WHY WE CAN NOT SPACE TRAVEL?

[tonebone2012]

JUST PUTTING THIS QUESTION OUT THERE TO SEE WHO KNOWS THEIR STUFF.
KINDA OF LIKE A POP QUIZ QUESTION. BUT WHY IS LONG VOYAGES LIKE TO MARS OR FURTHER OUT NOT POSSIBLE???

[GeeGee]

Voyages to Mars are possible, even with NASA spacecraft. Actually, NASA has stated they're planning a manned mission to Mars this century.