claim: The current Duke of York has no female heirs.
evidence: Solar sails -LRB- also called light sails or photon sails -RRB- are a form of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors .. spacecraft propulsion. spacecraft propulsion. radiation pressure. radiation pressure. propulsion. spacecraft propulsion. A useful analogy may be a sailing boat ; the light exerting a force on the mirrors is akin to a sail being blown by the wind .. High-energy laser beams could be used as an alternative light source to exert much greater force than would be possible using sunlight , a concept known as beam sailing .. laser beams. Laser propulsion. Solar sail craft offer the possibility of low-cost operations combined with long operating lifetimes .. Since they have few moving parts and use no propellant , they can potentially be used numerous times for delivery of payloads .. Solar sails use a phenomenon that has a proven , measured effect on spacecraft .. Solar pressure affects all spacecraft , whether in interplanetary space or in orbit around a planet or small body .. interplanetary space. Interplanetary spaceflight. A typical spacecraft going to Mars , for example , will be displaced by thousands of kilometres by solar pressure , so the effects must be accounted for in trajectory planning , which has been done since the time of the earliest interplanetary spacecraft of the 1960s .. Solar pressure also affects the orientation -LRB- Aircraft attitude -RRB- of a craft , a factor that must be included in spacecraft design .. Aircraft attitude. Aircraft attitude. spacecraft design. spacecraft design. The total force exerted on an 800 by 800 meter solar sail , for example , is about 5 N at Earth 's distance from the Sun , making it a low-thrust propulsion system , similar to spacecraft propelled by electric engines , but as it uses no propellant , that force is exerted almost constantly and the collective effect over time is great enough to be considered a potential manner of propelling spacecraft .. propulsion. spacecraft propulsion. electric engines. Electrically powered spacecraft propulsion