Electrodynamic Tethers in Space; Extreme Engineering; Exclusive Online Issues; by Enrico Lorenzini and Juan Sanmart¿n; 8 Page(s)

There are no filling stations in space. Every spacecraft on every mission has to carry all the energy sources required to get its job done, typically in the form of chemical propellants, photovoltaic arrays or nuclear reactors.

The sole alternative--delivery service--can be formidably expensive. The International Space Station, for example, will need an estimated 77 metric tons of booster propellant over its anticipated 10-year life span just to keep itself from gradually falling out of orbit. Even assuming a minimal price of $7,000 a pound (dirt cheap by current standards) to get fuel up to the station's 360-kilometer altitude, that is $1.2 billion simply to maintain the orbital status quo. The problems are compounded for exploration of outer planets such as Jupiter, where distance from the sun makes photovoltaic generation less effective and where every gram of fuel has to be transported hundreds of millions of kilometers.