11.   Later this year, the space shuttle may carry a solar sail into Earth orbit to prove the concept works.

12.   Paradoxically, solar sails might also be used to hold an object still.

13.   Yet the solar sail has been a main rallying point.

14.   After the spacecraft leaves Earth orbit, it will deploy its solar sail and begin its journey.

15.   Although a solar sail is at first slower than a conventional rocket, it continues to accelerate over time and achieves a greater velocity.

16.   NASA and several private groups are working on plans to use solar sail technology.

17.   On Tuesday, they unveiled a prototype solar sail designed to capture the energy of the sun and transport humans and cargo through space without engines or fuel.

18.   Since it is powered by sunlight, a solar sail spacecraft would require little or no propellent.

19.   The idea of a solar sail is not a new one.

20.   The solar sail is designed to use the steady pressure of photons hitting it to move forward, just as a sail uses the wind.