Flying across the ocean is no small feat. It takes the concerted efforts of dozens of people, working hard at lots of difficult problems, from modeling balloon volume and flight dynamics, to planning interactions with air traffic control. The diagram above gives a little bit of an idea of the effort involved in getting across the ocean. Any single block represents tens to many hundreds of man-hours worth of effort.
Components in Purple represent things which will actually be flying across the ocean. This hardware and software must perform flawlessly at all times. Components with a red heptagon represent significant software efforts. The red square shows the components which lie on amazon EC2, spread across three instances, with a total cost of $100 a month (during flight season) to maintain. Pink commands are sent using PubNub, a service without whose generosity our public page would not be possible.
All of these systems are in the critical path, and a failure of any single flight system will compromise science data. Fortunately, we always have positive control of our craft, thanks to a dead-man cutdown, which operates entirely autonomously, and a 9602 modem which will respond with rough location coordinates even if all other flight systems have failed. Our ground systems all have hot-backups, and can all be operated from anywhere on the Internet, so these systems are as redundant as they can be.