Commercial Orbital Transportation Services (COTS) was a NASA program to coordinate the delivery of crew and cargo to the International Space Station by private companies. The program was announced on January 18, 2006 and successfully flew all cargo demonstration flights by September 2013. NASA has suggested that "Commercial services to ISS will be necessary through at least 2015." COTS is related but separate from the Commercial Resupply Services (CRS) program. COTS relates to the development of the vehicles, CRS to the actual deliveries. COTS involves a number of Space Act Agreements, with NASA providing milestone-based payments. COTS does not involve binding contracts. CRS on the other hand does involve legally binding contracts, which means the suppliers would be liable if they failed to perform. Commercial Crew Development (CCDev) is a related program, aimed specifically at developing crew rotation services. It is similar to COTS-D. All three programs are managed by NASA's Commercial Crew and Cargo Program Office (C3PO).