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Slow Space Travel

  1. Sep 30, 2012 #1
    Hello. Thanks for previous responses. I asked a question about developing a vehicle that 'flies' in a vacumn instead of a rocket. Apparently the issue with space travel is the required speed. Not distance travelled per se above the Earth's surface or the fact that the vehicle has to travel thru a vacumn....per se.

    I might have further questions in the future.
    Bye
    SC
     
  2. jcsd
  3. Sep 30, 2012 #2

    phinds

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    2016 Award

    So you are talking about a solar sail?
     
  4. Sep 30, 2012 #3

    Astronuc

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    The bolded statement is a bit confusing. A vehicle in space usually requires propulsion (from a rocket) unless it has enough velocity to coast to it's destination.

    For spacecraft from the earth's surface to orbit, the rocket must provide sufficient thrust to overcome gravity (weight of the vehicle) and drag in the atmosphere while providing accelertion to orbital velocity - assuming that one wishes to achieve orbit. Then it is a matter of climbing the rest of the way out of earth's 'gravity well', and then getting up to a velocity to travel to some other destination.

    Time to destination is an issue for manned flights because of the deleterious effects of radiation exposure and 0-gravity. The time is a function of distance and velocity, and the achieve velocity is dependent on the acceleration, which is dependent on the thrust and mass of the craft (including expendable propellant). Thrust efficiency is expressed as specific impulse and ultimate that is dependent on the propulsive technology and specific energy, kJ/kg (or specific power, kW/kg) of the propuslive and power generation systems.

    Solar sails or the like are attractive since no on-board propellant is necessary, but the acceleration is so low, that is takes a long time to get going. The momentum imparted from photons or solar particles is rather low. The pressure from the solar wind is on the order of 1 nPa.

    Ref: http://www.swpc.noaa.gov/SWN/sw_dials.html [Broken]
    http://www.srl.caltech.edu/ACE/ace_mission.html#summary
    http://web.mit.edu/space/www/helio.review/axford.suess.html
     
    Last edited by a moderator: May 6, 2017
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