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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| North American DC-3 | 4/5 | https://en.wikipedia.org/wiki/North_American_DC-3 | reference | science, encyclopedia | 2026-05-05T13:21:41.394188+00:00 | kb-cron |
=== End of DC-3 === The new cross-range requirements doomed the DC-3 design. Satellites orbit around the center of the Earth, not the surface. If a spacecraft were launched due East from the equator into a 90-minute low Earth orbit, it will circle the Earth and return to the spot where it was launched 90 minutes later. However, the launch site will have moved due to the Earth's rotation. Over the 90-minute period, the Earth would rotate 2,500 kilometres (1,600 miles) to the east, escaping from the spacecraft as it returns. Given the orbital speed about 28,000 kilometres per hour (17,000 mph), simply starting the re-entry about 5 minutes later than the complete 90-minute orbit would make up this difference. At Kennedy Space Center's 28.5° north latitude the situation is more complicated. Over the 90-minute orbit KSC will rotate about 1,350 miles (2,170 km). Unlike the equatorial orbit case, however, letting the spacecraft stay in the inclined orbit a little longer will start taking it south of the launch site (for the most efficient launch eastward, where the orbital inclination is equal to the launch latitude, making the launch point the most northerly of its ground path), its closest point of approach being about 300 miles (480 km) to the southwest. A spacecraft wishing to return to its launch site will need about 300 miles of cross-range maneuverability during re-entry, and the NASA shuttle designs demanded about 450 miles in order to have some working room. Polar orbits from the Air Force's Vandenberg Air Force Base are another matter entirely. At almost 35° N, the distance it would move over a single orbit would be slightly smaller than KSC, but critically, the shuttle would be traveling south, not east. This meant that it was not flying toward the launch point as it traveled in its orbit, and when it completed one orbit it would have to make up the entire 1,350 miles during re-entry. These missions required a dramatically improved cross-range capability, set at 1,500 miles to give it a slight reserve. The ballistic re-entry profile of the DC-3 series simply could not come close to matching this requirement. On 1 May 1971 the OMB finally released a budget plan, limiting NASA to $3.2 billion per year for the next five years. Given existing project budgets, this limited any spending on the shuttle to about $1 billion a year, far less than required to develop any of the completely reusable designs. Based on these constraints, NASA returned to a Class II-like vehicle with external tankage, which led to the MSC-020 design. Later that year all straight-wing designs were officially abandoned, although Faget's team continued to work on them for some time in spite of this.