Questions about decoupler force

[iamthemoose]

Hello, I've got a couple of questions concerning decouplers. To give some context, what I'm attempting to do is launch a satellite into orbit and decouple with the right velocity and apoapsis so that the additional force from the decoupler carries the satellite into a circular orbit (hopefully leaving the debris behind to fall back into atmo).

My questions are as follows:

1. Is the decoupler force applied to both sides, or split between the two? ex. If I put a 100kN decoupler onto a rocket and separate, does each side receive a 100kN force, or a 50kN force?

2. Disregarding mass, is there any reason to avoid using a decoupler of the wrong size? Would a larger decoupler connected to a small section/satellite/whatever apply a smaller force (when compared to a smaller decoupler of equal force), since there would be empty space? Or are there no differences other than aesthetics and mass?

3. Is there any significant difference in behavior in atmospheric conditions as opposed to a vacuum?

I appreciate your feedback. Have an awesome day!

Edited July 20, 2013 by iamthemoose

[iamthemoose]

Zero views after several hours. Bumping for visibility.

[Johnno]

what I'm attempting to do is launch a satellite into orbit and decouple with the right velocity and apoapsis so that the additional force from the decoupler carries the satellite into a circular orbit (hopefully leaving the debris behind to fall back into atmo).

Decouplers add such a tiny amount that I wouldn't bother with that, they'll change your orbit a minimal amount.

Zero views after several hours. Bumping for visibility.

The views counter doesn't update straight off and a few hours isn't much when it comes to the forum.

[Kimberly]

Hello, I've got a couple of questions concerning decouplers. To give some context, what I'm attempting to do is launch a satellite into orbit and decouple with the right velocity and apoapsis so that the additional force from the decoupler carries the satellite into a circular orbit (hopefully leaving the debris behind to fall back into atmo).

My questions are as follows:

1. Is the decoupler force applied to both sides, or split between the two? ex. If I put a 100kN decoupler onto a rocket and separate, does each side receive a 100kN force, or a 50kN force?

2. Disregarding mass, is there any reason to avoid using a decoupler of the wrong size? Would a larger decoupler connected to a small section/satellite/whatever apply a smaller force (when compared to a smaller decoupler of equal force), since there would be empty space? Or are there no differences other than aesthetics and mass?

3. Is there any significant difference in behavior in atmospheric conditions as opposed to a vacuum?

I appreciate your feedback. Have an awesome day!

1. The force is applied to only one side, namely in the direction of the arrow on the decoupler. Newton's third law dictates that there will be an equal opposing force produced on your own craft, though; if your main craft applies 100 kN to a satellite, the satellite also applies 100 kN (in the opposite direction) to your main craft.

2. It doesn't really matter what decoupler you use, in terms of functionality. I wouldn't use decouplers with the intent of providing force, it's much better to use engines so you can tune to exactly the orbit you want. You may want low-force decouplers for satellites that need to remain in a particular orbit, though; even the force produced by docking ports can cause light satellites to be pushed out of a geosynchronous orbit. To decouple with zero force, use a docking port and attach a strut to the craft you're detaching: the strut will dissolve when you decouple, and there will be no force applied.

3. Not really. The usual physics apply; some of the decoupling force will be negated by drag, but that's mostly inconsequential.

[Tex_NL]

Decouplers add such a tiny amount that I wouldn't bother with that, they'll change your orbit a minimal amount.

This is not correct! Yes, the force is small but far from negligible!

If you're decoupling a heavy satellite you can ignore the decoupler. But if you're decoupling a light micro satellite it can easily increase the orbit by few dozen km. Or worse; throw it back into the atmosphere.

To avoid this you can use a docking port (you can use a single docking port the same way you can use a decoupler). You'll have to separate manually by right-clicking but it will not exert any force on either side.

[Kimberly]

This is not correct! Yes, the force is small but far from negligible!

If you're decoupling a heavy satellite you can ignore the decoupler. But if you're decoupling a light micro satellite it can easily increase the orbit by few dozen km. Or worse; throw it back into the atmosphere.

To avoid this you can use a docking port (you can use a single docking port the same way you can use a decoupler). You'll have to separate manually by right-clicking but it will not exert any force on either side.

Docking ports do exert a small force when decoupling. It can make a difference for microsatellites. You can negate this by also attaching a strut, as I suggested above.

[Johnno]

This is not correct! Yes, the force is small but far from negligible!

If you're decoupling a heavy satellite you can ignore the decoupler. But if you're decoupling a light micro satellite it can easily increase the orbit by few dozen km. Or worse; throw it back into the atmosphere.

To avoid this you can use a docking port (you can use a single docking port the same way you can use a decoupler). You'll have to separate manually by right-clicking but it will not exert any force on either side.

You're right, for microsatellites it becomes the opposite, big enough that you have to account for it and preferrably bring propulsion for station keeping. I should've written a more indepth post.

I wouldn't recommend it as a launch system though, simply because using a medium decoupler vs small decoupler, oscar-b tank and ant engine you're gaining 75kg less mass but losing about 1300 m/s delta-v.

[Crown]

1. Is the decoupler force applied to both sides, or split between the two?[...]

What Kimberly said about Newton's third law is correct.

A thing to keep in mind is the tiny red arrow (or triangle) on the decoupler. The part attached to the triangle's base is the one the decoupler keeps attached to after separation. Which means you have one rocket stage with the decoupler and one without it.

Stage separators detach on both sides, leaving two parts and the separator left. Resulting in one more piece of debris.

[...]Would a larger decoupler connected to a small section/satellite/whatever apply a smaller force (when compared to a smaller decoupler of equal force), since there would be empty space? Or are there no differences other than aesthetics and mass?

Generally anything can be welded together. So a huge decoupler would also attach to a tiny satellite.

But as already mentioned, a huge decoupler could catapult a tiny satellite quite far away. Might be used for advantage.

[iamthemoose]

Thanks for the replies! Sorry if I came across as pretentious earlier.

1. The force is applied to only one side, namely in the direction of the arrow on the decoupler. Newton's third law dictates that there will be an equal opposing force produced on your own craft, though; if your main craft applies 100 kN to a satellite, the satellite also applies 100 kN (in the opposite direction) to your main craft.

This helps clear things up. Thanks! Now if only I could change the prefix in the original post...

Edited July 20, 2013 by iamthemoose

[Kimberly]

This helps clear things up. Thanks! Now if only I could change the prefix in the original post...

Edit it and then click on "Go Advanced". In advanced editing mode, you can change the prefix.