Image courtesy of NASA
The objective of the mission is to test the possibility of using solar sails to slow down satellites in LEO as they are taken out of commission. As it is now the satellites are required to use boosters to manoeuvre into a lower orbit where they can burn up, which means that satellites must launch with extra useless weight (the fuel required to slow down the satellite).
Instead of using boosters in the future satellites can launch with a light weight solar sail which they can use to slow down (the atmosphere is dense enough in LEO to slow down the satellites).
You might have heard of solar sails in other places but they are usually mentioned as a means of propulsion and not braking. Such as the Japanese IKARUS mission which is on its way to Venus.
The reason the title of this post is '..rediscovered' is because shortly after the satellite was supposed to be ejected from the parent vehicle (on December 6th) contact with the satellite was lost and NASA was unable to relocate it. NASA asked amateur radio users all over the world for help in locating the tiny satellite by listening for its beacon signal.
Later is was discovered that the satellite might not have ejected properly from the parent and that might have been the cause for the loss of contact. On January 19th (this year) Nanosail-D was suddenly ejected from the parent and the 3 day timer to sail unfolding could begin.
And today the sail unfolded and the very first solar sail in LEO had been deployed.
The satellite is going to stay in orbit between 2 and 4 months until it burns up in the atmosphere.