Young Bae of Advanced Space and Energy Technologies in Tustin, California, has improved his photonic laser thruster. was developed with NASA funding. His thruster works because light exerts pressure when it hits something. In theory, it is possible to move an object like a CubeSat by nudging it with a laser beam. In practice, however, the pressure which light exerts is so small that a device able to do a useful amount of nudging would require a laser of unfeasibly large power.
Dr Bae has overcome this limitation by bouncing light repeatedly between the source laser and the satellite, to multiply the thrust. In his latest experiments, Dr Bae has managed to amplify the thrust imparted by a single nudge of the laser by a factor of 1,500, which is big enough to manoeuvre a CubeSat as well as a conventional thruster would. This brings two advantages. First, since no on-board propellant is required, there is more room for instruments. Second, there being no fuel to run out, a CubeSat’s orbit can be boosted as many times as is desired, and its working life prolonged indefinitely.
a suitable laser is required to provide the thrust. Dr Bae thinks it could be in orbit as well. The laser would be powered by solar cells and shepherd a veritable flock of CubeSats, providing the propulsion needed to move and arrange them as required.
In 2015, Bae had achieved 400 times amplification in 2015 with up to 3.5 millinewtons with a 500 watt laser. The new 1500 amplification should enable about 14 millinewtons of thrust with a 500 watt laser. There are 10 to 150 kilowatt lasers being tested by the US Military. A 150 kilowatt laser with 1500 times amplification would have 4.2 newtons of thrust. Compact high power lasers are being developed for integration in to US stealth fighters in the early 2020s.
Proven but classified technology should enable photonic propulsion to operate out to 100 kilometers.
An Economist magazine discusses the work at Bae Corp which could be used for moving cubesats in the near future.
Photonic Laser Thruster – Photonic Railway
An array of one thousand 100 kilowatt lasers would be 100 megawatts of power. Amplified ranges of 100,000 kilometers should be possible with a plausible 20 years of development. A 100 megawatt PLT with 1000 times amplification would enable trips too and from the moon in less than 15 hours for a 1 ton spacecraft.
A simple PLT system could provide continuous and constant thrust in a straight line. However, travel around the solar system involves interacting with planets and the sun, so trajectories and travel time calculations are more complex. Fu-Yuen Hsiao has investigated the trajectories of spacecraft relying entirely on a PLT.
Bae’s investigation concluded that the development of interstellar photonic railway will require development in x-ray lasers and future advanced material science and technologies. Bae further concluded that the realization of the interstellar photonic railway would require that the PLT technology developments ride on the Moore’s law as the 20th century silicon devices did.
Specific energy as a function of spacecraft velocity relevant to Mars missions. The flight time to Mars is for flyby missions, and rendezvous missions would take more than twice longer. For 3 day flight to Mars, the photonic railway (PLT-BLP) would be several orders of magnitude energy efficient than the conventional rockets with Isp of 3,000.
Y.K. Bae Corporation announced their proprietary Photonic Laser Thruster (PLT) has successfully accelerated a 450 gram (~1 lb.) spacecraft simulator with pure laser light for the first time in history. The project was funded by a Phase II grant of NASA Innovative Advanced Concepts (NIAC), which funds the most promising ideas for the next generation NASA space missions.
Conducted in a Class 1,000 cleanroom, Y.K. Bae’s demonstration amplified photon power 400-times to achieve photon thrust up to 1.1 milliNewtons by bouncing photons several hundred times between two laser mirrors. The amplified thrust successfully propelled a gliding platform along a 2 meter frictionless air track, simulating zero-gravity.
“Moving a 450 gram platform unequivocally validates the useful power-to-thrust ratio of PLT,” said Dr. Claude Phipps, Chair of International High Power Laser Ablation and Directed Energy Symposium. “I can see future development that includes optical cavities that span many kilometers achieved with precise mirror alignment to enable maneuvering spacecraft many kilometers apart, and propellant-free propulsion of satellites in formations.”
The PLT demonstration simulated beaming thrust between vehicles, which also included slowing and stopping the simulator. Benefits of a PLT spacecraft system include a dramatic reduction in fuel consumption in a wide range of space applications, such as orbit adjustments, drag compensation, and rendezvous and docking. The thrust-beaming capability of PLT further enables a distributed multivehicle approach, a revolutionary departure from the “all-in-one” single-spacecraft approach.
“PLT technology has the potential to revolutionize space mission designs,” said Dr. Mason Peck, Associate Professor in Mechanical & Aerospace Engineering at Cornell University, who has also served as NASA’s Chief Technologist. “Fully developed PLT could serve current commercial and non-commercial needs by increasing the life of LEO satellites, and therefore reducing mission costs. For the future, this unlimited-impulse technology opens doors to applications that are currently impractical, like persistent, precision formations of multiple satellites.”
Y.K. Bae Team is currently developing space-qualifiable PLTs, and scaling up PLT in thrust and operation range. “Our next milestone is a flight demonstration in low earth orbit, which will prove the technology of PLT-enabled precision formation flying and stationkeeping with small satellites,” according to Dr. Bae, CEO of Y.K. Bae Corporation.
Nextbigfuture focused on the second half with the talk by Young Bae.
Young Bae, Y.K. Bae Corporation – Propellant-less Spacecraft Formation-Flying and Maneuvering with Photonic Laser Thrusters
Young Bae used a diamond thin disk laser and increased the power to achieve 1.03 millinewtons of force with a laser photonic thruster.
It bounces lasers between mirrors. The bouncing amplification was 100-200 times.
He believes they can get bouncing amplification to 1000 times.
The mirrors can handle 50 megawatts per square centimeter and they are at 500 kilowatts per square centimeter.
The big-picture plan starts with using laser propulsion in the coming decades on near-Earth space missions, journeys to the moon, and visits to near-Earth asteroids. Within 50 years, he hopes for phase two: Mars. After that comes the gas and ice giants in the outer solar system and their intriguing moons. And then, beyond: “We envision that humans can fly to other stars or other planets in other solar systems,” he says.
One of the most intriguing parts about using laser propulsion for deep space journeys: There’s the potential for in-flight gravity, or something like it. The system would create acceleration similar to 1g, meaning that astronauts would have their feet on the ground. “Once you accelerate, then that acceleration acts like gravity,” Bae says. “Your feet will be toward the laser because of the acceleration. That way, I think the Star Trek–type of travel is possible.”
What’s holding Bae back? For one, you’d need tremendous power to realize such a mission with current technology. For even near-Earth and lunar missions, Bae estimates a requirement of 1 gigawatt of power, requiring a large amount of power to be generated by solar or nuclear power to generate the thrust.
Then there are the lasers themselves. As the distance between the photonic source and the craft increases, the signal spreads wider and wider, decreasing the precision of the guidance and reducing overall thrust. Think of it like shining a flashlight. Up close, the light is easy to narrowly direct to a particular object. But shining it on something farther away spreads the light out more, covering a wider distance but with less luminosity. Now, for a laser that’s supposed to be shooting precise guidance lasers, tshis becomes a problem. So while near-Earth and Martian flights will be okay, problems will arise getting farther and farther away. One compensation is the idea of doing smaller platforms to create a “photonic railway,” each acting as a sort of refueling station in between to get the craft where it needs to be. But Bae wants to also control the problem of the lasers spreading themselves too thin. Bae has his eye on research into Bessel beams, which don’t diffract, and therefore could be fired at a spacecraft from farther away.
Bessel beams are lasers that behave very differently from ordinary lasers. Consider how the typical laser pointer behaves, creating a small red dot where you point it. Instead of a single point on a wall, Bessel beams create a bullseye: one dot surrounded by concentric rings. The number of rings is some indication of the strength of the beam. Many commercial Bessel beam devices create beams with about eleven rings. The ideal Bessel beam would have an infinite amount – because an ideal Bessel would use an infinite amount of energy.
Unlike a typical laser beam, a Bessel beam does not diffract and get larger as the beam gets farther from its point of origin. One of the most prized attributes of Bessel beams is the fact that the central core of the beam can be blocked, without interrupting the beam. The laser essentially self-heals by using the rings which were not blocked. It’s the optical terminator.
Proven but classified technology should enable photonic propulsion to operate out to 100 kilometers
The German company Rheinmetall Defense demonstrated a 1-km long laser resonator similar to the PLT optical resonator in 1994-1995 with the use of a telescopic arrangement in the optical cavity, and that such long laser resonators can be scalable to 100 km with the usage of optics in the diameter of 70 cm. These successful demonstrations promise that PLT can be operated beyond distances in the order of 100 km. Further studies should be performed whether PLT can be used for interstellar scales, but so far there is no show stopper on this issue.
Another key technological issue in implementing PLT is in the intracavity laser beam aiming, aligning, and tracking, which will be addressed more in depth in the discussion section. With the rapid advancement in DE technologies, the aiming, alignment, and tracking of laser beams on rapidly moving uncooperative targets over the distance greater than 100 km have become technologically feasible.
Although the technical details of such aiming, alignment, and tracking system is grossly classified, the nut-shell of the technology is available in open literatures. Especially, the technology developed for ABL will play crucial role in PLT systems. Based on open literature, in ABL, the aiming, alignment, and tracking of the main laser rely on the scattered beam of the beacon laser (also diode pumped lasers at power level of a few kW). Similar to this, a small laser (power level of a few watts) in the mission vehicle can be used as a beacon laser. It seems that the aiming, aligning, and tracking system can be scaled to interstellar distances.
Other important issues involve the hardware weight and optical quality of the HR mirrors. The size of the HR mirrors to have the proposed high reflectance over long intracavity distances should be considerably larger than the one obtained with 1st order diffraction law. Therefore, the method to reduce beam divergence against diffraction law may be required eventually for long range operations of PLT/DEMB systems. One interesting approach needed to be investigated is to use Bessel beams for reducing the divergence of laser propagation. Another interesting approach needed to be investigated is to use Bose-Einstein Condensation (BEC) of photons
Young Bae recently received a $500,000 NASA phase 2 NIAC grant for Propellant-less Spacecraft Formation-Flying and Maneuvering with Photonic Laser Thrusters
Photonic Laser Thruster (PLT)
A photonic laser thruster bounces a laser between mirrors to boost the momentum transfer by recycling the photons.
Dr. Y.K. Bae demonstrated a Photonic Laser Thruster (PLT) built from off-the-shelf optical components and a YAG gain medium, and the maximum amplified photon thrust achieved was 35 µN for a laser output of 1.7 W with the use of a HR mirror with a 0.99967 reflectance. This performance corresponds to an apparent photon thrust amplification factor of ~3,000. More importantly, in the experimental demonstration, the author accidentally discovered that the PLT cavity is highly stable against the mirror motion and misalignment unlike passive optical cavities. In fact, in the demonstration experiment by Dr. Bae, the full resonance mode of the PLT was maintained even when one of the HR mirror was held by a hand. In a more systematic experiment, the PLT cavity was demonstrated to be stable against tilting, vibration and motion of mirrors. Subsequent theoretical analysis by the author showed that PLT can indeed be used for propulsion applications, and proposed Photonic Laser Propulsion (PLP), the propulsion with PLT. The reason for the observed stability results from that in the active optical cavities for PLT and PLP the laser gain medium dynamically adapts to the changes in the cavity parameters, such as mirror motion, vibration and tilting, which does not exist in the passive optical cavities.
A four-phased evolutionary developmental pathway of the Photonic Railway towards interstellar manned roundtrip travel is proposed:
1) Development of PLTs for satellites and NEO manipulation,
The first phase in the developmental pathway towards interstellar roundtrip manned flight is maturing PLT technologies and systematic scaling up of its power and operation distance capabilities. PLT is predicted to meet the needs of the next generation of space industry market by enabling a wide range of innovative space applications near the earth. In this phase, which is predicted to evolve over 5–30 year time frame, PLT would be capable of providing thrusts in the range of 1 mN–1 kN, which requires the operation power of 100 W–100 MW. The solar panel based space power currently can provide electrical powers up to 100 kW, therefore, the PLT capable of providing thrusts up to 1 N can be readily implemented in the near future.
2) Interlunar Photonic Railway,
3) Interplanetary Photonic Railway, and
4) Interstellar Photonic Railway.