ION DRIVE
STATUS: TESTED IN SPACE
RANGE: INTERPLANETARY
A conventional rocket works by expelling exhaust gases from a combustion reaction through a rear-facing nozzle, resulting in a forward thrust via the conservation of momentum. An ion drive also generates thrust by expelling material, but in this case it’s a stream of ions – atoms that have had electrons stripped off to create a positive electric charge. Before being ejected, these ions are accelerated to high speeds using an electric field. The energy to maintain this field – as well as that needed to ionise the propellant atoms – comes from solar panels. For this reason, ion drives are sometimes referred to as solar-electric propulsion. Ion drives powerful enough to propel a crewed spacecraft still lie in the future, but NASA has used them in some of its smaller interplanetary probes, such as the Dawn mission to the asteroid belt and the Double Asteroid Redirection Test, which slammed into an asteroid last year.
MACH-EFFECT DRIVE
STATUS: SPECULATIVE
RANGE: INTERSTELLAR
Propulsion systems such as rockets and ion drives work by
