nrh - 30/3/2008 5:31 PM
No flights with this upgraded version since Progress M1-11 (13P) in '04
As I understand this version can carry more fuel that the M series. Is that on the expence of dry cargo?
No, it is primarily at the expense of water. Since the shuttle fuel cells generate water as a byproduct of electricity generation, the space shuttle was to deliver all water to ISS, hence the development of the Progress M1 which replaced the water tanks with additional fuel.
After the Columbia accident, Russia reverted to the Progress M to deliver water to ISS while the shuttle fleet was grounded. Perhaps they could have reverted to the M1 after return-to-flight, but the announcement of shuttle retirement in 2010 has understandably made them reluctant to do so.