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Gary_P

How high should a Space Station be?

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I've tried a 100Km orbit.  When I uncouple one part to attach it to another it floats away too fast to grab.  I'm trying 500Km, to see if that works because I'm moving slower.

Is there a sweet spot or something I'm doing wrong?

Edited by Gary_P

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Here's a tip when you want to decouple something without it flying away too fast.

In the VAB and SPH you can right click on the decouplers on your craft and edit their ejection force, if you reduce this to zero the parts you decouple in space will not be pushed away from you.

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A 100km orbit shouldn't be a problem. Docking ports have a very small decoupling force so unless you're using decouplers on maximum force and very light parts they shouldn't move away too fast to be switched to using the [ ] keys.

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You mean kilometers and basically, the speed of your craft will not effect the ejection speed of your ejectable satellite. (Newton's F = m*a). 100km - 500km is a nice region to put your stations in.

What you're doing wrong is hard to tell here. Not enough data (with what are you grabbing? did your Kerbal activate his/her rcs (press "r") during eva). It is possible that you have a very light satellite (tiny "m") and an overpowered decoupler (Huge "F") giving you high acceleration ("a") when decoupling. If this is the case: use docking ports ^^

/e Clipping parts ^^ yep, imo Katateochi nailed it.

Edited by Knaapie

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Orbital altitude doesn't really matter just as long as you're above the atmosphere or highest surface feature. Lower altitude stations are cheaper to get to as it requires less dV. But it's always wise to leave some distance between the atmosphere and your station for easier rendezvous.

Altitude and orbital velocity have absolutely no influence on the speed at which objects will float since both sides of the decoupler are moving at exactly the same velocity before decoupling. Any difference in speed is relative and exists only between those two parts.
Decoupling force and mass are what determines at what speed the parts move away from each other.

Edited by Tex_NL

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Sounds like your undocking something and then trying to catch it with with another craft?

If the undocked thing is moving off too fast for that, then a change in orbit height won't make any difference.  As @Reactordrone says; are you using a powerful decoupler on a light part? OR are any of the parts clipping with each other?  If two parts from either module are clipped, when you undock that can create a lot of force (often quite explody) and can send things flying off.  

 

Edited by katateochi

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Thanks for the replies.  I edited my question to be Km, and not meters.  LOL, meters would be bad.

I sent 3 ships up with parts for my space station.  2 had 2 tanks, connected with Clamp-O-trons.  Each had tank1 and tank2.  I wanted to uncouple both tank1's and then uncouple tank2's.  Like a train that has to swap it's boxcars.

It's not the uncoupling that's pushing them away, it's the game itself.  I tried mechjeb to do the docking.  I tried an experiment. 

I set one part in a 100Km orbit then did a rendezvous planner set to 50m.  After it got into view and stopped, if I left it go the target will float away.  I thought 2 bodies moving at the same time should not "feel" like they have any movement.

Been a while since I played KSP and it's way fun learning all over again.

Thanks for your comments and help.

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Try "match velocity with target" in maneuver planer after rendezvous autopilot finished. Maybe mechjeb didn't kill relative velocity completely.

and can you tell the speed at target mode?

 

 

 

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Aha..  Well, I guess you can "park" as close as possible in the pro-retrograde direction from the space station. That should theoretically reduce "space floating".

Reducing relative difference in orbit between the two objects will make it better for you. It would mean that a higher orbit, like you suggested, works as well.

 

anyways gl, and imo..  dock faster ;)

Edited by Knaapie
"in" orbit.. Tex_nl has similar ideas.. Is he my neighbour? NL ftw

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54 minutes ago, Gary_P said:

...

It's not the uncoupling that's pushing them away, it's the game itself.  I tried mechjeb to do the docking.  I tried an experiment. 

I set one part in a 100Km orbit then did a rendezvous planner set to 50m.  After it got into view and stopped, if I left it go the target will float away.  I thought 2 bodies moving at the same time should not "feel" like they have any movement.

...

Yes, and no.
Only two objects in exactly the same orbit will not drift apart. Having a relative speed of 0m/s at one point does only very rarely mean the orbits are exactly identical. If one object has only a tiny bit more altitude than the other its orbital period will be ever so slightly longer and over time it will drift away.

Edited by Tex_NL

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I recently re-arranged the sections of one of my space stations, but the parts stayed where I left them, at least in the short term.

WSNqUWO.jpg

The whole process took about an hour, both real and game time, and nothing floated off very far. I did keep an eye on them, just in case.  One thing I did was to make remote "pod-haulers" to move things around.  Maybe that's why they behaved?
I did not try time advancing it, however, so I don't know if they would have drifted off over time.

Oh, this particular station is in near Kerbin orbit @ 100km. 

Edited by Just Jim

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How high should a Space Station be?

Not too high I would hope.

Space stations are serious business.

:wink:

Edited by Rocket In My Pocket
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Thanks for the replies.  It's practice I suppose.

I'm going to try out a few more times on a save, and see what I'm doing wrong.

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So this turns out to be two questions: Why are my parts drifting away? and How high should my station be? For the first, you could be having phantom forces from the model that are causing them to accelerate. Also, try to detach them so they're either prograde or retrograde from you. If you eject them closer to or farther from Kerbin, they would be in a different (and eccentric) orbit, but for things that start off very close, i would expect the effect to be small.

As to the other question, You want it high enough that you can be in a lower orbit to catch up with it in a reasonable time. You want it low enough that it doesn't take a huge amount of fuel or a very capable rocket to get there. But game mechanics has more to do with this than I would like. In a high orbit (300km? 500?) the game will not render the planet in as much detail, which will cut down on lag. Also, in a higher orbit, you can time warp at a higher rate. If you're waiting for a launch window before you leave the station, and that window is three months away, you don't want to do that at 100km. I don't build them as often as I used to--since they added the NASA-inspired parts I don't have much need to assemble and refuel ships for interplanetary shots--but when I do, I usually put them at 300-350km.

Hope this helps!

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4 hours ago, Gary_P said:

After it got into view and stopped, if I left it go the target will float away.

Can you be more specific?  Float away how fast?

Do you mean, like, "visibly fast, with a relative speed of many centimeters per second or more, so that in a minute or so it's gone a long distance"?

Or do you mean "they don't stay permanently there, and if I let them sit for several hours or more they eventually drift apart"?

Those are two different things.

If you mean the second one-- i.e. a really slow drift that takes place over multiple orbits-- then that's normal and pretty much unavoidable, in real life as well as in KSP.  Two things that aren't actually docked together will always eventually drift apart, since in practice they're never in exactly the same orbit as each other.  If one of them is in an orbit that has a period that's a few seconds longer than the other, they'll drift.  And getting the periods exactly in sync is practically impossible, unless you HyperEdit them or something.  The moral of the story is that it's not possible to leave things parked next to each other, at least not long-term.  They will eventually drift apart.  The only way to leave things together is to leave them docked.

If you're talking about a much faster drift, i.e. fast enough to show up as a relative velocity on the navball, what relative velocity are you observing?

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Snark, I'll do a test and time it and see.I didn't have time to switch to the other vessel and dock them.

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2 minutes ago, Gary_P said:

Snark, I'll do a test and time it and see.I didn't have time to switch to the other vessel and dock them.

I dunno... I've undocked parts of a station, rendez-voused and docked another part, and then redocked the first part that I undocked (I wanted the new part in between). Granted, it had floated away a few hundred meters but it was still inside the physics bubble.

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I'm not sure what was happening but I'm able to dock at 100km now.

MechJeb was doing weird stuff when I used the ronda-voo :) autopilot.  It started creating a vertical orbit.

I used HyperEdit, great add-on btw, to delete most of my ships and tried again.  I also learned to have a few more thrusters and how to use them.  (My bad).

Thanks for the help too.

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Okay I have a question, say I launch most of my craft into 80k parking orbits, what altitude  would give me the best phasing  (is that the right term?) For Hoffman transfer?

 

To me that would be a major factor in space station height  because I'm constantly grabbing cargo out of 80k parking orbit with my tug and dragging it to the station. If there is a particular altitude that would give me simpler transfer that  would be great.

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There are a bunch of factors to consider:

Delta-v for all rockets going there: anything over 70km will cost more.  You also get more Obereth effect *leaving* the station for parts beyond LKO from 70km.

70km allows for 4> (50*) time warp.  120km allows for 5> (100*).  240km allows for 6> (1000*)

Eccentric orbits allow for easier "brute force" docking because of the low velocity near apogee.  I think I'll try this for other cases (Munar docking and what not), but I don't think many players do this for space stations.  This even allows tricks like Munar insertion, (wait till the Mun is aligned with where you are going), and deinsertion for the right ejection angles to get your Obereth effect back for going to different planets, but that is a little odd.

Generally, a more or less circular 120km looks like your best bet.  If you have a contract, check that.  Typically you want to fulfill the contract, then move it where you want.

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