<em>If someone is not above doing something, they are prepared to do it, even if it is something usually done by someone of a lower status, or even if it is wrong. I'm not above doing <u>my own cleaning.</u> He is not above telling a few white lies. See also: above, not, something.</em>
The word astronauts in the sentence is functioning as the direct object.
Direct objects are often a noun phrase that refers to a person or thing that <u>receives</u> the action of the verb. In order to spot a direct object within a sentence, remember to ask yourself “who” or “what” is receiving the action. The answer in this case would be: <em>"the austronauts". </em>