Radiation pressure is the minuscule force exerted by a photon when it strikes an object. We don't experience radiation pressure in our everyday lives because it is drowned out by much, much larger forces. But in the vacuum of space, the feeble push of radiation pressure isn't opposed by significant aerodynamic drag. Over time, it can do real work.
A NASA study aims to do just that. The authors propose using a commercial, off-the-shelf telescope and laser to point a 5-10kW beam at potentially dangerous space debris. The radiation pressure won't be enough to de-orbit the debris, but according to simulations it should alter the debris' orbits enough to avoid a collision. And at orbital speeds, a collision is catastrophic.
The authors also suggest the telescope-and-laser system could be employed to boost the orbits of small satellites. This is an intriguing notion to me. Nano- and pico-satellites are a relatively recent development, but they're limited by a lack of thrusters. Without thrust, the orbits of tiny satellites inevitably decay and the vehicle burns up as it reenters the atmosphere.
But imagine if the satellite operators could purchase time on a ground-based laser facility. The laser would push their satellite to a higher orbit, provided it has the correct mass-to-area ratio. This sounds promising because it provides thrust "on demand", without much additional capital cost on the part of the satellite operator.