| abstract | - Nearly all spacecraft in existence today work based on Newton's third law -- for every action there is an equal and opposite reaction. The spacecraft creates a force to hurl some stuff out the back, and that action creates a reaction force to accelerate the spacecraft forward. This means that real-life and conceivable future spaceships are mostly containers full of stuff to throw out the back, with comparatively little volume for human habitation. Most Science Fiction stories, however are about humans, not reaction mass, so Science Fiction writers would prefer spacecraft to have much more of their volume dedicated to human activities. A reactionless drive or reactionless engine is a piece of advanced technology invented to make life easy for those Science Fiction writers. For our purposes it is sufficient to define the drive as follows: "any form of propulsion not based around expulsion of fuel or reaction mass". In other words the drive will propel a vehicle, almost always a starship, without having to waste space carrying propellant. Sometimes authors will try to control these drives by requiring a power plant to make it keep working but more than a few will keep working forever. Obviously this would be an awesome invention! So why don't we have them? Well, naively it would shatter the fundamental basis of all physics since Isaac Newton, as detailed here, and modern theories predict effects too small to be useful. Thoughtful Speculative Fiction writers have also noted that any sort of reactionless drive would provide those who possess it with an infinitely powerful weapon (compare Weaponized Exhaust, which is the use of a reaction drive as a weapon). Note that this would not be a problem if they required truly massive amounts of power but many examples don't. Some writers try to side step this potential danger by setting a maximum speed that the drive can go. Unfortunately while this eliminates the possibility of an infinitely powerful missile it still leaves the developer with an infinitely powerful energy source leaving the writer with most of the same problems. Other times, it may be limited to Higher-Tech Species or Sufficiently Advanced Aliens who presumably have some scientific understanding beyond the ken of "lesser races". Examples of Reactionless Drive include:
|
