 These methods are limiting in that rocket propellants have to be accelerated as well and are eventually depleted, and the stellar wind or the gravitational fields of planets can only be utilized locally in the Solar System.In interstellar space and bereft of the above resources, different forms of propulsion are needed to propel a spacecraft, and they are referred to as advanced or .If the Woodward effect is confirmed and if an engine can be designed to use applied Mach effects, then a spacecraft may be possible that could maintain a steady acceleration into and through interstellar space without the need to carry along propellants.