Most  segments of ISS cannot be delivered by any other vehicle. The Retirement of the Shuttle Poses Challenges to NASA’s Ability to Complete the International Space Station

It will be a challenge for NASA to complete the space station by 2010 given  the compressed nature of the schedule, maintenance and safety concerns,  as well as events beyond its control such as weather. Shuttle Flight Schedule Is Aggressive

In our July 2007 testimony, we reported that NASA planned to launch a  shuttle once every 2.7 months. NASA has launched shuttles at this rate in the past. The two contingency flights  of the shuttle have been designated to deliver these key replacement units,  which only the shuttle is capable of carrying. This includes elements needed  for the planned configuration to complete the station and delivery of  critical spares. Alternative Vehicle Options to Service the International Space Station Pose Challenges

In the event that NASA completes assembly of the ISS on schedule and  prepositions an adequate number of critical spares, the agency still faces a  myriad of challenges in sustaining the research facility until its retirement,  currently planned for fiscal year 2016. NASA will rely on an assortment of vehicles in  order to provide the necessary logistical support and crew rotation  capabilities required by the station. From the Columbia disaster in 2003 until return to flight  in 2005, the Russian vehicles were the sole source of logistical support and  crew rotation capability for the station. The new vehicles being developed by the European and Japanese space  agencies are very complex. The  Japanese vehicle is still under development and has faced some setbacks. NASA officials told us that the HTV’s first test launch is planned for July  2009.

		International Partner Vehicles Have Constraints in Ability to Ferry Crew and Cargo to and from the ISS in Comparison to the Shuttle

In addition to potential development challenges, the international partner  vehicles have constraints in terms of what they can take to and from the  ISS in comparison to the shuttle. NASA’s current plans to manage the gap  after the shuttle retirement do not take into account the possibility of  delays in the development of these vehicles, and even if they do come on  line on time, NASA officials estimate that there will be a significant  shortfall to the ISS of at least 114,199 pounds (or 51.8 metric tons) in cargo  re-supply capability. These vehicles were designed to augment the  capabilities of the shuttle and have significantly less capability to deliver  cargo to the ISS. Commercial Vehicles

NASA is working with the commercial space sector through its  Commercial Orbital Transportation Services (COTS) program to develop  and produce vehicles that can take equipment and crew to and from the  space station. NASA expects that these vehicles will be ready for cargo use  in 2010 and crew use in 2012. However, these vehicles have yet to be  successfully launched into orbit, and some NASA officials have  acknowledged that their development schedules leave little room for the  unexpected. Ultimately, NASA’s aggressive schedule  leaves little room for the unexpected. The  shortfall may well impact support for a six person crew and the quality of  research that can be conducted on the ISS. To determine the risks and challenges NASA faces in providing logistics  and maintenance support to the International Space Station after 2010, we    analyzed documents related to the up-mass and down-mass capabilities of  the International Partners and SpaceX vehicles, the shortfall in ISS up- mass for re-supply and sustainment, the new vehicles that will support ISS  NASA’s plans for using Russian vehicles to support ISS through what  NASA refers to as its “exemption,” and the impacts to the utilization of the  ISS.
Why GAO Did This Study

The International Space Station (ISS), the most complex scientific space project ever attempted, remains incomplete. NASA expects the station's final construction cost will be $31 billion and expects sustainment costs through the station's planned retirement in fiscal year 2016 to total $11 billion. The space shuttle, the only vehicle capable of transporting large segments of the station into orbit, is critical to its completion. NASA plans to complete ISS assembly and retire the shuttle in 2010 in order to pursue a new generation of space flight vehicles, which will not begin to be available until 2015. To provide crew rotation and logistical support during this 5-year gap, NASA plans to rely on spacecraft developed by the commercial sector and other countries. In light of these circumstances, GAO examined the risks and challenges NASA faces in (1) completing assembly of the ISS by 2010 and (2) providing logistics and maintenance to the ISS after 2010. GAO's work to accomplish this included reviewing budget, planning, and other documents from NASA; reviewing NASA officials' testimonies; and interviewing NASA and foreign space program officials.

What GAO Found

NASA faces significant challenges in its plans to complete assembly of the International Space Station (ISS) prior to the scheduled retirement of the space shuttle in 2010. Since GAO testified on this issue in July 2007, the shuttle flight schedule has remained aggressive--slating the same number of launches in a shorter period. While NASA thinks the proposed schedule is still achievable, the schedule (1) is only slightly less demanding than it was prior to the Columbia disaster when the agency launched a shuttle every other month with a larger shuttle fleet and (2) leaves little room for the kinds of weather-related, technical, and logistical problems that have delayed flights in the past. Unanticipated delays could result in changes to the station's configuration, that is, some components may not be delivered. We have previously testified that such changes could limit the extent of scientific research that can be conducted on board the ISS. After assembly is completed and the shuttle retires, NASA's ability to rotate crew and supply the ISS will be impaired because of the absence of a vehicle capable of carrying the 114,199 pounds of additional supplies and spares needed to sustain the station until its planned retirement in 2016. For crew rotation and logistics, NASA plans to rely on Russian, European and Japanese vehicles--these vehicles were designed to augment the capabilities of the shuttle, not replace them, and have far less capacity to haul cargo. Furthermore, aside from a single Russian vehicle that can bring back 132 pounds of cargo, no vehicle can return cargo from the ISS after the shuttle is retired; and Commercially developed vehicles--NASA has pledged approximately $500 million for the development of commercial vehicles. NASA expects these vehicles will be ready for cargo use in 2010 and crew use in 2012, even though none of the vehicles currently under development has been launched into orbit yet and their aggressive development schedule leaves little room for the unexpected. If one of these vehicles cannot be delivered according to NASA's current expectations, NASA will have to rely on Russian vehicles to maintain U.S. crew presence on the ISS until the new generation of U.S. spacecraft becomes available.