This is a follow-up on @DeerHunter's inquiry regarding Contacting space agencies PAO (public affairs' offices). Since we've more or less agreed there that it's about time we start sending invitations to our website to the greater space exploration, scientific and engineering communities out there, I was thinking it wouldn't go amiss having some readily made invitation letters, templates, or examples.
I'm fairly certain there already are some such texts prepared throughout Stack Exchange, but I am currently not aware of any. If you find links to such examples on Stack Exchange, then please post them as links and include a short description which cases you think it covers best, and post other invitation templates (your ideas, templates you can't link to because they'd need to be adapted to our use case,...) with their complete title and body as a new answer below. One answer per template - post more answers, if you have more ideas for invitation templates.
And just a reminder - please, do not spam people by sending unsolicited emails (or otherwise), and do not be too pushy! Take a template we'll post here, edit it to apply to your individual recipient, and make it personal. Remind them where you know them from, if that's needed. It will be received a whole lot better, if it doesn't look like another one of those massive recipient list emails. And do not use mailing lists or send invitations to people you do not know or don't expect they'd be interested, but wanted to send anyway for whichever alternative reasons. Thanks!