egg changed the topic of #principia to: Logs: https://esper.irclog.whitequark.org/principia | <scott_manley> anyone that doubts the wisdom of retrograde bop needs to get the hell out | https://xkcd.com/323/ | <egg> calculating the influence of lamont on Pluto is a bit silly…
_whitelogger has joined #principia
<queqiao-> ⟨yaboiant⟩ 30 mins??
_whitelogger has joined #principia
_whitelogger has joined #principia
<queqiao-> ⟨redtyro⟩ I did it last week, worked fine
<queqiao-> ⟨quattrorumbass⟩ I don't know if this is a stupid question or not but would Principia work on interstellar distances, say with the mod real exoplanets?
_whitelogger has joined #principia
<queqiao-> ⟨sichelgaita⟩ No.
<queqiao-> ⟨redtyro⟩ so principia's orbit analysis shows 3 slightly different periods measuring different things
<queqiao-> ⟨redtyro⟩ which one do I use to properly time a communications network with multiple sats on a single launch that I want to station keep?
<queqiao-> ⟨redtyro⟩ if I'm aiming for a matching orbital period of a specific time
<queqiao-> ⟨Quadrupole🇵🇸🇸🇾🇨🇺⟩ Sidereal, I think
<queqiao-> ⟨redtyro⟩ awesome, thanks!
<queqiao-> ⟨Quadrupole🇵🇸🇸🇾🇨🇺⟩ Nodal period is the time between two equator passage, and anomalistic is between two periapse. Sidereal is how long it takes for the satellite to traverse 360 degrees.
<queqiao-> ⟨egg⟩ The sidereal period is rarely useful.
<queqiao-> ⟨egg⟩ Typically if you care about the relationship between the orbit and the ground, the nodal period is the more relevant one.
<queqiao-> ⟨egg⟩ That is not a well-defined goal. Why do you want that period? what is the ultimate mission objective that you are achieving with that choice of orbit?
<queqiao-> ⟨redtyro⟩ roughly equidistant station-keeping communications satellites
<queqiao-> ⟨redtyro⟩ the standard "launch 3 or 4 sats into a resonant orbit, circularize them at peri or apo with the same orbital period" mission
<queqiao-> ⟨egg⟩ Are they geosynchronous, or something lower?
<queqiao-> ⟨redtyro⟩ lower
<queqiao-> ⟨redtyro⟩ I need to be above 6,500km
<queqiao-> ⟨redtyro⟩ for the contract
<queqiao-> ⟨egg⟩ (The contract is probably dumb and RP-1 commsat contracts should use #σκοπός, but I digress.)
<queqiao-> The typical way to deal with this to pick a ground track recurrence, and that gives you something to which you station-keep yourself. See https://github.com/mockingbirdnest/Principia/wiki/Orbit-analysis#the-tool.
<queqiao-> ⟨redtyro⟩ the contract is just 3 or 4 satellites in orbits above 6,500km
<queqiao-> ⟨egg⟩ > Mean solar time
<queqiao-> > (Not yet implemented)Ah, I should document that; it is implemented now.
<queqiao-> ⟨egg⟩ Yes, the contract is dumb.
<queqiao-> ⟨redtyro⟩ I wanted to do station keeping to figure it out and prep for later when I need comm networks to keep communication on missions
<queqiao-> ⟨redtyro⟩ it's a pretty early satellite contract
<queqiao-> ⟨redtyro⟩ figure if I screw it up now, I still accomplish the contract and learn how to do it for later
<queqiao-> ⟨egg⟩ Yes, and more importantly you learn to think about how to design satellite orbits.
<queqiao-> ⟨redtyro⟩ exactly
<queqiao-> ⟨redtyro⟩ I'm new to principia and rp-1, but I've got several thousand hours in stock ksp, so I'm constantly adjusting my thinking and approaches to stuff
<queqiao-> ⟨redtyro⟩ unlearning bad habits
<queqiao-> ⟨egg⟩ I suggest reading the page I linked, it gives a bunch of examples. Basically you want to think of the grid traced by the subsatellite point, and keep your satellite to some nominal grid.
<queqiao-> ⟨redtyro⟩ the orbital analysis page or the https://discordapp.com/channels/319857228905447436/982749809482027129 stuff?
<queqiao-> ⟨egg⟩ (Sadly the commsat contracts are all dumb in RP-1. I have been working on a framework to make them about, well, actually establishing telecommunications, but someone who understands RP-1 needs to wire that up into RP-1.)
<queqiao-> ⟨egg⟩ The orbital analysis page.
<queqiao-> ⟨redtyro⟩ * ⁠σκοπός
<queqiao-> ⟨redtyro⟩ ok, will do
<queqiao-> ⟨redtyro⟩ I skimmed it last night, but it was late and my head wasn't completely in it
<queqiao-> ⟨egg⟩ σκοπός is that framework I am alluding to, which, once it gets used, would make that actually relevant to fulfilling the contracts.
<queqiao-> ⟨egg⟩ The orbit analyser tool is based on a book, which I always recommend: https://twitter.com/eggleroy/status/1123556005042970624
<queqiao-> ⟨egg⟩ There is an English version too, _Handbook of Satellite Orbits: from Kepler to GPS_.
<queqiao-> ⟨redtyro⟩ I'll check it out
<queqiao-> ⟨redtyro⟩ I love learning about this stuff
<queqiao-> ⟨redtyro⟩ hence the rp-1 and principia thing
<queqiao-> ⟨redtyro⟩ I'd always wondered why mission control orbit tracking looked like this instead of a straight line:
<queqiao-> ⟨redtyro⟩ when I was reading the page last night, it clicked - I'd never considered the earth's axial tilt
<queqiao-> ⟨redtyro⟩ satellite goes in a straight line, earth moves
<queqiao-> ⟨redtyro⟩ head explody moment
<queqiao-> ⟨test_account9540⟩ what does a straight line means 🤔
<queqiao-> ⟨egg⟩ There is the rotation, but even if the earth did not rotate, there is the projection: great circles do not become straight lines.
<queqiao-> ⟨redtyro⟩ well, from an abstract, simplifying the concept enough to graspt it, perspective
<queqiao-> ⟨redtyro⟩ the thing orbiting follows it's momentum, it doesn't change directions
<queqiao-> ⟨test_account9540⟩ it follows the orbit, which isn't straight...
<queqiao-> ⟨redtyro⟩ ok, if you mean it's round around the planet, I'm still following you
<queqiao-> ⟨egg⟩ If the planet does not rotate, the ground track is a great circle, which is the shortest path, so straight in that sense. But then you are not looking at a globe, you are looking at a flat rectangular map.
<queqiao-> ⟨redtyro⟩ if you mean the orbit is moving up and down (I know those words are not actually applicable, but I'm stuggling at finding others), then I'm lost
<queqiao-> ⟨redtyro⟩ like in space
<queqiao-> ⟨redtyro⟩ I get that it would do that in reference to a point on the ground
<queqiao-> ⟨test_account9540⟩ up and down is probably north and south?
<queqiao-> ⟨redtyro⟩ I guess, but that's still in reference to the planet
<queqiao-> ⟨redtyro⟩ I mean, the satellite keeps going prograde and curving around the earth
<queqiao-> ⟨test_account9540⟩ well you didn't launch to an equatorial orbit, it's inclined, so it spends some time in the northern hemisphere and some time in the southern
<queqiao-> ⟨redtyro⟩ it's direction doesn't shift perpendicularly to the body underneath it
<queqiao-> ⟨redtyro⟩ well, right
<queqiao-> ⟨redtyro⟩ but if the earth were perfectly still, that orbit line wouldn't be a wave that goes up and down when translated onto a map, it would be a straight line like this:
<queqiao-> ⟨test_account9540⟩ if earth didn't rotate then yes, i suppose you would pass over same spots again and again
<queqiao-> ⟨test_account9540⟩ the line still wouldnt't be straight on this map because of the projection
<queqiao-> ⟨test_account9540⟩ it would be a bit curved
<queqiao-> ⟨egg⟩ Yes it would, if the orbital plane is inclined.
<queqiao-> ⟨redtyro⟩ -like this:
<queqiao-> ⟨quattrorumbass⟩ Egg(robin?) I have to ask, do you have a degree in physics?
<queqiao-> ⟨quattrorumbass⟩ +Unrelated to Principia but I don't know where else to ask
<queqiao-> ⟨redtyro⟩ oh wait, ok
<queqiao-> ⟨redtyro⟩ it just clicked
<queqiao-> ⟨redtyro⟩ thank you both for bearing with me
<queqiao-> ⟨redtyro⟩ so if the earth didn't move, an inclined orbit would look more like this:
<queqiao-> ⟨redtyro⟩ so if the earth didn't move, an inclined orbit would look more like this:
<queqiao-> ⟨redtyro⟩ (the blue line)
<queqiao-> ⟨test_account9540⟩ looks right
<queqiao-> ⟨egg⟩ the blue line is just a less-inclined orbit
<queqiao-> ⟨egg⟩ how far north/south it goes is just how inclined it is
<queqiao-> ⟨redtyro⟩ but the spacecraft isn't actually changing directions in space, it's moving along the inclined circular path
<queqiao-> ⟨egg⟩ literally, the maximum latitude is the inclination
<queqiao-> ⟨redtyro⟩ right
<queqiao-> ⟨redtyro⟩ got it
<queqiao-> ⟨redtyro⟩ right, my freehand line wasn't accounting for the actual inclination of the orbit to match the map, I just drew a rough shape to illustrate how I was understanding the concept
<queqiao-> ⟨egg⟩ But yes, the fact that it goes up and down _multiple times_ is due to the rotation of the Earth.
<queqiao-> ⟨redtyro⟩ but the earth spins as the craft goes around it, so it hits the peaks and valleys of its inclination at different points in the earth's rotation, which is why you see multiple waves on a map of the orbit
<queqiao-> ⟨egg⟩ Yeah, every period (southmost-to-southmost) is one revolution of the satellite along its orbit, with the Earth rotating under the satellite, it takes multiple revolutions for it to get back to flying over its starting point.
<queqiao-> ⟨egg⟩ It might also not match up the first time it goes around the Earth, and in that case C_T_o is greater than 1.
<queqiao-> ⟨redtyro⟩ and in the future, if I'm trying to do an equidistant array of communication satellites, the easiest way to handle it would be to put them in geosynchrinous orbits roughly 1/xth (x being the number of satellites) around the earth
<queqiao-> ⟨redtyro⟩ the simplest way to do it, I mean
<queqiao-> ⟨redtyro⟩ or least complex
<queqiao-> ⟨egg⟩ That is giving yourself a lot of homework, because synchronous orbits are not very stable. Since they are always in the same place with respect to the lumps in the Earth, satellites in those orbits tend to get kicked out of geosynchronicity.
<queqiao-> ⟨redtyro⟩ launch them into ascending or descending nodes 1/xth around the earth so that they are equitorial
<queqiao-> ⟨egg⟩ (Also, since they are high, they tend to get kicked by the Moon. Also, since they are far, you have latency and high power requirements)
<queqiao-> ⟨redtyro⟩ hmm, so stability is an issue at geosync
<queqiao-> ⟨redtyro⟩ how do they handle that IRL? just constant adjustments
<queqiao-> ⟨egg⟩ Yeah, and more generally for anything with a one-day ground track cycle (semisynch like GPS is not great either).
<queqiao-> ⟨egg⟩ A longer cycle is more stable.
<queqiao-> ⟨egg⟩ Either adjustments fairly regularly, or, in the case of GPS, not keeping very close to the nominal orbit.
<queqiao-> ⟨redtyro⟩ so basically, the resonant orbit approach to sats in stock ksp is kind of bullshit in the real world
<queqiao-> ⟨egg⟩ Yes.
<queqiao-> ⟨redtyro⟩ because you can't keep them that stable
<queqiao-> ⟨redtyro⟩ so how do the starlink launches work?
<queqiao-> ⟨redtyro⟩ they just get close enough and cover the world in so many satellites that them moving around doesn't matter?
<queqiao-> ⟨redtyro⟩ I know they launch an absolute ton of them
<queqiao-> ⟨egg⟩ GEO communication satellites are a thing though. The problem isn’t stability (that means you need to do more stationkeeping, but you can just do it). The stock GEO-to-GEO relay thing is nonsense for power and latency reasons.
<queqiao-> ⟨redtyro⟩ I'm guessing I should just read the book
<queqiao-> ⟨egg⟩ Starlink is another can of worms entirely, and yes, I recommend reading the book.
<queqiao-> ⟨redtyro⟩ I think it will probably help me get things that at this point I don't even know I'm missing or misunderstanding
<queqiao-> ⟨redtyro⟩ and satellite orbits are fascinating
<queqiao-> ⟨redtyro⟩ and for now, for RP-1 purposes, I should be looking at the ground track cycles and where the orbits fall in respect to ground communication stations to figure out how to get good comm coverage
<queqiao-> ⟨redtyro⟩ instead of messing with station-keeping and sat-to-sat relay
<queqiao-> ⟨egg⟩ Intersatellite communications are far rarer in the real world than KSP leads you to believe. But drveyl can probably elaborate.
<queqiao-> ⟨redtyro⟩ it makes sense, though
<queqiao-> ⟨redtyro⟩ in most of what I'm learning with RP-1 and Principia, it seems that complexity is the biggest killer of anything you plan, and intersatellite networks seem impossibly complex
<queqiao-> ⟨redtyro⟩ KISS rule applies
<queqiao-> ⟨redtyro⟩ just make sure it can contact a ground station and your craft can contact it, then repeat with multiple ground station/satellite pairs
<queqiao-> ⟨redtyro⟩ much more simplicity to that, which makes it more likely to actually work
<queqiao-> ⟨redtyro⟩ and for this contract (which I now get why you said it's a bad contract), just launch something close enough, check the completion box, and move on instead of using it as a test run for later communications
<queqiao-> ⟨redtyro⟩ is my head in the right place with the above or am I still missing something I should be considering?
<queqiao-> ⟨redtyro⟩ just make sure it can contact a ground station (or multiple) and your craft can contact it, then repeat with multiple ground station/satellite pairs (or groups)
<queqiao-> ⟨drveyl⟩ Primarily because it's not a great contract, and it's a holdover from long ago with a different comms mod and very different comms progression. It probably shouldn't be available when it is, so...
<queqiao-> ⟨drveyl⟩ Not as much as we'd hope.
<queqiao-> Starlink it is planned and satellites have the hardware but I don't think it's active yet or maybe that's a recent development.
<queqiao-> Iirc iridium does it.
<queqiao-> TDRSS was designed for it.
<queqiao-> ⟨Quadrupole🇵🇸🇸🇾🇨🇺⟩ This is a digression but I have strongly mixed feelings. I am sorry for the wrong answer and not realizing that the contract was unrealistic. I will read the book and not make guesses in this channel.
<queqiao-> ⟨redtyro⟩ well, there are clearly some experts in this channel, but hey, most of us are just figuring it out as we muddle through it
<queqiao-> ⟨redtyro⟩ I'm helping people who are behind me in the career help channel while asking questions here on stuff where I am now in progression, sounds like you're doing the same thing
<queqiao-> ⟨redtyro⟩ no worries
<queqiao-> ⟨redtyro⟩ in group settings like this, the right answer usually comes out in the end
<queqiao-> ⟨makoivis⟩ Which book?
<queqiao-> ⟨makoivis⟩ Handbook of satellite orbits?