I just tried my best to put the comments as my knowledge allow me to do:
1- The length of your essay is better to be longer, maybe from 426 word which it is now, to 600 words, at least.
2- I like your range of vocabulary, they will work.
3- I wish to see your side and thesis more clearly than it is as: " The question is whether is it worth spending so much to see space as venue for future scientific discoveries rather than directing such funds towards humanitarian science projects?" you didn't refer directly to the statement but provide your side per your hypothetical situation. maybe as: " the statement represent a view which I am not fully agree/ or agree with for the reason of ta ta ta..." refer directly to flaws in the statement.
4- your introductory part is mostly discuss about the space exploration and nothing about the humanitarian issues... and I did not find a good transition to your thesis.
5- I like your examples but the flow of your examples is not provided properly. It is better to expand one example in more detail in the other body paragraphs. avoid providing several unrelated examples. It will confuse the readers.6- I did not sense a good critical language which put both side of the issue in front of each other. Also you can take advantage of a concession points to be explainedas a separate paragraph.