My university sent out a mass email about a research opportunity for STEM students of a specific gender. The research involves a number of engineering and science concepts, but has absolutely no relation to gender, and there is no obvious reason why a male and a female would not be equally qualified for the opportunity. However, the research posting made it very clear that only female students are welcome to apply for this project. The position is unpaid but could seriously boost a selected candidate's career prospects due to the affiliation with the University and with NASA (the program head is a NASA engineer and the program utilizes NASA resources). Is this legally defensible?