While clean up missions might make sense for some of the largest and highest risk objects, for the much more numerous small stuff the most economical way to cle

While clean up missions might make sense for some of the largest and highest risk objects, for the much more numerous small stuff the most economical way to clean an orbit is likely ground based lasers. Whether you're ablating a bit of material on the object's surface with a quick pulse or just producing radiation pressure holding a beam on target, you can gradually lower an object's perigee until atmospheric drag is significant. It's not exactly cheap, but it's at least an order of magnitude less than in-space options. There's even a potential business case auctioning off laser time to guard specific satellites. A typical satellite costs about $200 Million to build, plus many millions to launch, and a few million per year to operate. There are about 2000 active satellites in high orbits where debris could be an issue. If operators pay $100k per satellite per year, about a 5% increase in annual operating cost and a 0.3% increase in lifetime cost (assuming 10 year satellite lifetime), that's $200M per year revenue. Assuming 300 m/s delta V to lower an object's orbit to the point it will decay naturally, and a 0.01% ground based electric to orbital kinetic energy conversion efficiency, a bank of lasers consuming 2 MW of electric power (not beam power) would be able to deorbit 140 tons of material per year. There are about 9000 tons of material in orbit, about 2000 tons of which are in medium and high orbits, so that's about 1/14th of long lived space junk. Assuming a 5 cent per kilowatt hour average electricity price, that's under $900k per year to power the lasers. Assume that's around 5% of annual operating costs, call it $20M/yr for ops and maintenance. For capex, assuming 10% laser efficiency, that's 800 kW of laser beam power, 1 kW of beam power is around $8k, though the optimal frequencies may be different, let's call it $30M. The optics and targeting system is likely to be the bulk of the cost. A university grade observatory, which is likely comparable in scale and complexity is around $500k, but this would be a custom build so it's likely substantially higher. The keck observatory cost $140M and is likely a good upper bound. Add another $30M for other technical components, and probably another $100M for non-technical aspects of the facility. Assuming capex is amortized over 5 years, we're looking at around $60M/yr for capex. For a $500M initial investment, in 10 years you're paid off and up an additional $1.5B, for an average annual return of about 15%. Not exactly the greatest investment as is, but within the realm of discussion. Further, these estimates are quite conservative and it's likely a decent portion of the initial cost could be covered by a government.