Solar thermal rockets have been proposed as a system for launching a small personal spacecraft into orbit. The design is based on a high altitude airship which uses its envelope to focus sunlight onto a tube. The propellant, which would likely be ammonia, is then fed through to produce thrust.

With SEP, the spacecraft collects energy from the Sun via solar arrays to generate thrust, eliminating many of the needs and limitations of storing propellants onboard. That solar energy is then converted to electric power and used to ionize – or positively charge – inert gas propellants like xenon and krypton.

With SEP, large solar cell arrays convert collected sunlight energy to electrical power. That energy is fed into exceptionally fuel-efficient thrusters that provide gentle but nonstop thrust throughout the mission.

Within a solar system, sunlight can continuously push on the sail, accelerating the spacecraft throughout its entire voyage. This means that solar sail-propelled spacecraft can reach speeds that would be practically impossible for chemical rockets to achieve.