the region of the craft from which the craft is controlled.  It would have a transparent bubble roof to provide excellent visibility in all directions.  This visibility would encompass slightly more than half a sphere.  Monitors inside the Flight Deck, which are connected to cameras, would give visibility for the remainder of the sphere.  During acceleration, this part of the craft will always be pointing forward, because the center of mass of the spaceship will hang behind the photonic crystal array.  During flight in a gravitational field, the Flight Deck will always be pointing upwards except for small fluctuations caused by maneuvers

MATHEMATICAL ANALYSIS

Each photon carries energy according to the formula:

E = (hc)/(l)                                     Equation I

In the equation, h is Planck’s constant (6.63 X 10-34Js), c is the speed of light (3.00 X 108 m/s), and l is the wavelength of the photon.  Further to this, photons carry momentum.  And so, if photons are allowed to escape in an appropriate direction from the photonic crystal array, since they carry momentum with them, the spacecraft would have to gain momentum in the opposite direction so that momentum is conserved.  The momentum of a single photon is given by the equation:

P = h/l                                           Equation II 

Ordinarily one would use the equation for thrust to make calculations for a rocket.  This equation is:

Ft = Vf(dMr/dt)                             Equation III

Where Ft is the thrust force, Vf is the velocity of the ejected fuel with respect to the rocket, and dMr/dt is the rate of change of mass of the rocket as a result of the ejection of fuel.  In our case, since light has no mass, as photons are ejected, the spacecraft would not change mass (only energy).  We must therefore approach a mathematical analysis a bit differently.

Given that the wavelength of the light used is 3.50 X 10-7m, and the mass of the spacecraft is 2.00 X 106 kg, we can calculate how many photons would be needed to reach escape velocity of 1.12 X 104 m/s.  We choose to use 3.50 X 10-7m for the wavelength of light because is it just outside the visible range on the blue end of the spectrum, and this won’t blind people.  Also, we don’t want to use too short of a wavelength since that may do environmental damage.  In space, however, environmental considerations would not be a factor, and so using shorter wavelengths would be advantageous.  As the space craft sits on the launch pad, the total momentum of the system would be zero.  Therefore, at any point of its flight, the total momentum would remain zero since conservation of momentum must be satisfied.  Choosing up to be the positive direction, we can write the conservation of momentum equation as:

MV –Nh/l = 0                                         Equation IV

N in the equation is the number of photons, and therefore the second term indicates the momentum of the N photons.  The negative sign is present because the photons are released downwards which gives them negative momentum.  M is the mass of the space craft and V is the spacecrafts velocity.  Rearranging the equation for N gives:

N = MVl/h                                              Equation V 

Substitution into equation V gives:

 N = (2.00 X 106 kg)(1.12 X 104m/s)(3.50 X 10-7m)/6.63 X 10-34kgm2/s)                       Equation VI

Or:

N = 1.18 X 1037 Photons

The energy in a single photon of wavelength 3.50 X 10-7 m is calculated by equation I above or         E = 5.68 X 10-19 J.  Therefore 1.18 X 1037 photons would have E = 6.71 X 1018 J. 

Conclusion

To escape Earth (escape velocity 11200 m/s), a spacecraft of mass 2.00 X 106 kg would require about 1.18 X 1037 photons of light with wavelength 3.50 X 10-7 m.  With such a system, one would not need to carry large solid or liquid fuel tanks with the craft as it accelerates forward.  As a result, the estimated mass of the craft at 2.00 X 106 kg would be far higher than what would actually be necessary.  This of course means that far less energy is needed to achieve escape from the Earth. 

When this idea was presented to the United States Secretary of Defense, the following reply was received.

"An exceedingly large amount of power would be required to produce the "effective magnetic field" needed to contain the photons.  Today, generating and using this amount of electricity is impractical from a cost and infrastructure perspective.  If, at a distant future date, a breakthrough were to occur that dramatically increases the ability to generate this amount of power, the potential viability of your concept would be enhanced."

What I find interesting in this reply is that they did not say that the Photonic Propulsion System will not work, but that cost and infrastructure make it impractical at this time.  I therefore encourage all physicists to work on increasing our ability to generate huge amounts of power.

January 03, 2024

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