Why does the electoral college not allow citizens living in U.S. territories to vote, as it is the only place in the universe (astronauts have voted) that U.S. citizens can't vote.

Because the electoral college is limited to a certain number by the U.S. Constitution, it would take a Constitutional Amendment to change this number. Apparently there has not been enough interest in letting the people in the territories be represented by the Electoral College to propose and pass an Amendment.

http://www.archives.gov/federal-register/electoral-college/about.html

http://www.archives.gov/federal-register/electoral-college/faq.html#538

with the exception of Washington DC Only states get electoral vote equaling the number of Representative in congress. Tn has 9 Reps and two senators so 11 electors is given to Tn. Astronauts, military or any one else can vote absentee being citizens of a state.

The reason why citizens living in U.S. territories generally cannot vote in the Electoral College is because of how the system is designed. The Electoral College is comprised of electors who are chosen by each state, and their role is to formally cast the votes for president and vice president on behalf of their respective states.

U.S. territories, such as Puerto Rico, Guam, and the U.S. Virgin Islands, are not considered states, but rather possessions or territories of the United States. While their residents are U.S. citizens, they do not have the same voting rights as those who live in the 50 states. This is because the Constitution grants each state the authority to determine how its electors are chosen, and historically, states have limited eligibility to their own residents.

In the case of astronauts, they are a unique exception to the general rule. They have the ability to vote from outer space because of the specific logistical arrangements made by NASA and the states they are registered to vote in. Special procedures are put in place to ensure that astronauts can cast their ballots while on missions, despite being outside the Earth's boundaries.

If there were to be a change allowing residents of U.S. territories to vote in the Electoral College, it would require an amendment to the U.S. Constitution, as it is the governing document that outlines the powers and structure of the Electoral College.