A new solution for the growing space junk (debris and non functioning satellites in orbit) problem is the use of robotic repair and resupply satellites. The second one (the Space Infrastructure Servicing, or SIS satellite) is going up in four years, to refuel communications satellites. Many satellites cost a billion dollars to build and put into orbit. But their lifespan is often limited by the amount of fuel they can carry (to make minor, but essential, adjustments in their orbit). While many satellite experts believe the technology is not yet there to do this sort of thing, a successful test was carried out four years ago.
This experiment was called Orbital Express, which consisted of two satellites. One of the satellites tested robotic hardware and software, to do maintenance work on the other bird, as well as transferring fuel. With satellites costing so much, it's become cost effective to develop and build satellites that can do repairs, upgrades and refueling while these expensive birds are still up there. Unlike in the past, satellites can be built to last for a decade or more, especially if they can be serviced. Previously, the only option was to get the Space Shuttle to do it, but that cost over a hundred million dollars per repair mission (because each Shuttle mission was so expensive, and overbooked). Robotic repair satellites are a lot cheaper. Orbital Express was test of the concept, which many satellite engineers had been demanding for decades. The test was a success, and that led to the SIS bird, which will do it for real, and get paid for it.
Most of these service missions will be for refueling satellites, which often have small jets, used to reposition themselves. But other can replace worn or damaged components, install upgraded equipment (like a more powerful onboard computer). Future satellites can be designed to accommodate SIS tools and capabilities, further reducing the cost of these services, and expanding the number of satellites that can be tended to per SIS mission. The plan is to have a supply satellite come up regularly to replenish the SIS fuel and spares, and then return to earth for reuse. But the larger, and more expensive, SIS satellite will stay in orbit for as long as it is able, because it will probably not be built for re-entry and reuse.
Once robots are doing the satellite servicing, the cost of building and operating satellites will come down 50 percent or more in a decade or so, and even more after that. Plus, there will be fewer retired (to being a traffic hazard) satellites in orbit.