Thanks for your question. We also were concerned about SD card memory. So, for both Arduino Uno devices, a 16GB SD card was used. The Nano Logger kit came with a 1GB SD card.
We did some calculations and incorporated them into our Final Design Decision post here:
In short, in order to determine if a 16GB SD card was appropriate for use, we wanted to know how long a 16GB SD card would last, assuming that data was collected continuously. It was concluded that 16GB would last for about 8 years. This is more than enough as the MROC won’t be on and recording data for 8 years straight. In fact, we decided that a 1GB SD card would suffice.
The data logger doesn’t record information when the MROC is powered off; therefore, no information is appended to the SD text file. Also, the logger does have the ability to collect information over extended time periods, but the children won’t be using the MROCs continuously, and it is likely that they will only use the vehicle for a few years as they may grow out of it.
Right now, the logger records information every second. However, we are working to program the device to document only when a case begins and ends. This will eliminate much of the unneeded data within the text file and consume less storage.
Hope this answered your question!