Docking freefall item to an orbiting one (solved, heh.)

[Dedjal]

So there is something that I have been wondering about.

You have a space station in a stable orbit, and then you launch an object that will not orbit, but meet the orbiting space station at its peak. In as, 0 ms/s and dock with the space station.

If it does not dock, it would return back to kerbin.

I have been trying this with no luck as of yet.

But, what would happen to the space station if the object managed to dock?

Would the space station be affected because the item is really on a freefall path. Or will the speed of the object on the time of connection, simply add or substract equal amount of ms/s from the orbit of the space station?

In as, docking when the object is at 0 ms/s would make no changes, while docking before reaching the peak would add X ms/s and visa versa?

Edited June 5, 2014 by Dedjal

[nettcod]

You cannot dock an object moving at 0 m/s to an object moving at 2500 m/s. If the docking ports came into contact, both objects would be destroyed from the impact of the collision.

[Tortoise]

I don't think anything will happen.

[SpenSpaceCorp]

If the object in freefall is not in an orbit (like the station), it is moving much slower. For example, your station would be orbiting at 2500 m/s and your object when it reaches the same height at the station intersect would be going 1800 m/s, 700 m/s slower, colliding hard and explosively.The ONLY way to make the speed of one thing relative to another is to match orbits, basically.

[Franklin]

Like catching a fastball barehanded.

[Dedjal]

Doh! Ofcourse.

I feel a tad stupid now.

I was thinking about docking and the ms/s related to that. But the ms/s for the object is related to kerbin and not the spacestation.

I'll go and hide on the airfield island now.

[michaelhester07]

Like catching a fastball barehanded.

Except the fastball is going 10 times the speed of a bullet, your mitt is a slab of metal and the baseball field is 10,000 miles wide.

[Skyler4856]

The concept sounds very similar to a sky-hook

[rosenkranz]

Even if you could 'hook' it, the station would have to be able to impart the force to bring the 'hooked' item up to speed or be pulled out of orbit itself as the inertia equalized.

[Sirrobert]

Asuming you WERE able to do this.

Say by connecting the 2 crafts with some kind of invincible tether, AND asuming this does not rip the ships apart at the points where they are connected:

The new speed of the craft would be a vector of the speeds of the 2 old ships. So if the station was going fast and the freefalling was going slow, the new craft would be go slower than the station, but faster than the freefalling craft.

Depends on how massive each is how fast the total will go offcourse

[magnemoe]

One thing you could do is to brake the ship in orbit into a return trajectory who is similar to the suborbital one, dock and burn back into orbit.

This would require very good timing and precision also a ship in orbit with good TWR and plenty of dV.

People has thought about it for Eve exit scenarios. especially before we got rover seats but don't think any has tried. For moons it might be more plausible

[PlonioFludrasco]

That's my minmus RV tecnique: launch the lander, have an appropriate intersect, meet velocities, dock, and hope you are not suborbital. If that happen (everytime), hope you have enough fuel to circularize.

[henryrasia]

What about in Gilly orbit? The station would be moving at less than 34 m/s (IIRC). Surely that would not cause an explosion...

Furthermore, the object trying to dock could be moving towards the ground at the horizon, so the speed relative to the station is even lower. The question here really is: How does KSP "merge" two orbits when docked if they aren't negligeably close?

[nobbers12345]

What about in Gilly orbit? The station would be moving at less than 34 m/s (IIRC). Surely that would not cause an explosion...

Furthermore, the object trying to dock could be moving towards the ground at the horizon, so the speed relative to the station is even lower. The question here really is: How does KSP "merge" two orbits when docked if they aren't negligeably close?

34 m/s will not let the ports attach, you need less than 1 m/s to dock i think. If anything, impact tolerance is lower than 34, so it will still destroy stuff.

And if you did manage to hook it, your momentum would change your velocity enough to bring the station out of orbit.

[Padishar]

What about in Gilly orbit? The station would be moving at less than 34 m/s (IIRC). Surely that would not cause an explosion...

Errr, 34 m/s is approximately 70 miles per hour. Good luck with that not causing significant damage...

[Dkmdlb]

If you had a station in Gilly orbit and a ship on a sub-orbital trajectory but which was just barely under orbital speed, the relative speed between the two would be just a couple of m/s. I'd say it's technically possible. Have the station's docking port facing prograde and the ship's docking port facing retrograde and let the station um, bring up the rear.

[Sirrobert]

What about in Gilly orbit? The station would be moving at less than 34 m/s (IIRC). Surely that would not cause an explosion...

Furthermore, the object trying to dock could be moving towards the ground at the horizon, so the speed relative to the station is even lower. The question here really is: How does KSP "merge" two orbits when docked if they aren't negligeably close?

KSP doesn't merge orbits. If you were to somehow dock while the crafts have a different speed, the resulting total craft will have a new speed vector. This new vector deceides the new orbit, in exactly the same way as burning the engines would change the orbit

[kidolvski]

[Commander Jebidiah]

ive also been wondering this although more to do with real life

e.g.

If you have a space Station at Geo orbit with a gappler on it.

you send a rocket up to an Ap of whatever geo is at

the station will reach the same place as the rocket at the same time

The rocket would slow down to 0 m/s at ap

at this exact time the station would fire the grappler what would happen once the grappler attatched to the rocket?

[Taki117]

ive also been wondering this although more to do with real life

e.g.

If you have a space Station at Geo orbit with a gappler on it.

you send a rocket up to an Ap of whatever geo is at

the station will reach the same place as the rocket at the same time

The rocket would slow down to 0 m/s at ap

at this exact time the station would fire the grappler what would happen once the grappler attached to the rocket?

Once said Grappling device attached to the rocket the entire assembly would begin moving, unfortunately said rocket is not moving at all (Relative to the planet) and as such it would be yanked by the grappling device into orbit, subsequently (According to Newton) the station would be slowed by the same amount of energy it took to accelerate the ship.

[EdFred]

ive also been wondering this although more to do with real life

e.g.

If you have a space Station at Geo orbit with a gappler on it.

you send a rocket up to an Ap of whatever geo is at

the station will reach the same place as the rocket at the same time

The rocket would slow down to 0 m/s at ap

at this exact time the station would fire the grappler what would happen once the grappler attatched to the rocket?

Imagine this scenario. You riding a horse on a spinning carousel, and I am say, 20 meters from the outside edge of the carousel running at a speed that keeps that horse directly between myself and the center. You hop off the horse and stand at the edge of the carousel and wait for the right moment to run directly away from the carousel so you and I meet at that same spot 20meters away from the edge. What happens when we meet? I basically run you over. Same thing with your above scenario.

[makinyashikino]

ive also been wondering this although more to do with real life

e.g.

If you have a space Station at Geo orbit with a gappler on it.

you send a rocket up to an Ap of whatever geo is at

the station will reach the same place as the rocket at the same time

The rocket would slow down to 0 m/s at ap

at this exact time the station would fire the grappler what would happen once the grappler attatched to the rocket?

You wouldn't need a grappler if you timed the docking right. But doing this would be worse than achieving orbit then changing Apoapsis because burning straight up is incredibly fuel inefficient. Also, atmospheric drag lowers your horizontal speed and you would pretty much need to time it perfectly. Complicated but theoretically do-able.

[cantab]

In answer to the original question, in order for two things to dock they need to be in virtually the same place, going at virtually the same speed, in virtually the same direction. But that means they're in virtually the same orbit to start with!

A potential way around this is to have one or both objects spinning, such that their tips can match speeds while their centres of mass are at quite different speeds. The two objects can then share their momentum and energy more gradually as they rotate. Such schemes are known as momentum exchange tethers or "skyhooks".

This would be limited and difficult to pull off in stock KSP due to the physics range limit. A short "tether" would need a rapid rotation rate for a significantly slower spacecraft to be able to dock with it, and that would mean you'd require extraordinarily precise timing. That said, with trial and error or an autopilot it might be possible.

[Sirrobert]

ive also been wondering this although more to do with real life

e.g.

If you have a space Station at Geo orbit with a gappler on it.

you send a rocket up to an Ap of whatever geo is at

the station will reach the same place as the rocket at the same time

The rocket would slow down to 0 m/s at ap

at this exact time the station would fire the grappler what would happen once the grappler attatched to the rocket?

Well you'd need something that can survive getting accelerated 2km/s (for kerbin. For earth it's more 8km/s) the instant your grappler attatches to it.

Because that's what would happen. Also you'd need to make sure the grappler doesn't get torn off the space station because whatever it grabbed will have inertia resisting the acceleration.

The point is, something WILL break

You wouldn't need a grappler if you timed the docking right. But doing this would be worse than achieving orbit then changing Apoapsis because burning straight up is incredibly fuel inefficient. Also, atmospheric drag lowers your horizontal speed and you would pretty much need to time it perfectly. Complicated but theoretically do-able.

No you can't 'time the docking right', because the station isn't stationairy. It's moving extremely fast

[Kerba Fett]

On Minmus and to a lesser degree the Mun you can do a sub orbital rendezvous. You time your launch so that your path crosses your target's path close enough for an intercept. This usually happens near your AP. Then you put a maneuver node at the intercept point and adjust it to match orbits. Once you do your burn you should be moving in the same orbit as your target and close enough to approach on RCS.

While you can do this anywhere, it's much easier on low gravity worlds since theres a smaller speed difference between the suborbital arc and an orbital path.