Synchronous Orbit around Kerbol - how to save time?

[kerbalfreak]

I've done several synchronous orbits around Kerbin, Mun and Minmus. I usually use 4 satellites, 90º apart and set an resonant orbit of 3/4. Every time the vessel is about to reach Ap, I release one satellite and circularize at Ap with it. 

Now I want to do the same at Kerbol, at an altitude of 17x10^9 meters (between Kerbin and Duna). Same deal, 4 vessels, 90º apart. In the future I may do something similar around Dres/Jool.

Problem is, this will take some years, and I don't like warping too much. Is possible to reduce the time needed? Like making 4 releases from Kerbin, over one year.

PS: I plan to use Alarm Clock to do other things while I wait for the maneuvers. I'm also ok with MechJeb2 for creating and executing nodes.

Many thanks!!

 

[OhioBob]

23 hours ago, kerbalfreak said:

Like making 4 releases from Kerbin, over one year.

That's probably what I'd do.  Just make it four separate launches, each separate by 1/4th of a year.  (edit) This won't work - see follow-up discussion.

By the way, I don't think "synchronous orbit" is the correct term for what you're describing.  A synchronous orbit is one in which the orbital period of the satellite is synchronized with the rotation period of the planet.

Edited December 2, 2017 by OhioBob

[kerbalfreak]

1 hour ago, OhioBob said:

By the way, I don't think "synchronous orbit" is the correct term for what you're describing. 

I think you're right. You know the correct name? I can't find out.

[OhioBob]

1 hour ago, kerbalfreak said:

I think you're right. You know the correct name? I can't find out.

When you have a group of satellites working together like that in a coordinated way, I've just typically heard it referred to as a satellite constellation.  The type of orbit that those satellites are in can be a variety of things.  For instance, it's possible that the satellites could be in "synchronous orbits", but that's because they are synced to the rotation of the planet, not because they are synced to each other. 

[GoSlash27]

20 hours ago, OhioBob said:

That's probably what I'd do.  Just make it four separate launches, each separate by 1/4th of a year.

OB,

Actually, I don't think that'd work. If the final orbit has the same solar period as Kerbin, then the sats would all wind up at the same phase relative Kerbin regardless of when the launch happens.

If you want them to get in position quickly, you'd have to launch one into a 5/4 seeder/final orbit, one into a 3/4, and one into a 1/2. That 1/2 would take a lot of DV. It could be accomplished with a 3/2 for less DV, but it would take a year and a half to complete.

Best,
-Slashy

[OhioBob]

1 hour ago, GoSlash27 said:

... If the final orbit has the same solar period as Kerbin ...

He said he wants to place them between Kerbin and Duna, so we're looking at a solar orbital period of about 600 days.

[GoSlash27]

7 minutes ago, OhioBob said:

He said he wants to place them between Kerbin and Duna, so we're looking at a solar orbital period of about 600 days.

OB,
 Oh, gotcha. I missed that part

 In that case, it'd work a bit differently. Since Kerbin's period is 3/4 the final period (I would adjust the final altitude to make it *precisely* 3/4; 16.215Gm altitude), you would need one launch every 1/3 of a Kerbin year to put the sats in a square constellation.

Best,
-Slashy

 

[OhioBob]

2 hours ago, GoSlash27 said:

OB,

Actually, I don't think that'd work. If the final orbit has the same solar period as Kerbin, then the sats would all wind up at the same phase relative Kerbin regardless of when the launch happens.

If you want them to get in position quickly, you'd have to launch one into a 5/4 seeder/final orbit, one into a 3/4, and one into a 1/2. That 1/2 would take a lot of DV. It could be accomplished with a 3/2 for less DV, but it would take a year and a half to complete.

Best,
-Slashy

You're right, launching them 1/4 of an orbit apart doesn't work.  I think they need to be launched about 362 days apart.  If we assume we're placing the satellites in an orbit halfway between Kerbin and Duna, and we're using a Hohmann transfer to get them there, then the transfer takes 256 days and the final orbital period is 604 days.  If the first launch occurs with Kerbin at 0 degrees longitude, then when the first satellite arrives in position, it will be at a longitude of 180^o and Kerbin will have raced ahead to 216^o.  In order to create the 90^o separation between the satellites, we need to wait another 106 days before launching the second.  In another 106 days, 362 days since the first launch, Kerbin will be at 306^o longitude, and the first satellite will be at 243^o.  If we launch now, the second satellite will be in position 256 days latter.  At that time the first satellite will be at 36^o longitude, and the second will be at 126^o, i.e. 90 degrees apart.  That means the whole process will take over 3 years to complete.

[GoSlash27]

OB,

 We can safely ignore the transfer time, since it applies to all sats equally. All that matters, then, is the resonance between Kerbin's orbit and the final orbit. It could be done in under 2 years. 1 1/3 years to launch them all, plus a little over half a year for the final sat to transfer.

Best,
-Slashy

[OhioBob]

3 minutes ago, GoSlash27 said:

We can safely ignore the transfer time, since it applies to all sats equally. All that matters, then, is the resonance between Kerbin's orbit and the final orbit. It could be done in under 2 years. 1 1/3 years to launch them all, plus a little over half a year for the final sat to transfer.

Transfer time isn't important in determining the time between launches, but it does factor in to how long the entire process will take.

What's important for determining time between launches is the angular velocities of Kerbin and the satellites in their final orbit.  Kerbin's orbital period is 426.09 days, and let's say the satellites have an orbital period of 604 days.  The angular velocities are,

Kerbin:  360 / 426.09 = 0.8448919 degrees/day
Satellite:  360 / 604 = 0.5960265 degrees/day

Each day Kerbin will move farther ahead of the satellite by an angle equal to the difference in the angular velocities, i.e. 0.8448919 - 0.5960265 = 0.2488654 degrees/day.

So for the next launch to occur, Kerbin needs to gain 90 degrees on the previously launched satellite.  That takes a period of time equal to, 90 / 0.2488654 = 361.64 days.

The total time to complete is the time between launches plus the transfer time of the last satellite, 361.64 * 3 + 256 = 1,341 days.
 

[GoSlash27]

OB,

 Yeah, I see what you're saying. If you shorten the period of the sats to 568.12 days (4/3 resonance with Kerbin) it would give you one launch window per year, so 3 years from the first launch, plus the transit time of the last sat. It wouldn't actually save much time over chucking all of them to a higher orbit on a bus.

So we're back to staggering the seeder/ feeder orbits. The math for the launch windows gets a little hairier and I really don't feel like digging into it right now, but it'd seem to be the quickest option.

Best,
-Slashy

Edited December 2, 2017 by GoSlash27

[OhioBob]

4 hours ago, GoSlash27 said:

Yeah, I see what you're saying. If you shorten the period of the sats to 568.12 days (4/3 resonance with Kerbin) it would give you one launch window per year, so 3 years from the first launch, plus the transit time of the last sat. It wouldn't actually save much time over chucking all of them to a higher orbit on a bus.

To complete the three launches more quickly, it would actual the beneficial to boost the satellites into even higher orbits.  The more slowly the satellites orbit, the less time it takes for Kerbin to pull 90 degrees ahead.  If the satellites had orbital periods of, say, 900 days (a little beyond Duna's orbit), then the time between launches is,

90 / ( 360 / 426.09 - 360 / 900) )  = 202.3 days

The transfer time for each satellite will be longer, but the overall deployment time should be less because there is less wait time between launches.

[kerbalfreak]

Thanks for the replies! Will read everything with attention and test the suggestions.

So far I've made a test with 152 days, 4 relays, orbit of 17 Gm (~608 days)... Got this 

 

[Plusck]

Interesting discussion folks.

Once you've got your first satellite up, you can eyeball the rest using manouvre nodes and target rendezvous markers, especially if you get your first satellite there quickly using a radial-out ejection. It'll cost dv to do that, but you should be able to get three out of the four satellites in place relatively quickly:

- first one radial out and into the final orbit quite quickly;
- second one heading purely prograde, probably not too long after the first satellite gets into its final orbit (six months?);
- third one heading radially in, not too long after that.

Whatever happens, though, there's not much you can do to get the fourth one into position quickly, unless you start by sending it way higher than Duna at the beginning of the process and bring it back down once the first satellite has started to pull ahead of it. Otherwise it's going to be a nearly 3-year wait.

 

[kerbalfreak]

Seems that the time of launch needs to be very high, consuming almost the same as if I did the "old way". I think I can do the old way in 3 years, even less in a lower orbit. The constellation will be functional before finished, and KAC works very well for alerting me about the maneuvers. And I'm already very familiar with this method, I know it will work. Heres my constellation around Kerbin: 



I'm thinking in making a challenge out of this, the fastest method to get the 4 relays 90º apart around Kerbol, at 17 Gm.

Thanks!!