Commercial Orbital Transportation Services (COTS) was a NASA program to coordinate the development of vehicles for 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, when the program ended. NASA's Final Report on the Commercial Orbital Transportation Services program considers it an unqualified success and a model for future public-private collaboration. Compared to traditional cost-plus contracts employed by NASA, such as the $12 billion Orion (spacecraft) contract, the unprecedented efficiency of the $800 million COTS investment resulted in "two new U.S. medium-class launch vehicles and two automated cargo spacecraft". NASA signed COTS agreements with SpaceX and Rocketplane Kistler (RpK) in 2006, but later terminated the agreement with RpK due to insufficient private funding. NASA then signed an agreement with Orbital Sciences in 2008. Independently, NASA awarded contracts for cargo delivery to the International Space Station in December 2008, to Orbital Sciences and SpaceX to utilize their COTS cargo vehicles. COTS is related but separate from the Commercial Resupply Services (CRS) program. COTS related to the development of the vehicles, CRS to the actual deliveries. COTS involved a number of Space Act Agreements, with NASA providing milestone-based payments. COTS did 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). Purpose Unlike any previous NASA project, the proposed spacecraft are intended to be owned and financed primarily by the companies themselves and will be designed to serve both U.S. government agencies and commercial customers. NASA will contract for missions as its needs become clear. This is more challenging than existent commercial space transportation because it requires precision orbit insertion, rendezvous and possibly docking with another spacecraft. The private spaceflight vendors are competing for four specific service areas: Capability level A: External unpressurized cargo delivery and disposal Capability level B: Internal pressurized cargo delivery and disposal Capability level C: Internal pressurized cargo delivery, return and recovery Capability level D: Crew Transportation (was not funded, but formed the basis of CCDev) Program rationale NASA explored a program for ISS services