Answer:
so you don't get copyrighted because of plagiarism
Explanation:
"The space shuttles is the subject."
Simple formula: find the verb of the sentence then ask the question "who or what performs the verb" and the answer to that question is the SUBJECT of that sentence!
In your sentence; ask the question;
"Who or what have made travel to the International space station convenient and possible?
Answer: The space shuttles (that's your subject)
It is false that the connotations of a word have little effect on its literal meaning. Connotation are your personal feelings that a certain word evokes when you think about it/read it/write it.
For example, the word home means a house, but its connotation is usually positive - you connect it with love, warmth, etc.