drinkable water and 420 man-days of food. Before Skylab 4 left they did one more boost, running the Skylab thrusters for 3 minutes which added 11 km in height to its orbit. Skylab was left in a 433 by 455 km orbit on departure. At this time, the NASA-accepted estimate for its re-entry was nine years. The studies cited several benefits from reusing Skylab, which one called a resource worth "hundreds of millions of dollars" with "unique habitability provisions for long duration space flight". Because no more operational Saturn V rockets were available after the Apollo program, four to five shuttle flights and extensive space architecture would have been needed to build another station as large as Skylab's volume. Its ample size – much greater than that of the shuttle alone, or even the shuttle plus Spacelab – was enough, with some modifications, for up to seven astronauts of both sexes, and experiments needing a long duration in space; even a movie projector for recreation was possible. Proponents of Skylab's reuse also said repairing and upgrading Skylab would provide information on the results of long-duration exposure to space for future stations. The most serious issue for reactivation was attitude control, as one of the station's gyroscopes had failed and the attitude control system needed refueling; these issues would need EVA to fix or replace. The station had not been designed for extensive resupply. However, although it was originally planned that Skylab crews would only perform limited maintenance, they successfully made major repairs during EVA, such as the Skylab 2 crew's deployment of the solar panel and the Skylab 4 crew's repair of the primary coolant loop. The Skylab 2 crew fixed one item during EVA by, reportedly, "hit[ting] it with [a] hammer". Some studies also said, beyond the opportunity for space construction and maintenance experience, reactivating the station would free up shuttle flights for other uses, and reduce the need to modify the shuttle for long-duration missions. Even if the station were not crewed again, went one argument, it might serve as an experimental platform. Shuttle mission plans The reactivation would likely have occurred in four phases: An early Space Shuttle flight would have boosted Skylab to a higher orbit, adding five years of operational life. The shuttle might have pushed or towed the station, but attaching a space tug – the Teleoperator Retrieval System (TRS) – to the station