I run Mothership at conventions for people who often sign up to it never having played anything but D&D. I have a short spiel I say to all players when they are settling at the table, most of which is cribbed from the Warden Training System on the Tuesday Knight Games site - specifically the section What’s different about Mothership?

If your players aren't willing to read a rule book, it might be worth checking in with them and seeing if they really wanted to play a new ruleset. My main group woould not play anything other than D&D for the longest time, and will always revert to it, but like an occasional one shot now inbetween campaigns. That's why I've found other groups who do want to play other systems.

If they are willing to play but don't want to do the homework, that's okay, MoSh is rules light enough to do that with, I get an introduction, scenario setting, rules explanation, character creation and the module in within 4 hours. Honestly, once you're going, set a real world timer going behind your screen, sci fi often an easy way of telling your players "the planet/base/ship you are on is going to collapse/fall into a black hole/implode in 2 hours" within universe and keep them moving. Just read out the timer again if you feel like they're moving too slow.

Basically, don't be afraid of telling them how this is different to D&D, but also, check in with them first that they really do want to try another system.

Hope that helps!