Work on the roof had begun for a maintenance project, whose equipment is thought to have contributed to the collapse. Also, before the day of collapse, there had been several days of heavy rain. Revival possibilities Over time, several scientists looked into trying to revive the Buran program, especially after the Space Shuttle Columbia disaster. The 2003 grounding of the U.S. Space Shuttles caused many to wonder whether the Energia launcher or Buran shuttle could be brought back into service. By then, however, all of the equipment for both (including the vehicles themselves) had fallen into disrepair or been repurposed after falling into disuse with the collapse of the Soviet Union. In 2010 the director of Moscow's Central Machine Building Institute said the Buran program would be reviewed in the hope of restarting a similar crewed spacecraft design, with rocket test launches as soon as 2015. Russia also continues work on the PPTS but has abandoned the Kliper program, due to differences in vision with its European partners. Due to the 2011 retirement of the American Space Shuttle and the need for STS-type craft in the meantime to complete the International Space Station, some American and Russian scientists had been mulling over plans to possibly revive the already-existing Buran shuttles in the Buran program rather than spend money on an entirely new craft and wait for it to be fully developed but the plans did not come to fruition. On the 25th anniversary of the Buran flight in November 2013, Oleg Ostapenko, the new head of Roscosmos, the Russian Federal Space Agency, proposed that a new heavy-lift launch vehicle be built for the Russian space program. The rocket would be intended to place a payload of in a baseline low Earth orbit and is projected to be based on the Angara launch vehicle technology. Vehicles Energia launch vehicle Buran orbiter Antonov An-225 Mriya Energia liquid rocket booster Energia-Buran and the US Space Shuttle Comparison to NASA's Space Shuttle Because Buran debut followed that of , and because there were striking visual similarities between the two shuttle systems—a state of affairs which recalled the similarity between the Tupolev Tu-144 and Concorde supersonic airliners—many speculated that Cold War espionage played a role in the development of the Soviet shuttle. Despite remarkable external similarities, many key differences existed, which suggests that, had espionage been a factor in Buran development, it would likely have