A new laser thruster could be a step towards new technology to push satellites rapidly between planets.
The demonstration model of the Photonic Laser Thruster (PLT) moved a 750-gram mock satellite along a track in the laboratory using only the power of light.
Laser thrusters, which exert force through light pressure, usually need extremely powerful lasers to generate tiny amounts of thrust. For instance, a different project 鈥� Breakthrough Starshot 鈥� envisages using gigawatt-scale lasers to accelerate probes the size of a postage stamp towards the Alpha Centauri star system, 4.37 light years away, at up to 20 per cent of light speed.
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However, the PLT overcomes this need for extreme lasers by bouncing the laser beam back and forth many times between the spacecraft and the laser source, imparting a little extra energy to the craft each time in a process called laser recycling.
The work was sponsored by NASA and carried out by the Y. K. Bae Corporation, California.
The experimenters previously demonstrated laser recycling with a low-power system. The new demonstration was 100 times more powerful and produced 3 millinewtons. As shown in the movie below 鈥� which has been speeded up 鈥� this was enough force to accelerate a mock satellite similar to existing CubeSats聽along a low-friction rail.
The researchers used a ytterbium-doped yttrium aluminium garnet laser. Recycling the beam magnified the thrust by a factor of several hundred. The experiment showed that the beam arrangement is stable and can maintain its alignment with a moving target.
According to lead researcher Young Bae, the next stage of development should increase PLT thrust to a level comparable to that of the electric thrusters on existing satellites. This would make it possible to use PLT-style devices to manoeuvre satellites, or help them keep their position, without the satellites having to carry their own thrusters. In this scenario, photonic laser thrust could be beamed to the satellite that is being manipulated from another, larger satellite carrying the PLT technology.
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鈥淭his is analogous to aerial refuelling in which jet fuel is delivered to fighter jets from a much larger and less-costly tanker airplane,鈥� says Bae.
As an added advantage, powering satellites externally via PLT could extend their useful life. At the moment, satellites need to carry propellant to operate their thrusters, which limits their longevity because, as soon as they run out of propellant, they can no longer adjust their position or maintain their orbit.
Philip Lubin of the Space Research Laboratory at the University of California, Santa Barbara, says the laser recycling technique works best at close ranges.
鈥淭he issue for spacecraft propulsion becomes one of distance between the emitter and the reflector sides,鈥� he says, noting that as the range increases the beam diverges and thrust falls off.
Bae accepts this, but says that with current optics, the PLT should still provide workable amounts of thrust over distances of about 1000 kilometres, enough to work with satellites in Earth鈥檚 orbit. He believes technology improvements will increase the range over the coming decades.
Ultimately, Bae hopes the PLT, funded through NASA鈥檚 Innovative Advanced Concepts programme, could provide the infrastructure for what he terms a Photonic Railway. This would have high-power laser installations at each end shuttling unpowered 鈥渟pacetrains鈥� between them, accelerating and decelerating the craft across interplanetary and even interstellar distances. He says such a set-up could send payloads between Earth and Mars in days rather than months.
聽Journal of Propulsion and Power
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