... very good introduction :)
I would talk more about space, and how much is being used to fund the space program, but I like how you are saying facts. I would not spend a whole paragraph talking about AIDS also.
Yes, I too agree... Your introduction is superb. However, your body paragraphs do not really deal with the task that prompt has given you. You need to tackle why it is unethical to spend such large amounts on space exploration. Your reasons are fine, but you need to have a better connection with the topic.
You have excellent writing skills. I think you are preparing for IELTS or TOEFL. If so, you really don't have to worry about this task. Also, one small request - please open this type of essays in Writing Feedback forum.