If we have already downloaded this when it was first released for free do we have to pay for each new update?
A nuclear conflict simulation and visualisation tool · By
If you payed anything, even one cent, you should have received a link which will make all future updates available. If you downloaded it without donation, then yes you will have to pay, but you will have access to all future updates.
If you absolutely cannot afford it or need it for uni and its complicated to purchase it, write me an email and I will send you a download link.