Interstellar travel is the hypothetical travel of spacecraft between star systems. Due to the vast distances between the Solar System and nearby stars, interstellar travel is not practicable with current propulsion technologies.
To travel between stars within a reasonable amount of time (decades or centuries), an interstellar spacecraft must reach a significant fraction of the speed of light, requiring enormous amounts of energy. Communication with such interstellar craft will experience years of delay due to the speed of light. Collisions with cosmic dust and gas at such speeds can be catastrophic for such spacecrafts. Crewed interstellar travel could possibly be conducted more slowly (far beyond the scale of a human lifetime) by making a generation ship. Hypothetical interstellar propulsion systems include nuclear pulse propulsion, fission-fragment rocket, fusion rocket, beamed solar sail, and antimatter rocket.