Evenly spacing satellites

[Kimberly]

For my RemoteTech and GPS constellations, it is desirable to evenly space out satellites. I can't seem to get it just right, though. What's best way to go about it, if the satellites themselves don't have any propulsion? So far I'm getting into the right orbit, releasing satellite one, lowering my apoapsis and then going through a few orbits, progressively increasing my apoapsis again so I don't go too far ahead of the previously released satellite, and then I eyeball when I'm the right distance and increase my apoapsis to more or less the right orbit. Is there a more elegant method?

(On a related note, is there a particular trick achieving polar orbits without wasting ridiculous amounts of fuel? I'd just launch northwards, but that doesn't give me control of the separation between various polar orbits.)

Edited July 4, 2013 by Kimberly

[SRV Ron]

Best bet is to launch several smaller rockets with one satellite each containing a thruster pack. Just stagger the launch times to achieve the orbital spacing. If you use a standard two stage booster, shut it down when paragee reaches about 60,000 meters, separate the satellite package from the second stage, and and use the thruster pack on the satellite to bring the paragee up to the desired altitude. That way, there will be no dead boosters orbiting in your path as atmospheric resistance will bring it down after a couple of orbits..

To place a satellite into a polar orbit, just make the gravity turn on a heading of 0* or 180*. It will only take a little more fuel for the launch as you won't get the rotation boost from Kerbal.

Either way, due to rounding error, you will find it difficult to maintain the even spacing in the long term.

[Kimberly]

I'd rather not use staggered launch times, because that's a very imprecise method; the time it takes to get into a proper orbit will vary significantly.

[Luuko]

I tend to favor getting all my sats up at once with a single launch vehicle. Usually an RCS tank, 4x RCS thrusters, 2x solar panels, 1x 1m battery, a probe core, a sat dish and 2-4x omni antennas. Usually 4-6 sats in a single launch.

I'll launch, get my parent taxi craft into orbit, detach all the sats and send the taxi craft back for recovery. Then it's childs play to use the RCS to get the sats into differing orbits to adjust their orbital period before bringing them back down into a single orbit, spaced out.

I'll do the same when I send craft to other planetary bodies - each ship is multi-purpose and usually carries a sat network with it.

Examples:

Early Multi-Mission Craft

Recent Duna Mission

[mootavic]

the easiest way i found was to create a heavy lifter able to carry all of the satellites [each with at least an ion engine] on a large truss segment to your desired orbit altitude. then perform the following.

1: undock one sattelite

2: target the lifter

3: create a maneuver node boosting your Apoapsis while observing the closest approach markers.

4: perform your burn at the node ensuring inclination is as close as possible to NaN as possible

5: after the burn is completed ensure the node is removed and note the closest approach distance.

6: at the next periapsis burn to bring your apoapsis back down. ensure you match semi major axis between the satellite and the targeted lifter*.

7: repeat steps 1 through 6 for each satellite but ensure you use the last satellite you moved as the target and remember that for each satellite the boosted apoapsis will be higher until you reach a position 180 degrees away from your lifter. after that point it is cheaper on fuel to flip the procedure to drop periapsis instead. given your desired orbital altitude permits this of course.

please note that the first time you try this your final satellite may not be placed perfectly evenly apart from the 2 satellites either side of it unless you do some maths to figure out the spacing before hand. but this method will have near perfect spacing for all but 1 satellite on the first attempt.

* dont worry about having all the orbits perfectly circular with AP and PE all matching. just make sure the semi-major axis for the satellite is as close as possible to the lifters and their orbital period will be as close to identical as possible regardless of any eccentricity as long as your inclination to target is NaN.

[Kimberly]

I tend to favor getting all my sats up at once with a single launch vehicle. Usually an RCS tank, 4x RCS thrusters, 2x solar panels, 1x 1m battery, a probe core, a sat dish and 2-4x omni antennas. Usually 4-6 sats in a single launch.

I'll launch, get my parent taxi craft into orbit, detach all the sats and send the taxi craft back for recovery. Then it's childs play to use the RCS to get the sats into differing orbits to adjust their orbital period before bringing them back down into a single orbit, spaced out.

I'll do the same when I send craft to other planetary bodies - each ship is multi-purpose and usually carries a sat network with it.

Examples:

Early Multi-Mission Craft

Recent Duna Mission

Hm...so there's no simple method that doesn't involve giving the satellites their own propulsion, then?

[Luuko]

Not really no. Once you get them up there, the small probe fuel tank and tiny engine or the 1m rcs tank and thrusters are generally more than sufficient to get into proper orbit.

[maackey]

You really should just consider putting a single ion drive, ant engine or RCS on your satellites to make your final adjustments. Your satellites will never have a perfectly similar orbital period and will drift out of position over time.

Also what do you mean by this?

doesn't give me control of the separation between various polar orbits.

Launch northwards (or southwards) and adjust your orbit from there. A polar orbit is no different than a horizontal orbit (other than its inclination).

Anyway, since even mechjeb controlled ion driven satellites get out of sync eventually, I recently just went into the save file and manually set the orbits to all have the same period. So as long as I never focus on them again, they will continue to provide full coverage to the Kerbin system.

[Colonel_Panic]

I would also suggest staggered launch times, as I've had good success with it... the orbital position shouldn't be off by much from your target if you're consistent about your launch phase angle. Easy mode: just launch when the last satellite is directly overhead, and put the next into orbit behind it.

Ultimately though your sat networks won't stay perfect and pretty forever. Your orbit could be off by as little as 100m, and given enough time, they'll all get out of order again. I tend to prefer to make the distribution of inclinations and planes pretty and the orbital periods 'close enough', since the plane and inclination will never change as the satellites orbit.

[Kimberly]

Thanks for all the advice, guys...I'm still not too fond of the idea of giving satellites their own propulsion, as I like to keep it simple, but I'll consider my options.

As for polar orbits...how do you adjust a polar orbit's separation from another polar orbit, other than getting into the orbit at a different time?

[Colonel_Panic]

Thanks for all the advice, guys...I'm still not too fond of the idea of giving satellites their own propulsion, as I like to keep it simple, but I'll consider my options.

As for polar orbits...how do you adjust a polar orbit's separation from another polar orbit, other than getting into the orbit at a different time?

Giving sats propulsion is a generally good idea since it allows you to adjust and deorbit them easily. It also doesn't take much... a single oscar b fuel tank and ant engine will give it everything it needs to get around without a lot of weight or parts.

I presume you mean the relative inclination, as no two orbits will ever have non-intersecting planes. You adjust it the same way you adjust inclination between any other two orbits. You burn at the normal or anti-normal at the ascending or descending node between the two orbits (where they intersect).

As for spacing out satellites on the same orbit (this isn't something I do, by the way...) a hohmann transfer to a higher orbit and back again will do it.

Edited July 4, 2013 by Colonel_Panic

[SRV Ron]

Played with the following design and settled on this I call Redstone Probe 4. It placed 2.27 tons, which included the second stage with fuel left in a 125K orbit. One could go higher until the fuel is gone, then eject the second stage and use the RCS thrusters for additional maneuvers, or to bring the probe back to Kerbin.

Satellite; Stayputnik, 4 antennas, 2 Z-100 battery packs, set of instruments, SAS stabilizer, 8 OX Stat solar panels placed around the FL R25 RCS tank which is below the stabilizer, 4 RV 105 thruster pack on the stablizer ring.

Second stage; Decoupler, FL-T400 fuel tank, LV 909 engine.

First stage; Decoupler, FL-T200 fuel tank, FL-T400 fuel tank, FL-T800 fuel tank, LV-45 engine, set 4 Delta Winglets placed as low as possible, two launch stabilizer. That is about the limit in weight for the LV-45 engine to launch the rocket in an efficient manner.

This two stage is easy to fly with plenty of fuel to reach orbit, circularize, or go higher where the thrusters can be used to fine tune the orbit.

You can also eject the second stage when paragee is about 65K and circularize with the thruster pack. It won't take much RCS fuel to circularize the orbit. That way, the second stage will eventually crash back to Kerbal due to atmospheric drag at the paragee.

Edited July 4, 2013 by SRV Ron

[GJames]

I figured out a pretty neat way of doing this last night, but you do need propulsion on your satellites.

I put a nuclear-powered probe carrier into orbit that was carrying five ion-powered probes. I raised the carrier's periapsis to geosynchronous altitude (2868.4km) and then moved it's apoapsis to 1225km. With a bit of tweaking this gave me an orbit with an orbital period of 4 hours.

Then I released a probe at apoapsis and put it into a rough geostationary orbit with it's ion engine. I repeated this twice more, creating a network of three satellites each 120 degrees apart. I fine tuned the orbits to make sure that they stayed in roughly the same place for the next few months of in-game time

The last equatorial probe leaving the carrier. The other two are going to be put onto a geosynchronus polar orbit using the same method, but where the carrier has an orbital period of three hours so they are placed 180 degrees apart.

[Kimberly]

Propulsion totally ruins my cubesat designs...but I'll give it a try, thanks guys.

[Kegereneku]

Well, one alternative is to use a carrier-vehicle capable of several orbital maneuver, circularizing for one satellite, lowering your orbit precisely, then circularizing and dropping another satellite.

Basically it only ask for more fuel and time.

The carrier-ship could use ionic engine but it certainly won't accelerate fast.

Oh and use junior docking for separation if you don't want debris in orbit or to push away the satellite.

[arq]

Thanks for all the advice, guys...I'm still not too fond of the idea of giving satellites their own propulsion, as I like to keep it simple, but I'll consider my options.

As for polar orbits...how do you adjust a polar orbit's separation from another polar orbit, other than getting into the orbit at a different time?

To adjust the East/West longitude of polar orbits, simply wait to launch until you are where you want to be. After launch, your ship will stay at that longitude, so if it happens that another one is 45deg behind it at launch, that polar orbit will be 45deg away in orbit too. To change the longitude after launch, make burns in the desired direction (and perpendicular to pro/retrograde) at the north/south pole. However, changing is very expensive so it's easier to get it right the first time.

[maackey]

Propulsion totally ruins my cubesat designs...but I'll give it a try, thanks guys.

You can place the little oscar-b tank and an ant engine *inside* the probe body using a cubic strut (or noclipping in the cheats menu -- alt f12) to keep your probe aesthetically pleasing and small. I really only did this with the sputnik probe to make it look more legitimate, but it could work with the others as well.

[Colonel_Panic]

Propulsion totally ruins my cubesat designs...but I'll give it a try, thanks guys.

I use cubesats with propulsion and it fits in there rather nicely in my experience... just drop an oscar b right below the probe core and an ant engine on the end, enclose in cube except for the back end, where you can stash your batteries and any other instruments you want to carry discretely.

[Colonel_Panic]

I figured out a pretty neat way of doing this last night, but you do need propulsion on your satellites.

I put a nuclear-powered probe carrier into orbit that was carrying five ion-powered probes. I raised the carrier's periapsis to geosynchronous altitude (2868.4km) and then moved it's apoapsis to 1225km. With a bit of tweaking this gave me an orbit with an orbital period of 4 hours.

Then I released a probe at apoapsis and put it into a rough geostationary orbit with it's ion engine. I repeated this twice more, creating a network of three satellites each 120 degrees apart. I fine tuned the orbits to make sure that they stayed in roughly the same place for the next few months of in-game time

The last equatorial probe leaving the carrier. The other two are going to be put onto a geosynchronus polar orbit using the same method, but where the carrier has an orbital period of three hours so they are placed 180 degrees apart.

This is actually a really good idea and I might do something like this in the future.

ion engines are probably overkill tbh, you don't need a lot of delta v for a sat like that, better to use an oscar b and ant engine. More acceleration, less weight, smaller size, no need for large batteries or solar panels.

[Kimberly]

I use cubesats with propulsion and it fits in there rather nicely in my experience... just drop an oscar b right below the probe core and an ant engine on the end, enclose in cube except for the back end, where you can stash your batteries and any other instruments you want to carry discretely.

The Oscar B tank is wider than the cube, so it sticks out when you try to clip them.

[Colonel_Panic]

The Oscar B tank is wider than the cube, so it sticks out when you try to clip them.

I'm using an octo with structural panels in a cube form, not the cube core.

[Wikkyd]

Here is the best way I have found to evenly space out satellites. Plus I derive the math behind this method in the video. Enjoy

 

[Streetwind]

1 hour ago, Wikkyd said:

Here is the best way I have found to evenly space out satellites. Plus I derive the math behind this method in the video. Enjoy

Please don't dig up four year old threads. Like, only a single person in the entire discussion has even visited the forum more recently than one and a half years ago. And it's not the person who asked the question.

[Red Iron Crown]

People wanting to discuss the new tutorial shared can check out the thread here:

Closing this one.