What is an alternative to rockets for space travel?

Rockets are very inefficient ways to travel. They require a lot of fuel, which greatly limits the payload they can carry.

They remain relatively useful for leaving the atmosphere, but they are a very bad way to move within the solar system, which should be replaced.

There are alternatives, such as ion engines. But I will focus on an idea that I find more interesting: an interplanetary (and potentially interstellar) highway.

A not-too-futuristic and very interesting idea, it involves equipping ships with solar sails and using lasers as means of propulsion.

The way solar sails work is extremely simple: basically they are large surfaces that are propelled by the radiation pressure of electromagnetic waves, which not only carry energy but also momentum.

It is an underdeveloped technology, but one whose underlying physics is flawless. The real novelty would be to couple the solar sails to a pre-existing “infrastructure” consisting of very powerful lasers, placed at strategic points within the solar system.

Light generated by lasers tends to spread out much less than non-coherent light, which increases the range within which they can provide a significant boost to solar sails. And that would make the spacecraft independent of sunlight…