Exploration of outer planets using tethers for power and propulsion

a = radius of circular orbit a(max) = radius at mechanical-energy maximum ast = radius of stationary orbit B = planetary magnetic field Em = motional electric field ht = thickness of tape tether I = current on tether Iav = length-averaged tether current Lt = tether length Msc = overall spacecraft mass mt = tether mass Npl = ionospheric electron density RJ = radius of Jupiter r = radial distance rper = radius at perijove T = tether temperature Te = ionospheric electron temperature vorb = orbital velocity vpl = ionospheric plasma velocity vrel = relative velocity vorb − vpl v∞ = hyperbolic excess velocity wt = width of tape tether e = tether emissivity emech = mechanical energy ρAl = aluminum density σAl = aluminum conductivity σB = Stefan–Boltzmann constant