Photonic laser thruster

Photonic laser thruster

A photonic laser thruster (PLT) is an amplified photonic propulsion thruster for space propulsion that works on the principle of a photon-pushed sail, generating thrust directly from the momentum of a photon from a laser reflected from a mirror.

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Edits on 26 May, 2020
Charlie Hilton
Charlie Hilton approved a suggestion from Golden's AI on 26 May, 2020
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Bae proposed a 4-staged developmental map towards interstellar flight. This would involve the photonic railway, a permanent energy-efficient transportation infrastructure based on Photonic Laser Thruster (PLT) in combination with Forward's model of beamed-laser propulsion (BLP), a PLT-BLP hybrid. This would reduce the cost and duration of interstellar commutes via proposed spacetrains. The Stage-1 focuses on the near-earth space endeavors, such as orbit tuning, with Photonic Laser Thruster. The Stage-2 focuses on Interlunar photonic railway between the earth and the moon. The Stage-3 focuses on Interplanetary photonic railway between the earth and planets, moons and asteroids in the solar systemsolar system. The Stage-4 focuses on Interstellar photonic railway between the planets and moons of the solar system and those of other star systems.

Edits on 21 May, 2020
Charlie Hilton
Charlie Hilton approved a suggestion from Golden's AI on 21 May, 2020
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To date the experimental tests of the photonic thruster are limited to laboratory-scale distances. The maximum range of operation for a photonic laser thruster, PLT, is yet to be established. BohnBohn demonstrated a 1 km-long laser resonator similar to the PLT cavity, which is an active cavity, in 1995 and proposed that such resonators could scale to 100 km. Recently, 4-km Fabry–Pérot cavities, which are passive cavities, but share the same intracavity power multiplication principle with the PLT cavity, have been demonstrated in LIGO for gravitational wave detection with an intracavity multiplication factor of 280 and an intracavity laser power on the order of 100 kW. Based on these results and the state-of-the-art technologies in precision optics, the PLT cavity length over 1,000 km is promising. Further studies need to be performed to determine whether the PLT cavity could be scaled for astronomical distances.Likewise, use of the amplifying cavity has not yet been demonstrated for the case when the sail is moving at velocities approaching fractions of the light velocity. The Doppler shift of the moving sail will, as noted earlier, mean that the amplification medium will need to operate at a different wavelength for each pass of the photons through the system. The mode of the Fabry-Perot cavity will likewise be changing with time.

Charlie Hilton
Charlie Hilton approved a suggestion from Golden's AI on 21 May, 2020
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To date the experimental tests of the photonic thruster are limited to laboratory-scale distances. The maximum range of operation for a photonic laser thruster, PLT, is yet to be established. Bohn demonstrated a 1 km-long laser resonator similar to the PLT cavity, which is an active cavity, in 1995 and proposed that such resonators could scale to 100 km. Recently, 4-km Fabry–Pérot cavities, which are passive cavities, but share the same intracavity power multiplication principle with the PLT cavity, have been demonstrated in LIGOLIGO for gravitational wave detection with an intracavity multiplication factor of 280 and an intracavity laser power on the order of 100 kW. Based on these results and the state-of-the-art technologies in precision optics, the PLT cavity length over 1,000 km is promising. Further studies need to be performed to determine whether the PLT cavity could be scaled for astronomical distances.Likewise, use of the amplifying cavity has not yet been demonstrated for the case when the sail is moving at velocities approaching fractions of the light velocity. The Doppler shift of the moving sail will, as noted earlier, mean that the amplification medium will need to operate at a different wavelength for each pass of the photons through the system. The mode of the Fabry-Perot cavity will likewise be changing with time.

Charlie Hilton
Charlie Hilton approved a suggestion from Golden's AI on 21 May, 2020
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In August 2015, under another NASA program (NIAC, NASA Innovative Advanced Concepts) he demonstrated additional 100-fold improvement, achieving a photon thrust of 3.5 millinewtons. In addition, a small 1U CubeSatCubeSat satellite was propelled and stopped in simulated zero-gravity. The laser power of the trapped photon beam exceeded 500 kW, which was powered by a 500 W laser. The concept is proposed for beaming thrust from a conventional heavy "tanker" vehicle to a more expensive, lightweight mission vehicle, similar to aerial refueling.

Charlie Hilton
Charlie Hilton approved a suggestion from Golden's AI on 21 May, 2020
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Photons transfer their energy to the spacecraft by redshifting due to Doppler shift upon reflection, thus the higher the spacecraft speed, the higher the efficiency. The energy transfer efficiency from photons to the spacecraft's kinetic energy as a function of β=v/c (the spacecraft velocity divided by the light velocity) in photon propulsion. As the spacecraft velocity approaches the light velocity (v≈c), the efficiency of photon propulsion approaches 100%, as if the spacecraft acts like a black hole in the moving direction. At low β, the recycling rocket can have a high thrust amplification factor (in this example, ~3,000), however as β approaches 1, the amplification factor converges to 1 and the overhead of recycling is unneeded. Therefore, these rockets are projected to bridge the efficiency gap. The simplest recycling scheme is a Herriot cell with multi-bouncing laser beams between two high reflectance mirrors that do not form a resonant optical cavity. This cell type approach was first proposed by Meyer, et al., followed by Simmons and McInnes. Mertzger and LandisLandis proposed a multi-bounce lightsail craft, such that the beam is reflected back and forth between the lightsail and a source reflector. Advanced reflectors permit more than 1000 bounces, reducing power requirements by 1000× compared to single bounce proposals. Using 100 MW to 1 GW lasers, a sub-100 day Mars transit is possible. The first experimental attempt on photon thrust amplification in a non-resonant Herriot-cell type optical cavity was performed by Gray et al. who obtained amplified photon thrust of ~0.4 μN with a 300-W laser and a photon thrust amplification factor of ~2.6.The passive resonator in the Fabry-Perot interferometer has been extensively used in high-sensitivity optical detection methods, such as the cavity ring-down spectroscopy. One experiment produced 20,000 photon bounces using mirrors with 0.99995 reflectance. in which even one nanometer perturbation in cavity length destroys the resonance and nulls the photon thrust. The injection of laser power into the cavity remains challenging.

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