Until you realize that a net thrust of only 0.5 lbs is quite noticeable for a 250,000 lb Shuttle. For a 5,000 lb vehicle, that same tiny mouse-fart would provide 120 km of orbit raising per day in low earth orbit.
By comparison, it would require over 60 lb of hydrazine per day to get the same result.
Same with tethers. They are only "momentum transfer" devices, providing modest increases in velocity which is given to the payload at the tether's expense...ultimately paid by a small dimunition of the Earth's momentum.
Which will undoubtedly be fuel for the next generation of enviros: "The United states has just 3% of the world's population, but uses almost 100% of the Earth's momentum....."
Neither technology will work for boosters or deep-space propulsion. In this sense they are just stupid stunts
In the same way that spy, weather, and communication satellites are stupid stunts?
How much delta-V can be provided by such systems?
The key to access to space is in the earth-to-orbit phase.
You have no spy, weather, or comm sats without ETO. $10,000 a pound and you are worrying about mouse farts.
--Boris