UmbralRaptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Fuchs. We currently target 1.5.1, 1.6.1, 1.7.x, 1.8.1, and 1.9.1. <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… | <egg> also 4e16 m * 2^-52 is uncomfortably large
armed_troop has joined #principia
<discord->
lpg. — well I'll be hitting the point I was aiming for; this is a guided lander. but good to know; the biome map isn't quite so fine-grained
raptop has quit [Read error: Connection reset by peer]
raptop has joined #principia
egg|cell|egg has joined #principia
Raidernick has quit [Read error: Connection reset by peer]
Raidernick has joined #principia
egg|upstairs|egg has joined #principia
egg|cell|egg has quit [Ping timeout: 190 seconds]
<discord->
Pteropodidae. — I'm not sure if this is the right place, but it's a physics-y question and the denizens of this channel seem like a better fit
<discord->
Pteropodidae. — So someone in a different server claimed that lidar would be significantly better than radar for detection of other spacecraft
<discord->
Pteropodidae. — They said that radar signals degrade much more rapidly in space, and there's more interference from solar radiation, cosmic dust, and "other factors"
<discord->
Pteropodidae. — How accurate is that claim, if it's specific enough to make that judgement?
<discord->
Pteropodidae. — Or should I ask in #offtopic?
egg|upstairs|egg has quit [Remote host closed the connection]
<raptop>
the correct answer at any sort of range is passive IR telescopes, as both lidar and radar are 1/r^4
<raptop>
(Why not 1/r^2? Because the signal has to go from your craft to theirs, and back)
<discord->
Pteropodidae. — That's a point I didn't think about
<discord->
Pteropodidae. — What if you *had* to use active detection for some reason or another?
<raptop>
Like, there's a reason that those radar images of asteroids use a 70 m dish in Goldstone, or a 300 m one in Arecibo
<raptop>
Uh, I'd only want active for characterization
<discord->
Pteropodidae. — Hmmm
<discord->
Pteropodidae. — So basically only once you have a general idea of direction and maybe distance, and want to get more details?
<raptop>
Yeah. eg: radial velocity, some surface composition, etc
<raptop>
Also AIUI, you can git the distance to much higher precision. But I'd want to double check with eg: egg
egg|cell|egg has joined #principia
<raptop>
I suspect that the friend isn't big on radar because there are various big radio sources (hi, jupiter), but I'm not sure on if they're powerful in the right frequency range
<discord->
Pteropodidae. — Their reasoning also includes nebulous "things I'm not allowed to talk about" because they claim high-ranking military knowledge, but that isn't exactly helpful for this particular conversation
<discord->
Pteropodidae. — For a little more context, he and someone else were discussing some fantasy setting
<discord->
Pteropodidae. — For a little more context, he and someone else were discussing some fantasy/sci-fi setting (edited)
<discord->
Pteropodidae. — Including tech to reduce IR radiation, and locations potentialy not near fun radio sources like Jupiter
<discord->
Pteropodidae. — Although the specific claims about radar signals degrading more quickly in space and increase interference were based on real-world knowledge as far as I know
<raptop>
Probably working with some assumptions wrt the van allen belts or the like?
<discord->
DRVeyl. — 1/r^4 because it is absorption and [isotropic?] re-emission? There-and-back is just a doubling of the distance, so as 1/(2r)^2.
<raptop>
Well, reflection acting as re-eimission
<mofh>
yeah radar ranging gives good distance values for near-earth objects and anyting you can talk to
<discord->
Pteropodidae. — I have no idea. I wasn't directly involved in the conversation and only caught it after the fact, so I didn't have an opportunity to ask for specifics
<discord->
Pteropodidae. — Including tech to reduce IR emission, and locations potentialy not near fun radio sources like Jupiter (edited)
<raptop>
And while not necessarily isotropic, certainly incoherent
<discord->
DRVeyl. — Ok. So more about the loss from reflections not back towards the receiver. 1/r^4 assumes that it reflects isotropically. I suppose that's a good general/practical assumption. Some things might be better, some worse, depends on geometry and a bunch of material properties. Cool.
<raptop>
IIRC, focus over some cone still gives you the 1/r^4 (or 1/r^2 if you only care about one direction) relation. You just get a nicer constant.
<raptop>
Physicist assumptions~
<discord->
Conventia. — I just put up a 4 sat comms network. They are in a 3 hour orbit around 4189km (~5 degree inclination). After about 120 days, they seem to have drifted far enough apart to break the cycle. Is that expected? Should the orbit be higher?
raptop_ has joined #principia
raptop has quit [Ping timeout: 189 seconds]
raptop_ is now known as raptop
Mike` has quit [Ping timeout: 204 seconds]
<raptop>
Yeah, that happens. eggcentric orbits with the periapses at different points can help. (eg: Draim tetrahedron)
<raptop>
Part of the problem is with simulating stationkeeping maneuvers with timewarp
<discord->
Pteropodidae. — What should I google if I want to find plots of how strongly cosmic dust absorbs EM radiation at different wavelengths?
<discord->
Pteropodidae. — What should I google if I want to find plots of how strongly cosmic dust/other "stuff" absorbs EM radiation at different wavelengths? (edited)
Mike` has joined #principia
<discord->
Kirk. — From my understanding IR is by far the best to use in space for detecting other spacecraft. Even if your target somehow drops their surface temperature to that of the solar system background (using massive LH2/LHe tanks as a heat sink), the second they fire their engines any IR scope looking their way within a few million kilometers will see them easily
<raptop>
Yeah, that's the standard lore
<discord->
Kirk. — Even ion engines aren't safe, their exhaust is hot enough that the plume would show up
<discord->
DRVeyl. — Well. A few seconds later, anyway 😉
<discord->
Kirk. — And anyway, if you're running ion engines on a manned spacecraft, you're gonna be using nuclear reactors that will be putting out a ton of waste heat
<raptop>
Uh, for absorption, most wavelengths are visible over interstellar (and many intergalactic) distances. Though there's the occasional dust cloud that limits things
<discord->
Pteropodidae. — Hmmm
<discord->
Pteropodidae. — I feel that they'll handwave away the emissions part with "sci-fi"
* raptop
is also checking an ISM textbook
<discord->
Pteropodidae. — But that argument definitely makes sense
<discord->
Kirk. — If you can handwave the waste heat from a nuclear plant, thats some pretty magic tech
<raptop>
If you really want stealth along the lines of star trek, go with a soft sci-fi setting along the lines of star trek
<discord->
Kirk. — From what I can find, space dust mostly absorbs in the IR band anyway, although its not enough to matter for ranges below a few AU
<discord->
Pteropodidae. — A nuclear plant isn't involved, but their power source is probably just as magical
<raptop>
It also depends on the dust and the IR. *gestures at those images that WISE and 2MASS took of Maffei 1 and 2
<raptop>
*
<discord->
Kirk. — Radar and such will also be effected, although far less than, say, the atmosphere does. If you're blasting away with active you detection range will still be pretty far (although still much less than passive IR)
<discord->
Kirk. — And of course, if you're blasting away on active, you can be detected over twice as far away as you can detect by passive radar
<discord->
Pteropodidae. — Seems I should be on the more skeptical side of this guy's claims
<discord->
Kirk. — In general using any active sensors in space is an awful idea, without anything to really diffuse your emissions, people can detect them from extremely far away (like, AUs for a few kilowatt radar)
<discord->
Kirk. — While your range is generally still only gonna be a few million km to get vague returns, and only a few hundred to actually get solid data
<discord->
Pteropodidae. — I think in this specific case the active detection is being done by a blatantly obvious station of some sort, so being detected isn't as much of an issue
<raptop>
Yeah, having some big dishes blasting away for detection (or usually characterization), and passing the data on makes sense
<discord->
Kirk. — Fair enough, with a 100 meter dish or something you can definitely pick up a ship-sized object at some pretty good range
* raptop
meeps
<raptop>
100 m in radio, I assume?
<discord->
Kirk. — Although, modern radar absorbing techniques can drop aircraft to RCS of a few square centimeters
<discord->
Kirk. — A spaceship that doesn't care about aero at all can probably keep its RCS within the small meteorite range pretty easily
<raptop>
Seems reasonable. Though I bet you get some weird position dependencies if you have much in the way of solar panels or radiators
<discord->
Kirk. — True
<discord->
Kirk. — Although if you're going with whatever magical zero-waste-heat power source they seem to be talking about
<discord->
Kirk. — You can make those reflective areas very small
<discord->
Kirk. — Generally passive IR should be the best, your target can't maneuver without giving away their position, and they can't do anything useful without maneuvering
<discord->
Pteropodidae. — The particular method they use to deal with heat is to divert it into internal heatsinks
<discord->
Pteropodidae. — Which will have to be jettisoned after some period of time
<raptop>
Huh, found a vague estimate of V-band attenuation in the galactic plane as ~1 mag/kpc
<discord->
Pteropodidae. — They said it has some precedent somewhere?
<discord->
Kirk. — Elite: Dangerous
<discord->
Kirk. — Lol
<raptop>
(You're never looking at kpc distances if you're looking for spacecraft)
<discord->
Pteropodidae. — What's a mag?
<raptop>
magnitude, as in a factor of ~2.5
<discord->
Pteropodidae. — Ah
<discord->
Kirk. — I mean, internal heatsinks work, but as soon as you dump one everyone is gonna see it
<raptop>
uh, 100^0.2 to be exact
<discord->
Kirk. — and start paying very close attention to the area it came from
<raptop>
Kinda curious as to how much you can actually store if you go from, say, 250 K ice to 373 K water
<discord->
Pteropodidae. — Right, the idea is that you get in and out before you have to dump the heatsinks
<discord->
Kirk. — You're much better off keeping a giant slush LH2 tank, and letting it heat to about 5 kelvins before venting it
<discord->
Kirk. — Even high gain IR scopes can't see 4 kelvin hydrogen until very close
<discord->
Pteropodidae. — Huh
<discord->
Pteropodidae. — That's an interesting idea
<bees>
0.05 au, hundreds KW power radar, 2 km target
<bees>
i'd assume that anything with the size of a small spaceship is almost invisible even at this distance
<discord->
Kirk. — And yet that hundreds of kW can probably be spotted pretty easily from a few AU
<discord->
Kirk. — The background temp of interplanetary space varies, but its around 165K, albeit very rareified
<discord->
Kirk. — If you keep the temperature of the hydrogen you're dumping below about 10K, IR scopes won't have the gain to see it
<discord->
Kirk. — Even better if you can stay near a planet or moon, in which case you can probably dump a lot hotter hydrogen without getting seen
<discord->
Kirk. — Of course, maneuvering will still give your position away, unless you maneuver with the aforementioned hydrogen. But in that case you're basically using cold gas thrusters, you're limited to a few hundred newtons and maybe 100 seconds ISP
<bees>
NASA Deep Space Network seems to use 20 kW transmitters, and they can reach beyond pluto
<bees>
i wonder what % of that power goes off-beam
<discord->
Conventia. — Perhaps I'll try Draim's Tetrahedron another day. 😛 I'm guessing the easiest way to figure out the orbits is to cheat something into the right location and rendezvous?
<bees>
to be detected from a different part of the sky
<discord->
Kirk. — Yeah, at that power level you can be detected from the next solar system over, assuming you sweep your beam over them
<raptop>
bees: if we're doing that, there's a woodpecker outside of Chernobyl that is supposed to be the most powerful radar actually used? >_>
<raptop>
10 MW
<raptop>
Oh, not actually 10 MW. *glares at radio numbers*
<bees>
the whole point of it was to bounce waves from ionosphere, though
<bees>
not send them to space
<discord->
Kirk. — Off-axis emissions depends of the dish size
<discord->
Pteropodidae. — Does DSN do detection of previously unknown objects, or just communication with things whose positions are already approximately known?
<discord->
Kirk. — DSN is generally only used for communicating with spacecraft
egg|cell|egg has quit [Ping timeout: 204 seconds]
<raptop>
^
<discord->
Kirk. — But yeah, even the 300 meter Arecibo Radar pumping out a few hundred kWs can't even detect pluto
<discord->
Kirk. — While a 4 meter dish can detect it loud and clear from pluto
<discord->
Kirk. — But yeah, even the 300 meter Arecibo Radar pumping out a few hundred kWs can't even detect pluto I'm pretty sure (edited)
<bees>
it can detect Pluto at ~1-2 AU, probably
<raptop>
Huh, Pluto was found with a 13 telescope. No idea what the exposure time was with the glass plates
<discord->
Kirk. — Yeah, pluto is reasonably reflective
<discord->
Kirk. — iirc Arecibo can get Venus's surface at a few kilometer resolution
<bees>
so, if you rely only on a radar to spot enemy ships, and you keep it active, then enemy ships can wait ~0.2 AU from the station, drop missile pod, slowly boost away and launch ze missiles. when ze missiles burn their boost stages, they can also slowly track you, and you can even miss their initial boost if you dont scan 100% of the sky all the time. a few weeks later your ships would be destroyed, and you would have no idea what hit you.
<bees>
every large stationary or near stationary target has almost zero change in real space war, imho
<bees>
the only exception would be deep and heavy atmosphere worlds, where you can float your launch facilities to the edge of it and use them only when neccesary
<bees>
something like Titan
<discord->
Kirk. — I mean, you could have surface facilities
<discord->
Kirk. — On colonies
<discord->
Kirk. — And rely on the fact that your opponent probably doesn't want to lob weapons at civilian targets
raptop_ has joined #principia
<bees>
tbh, all space-faring civilizations are inherently doomed by the fact that you can _so_ easily throw a few retrograde rocks on whatever stationary thing you dont like
<discord->
Kirk. — Indeed
<bees>
maybe you can counteract that by digging _really_ deep into a big asteroids
raptop has quit [Ping timeout: 378 seconds]
<bees>
it should be much easier, and you can have available volume even greater than Earth for some large ones
<bees>
so no space bases under the sun
<bees>
only deep nukular bases inside asteroids
<discord->
Kirk. — But for a space station with a 300 meter radar, you can throw a missile at it from say, the outer solar system
<discord->
Kirk. — Give it cold gas thrusters to make terminal corrections
<discord->
Pteropodidae. — Hmmm
<discord->
Kirk. — And radar absobtive coating
<bees>
yes, everything in open space should be as small and agile as possible
<discord->
Kirk. — And radar absorbtive coating (edited)
<discord->
Kirk. — And your 300 meter radar won't be able to see it until its around 500 kilometers out
<discord->
Pteropodidae. — Defense sounds really hard in the space age
<discord->
Kirk. — If you threw it from the outer solar system, its probably moving at over 50 km/s relative
<discord->
Kirk. — So you have about 10 seconds to hit something the size of a small car before it hits you
<bees>
you can boost from behind some relatively big asteroid
<bees>
and rely on gravity assist to guide you to the target
<discord->
Kirk. — And realistically, it won't be one, it'll be a few dozen all at different angles that you detect at roughly the same time
<bees>
this way you can even use chemical rockets for initial speed bump
<discord->
Kirk. — Bonus points if they're actually casaba howizters, in which case they can probably neutralize a 300 meter radar from 500 kilometers out
<discord->
Kirk. — In which case your only warning will be your radar, and anything near it, evaporating in a wave of gamma radiation and relativistic plasma
<bees>
key question would be - if you throw 50m asteroid at some minor planet on retrograde trajectory and 50 km/s approach speed, what effect it would have for a 10-100 km underground base near the impact location?
<discord->
Kirk. — Oh wait, I grossly overestimated the radar cross section of a stealthed nuke
<discord->
lpg. — seems like defense in depth would be the name of the game. don't give it one target, give it lots that can back each other up
<bees>
if base would be likely destroyed, then space civilization would be either peaceful or it would not be at all
<discord->
Kirk. — Yeah no, a 300 meter radar isn't detecting a stealthed missile until it's about 20 kilometers out
<discord->
Kirk. — And if you have that level of space presence, getting something over 20 km/s isn't hard at all
<bees>
i think you forgot a zero in distance
<discord->
Pteropodidae. — Would Newton's impact depth approximation apply in this case?
<discord->
Kirk. — I did not forget a zero
<bees>
because existing anti-air systems are better
<bees>
and they do not have 300m radars
<discord->
Kirk. — They're not dealing with stealthed missiles
<discord->
Kirk. — What range can one detect, say, a B22
<bees>
a few hundred kilometers, probably
<discord->
Kirk. — What range can one detect, say, a B2 (edited)
<bees>
well, you would not know that it would be B2, but _something_ at that direction
<bees>
200 km, lets say
<discord->
Kirk. — Existing theater radars can get a fix on a B2 at around 50 km
<discord->
Kirk. — 50-100 km, allegedly'
<discord->
Kirk. — 50-100 km, allegedly (edited)
<bees>
fix yes, knowing that _something_ is there is probably close to 200 km
<discord->
Kirk. — A missile is a lot smaller
<discord->
Kirk. — Ok, turns out the Arecibo telescope has an awful angular resolution
<bees>
and 300 meters are a lot bigger than existing theater radars
<discord->
Kirk. — So, using the Atacama Large Millimeter Array as a reference instead
<bees>
you can actually deploy an active detection net without using radars
<bees>
lots of swarm satellites that shine a laser on your station from as far as orbits allow
<bees>
if you can make them stable enough, you can detect every intersection with a laser ray by something
<bees>
or radar, it probably would be better
<discord->
Kirk. — That would need insane amounts of emitters to have any useful range
<discord->
Kirk. — I found actual equations for radars, give me a second to do the math
<bees>
tbh, whatever radar detection could be there, it would lose compared to a swarm of IR stations
<bees>
althrough
<bees>
how long can you keep absorbing all sun radiation for a several meters missile?
<discord->
Kirk. — You could cool your missiles to 3 kelvin before launching them
<discord->
Silavite. — This is probably just me being a dumb-dumb (I'm not even sure if this is a Principia issue), but I seem to be unable to select a target in map view. I've been able to do this before in previous flights, but the UI seems to stop cooperating just when I want to send something to Mars. (Inconveniently enough)
<bees>
reflecting in any frequency is strictly forbidden
<discord->
Kirk. — assuming a reflective skin
<discord->
Kirk. — ah
<discord->
Kirk. — Well, a few minutes at most
<bees>
because then you would be shining bright in visual range
<bees>
if you actively cool the skin and melt something inside
<_whitenotifier-d13c>
[Principia] pleroy opened pull request #2601: Change the solar system test to use the integrator we use in real life - https://git.io/Jf1dz
<discord->
DRVeyl. — dB scales make some of these numbers easier. What are you using as your minimum receiver sensitivity?
<discord->
DRVeyl. — (Also hand waving the idea of 100m dishes scanning all directions in 3D. I suppose you really have a few planar arrays and massively parallel processing to steer the response.)
<_whitenotifier-d13c>
[Principia] eggrobin labeled pull request #2601: Change the solar system test to use the integrator we use in real life - https://git.io/Jf1dz
egg|upstairs|egg is now known as egg|laptop|egg
egg|laptop|egg has quit [Remote host closed the connection]
egg|laptop|egg has joined #principia
egg|cell|egg has quit [Ping timeout: 189 seconds]
egg|cell|egg has joined #principia
egg|laptop|egg has quit [Remote host closed the connection]
<_whitenotifier-d13c>
[Principia] pleroy closed pull request #2601: Change the solar system test to use the integrator we use in real life - https://git.io/Jf1dz
<_whitenotifier-d13c>
[Principia] pleroy pushed 2 commits to master [+0/-0/±2] https://git.io/Jf1jD
<_whitenotifier-d13c>
[Principia] pleroy c7e227e - Use the proper integrator and adjust the tolerances.
<_whitenotifier-d13c>
[Principia] pleroy c4766d1 - Merge pull request #2601 from pleroy/SolarSystemTest Change the solar system test to use the integrator we use in real life
egg|laptop|egg has quit [Remote host closed the connection]
egg|laptop|egg has joined #principia
<mofh>
///win 15
<discord->
Kobymaru. — how can I see celestial predictions in the Tracking Station?
<discord->
Kobymaru. — Oh man this principia maneuver node executor in MechJab is a godsent
<discord->
Kobymaru. — works perfectly
egg|laptop|egg_ has joined #principia
egg|laptop|egg_ has quit [Ping timeout: 204 seconds]
egg|laptop|egg_ has joined #principia
<discord->
Diego_. — hi! I'm having trouble using the maneuver node executor for Principia. It leaves it short of 100 m/s, which is not a tolerance I'd expect. Am I doing something wrong? I've seen threads saying to select specific options on principia, but even so, the outcome is the same. Does it count the time it take to the engine to get to full thrust?
<discord->
lpg. — it does not take spool-up time into account at all
<discord->
Diego_. — is there anyway of stopping the burn in term of total delta V spent, rather than burn time?
<discord->
lpg. — It'll start the burn on the dot, "lose" some time while thrust climbs, and cut the burn on the dot as well, leaving you short the very end of the burn, where TWR is highest
<discord->
lpg. — no
<discord->
lpg. — I've just started experimengint with pulling ignition time back manually, and adding dv to extend burn duration. it works, but is very clunky
<discord->
Diego_. — jeez, that pretty much makes the whole thing unplayable, at least in the early career
<discord->
lpg. — I've just started experimenging with pulling ignition time back manually, and adding dv to extend burn duration. it works, but is very clunky (edited)
<discord->
lpg. — yup
<discord->
Diego_. — it's a shame, it was looking great
<discord->
lpg. — crazy people rely on kOS and kRPC to do their burns
<discord->
Diego_. — lol
<discord->
Diego_. — maybe kOS can check the deltaV?
<discord->
Diego_. — I'll have a look, I haven't really looked too much into it
<discord->
Diego_. — thanks!
<discord->
egg. — ultimately, nothing will solve that issue (in particular, the half-measures suggested here won't) but proper closed-loop guidance
<discord->
egg. — and control theory is hard
<discord->
egg. — @lamont has given us PVG for launch so I guess the first step is there on that long trek towards manoeuvre execution by MechJeb