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B Question about suborbital flight and ballistic missiles

  1. Jan 20, 2017 #1
    Question on suborbital flight and ballistic missiles.

    When they are in space, past 100 km above the surface of earth where there is little air, when it's in the ballistic arc, past apogee does it slow down when it drops or speeds up due to gravitational acceleration without drag? I Am talking about the velocity heading to earth.
     
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  3. Jan 20, 2017 #2

    Drakkith

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    The radial velocity (the part of the velocity pointed towards/away from the Earth) increases as it falls back to Earth.
     
  4. Jan 20, 2017 #3
    So if the launch vehicles final boost is Mach 20 what decrease usually would it have at apogee? By the time it its almost about to reach the atmosphere does it going to Mach 20 again?
     
  5. Jan 20, 2017 #4

    Drakkith

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    Well, the vehicle is not going Mach 20 in a radial direction. Most of that is in a tangential direction. The radial velocity upon reentering the atmosphere is probably fairly small compared to the tangential velocity, but I really don't know an accurate number.
     
  6. Jan 20, 2017 #5
    What is the difference between radial and tangential?
     
  7. Jan 20, 2017 #6

    Drakkith

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    Radial heads directly away from a point, like how the spokes on a bicycle wheel head directly away from the hub.

    Tangential is basically the direction perpendicular to any of these spokes. Put simply, if we look at a spoke that runs straight up away from the hub, then the tangential direction is basically the directions straight left or right (or out and away, or any direction that runs perpendicular to the spoke).

    See this image for a visual.

    In short, radial is the up/down direction while tangential is the left/right direction if you're looking at the trajectory in 2d (like on a map or a graph).
     
  8. Jan 20, 2017 #7

    berkeman

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    Wikipedia gives a pretty good idea of the flight envelope of an ICBM...

    https://en.wikipedia.org/wiki/Intercontinental_ballistic_missile
     
  9. Jan 20, 2017 #8

    Janus

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  10. Jan 20, 2017 #9
    My question is are ascent speeds greater than descent speeds(before reentry) in a space enviornment. I am just talking about midcourse phase.
     
  11. Jan 20, 2017 #10

    berkeman

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    Now that you understand the radial and tangential components of vector velocity, and given that air resistance is very low in near-Earth space, what do you think happens to the speed of the projectile?
     
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