Continuous thrust orbit changes

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Discussion Overview

The discussion revolves around the concept of making continuous thrust orbit changes, specifically focusing on how to increase the radius of a circular orbit using a small constant thrust. Participants explore the implications of applying thrust tangentially and seek to understand the rate of change of the orbit's radius over time, considering various parameters of the orbit.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the traditional assumption of impulsive changes in velocity and proposes a scenario involving continuous thrust to increase orbital radius.
  • Another participant suggests using free body diagrams (FBD) and the third law of motion to approach the problem, implying a technical method for analysis.
  • A participant references an ongoing thread about the Dawn spacecraft, which is using an ion engine to alter its orbital radius, suggesting that this real-world example could provide insights into the discussion.
  • One participant reiterates the initial question about the effect of small constant thrust on orbital radius and mentions the conservation of energy and angular momentum as key factors in understanding the dynamics involved.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as multiple viewpoints are presented regarding the application of thrust and the analysis methods. The discussion remains open-ended with various approaches being suggested.

Contextual Notes

Participants mention the importance of energy and angular momentum conservation in the context of thrust application, but the specific mathematical relationships and assumptions underlying these concepts are not fully explored or resolved.

ScramjetCCO
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Most threads about making orbit changes assume impulsive changes in velocity (short period bursts). What if one wants to increase the radius of a circular orbit with a very small constant thrust? I assume the thrust should be applied tangentially in the direction of travel, but what would be the rate of change of the orbit's radius be at any point in time given the acceleration applied and the other parameters describing the orbit at that time?
 
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k61.jpg

You may look at FBD and do 3rd Law. The solution should not be far from there.
 
ScramjetCCO said:
Most threads about making orbit changes assume impulsive changes in velocity (short period bursts). What if one wants to increase the radius of a circular orbit with a very small constant thrust? I assume the thrust should be applied tangentially in the direction of travel, but what would be the rate of change of the orbit's radius be at any point in time given the acceleration applied and the other parameters describing the orbit at that time?
You can keep track of energy and angular momentum. Both are conserved in free-fall, so only thrust is changing them. If thrust is small enough the (ideal) orbit is nearly circular, so you can relate energy and angular momentum to orbital height, speed and so on, which is then needed to determine the effect of thrust.
 
anorlunda said:
https://www.physicsforums.com/threads/dawns-altitude-now-1000-km.793140/page-34#post-5278365

You should read this thread, active right now. The Dawn spacecraft is using an ion engine to decrease its orbital radius around the asteroid Ceres. Fascinating.
Sample simulated view of Dawn spacecraft retrothrusting so as to spiral in closer to Ceres, as anorlunda mentioned:
6Nov-1.jpg

This is the view as of around 6:25 PM pacific time on 6 November. (UTC is 8 hours ahead of pacific time).
Dawn is in roughly polar orbit and is heading north to pass above Ceres north polar region, after which it will come south over the dayside.
 

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