Satellite Spacing

[IllicitMedic]

I'll be launching 4 comsats into a 300km, 0 degree orbit...how long after I put each one in orbit should I wait to launch the next one to get even spacing?

I'll also be launching 3 geosync sats, whats the timing for this?

I've done it before but don't remember my timing method.

-Thanks

[legoheli]

If you want them to be perfectly spaced, you need to first figure out how long time it takes to orbit Kerbin in the given orbit.

With the synchronous orbit, you ideally would want to launch every 2 hours. Burn so your apoapsis is in the desired synchronous altitude. It will take longer than that to coast to apoapsis, so just launch, time warp until MET=1:59:30, go to the space centre, get the next rocket ready to launch, launch and warp to 1:59:30. Then launch the last one.

[IllicitMedic]

Thanks! I'll try the geosync first.

Orbit time for the 300km sats is right around 50 minutes. Sooooo?

[PakledHostage]

This was discussed a fair bit in my Kerbal GPS mod's thread. There's even a video. You can find the thread by clicking on the links in my signature.

[legoheli]

Since it's 50 minutes and 3 satellites, you'll have to launch every 50/3=16.67 minutes, so around MET=00:16:40 you'll go back to the launch pad. I'm not sure that'll be enough.

Then what you'll do is wait in your 300 km orbit until you are just above KSC again, then wait the 16:40 until you launch the next one.

[IllicitMedic]

The 300km orbit will actually have 4. I'm going to that video a look.

[rosenkranz]

Well, this link http://www.1728.org/kepler3a.htm is for a keppler calc which i've found very useful for problems like what your're asking.

A 300km orbit (900km including Kerbins 600km radius) has a period of 47.587 min (47m:35s). One quarter of this is 11m:54s.

Thus, launch your first satellite and once in orbit, retreat to the tracking station and wait until the first one has a MET of 11m:54s. Then goto the VAB and launch the next one.

Using the first one as the standard you launch the other three at MET 11m:54s, 23m:47s, and 35m:41s.

For the KSO orbits remember that the period is 6 hrs. So launch the first KSO sat and then launch the others at MET+2hr and MET+4hrs

[IllicitMedic]

Ok so I launched 1 Geosync sat...to the correct altitude and speed...and then launched my next one at MET 2h...and they ended up in the same exact spot...

[rosenkranz]

Really? That should have worked. When i did it, i hadn't tried to do it from the tracking station though but i thought that should work as well. I just stayed with the first satellite until its MET read 2hr. Sorry, i thought waiting in the tracking station would amount to the same thing.

[IllicitMedic]

Really? That should have worked. When i did it, i hadn't tried to do it from the tracking station though but i thought that should work as well. I just stayed with the first satellite until its MET read 2hr. Sorry, i thought waiting in the tracking station would amount to the same thing.

I tried both...hmmmm. Do I wait until all 3 sats are in orbit before circularizing?

[PakledHostage]

Why not launch 3 satellites at a time as shown in the video below, but use a 1225.35 km x 2868.35 km transfer orbit instead?:

The 1225.35 km x 2868.35 has a 2:3 orbital resonance with the geosynchronous orbit. If you release one satellite each time you reach apoapsis and then burn the engines on that satellite to circularise at the 2868.35 km Ap, they'll automatically be in a geosyncronous orbit and spaced at 120 degrees. Circularisation at Ap requires a bit over 170 m/s delta-V, so your satellites don't need a lot of fuel.

Edited May 23, 2013 by PakledHostage

[Eric S]

Why not launch 3 satellites at a time as shown in the video below, but use a 1225.35 km x 2868.35 km transfer orbit instead?

Definitely sounds like the way to do it. Just waiting won't help, since the in-place satellite is orbiting at the same rate of rotation as the planet, so it isn't moving (relative to the planet).

[IllicitMedic]

Why not launch 3 satellites at a time as shown in the video below, but use a 1225.35 km x 2868.35 km transfer orbit instead?:

The 1225.35 km x 2868.35 has a 2:3 orbital resonance with the geosynchronous orbit. If you release one satellite each time you reach apoapsis and then burn the engines on that satellite to circularise at the 2868.35 km Ap, they'll automatically be in a geosyncronous orbit and spaced at 120 degrees. Circularisation at Ap requires a bit over 170 m/s delta-V, so your satellites don't need a lot of fuel.

Worked perfect, thank you. Now, will this work for lower orbits too? I'm terrible at math lol been trying to do the math for a 300km orbit.

Timing the launches work for the 300km but I'd like a more consistent, non variable way to do it for future deployments.

[PakledHostage]

Worked perfect, thank you. Now, will this work for lower orbits too?

Yes, but you obviously need different numbers... You could use 7:8 orbital resonance to space four satellites out around an orbit. In that case you'd use a 147.6 km x 300.0 km transfer orbit to reach your 300 km circular working orbit. You'd just have to wait two orbits between releasing your satellites. It might be difficult to build a 4-satellite launcher that isn't wobbly though, so you might have to do it in two separate launches.

The challenge when using more than one launch, as legoheli mentioned, would be spacing the first two satellites and the second two satellites equally. You could use one of the clock mods to help you out. One option may be the Figaro receiver in my GPS mod; it displays UT on its UI so you don't have to switch back and forth between the tracking station and launch pad while waiting for your launch window.

[IllicitMedic]

Yes, but you obviously need different numbers... You could use 7:8 orbital resonance to space four satellites out around an orbit. In that case you'd use a 147.6 km x 300.0 km transfer orbit to reach your 300 km circular working orbit. You'd just have to wait two orbits between releasing your satellites. It might be difficult to build a 4-satellite launcher that isn't wobbly though, so you might have to do it in two separate launches.

The challenge when using more than one launch, as legoheli mentioned, would be spacing the first two satellites and the second two satellites equally. You could use one of the clock mods to help you out. One option may be the Figaro receiver in my GPS mod; it displays UT on its UI so you don't have to switch back and forth between the tracking station and launch pad while waiting for your launch window.

4 sats at a time was actually fairly easy. Anyway, all 8 sats are now in perfect orbits.

Thanks so much for your help.