NASA will not ask Congress for permission to continue buying cargo space on Russian Progress resupply vehicles for the International Space Station (ISS) after 2011, opting instead for an all-commercial approach under its nascent Commercial Orbital Transportation Services (COTS) program.

Administrator Michael Griffin has sent a letter to Capitol Hill specifically excluding Progress from a request to continue using Russian Soyuz capsules to deliver crew to the ISS after the shuttle retires in 2010. Griffin had no immediate comment, but William Gerstenmaier, associate administrator for space operations, said April 16 that NASA believes one of the commercial vehicles in development under the COTS program will be able to meet its ISS-supply needs.

Until a COTS vehicle is available, Gerstenmaier said in an interview, NASA plans to rely on prepositioned spares to be sent up before the shuttle retires. Two "contingency flights" to the ISS are planned among the 11 remaining shuttle flights to deliver station spares too large to get to orbit on any other vehicle, he said.

"We recognized that there may be a little bit of a delay in the delivery of those [commercial] services," Gerstenmaier said. "Our plan is that if we have a delay we would live off the spares we flew up on shuttle and take some limited degradation in space station capabilities until those commercial services come on line." Under the COTS program, SpaceX and Orbital Sciences Corp. are splitting a pot of almost $500 million in NASA seed money intended to spur development of a commercial route to the ISS. Several other entrepreneurial space companies also have unfunded Space Act agreements with NASA for the data they need to develop station resupply capability. None of them, whether funded or not, is ready yet to demonstrate the ability to resupply the ISS.

In a request for proposals (RFP) published April 14, NASA says it intends to purchase transportation to the ISS for at least 20 metric tons of cargo between 2010 and 2015, when NASA's Orion crew exploration vehicle is scheduled to begin flying astronauts and cargo. Overall NASA expects to require delivery of 39.6 metric tons of pressurized cargo to the station during that same period, not counting bartered transportation services on Europe's new Automated Transfer Vehicle (ATV) and Japan's planned H-II Transfer Vehicle (HTV). Another 8.3 metric tons of external "upmass" will be required during the same period, according to an estimate published with the RFP.

NASA has been buying space transportation services from Russia under an exemption to the Iran, North Korea and Syria Nonproliferation Act that would otherwise prohibit the transactions. The exemption expires in the fall of 2011.

On April 11 the agency sent Congress a proposed amendment to the nonproliferation act designed to permit continued purchase of rides for U.S. space station crew members on Soyuz vehicles. But NASA's language specifically excludes "any cargo services provided by a Progress vehicle" and on Soyuz as well after Orion or a U.S. commercial provider begins delivering crews to the ISS.