So I did some poking around and found the 3rd edition Vassal module here: https://www.dropbox.com/sh/yx04l0yl1wquzek/AACzSW0w5eKPIClXrOr2Ta3na?dl=0
Vassalengine.org is where you go to download Vassal itself.
Oh and there’s an interesting technical note about the HF3E module here: https://boardgamegeek.com/thread/1399748/high-frontier-3rd-edition-vassal-module
There are also Cyberboard and Tabletop Simulator modules available but for various reasons I think I like Vassal the best.
Actually I should amend: I’ve fumbled around with Vassal before (for Fire in the Lake) and it’s semi-clear how things work, but it’s kind of alarming how manual all three versions are: you absolutely must know the rules yourself and there will be no automated auditing. I happen to have three monitors in my office so I can sprawl a dozen screens across them to contain all the game-state windows at once. Just like the analog version, it takes up a ton of space.
I’m fiddling with a solitaire game right now just to see if it’s tolerable. TBQH I kind of hate it, especially trying to suss out the board. Yes yes you can zoom in but jeez, route-finding on even a rather large monitor isn’t nearly as easy as doing it on the board.
I may in fact end up duplicating the gamestate with my physical copy, although you can’t see the card decks card-by-card I don’t think.
Anyway, gimme a couple days and I suggest others experiment as well. Then I’ll figure out how to set up a PBEM thing.