Changing the orbit of a satellite, minimum rocket burns.

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Discussion Overview

The discussion centers around the mechanics of changing the orbit of a satellite, specifically focusing on the minimum number of rocket burns required to rotate the major axis of an elliptical orbit by 90 degrees while maintaining the same energy level. The scope includes theoretical considerations of orbital mechanics and energy efficiency in propulsion methods.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes that two rocket burns are necessary: one to slow down the satellite at closest approach to circularize the orbit and another to speed up the satellite 90 degrees later.
  • Another participant suggests that while the initial method may be energy-efficient, it is possible to achieve the desired orbital change with a single short burn at various points along the orbit, depending on the desired outcome.
  • A later reply discusses the relationship between impulses acting on a satellite and the resulting changes in orbit, noting that there are impulses that can change both energy and orbit, and those that only change the orbit.
  • One participant confirms that applying a force perpendicular to the satellite's velocity does not change its energy, which is a key point in understanding orbital mechanics.

Areas of Agreement / Disagreement

Participants express differing views on the number of burns required and the methods for achieving the orbital change. There is no consensus on the optimal approach, and multiple competing strategies are presented.

Contextual Notes

The discussion involves assumptions about the nature of orbital mechanics and the specific conditions under which the satellite operates, including the definitions of energy and orbit changes. The implications of different burn strategies on energy conservation are also considered but not resolved.

Who May Find This Useful

This discussion may be useful for those interested in orbital mechanics, satellite propulsion strategies, and the theoretical aspects of energy conservation in space dynamics.

Spinnor
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Suppose we have a satellite in an elliptical orbit around the Earth with the major axis pointed towards some fixed point in the heavens. What is the minimum number of rocket burns so that the major axis is rotated 90 degrees and the final and initial energy are the same. Is the number 2?

At closest approach to the Earth, slow down, one burn, orbit circular, 90 degrees later speed back up, one more burn or at farthest approach speed up, 90 degrees later slow down, again two burns?

Thanks for any help!
 
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While your way might be the most energy-efficient method: You can accelerate at other points, too, achieving every orbit which intersects the old orbit in one point, with a single, short burn. With a longer time for the acceleration, you can reach non-intersecting orbits, too.
 
mfb said:
While your way might be the most energy-efficient method: You can accelerate at other points, too, achieving every orbit which intersects the old orbit in one point, with a single, short burn. With a longer time for the acceleration, you can reach non-intersecting orbits, too.

Thank you mfb! I have to think about the above. This problem I think is related to a similar problem, given a 2 dimensional harmonic oscillator that has some "orbit", what impulses acting on the "point mass" change the orbit? Seems like there are 2 classes of change? Impulses that change the energy and orbit and impulses that only change the orbit?

If I always "push" on a satellite perpendicular to its velocity then I don't change the energy, right?

Thanks for any help!
 
impulses that only change the orbit?
That is just a special case in the whole range of energies which can be reached.

If I always "push" on a satellite perpendicular to its velocity then I don't change the energy, right?
Right
 

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