The 502SSD is being replaced by the 502MFC. Expected availability is 7/15/17.
502MFC - Multi-Function I/O Shield
The 502MFC, designed and manufactured by PI 2 Design, is a professional Raspberry Pi I/O Shield designed for Embedded apps such as Machine Control, Robotics and more. The shield converts one RPi USB Host Port to two high power (5V@1A) USB Host Ports, two 2Mbps UART’s and an mSATA Socket for Solid State Storage up to 1TB.