Why is it so hard to send humans back to the moon? 

 The Apollo program put humans on the moon in 1969. So why haven't we sent any more since? 

https://cdn.mos.cms.futurecdn.net/q3yhCiTsnCTfmhh3AcGyLF.jpg

https://www.space.com/why-is-getting-to-the-moon-so-hard