Other pressures on O'Neill's colonization plan were the high cost of access to Earth orbit and the declining cost of energy. Building solar power stations in space was economically attractive when energy prices spiked during the 1979 oil crisis. When prices dropped in the early 1980s, funding for space solar power research dried up. His plan had also been based on NASA's estimates for the flight rate and launch cost of the Space Shuttle, numbers that turned out to have been wildly optimistic. His 1977 book quoted a Space Shuttle launch cost of $10 million, but in 1981 the subsidized price given to commercial customers started at $38 million. A 1985 accounting of the full cost of a launch in 1985 raised this as high as $180 million per flight.