PLANNING THE END

Even as STS-117 continued the construction of ISS, NASA was thinking about its end. Under the original plan for the present ISS configuration, as defined in the Memorandum of Agreement signed by all ISS partners, the station was intended to be operational until 2016, at which time it would be de-orbited in such a way that any items that survived re-entry would fall harmlessly into the Pacific Ocean. To achieve that end, NASA had originally planned to dock a Shuttle to the station and use its thrusters to fire the de-orbit burn. As the operational portion of the programme was continually delayed the possibility of operating ISS beyond 2016 came under discus­sion, but the 2016 end date remained as a NASA budget planning tool. Recently, NASA had been openly talking of funding and operating ISS beyond 2016 (which had always been a distinct possibility), but now the Shuttle was due to stop flying in 2010, so it would no longer be available to de-orbit the ISS at the end of its operational life.

In mid-2007, one possibility that NASA was considering to replace the Shuttle in the vital ISS de-orbiting role was the ESA ATV. In the plan NASA would purchase an ATV and its Ariane-V launch vehicle from ESA. When the final flight was required ESA would launch the ATV for NASA and fly it to a docking with Zvezda’s wake. The ATV’s thrusters would then be used to perform the de-orbit burn, bringing ISS down as planned, with any surviving debris falling in the Pacific Ocean.

ESA’s original contract was for six ATVs, but only five ATV launches were currently shown on the ISS launch manifest up to 2016. If the sixth vehicle was not built, ESA would suffer financial penalties. The NASA de-orbit plan, which offered a possible customer for the sixth ATV, was raised during discussions between NASA and ESA regarding ATV launch schedules which had been subject to numerous delays.

As the negotiations continued, the first ATV launch was due in January 2008. Jules Verne, the first ATV, was undergoing pre-flight review in Noordwijk, Holland, to clear it for shipping to the Ariane-V launch site in Kourou, French Guiana.

One major problem with the ATV de-orbit plan lay in the fact that NASA was now budgeting for America’s continued use of ISS, using the proposed Orion spacecraft, through 2020. ESA could not promise to fund the ATV and Ariane-V programmes, with their associated infrastructure through 2020, if the fifth and final ATV cargo delivery flight was scheduled for 2016. Meanwhile, ESA was reviewing the computers to be used on the ATV, which were the same as those that ESA had supplied for Zvezda.