http://www.nasa-se.com/2017HolidayPromotion.php
If you pay for events early, you can get them at a big discount. Historically, this offer is good only until 31Dec. The way to do this smart is to pay early for a bunch of the events in the first half of the year, but don’t pay early for events late in the year. The reason for this is that you can’t move these credits to 2018, so if you have to miss some 2017 events that you paid for early, you’ll want to be able to move those credits to late 2017 events.