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Calculating relativistic effects of motion in solar system

  1. Aug 1, 2015 #1
    This question and answer are posed in Kim Stanley Robinson's novel "2312".

    My question is, is this all made up? Or might it be accurate?
  2. jcsd
  3. Aug 1, 2015 #2


    Staff: Mentor

  4. Aug 1, 2015 #3
    Interesting. The numbers are in the novel the way I typed them.

    Even though Pauline answered only the precession part of the question, I was fascinated by the possibility of the whole calculation. In recent years, NASA and other countries' space agencies have sent probes to Mars, asteroids and even a comet. But I think they all had thrusters to do course corrections along the way.

    But if you throw a rock at Mercury from the asteroid belt, how would you calculate (even in theory) the direction and speed to make it hit a specific spot after a year's travel--with no mid-course corrections!?
  5. Aug 2, 2015 #4


    Staff: Mentor

    They did, but the course corrections are very small; a probe can't carry enough fuel to make large course corrections, so it has to be launched very accurately to begin with. The course corrections are not always needed, but NASA allows for the possibility to be safe.

    You would have to know the precise positions of the asteroid, the Sun, and the planets at launch, so you could compute the rock's trajectory to the required accuracy. It's tedious, but straightforward; you start out with the asteroid and Mercury moving in the field of the Sun as your first approximation, then just add in effects of other planets until you've taken into account every effect that's large enough to matter. Nowadays computers would do all the grunt work anyway.
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