Impulse and step response related to the angular position of a spacecraft

In summary, a satellite needs two impulses to change its orbit. One to get it from its old orbit to the intermediate orbit, and the second to take it to the final required new orbit.
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Imagin_e
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Hi!

I don't know if I'm in the right forum of this site but I'm trying anyway. I was just wondering if someone could explain how the step- and impulse response is related to an angular position (of e.g. a spacecraft )? Just a little about the theory since I am trying to actually understand how/why my MATLAB plots and the results are related to this subject.

Thanks!
 
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  • #2
It is important when trying to control something like the angular position (i.e. orientation). Its response to an impulse or step input shows how it will respond to any disturbance or frequency input. Obviously, when you try to correct an error, you do not want to push it in the wrong direction. That would just cause it to go off exponentially. Just as important is that you don't want to be too slow and then overdo it. That would cause it to oscillate back and forth. To analyse which frequencies of oscillation will die out and which will grow (diverge), it is necessary to know how the system responds to every frequency. Any divergent frequency is bad unless it is so slow that it is easy to control in other ways.
 
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  • #3
FactChecker said:
It is important when trying to control something like the angular position (i.e. orientation). Its response to an impulse or step input shows how it will respond to any disturbance or frequency input. Obviously, when you try to correct an error, you do not want to push it in the wrong direction. That would just cause it to go off exponentially. Just as important is that you don't want to be too slow and then overdo it. That would cause it to oscillate back and forth. To analyse which frequencies of oscillation will die out and which will grow (diverge), it is necessary to know how the system responds to every frequency. Any divergent frequency is bad unless it is so slow that it is easy to control in other ways.
Thanks buddy!
 
  • #4
For a spacecraft orientation change or rotation, as opposed to a change in velocity or direction of travel, any impulse force-time sum in one direction must be countered with an equal impulse force-time sum in the opposite direction in order to arrest the imposed rotation of the craft.
 
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JBA said:
For a spacecraft orientation change or rotation, as opposed to a change in velocity or direction of travel, any impulse force-time sum in one direction must be countered with an equal impulse force-time sum in the opposite direction in order to arrest the imposed rotation of the craft.
Good point. I guess that stopping the rotation would boil down to just canceling the disturbance impulse because there is no aerodynamics to mess it up. Unless you want to get it back to some particular orientation, the problem would be solved. Getting it back to a desired orientation would reintroduce the threat of oscillatory control behavior.
 
  • #6
The orientation of a satellite is usually adjusted so it points it's antennas towards the Earth while pointing it's solar panels towards the Sun. Under normal conditions the satellite rotates about it's centre of mass at a fixed rate that maintains those orientation directions. As an axis orientation or rotation rate error begins to accumulate, and so becomes apparent, a short correction impulse is applied to correct the drift of rotation. Over time that impulse will accumulate to bring the satellite back towards the required orientation.

Satellites move in elliptical orbits. To change position from an old orbit to a new orbit, two impulses are usually required. An intermediate elliptical orbit is used that intersects both the old and then the new orbit. The first impulse transfers it from the old orbit to the intermediate orbit, the second impulse, applied at the appropriate time, takes it onto the final required new orbit.
 
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Thank you for explaining, now I understand. Cheers!
 

1. What is impulse and step response in relation to the angular position of a spacecraft?

Impulse and step response refer to the behavior of a spacecraft's angular position when it is subjected to an external force or input. Impulse response describes the angular displacement or change in velocity of the spacecraft in response to a single, instantaneous force applied to it. Step response, on the other hand, describes the spacecraft's angular position or velocity in response to a sustained input or force over time.

2. How are impulse and step response related?

Impulse and step response are related in that they both describe the behavior of a spacecraft's angular position in response to an external input. However, they differ in the duration and magnitude of the input. Impulse response is a short-term response to a sudden input, while step response is a long-term response to a sustained input.

3. What factors affect the impulse and step response of a spacecraft's angular position?

The impulse and step response of a spacecraft's angular position can be affected by various factors, such as the spacecraft's mass, inertia, and external forces acting on it. Additionally, the spacecraft's control system and its response to inputs can also impact its impulse and step response.

4. How is the impulse and step response of a spacecraft measured?

The impulse and step response of a spacecraft's angular position can be measured through sensors and instruments on board the spacecraft. These sensors can detect changes in the spacecraft's angular position and velocity, allowing for the calculation of its impulse and step response. Additionally, simulations and mathematical models can also be used to predict and analyze the spacecraft's response.

5. Why is understanding impulse and step response important for spacecraft control and navigation?

Understanding impulse and step response is crucial for spacecraft control and navigation as it allows for the prediction and analysis of the spacecraft's behavior in response to external inputs. This information is essential for ensuring the spacecraft's stability and maneuverability, as well as for making necessary adjustments to its control system. It also plays a significant role in the overall success and safety of the spacecraft's mission.

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