Short answers, pulled from the story.
Deep space exploration is the branch of astronomy, astronautics, and space technology concerned with exploring distant regions of outer space. There is no single agreed definition: the International Telecommunication Union sets the threshold at 2 million kilometers from Earth's surface, while NASA's Deep Space Network has applied criteria ranging from 16,000 to 32,000 kilometers at different times.
Voyager 1 is the farthest human-made spacecraft from Earth. NASA announced on the 5th of December 2011 that it had reached the outer edge of the Solar System, and it entered interstellar space on the 25th of August 2012.
Nuclear fusion propulsion, laser and maser propulsion, and antimatter engines are among the leading candidates. Beamed propulsion is considered especially promising because it relies on known physics and technology already being developed for other purposes.
The 100 Year Starship is a project funded by the Defense Advanced Research Projects Agency with a $500,000 award given to former astronaut Mae Jemison in 2012. Its goal is to develop the knowledge needed to send future astronauts beyond the Solar System and to increase public interest in deep space exploration.
Following the Space Shuttle's retirement in 2011, NASA announced three priority technologies: a deep space atomic clock, a large solar sail, and an advanced laser communications system. These were intended to improve communication, navigation, and propulsion for future missions.
In June 2013, NASA selected eight American astronauts to train for deep space missions beyond low Earth orbit. The intended destinations for this training were Mars and asteroids.