I've run Traveller at many conventions over the years (I started DMing at conventions in 1979 - gulp!) and I agree with Gypsy Knight Games that Traveller is a very easy system to introduce to players.
I've never been to Origins (it's a bit far from the UK), but if it is like the UK and European conventions the slots are generally too short to include character generation. I've always used pregens and I've never had a complaint yet. However, I will say that players will always
expect their characters to have gun combat skills (or maybe that's a UK player thing
The first thing I ask the players when they sit down is who has played Traveller before. If everyone has, we can just get into the scenario. If not (or if there are any who have played TNE, which uses different rules) I find a quick scene to introduce the players to how the rules work is useful. It helps them make sense of their characters and gets them into the mindset for playing. Think something like the teaser scenes at the start of most James Bond movies.
Generally I find the hardest thing to get players to understand is the damage rules, so I usually make a point of guiding them through it again the first time a PC is hit.
Don't have anything that involves the players being captured. Unlike home games, players tend not to get too attached to convention characters and will fight to the bitter end rather than give in to NPCs...
While you can use any scenario for Traveller (as long as it fits into the slot length, obviously), I usually try to run something which has a little bit of spaceship action and a little bit of ground action to show off the scope of the system and background. I also have some extra scenes in my notebook in case things run really quickly - although I find that convention players can make the simplest scenarios overcomplicated.
Another thing I've found especially good for convention games is giving the players lots to look at - starmaps, ship deck plans, prop letters, etc. That really seems to focus their attention on the game (it looks good to passers-by too).
Be sure of your scenario before you run it at a show. Run through it at home a couple of times and make sure you know the more obvious points where the players might go off-map. They will still surprise you (which is a lot of the fun) but you can prep for a lot of things. If you want someone to look over your scenario for you, I'd be happy to help.
Finally, enjoy it. It's supposed to be fun for you too. I like it best when the players get up from the table smiling. Even better if they get up from the table and go to the trade area to buy the rules, but that's a rarer pleasure.
Good luck and let us know how it goes.