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Sub-orbital spaceflight (527 words) |
 | A sub-orbital spaceflight (or sub-orbital flight) is a spaceflight that does not involve putting a vehicle into orbit. |
 | Sub-orbital flights have been undertaken to test spacecraft and launch vehicles intended for later orbital flight, but some vehicles, such as the X-15 and SpaceShipOne have been designed exclusively to reach space sub-orbitally. |
 | Sub-orbital flights are appealing because it is very much easier to reach space (which simply means going higher than the edge of space) than to achieve orbit (which requires a velocity of about 18,000 mph). |
| Project Mercury - A Chronology. Part 3 (A) (7676 words) |
 | Overall, the flight was highly successful: the Atlas booster performed well and demonstrated that it was ready for the manned flight, the spacecraft systems operated well, and the Mercury global tracking network and telemetry operated in an excellent manner and was ready to support manned orbital flight. |
 | Especially relevant to manned space flight were its measurements of solar radiation in high frequency ranges, of cosmic dust effects, and of the thermal properties of spacecraft surface materials. |
 | Flight and ground tests disclosed that retrorocket heater blankets were unnecessary to the spacecraft, and this item was removed. |