Simply put, you cannot get enough propellant on board to attain useful flight duration.
Or, rather, lengths, by setting a new US record for flight duration of 49.9 seconds with its Gamera II rotorcraft.
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But Mr Aldrin disagreed with the view that astronauts should test capabilities for a long-duration flight on the Moon before attempting a journey to Mars.
For the Space Shuttle, being a shorter-duration flight of just a couple of weeks, we still train for over one year just specifically on the task that we'll accomplish on our mission.
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And if the crew assigned to man the deep-space mission travels up separately to the station, it would also mean all the elements for their long-duration flight could be launched without the complications of ultra-safe abort systems that complicate manned rockets.
In busy airports, such as Detroit, Dallas-Fort Worth and Chicago's O'Hare, the number and duration of flight delays doubled.
And last year, defence firm Qinetiq flew a solar-powered plane for 54 hours, smashing the official world record for the longest-duration unmanned flight.
And that's a great question because one of the hard things about long-duration space flight is the human body dealing with weightlessness and a lack of gravity.
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"Once the passenger was restrained he sat calmly in the seat for the short duration of the flight, " Egan said.
For example, the Wales Office's travel and subsistence policy on air travel is governed by the airline's fare structure and the duration of the flight.
Just as airlines require passengers to turn off their mobile devices for the duration of the flight, the withdrawal is confined to a limited period.
For instance, InsideTrip awards different scores for the duration of a flight and the airline's on-time performance, its lost-luggage track record, even the amount of legroom aboard planes.
"To ensure the safety of those on board, he was restrained by passengers and crew and was monitored for his own safety for the duration of the flight, " he added.
Each time you jump while snowboarding or skying, the accelerometer data from the goggles is sent to the handset which posts a graphic to Facebook showing the distance, height and duration of your flight.
The digEplayer 5500 has a 7-inch 16:9 widescreen LCD and comes loaded with about 10 movies, a few TV shows, and over 100 songs, which should be more than enough to keep you busy for the duration of your flight, and is probably more than the poor battery can handle (heaven knows our laptop batteries are looking pretty low after just an hour and a half of watching DivX movies).
They collected data from commercial aircraft flight recorders, which record the location, duration and intensity of turbulence.
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