One could combine this with the HASTOL concept to get very cheap launches to earth orbit.<p><a href="http://en.wikipedia.org/wiki/Tether_propulsion#HASTOL_.E2.80.94_Earth_launch_assist_rotovator" rel="nofollow">http://en.wikipedia.org/wiki/Tether_propulsion#HASTOL_.E2.80...</a><p>Basically, a rotating tether substitues for the upper stage(s) of a launch system. But for each assisted cargo, the rotating tether needs to accelerate again. Ion engines can do this, but their low thrust and short lifespan make them less than idea. VASIMR has a longer lifespan and higher thrust.