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Comment #3677837 by Tom Kenny

Tom Kenny Apr 15th 2015, 8:34 AM #

That works out that it will be traveling at approx 2170 mph. Can some knowledgeable person explain (in lay mans terms) why it is not possible to travel at 10 times this speed. With no atmosphere I always imagine building momentum should be easily done ?

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An Irish company's product will become the closest man-made object to the Sun

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    Favourite Ronan Fahy
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    Apr 15th 2015, 8:45 AM

    It doesn’t travel in a straight line it has to break earth orbit and then loop towards solar orbit in such a way that it can slow down enough when it gets there not to fall straight into the sun. So the distance covered is not just the straight line path from here to there. Think of it as like how you walk at the same speed after a night out but it takes you twice as long to get anywhere since you’re zigzagging all over the place… You’ve also got the problem of the fuel needed to produce acceleration and deceleration on a straight line path being impractical in terms of launch weight etc.

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    Favourite Tom Kenny
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    Apr 15th 2015, 8:58 AM

    thank you

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    Favourite Tom Kenny
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    Apr 15th 2015, 9:07 AM

    Would it not be possible to use the energy of the sun to power it, also I thought most satellites etc were carried into space free of earths gravity, thus removing the need for a big load of fuel ?
    I know it’s my imagination and I understand they do every minute thing for a reason.
    I suppose really what I don’t comprehend is why it requires much energy to build and reduce momentum in empty space.

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    Favourite Ronan Fahy
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    Apr 15th 2015, 9:25 AM

    Think of it this way – Earth is orbitting the sun meaning the sun’s gravity manages to keep something as big as the whole planet in its grasp. Earth needs to keep moving at the fairly enormous speed it’s moving, around the sun, in order to stay the same distance away (more or less). Same with the space station in orbit – it has to keep trying to travel really fast in a straight line in order to counter the pull of gravity from earth. So when this probe launches, the rocket that carries it works really fecking hard to get it off earth into orbit, then either the rocket or another stage of the rocket works really fecking hard again to reach escape velocity and break out of earth orbit. If it tried to go straight up, the energy requirements to break orbit would be immense. So they don’t go straight up they swing round and round in a ellipse going faster and faster and consequently higher and higher until eventually they are high enough and fast enough that they can break away from the influence of earth orbit BUT at that point all that happens is the influence of the sun takes over – remember it’s holding something the size of the planet in orbit no problem, so imagine what would happen if the little rocket tried to point itself straight at the sun, it would just get pulled in faster and faster and then you have the same problem in reverse – it has to try fight the pull of the sun’s gravity in a straight line. So again, instead it angles in in an ellipse, lower and lower until it gets to a point where its speed in a “straight” line and the pull of the sun’s gravity counter each other and it’s stable. We don’t have the technology at the moment to build propulsion systems that can do this. The other thing to think about is that not only is the earth moving around the sun but the sun is moving around the galaxy and the galaxy is moving outward in the universe so there’s no concept of standing still in space, all motion is relative to something else. Even going in a straight line at the sun, if it was feasible, the probe would still be moving sideways at some mental speed, since it launched from a planet that was itself hurtling around in circles.

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    Favourite Hipster Enda
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    Apr 15th 2015, 10:07 AM

    “it can slow down enough when it gets there not to fall straight into the sun.”

    This is not true. It’s speed it exactly what stops it falling into the sun. In reality once it leaves Earth orbit it’s major sphere of influence is the sun and the satellite is travelling at much the same speed as the Earth. A retrograde rocket will be fired to slow the satellite which will set it on a orbital path closer to the sun. A prograde rocket will need to be fired to speed the satellite up to stop it falling into the sun. A orbital mechanics is a bit counter intuitive until you think about it in terms of escape velocities.

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    Favourite Ronan Fahy
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    Apr 15th 2015, 11:54 AM

    actually now that i think about it you’re right in the sense of orbital velocity – the closer you go to the thing you’re orbitting the faster you must move to stay there without gravity pulling you down. But in order to get there, you would slow down in order to drop you to a lower orbit whereupon you speed up again to stay there. In any event I was trying to highlight the difference between an orbital route and a vertical descent straight at whatever it is you’re aiming for

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