The argument over propellentless space drives has raged for decades. Advocates say the drives will transform the space industry and open up the Solar System, critics see them as a scam (see FT320:12). Now the debate has moved to a new level as the first such drive is tested in space.
The debate is simple. Newton’s laws of motion say that you can only move forward in space by ejecting exhaust material backward. There are a few potential tricks to get around this, for example using light sails, which capture the momentum of light from the Sun, but these