Pragmatic alternative to perfect orbits

[lodestar]

Everyone who tried to get a satellite network in orbit for RemoteTech communications knows that no matter how carefully you fine tune their orbital period, they will eventually get all messed up. Some players edit the save files for perfect orbits, or use hyperedit, but even doing that, the satellites will keep their perfect orbits only as long as you never control them or get within physics range.

So, while it's very cool to have those perfect polygons around your planets and moons and 100% coverage all the time with the minimum number of satellites, I'd rather find some other configuration that works most of the time without maintenance or cheating.

Is there any more pragmatic configuration that gives you coverage most of the time without cheating, without having to stay out of control and physics range, and without being affected by the orbital drift? Pairs of satellites in opposite orbits? Molnyia orbits? How do you do it?

Update: By "perfect orbits" I mean perfect orbital period or SMA, not Ap/Pe. I know that Ap/Pe and inclination don't really matter. That's not the problem here. The problem is that even perfect orbital periods aren't maintenance free if you take control of the satellites or get within physics range, and I'd like a configuration that can be maintenance free, even if I have to sacrifice some SLA or put more satellites in orbit. All the suggestions being posted here on how to maintain circular orbits, correcting them with the LV-1 or RCS before leaving control are all things I already do.

Edited January 28, 2014 by lodestar

[Kasuha]

Personally I believe orbital period is much more important than perfect Ap/Pe setting. It is easier to set up and maintain and as long as the orbit is at least roughly circular it's as good as perfectly circular for most practical applications.

If you expect random fluctulations in any direction, then the only solution is to install as many satellites as possible. The bigger swarm you have above the less are chances there will appear a hole big enough to deprive you of connection. I'd probably put them all on more or less the same high orbit so they don't fill the map too much.

[Jimbimbibble]

I put 4 satellites in a 500km orbit and it seems to work just fine. As long as they have the same period it shouldn't matter if the orbits are perfect (as mentioned above). There are mods that give you exact read outs on this information, so I would get one of those and use that to fine-tune your satellites with an ion engine. I like using a medium orbit like 500km because you get good coverage without your period being too sensitive to adjust accurately.

[Kasuha]

You don't need a mod to determine orbital period. Click on both Ap and Pe markers so they stay visible and make sure their difference is half the orbital period you're aiming for. It's easiest if you're going for exact mutliples of 2 hours. E.g. if one says 2:49:13 while the other says 5:49:13 you're in a stationary orbit (oribital period 6 hours)

[lodestar]

By perfect orbits I actually mean perfectly matching orbital periods or SMA, not Ap/Pe. The problem is that even with perfectly matching orbital periods, if you take control of the satellite or get within physics range, you get it out of rails and you'll get deviations over time if you don't correct them. I'd like a configuration that's maintenance free, even if it needs more satellites or doesn't guarantee coverage all the time, but most of the time.

[Soda Popinski]

Suggest setting the antennas pointing in the most optimal way, so you can keep your hands off them. That way, once you have them in the perfect orbit (SMA wise), you can leave them be.

Set all the KSO sats to point one antenna to Kerbin (the 45 degree cone one), keep one set to Active Vessel, and if you have another set of satellites (I keep 3 satellites in very high polar orbits for my interplanetary coms). I have 4 comsats in KSO, so I can just set the 2 opposite sats to Active Vessel, and the other 2 to whichever secondary satellite network I want (either my high polar or around another planet/mun).

If you keep all of them pointed at Kerbin, and not at Mission Control, it doesn't matter which satellite is patched into Mission Control. So really, they don't need to be synchronous, just have them all matching orbital periods. If you're OK with mods (and you better be, since you use RT2), I suggest Kerbal Engineer Redux.

Edited January 27, 2014 by Soda Popinski

[Duxwing]

You can maintain orbital perfection by:

-To each satellite attaching an LV-1 and an Oscar-B and adjusting your orbit after each use. When their fuel nearly runs out, boost them to a graveyard orbit.

-Avoiding controlling your satellites, thereby preventing the problem.

You can approximate orbital perfection by:

-So adding new satellites as to fill old gaps

-Molynia orbits

-Not caring if your network has a few roaming dark spots

-Duxwing

[User Unrelated]

I've got 8 different comms sats up right now. 4 in LKO, 2 a big higher up with comm dish coverage out to Minmus, and 2 around Mun for surface exploration.

I used Engineer redux to get the orbital periods perfect, to within 1 second (If the accuracy went lower, I would have done that, too)

so far, I'm about 2 years in after the first LKO sat launched... None of them have really moved

and I have even used one of the comm dish sats as a time-warp ship (to wait for the Mun to turn around so I could land on the bright side)

As long as the orbital periods are good, then everything should be fine.

My LKO cluster is pretty messy on the inclination end, but all of the orbits are relatively round...

I use a combination of designing heavy satelites, and a single ANT engine, or linear RCS port to get the fine-adjustment necessary to form nice orbits.

[mic_e]

Ap/Pe don't really matter; if you get them wrong, your satellite's longitudes will just fluctuate by a few degrees during the course of their orbits. The same goes for inclination.

All you really need is an orbital period of precisely 6 hours (for kerbostationary orbits) - use Kerbal Engineer or Mechjeb for that.

A error in the orbital period of 0.1 seconds (you usually get it to about that precision) will mean the satellite's latitude shifts by about 2.4 degrees per year - pretty neglegible.

[lodestar]

Well... since everyone seems to be missing the point, I added an update to the OP clarifying the problem.

[Soda Popinski]

Well... since everyone seems to be missing the point, I added an update to the OP clarifying the problem.

Then you didn't read my post on setting the antennas properly once, and leaving them be.

For each satellite, set one antenna to Kerbin, the other to Active Vessel (you can get away with 2 opposite side satellites if you have a 4 comsat system in equatorial orbit). If you have another satellite network, set a 3rd antenna to that. With the antennas set to Kerbin (not Mission Control), you don't even need to be in synchronous orbit, just have all your satellites with the same SMA.

Edited January 28, 2014 by Soda Popinski

[mic_e]

Suggestion 0 remains to use kerbosynchronous orbits.

Suggestion 1 is highly elliptical orbits: Pe = 70, Ap just out of the Mun's reach (9000 km).

Your satellite will be within 90 degrees of the Ap for 97.5% of its orbit, and within 60 degrees of the Ap for 94.4% of its orbit.

For example, use 4 satellites, with their Longitude of Periapsis shifted by 90 degrees each. Your coverage won't be perfect, but it will do in most cases.

Suggestion 2 will give you guaranteed connectivity for half the time: Put two to three satellites into high altitude circular polar orbits around the Mun, with their LAN spread equally across 360 degrees.

As long as the Mun is visible from KSC, you'll have contact to almost everywhere.

Suggestion 3 is to improve your coverage with ground-based comm relays. For example, a relay on the 6-km mountains next to KSC will cover a circle of 8 degrees in radius. A relay on a 100-meter tower will cover 1 degree (I'm not sure how well comm towers work with remote tech, though).

Suggestion 4 is to spam Medium Kerbin orbit (~300km) with omnidirectional comsats, and just hope for the best. Should work pretty well, but your computer might hate it. For extra fun, mix prograde and retrograde orbits.

Combination of some of the options might yield better results; for example, combine 2 and 3:

Put your commsats around the mun in 1000x1000 orbits, and build a land-based comms bridge towards the north pole. Build a ring of comms relays around the pole at around 80 degrees latitude, and your coverage will be precisely 100% (if you put the ring too far towards the pole, the commsats might become invisible while above the mun's south pole).

Edited January 28, 2014 by mic_e

[wmheric]

I think I get what the OP means by people missing the point. Speaking of the impossibility of perfectly circular orbits, orbits exactly matching a desired semi-major axis or a period, even with readouts from mods like Engineer Redux or MechJeb, are also, in principle, impossible because of the floating-point calculations. The issue is negligible in the beginning but if the player spends long enough with a save (e.g., multiple interplanetary missions could make you time-warp for tens or even hundreds of years), the errors start to show up as they propagate. Therefore, I'd say it is impossible to make maintenance free orbits currently in KSP.

Having said that, I'd go for keostationary orbits for low latitude coverage and Molniya orbits for polar coverage (and that's what I have done).

For low(er) latitudes:

In reality, geostationary orbits have a big practical advantage for communication uses over other type of orbits because they appear to be stationary to a ground observer, which means that as long as there is a satellite visible high enough above the horizon, an antenna can be pointed at it from a roof of any building anywhere in the world. On the other hand, in KSP, unless you are setting up ground stations around Kerbin, the KSC is the only place you want to keep 100% connection to, and the antennas at the tracking center are omni-directional with a range of 75 Mm, so it doesn't really matter whether a satellite remain stationary to KSC as long as there is another one to take over when it goes below the horizon; you may as well decide the altitude of your network to be, say, 1000 km, as a round number. My choice of the stationary altitude (2868.75 km) is because it is easier to launch very first few satellites if you're doing it unmanned -- if the first one is "always" in front of KSC there is less panic to set up those behind. Another reason is that the orbit is quite far out so the LKO region remains quite clear for me to see. So I could say it is entirely up to you.

For polar coverage:

I use polar Molniya orbits because I want the satellite to spend most of its time above the poles (besides the coverage advantage, you can also bring less battery because the satellite spends less time in an eclipse). But then again unless you're flying unmanned in a very low orbit or you want to communicate with something on the ground near the poles, these are less important. Also, if you're apoapsis is too high up the Communotron 32 stops working and you have to use dishes. You either need pointing from the keostationary ones (if you have bring extra ones on board), or from the ground by setting up a station at intermediate latitudes (so the signal goes Molniya probe <-> ground station <-> keostationary probe(s) <-> KSC). If you are doing the latter unmanned (an interesting task!), you can try the Reflectron KR-7 to ensure connection descend as it is the earliest one in the tech tree that does not break in the atmosphere while having the range to reach out far enough.

(For Molniya orbits you need to set up at least two to ensure coverage, which brings us back to the impossibility of matching their orbits exactly...)

If you're playing in the Carrer Mode (IMO RemoteTech is challenging (and thus fun!) only in this mode), eventually you will find yourself launching more and more probes (upgraded with Communotron 32 / upgraded with Duna coverage / upgraded with Jool coverage) to complement the old ones, so coverage "holes" will become less of a worry. Satellites crashing into each other is quite rare, and if crowded orbits really concern you, try separating them in group by changing the inclination slightly (e.g., a 0.5 deg is already a lot at the synchronous altitude).

Edited January 28, 2014 by wmheric

[Claw]

Suggestion 1 is highly elliptical orbits: Pe = 70, Ap just out of the Mun's reach (9000 km).

Your satellite will be within 90 degrees of the Ap for 97.5% of its orbit, and within 60 degrees of the Ap for 94.4% of its orbit.

For example, use 4 satellites, with their Longitude of Periapsis shifted by 90 degrees each. Your coverage won't be perfect, but it will do in most cases.

I was also going to suggest highly elliptical orbits in a petal shaped distribution (like a flower). For each satellite, it would maximize their time on the desired side of Kerbin. However in their elliptical orbits, even if they are a little out of time sync, they shouldn't be running each other over but rather be at slightly different points in their own ellipse. You might have to put up a couple extra satellites to guarantee overlapping cover (for those times when one satellite is outbound while the next one over is inbound). You might have a few minutes of blackout, but the orbits should be maintenance free.

[DisarmingBaton5]

Uh... Spam the sky with comsats?

[lodestar]

Suggestion 3 is to improve your coverage with ground-based comm relays. For example, a relay on the 6-km mountains next to KSC will cover a circle of 8 degrees in radius. A relay on a 100-meter tower will cover 1 degree (I'm not sure how well comm towers work with remote tech, though).

That's an interesting idea that hadn't occurred to me. I'll experiment with that.

[lodestar]

Having said that, I'd go for keostationary orbits for low latitude coverage and Molniya orbits for polar coverage (and that's what I have done).

That's what I've been doing too, and while it works reasonably well for Kerbin, as long as you don't touch your satellites too often, my networks in other planets, mainly Duna and Eve, are always a mess. More than once I warped through the ~150d of waiting for transfer windows and cruising to these planets, got there and didn't have coverage as planned, which is essential since I have to retract the long range omni antennas for aerobraking.

[Mystique]

My current setup is: one sat above KSC in KSO, one antenna alway pointed and KSC, whole bunch of others (with range just enough to cover Minmus missions) - other sats.

3 sats are orbiting at altitude of about 2000 km, don't remember exactly. Even though they have almost perfectly matching orbital periods, they shift a little bit in a year or two. But at this altitude it'll take long years before they stop to "see" each other. Those 3 target one another, forming constant triangle and at least one of them alway has contact with KSO sat. They also have antennas targeting active vessel, just in case.

And I have quite massive long-range relay satellit just outside Minmus SOI. It's targeting Kerbin all the time and has full-time contact with at least one of a/m sats and it has that huge orange dish. Kept access to social networks for 4 of my brave kerbonauts on they 2-year long mission to Jool and moons, Eeloo and Dres. Blackouts were quite rare (though it was manned mission and I needed comms for science reports only).

It's also good to add 1 sat on KSO or higher and 90 degree inclination, it may help avoiding blackouts a bit, especially on early stages of setting up network.

[SpeedDaemon]

Compensating for the lack of station-keeping is one time when I actually don't mind editing the save file.

My current RemoteTech setup has 6 tiny relays in 500km orbit that have a single 5Mm omni. I included RCS for "station keeping," and they're powered by a KSPI reactor that requires maintenance or replacement every few years (when the station-keeping fuel "runs out"). I launch and position them manually, then edit the save to lock them in place. Since they're omni-only, you never need to switch to them and disturb the perfect orbit until they need to be deorbited for replacement.

Then there are six massive satellites in Molnya orbits (4 equatorial, and two polar, all 90 deg. off of each other). These have enough antennas on them that one can be pointed at each planet, and one to active vessel, so I don't normally have to mess with these, either (yes, I'm lazy that way). They communicate directly to KSC or with the relays with another 5Mm omni. It's very rare to have a blackout with this setup.

[Seret]

Therefore, I'd say it is impossible to make maintenance free orbits currently in KSP.

Bug or feature? Is making maintenance-free satellite networks the objective of installing RemoteTech? Or is it to give you more stuff to manage?

[wmheric]

Bug or feature? Is making maintenance-free satellite networks the objective of installing RemoteTech? Or is it to give you more stuff to manage?

I wouldn't consider this as a bug/feature. It is the nature of floating-point arithmetics. I think the objective of the mod is to add realistic features to the game by introducing possible communication blackout. It does gives the player more stuff to manage (to set up networks, to plan ahead, etc.). In reality, although there are no floating-point errors, there are perturbations (from the Moon, the Sun and other planets; from the asymmetry of the gravitational field, etc.) and engines have to be fired from time to time to keep a satellite in a stable orbit, though everything is controlled by computers. In this case the mod shouldn't give too much of a burden as the player can control only one vessel at a time. I think the ability to somehow "snap" a satellite into some preset orbits so that the position of a satellite is reset regularly is a good workaround.

[lodestar]

In reality, although there are no floating-point errors, there are perturbations (from the Moon, the Sun and other planets; from the asymmetry of the gravitational field, etc.) and engines have to be fired from time to time to keep a satellite in a stable orbit, though everything is controlled by computers. In this case the mod shouldn't give too much of a burden as the player can control only one vessel at a time. I think the ability to somehow "snap" a satellite into some preset orbits so that the position of a satellite is reset regularly is a good workaround.

Precisely. Remote Tech adds a new dimension to the game, but sometimes it becomes a burden. It would be fine if we could program a satellite to fire its RCS in the background to keep orbit, for instance, and you retire them when the RCS fuel is over. That would be realistic, fun, and interesting in the career mode, since you could have generations of satellites according to your tech tree evolution. Maybe I'll end up writing a plugin that does something like that in the background, reset the satellite back to the preset orbit and remove the equivalent delta-v needed from the monopropellant resource.

[Kermunist]

I think this could be done fairly easily with a plugin. Roughly like this:

On putting the craft on rails:

1) Check if there are any other satellites around the same parent body with a SMA of within 0.1% of this one

2) If so, set this one's SMA to be the same

3) Record the time at which it was put on rails

Every so often (1 month?) or when taking a craft off rails:

1) Calculate the time since last flown

2) Subtract monoprop equal to time x mass x constant

3) If monoprop would be less than 0, set it to 0 give the craft a random small change to one of the orbital parameters.

I don't really have time to code it up though.

[RoboRay]

The newest MechJeb builds display orbital period to the hundredth of a second. With periods matched to that precision, even years of maximum timewarp produces no significant drift as measured with the phase angles to other satellites in the constellation.

Prior to this improvement, with period only displayed in whole seconds, I had about 15 degrees of drift after three years. These are in a 90-minute medium-orbit, not KSO, so the drift was faster than for stationary sats.

I don't return to my comsats and diddle with them once they are set up, so they stay where I leave them. The hard part is just having the orbit exactly right before they go on rails forever.

Edited January 31, 2014 by RoboRay

[LiveHereNow]

I think this could be done fairly easily with a plugin.

I think this is a great mod feature idea. You got it to orbit, you did the mission. You just don't want to spend two hours micro-adjusting satellites every few times you fly. Auto-reset and then like you mention... some sort of cost in monoprop and then "drift" sets in and you have to refuel, recover or kill (or whatever). May want to write that up in further detail and share with the RemoteTech folks?