Question

a proposed method for transportation between the planets within our solar system is "space sailing", wherein a spacecraft carries a very large sail. Sunlight striking the sail exerts a force, accelerating the spacecraft. Should the sail be absorptive or reflective to be most effective? Justify your choice using your understanding of the underlying physics. What other characteristics does the sail need to have?

Answer 1

impulse=force*time=change in momentum

larger the impulse, larger the force for the same time of interaction between the sunlight and the sail.

to maximize the impulse, the change in momentum needs to maximized

change in momentum=initial momentum-final momentum

as direction of reflected light is opposite to direction of incident light

total change in momentum=magnitude of initial momentum + magnitude of final momentum

hence the sails should be reflective in nature to ensure change in momentum is maximum and hence the impulse and the force therefore is maximum.