How to time launch to Rendezvouz

[paxy97]

I am building a big Space station in LKO. I have the core up and want to add a power module. The problem is that I don't have enough fuel to get it into a phasing orbit and then transfer to the stations orbit. So I thought i time my launch to get to 100km at the same time as my station passes. At what distance from the station should I launch? Or what time?

[Johnno]

I am building a big Space station in LKO. I have the core up and want to add a power module. The problem is that I don't have enough fuel to get it into a phasing orbit and then transfer to the stations orbit. So I thought i time my launch to get to 100km at the same time as my station passes. At what distance from the station should I launch? Or what time?

Atmosphere ends just after 69km. Get into a 75km orbit then raise your apoapsis to 100km, wait for station, circulize, dock.

Or the easier way to do it, add more fuel. Don't really see how that would be an issue unless you're doing a challenge and are limited to a specific ship/design.

[Mr Shifty]

I am building a big Space station in LKO. I have the core up and want to add a power module. The problem is that I don't have enough fuel to get it into a phasing orbit and then transfer to the stations orbit. So I thought i time my launch to get to 100km at the same time as my station passes. At what distance from the station should I launch? Or what time?

The fuel cost for a phasing orbit is minuscule: a few m/s. For instance, to raise your apoapsis from 100km to 110km costs 8 m/s.

[capi3101]

I find that if the target is about 450,000 m downrange when I launch, I usually close to a rendezvous within an orbit or two. You usually want that much to kill any difference in declination anyway (that's if you're doing it with just RCS; LOX you can get it in one go usually if you're careful about it).

While I'm at it, add RCS if you haven't got it already; assuming you're attempting to rendezvous with LOX you could use it as a backup when your tanks run dry.

Edited July 17, 2013 by capi3101

[paxy97]

Thank you @capi3101, it worked . I launched 450kms away and got there at almost the same time

[capi3101]

You're very welcome.

The 450k works reasonably well in most situations - largely it's dependent on the altitude of the target's orbit in the vicinity of KSC but it can be closer to 400k when the target's higher up and about 500k when it's in a very low orbit. You also have to watch how you fly...one time, I got up there, got the orbital insertion burn set up, saw the target zip by at 2,250 m/s passing within six kilometers of my craft......

[Evan]

How you can tell when the craft is 450km away?