<awang>
For example, at this moment my aerobee has expended 704.7 m/s, currently at 391.7 m/s, with no steering losses, 278.2 m/s gravity losses, and 14.9 m/s drag losses
<awang>
Still leaves 19.9 m/s of losses from... somewhere
<ProjectThoth>
Is the loss value constant?
<awang>
No
<awang>
Right after liftoff it was actually negative
<awang>
Right now it's 45 m/s
<lamont>
if you’re in an elliptical orbit your velocity won’t be constant even though you’re not burning and there’s no losses anywhere
<ProjectThoth>
Strange...
<awang>
Quite possible I'm not calculating drag losses right
<awang>
Drag reported by MJ matches that reported by FAR
<awang>
so that part is right at least
<awang>
At apoapsis, the difference is 166.2 m/s
<awang>
Hmmm
<awang>
What other sources of loss are there during a launch
<awang>
Also seems parachutes don't contribute directly to the vessel's drag?
<ProjectThoth>
Isp inefficiency?
<awang>
I think that's accounted for in the dv expended field?
<ProjectThoth>
Worth testing, imo.
<awang>
How am I supposed to test that?
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<NathanKell>
o/
<Qboid>
NathanKell: TheKosmonaut left a message for you in #kspmodding [30.10.2017 04:56:25]: "You didnt know? It went by quick so I could be mistaken, but I am almost certain that there was a loading message w/ you name"
<awang>
Looks like MJ calculates dv expended as dt * acceleration
<awang>
So should take into account isp
<awang>
Indirectly
<NathanKell>
awang, Sarbian: I believe that's because I wanted, for aerogui, to display the up force rather than the pure lift force.
<awang>
NathanKell: Misleading names :(
<awang>
Anyone see this with the VSR RD-100 series?
<awang>
Figured it was easier to point you in the right place than describe it
<ProjectThoth>
I don't speak smart.
<awang>
Uh
<ProjectThoth>
Oh, wait, it's just that line of code. So it's based off of the velocity vector and any divergence of the vehicle's orientation in space from that vector?
<awang>
Yep
<ProjectThoth>
Ah, that's not something I've been accounting for in my rocket stuff.
<ProjectThoth>
I'm assuming you can dead reckon approximate burnout velocity (neglecting drag, because I don't have a Navier-Stokes summoning circle handy) based off of the delta-v of the stage and losses.
<awang>
Maybe?
<awang>
idk that kind of stuff
<awang>
Hmmm
<awang>
Drag reported by MJ still doesn't match drag from FAR
<awang>
But it's much much much closer now
<awang>
Or at least so far
<awang>
Yep, doing a heck of a lot better
<awang>
1.1 m/s difference between dv expended and losses + speed
<lamont>
shouldn’t all those surfaceVelocities be orbitalVelocities?
<lamont>
gravity drag shouldn’t care that the earth is rotating or how fast it is rotating
<ProjectThoth>
So is gravity loss given as a function of the vehicle's orientation in space, then?
<lamont>
gravity loss is the loss due to the alightment of thrust + gravity. steering loss is the loss due to the alignment of thrust + velocity.
<ProjectThoth>
lamont: So physical orientation in space rather than the velocity vector?
<lamont>
oh my god, someone corrected the gravity losses for the rotation of the mainBody
<ProjectThoth>
And steering losses are... cosine losses?
<lamont>
cosine losses are off axis thrust
<ProjectThoth>
I'm just trying to understand how to calculate them.
<ProjectThoth>
Because I have a sample trajectory handy (as well as vehicle orientation).
<lamont>
so if you build a 2 engine centaur and angle them so that they can each gimbal into the CoM of the vessel then you can have one get nuked by agathorn and the other can still complete the mission — but you’ll have to flair the engines out a bit and then you’ll get cosine losses, beause each engine is pushing a bit against the other in addition to pushing the whole thing forwards.
<ProjectThoth>
Ah, that I see.
<lamont>
that is what mechjeb means by “cosine losses” which is losses due to off axis thrust compared to forward of the vehicle
<ProjectThoth>
Is it possible to dead reckon steering losses if velocity angle and pitch angle are both known, or do they have to be calculated incrementally?
<lamont>
steering loss is just a function of AoA, although i’m pretty certain its the orbital AoA and not the surface velocity AoA
<lamont>
which is most likely why your steeringLosses calculation wasn’t working
<lamont>
steering and gravity losses don’t depend on the rotation of the planet below — think about an orbit over a spinning airless planet — so surfaceVelocity has to be incorrect
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<awang>
Ah, I see
<awang>
Time for another MJ PR?
<awang>
I'll check the numbers next time I have to start KSP
<ProjectThoth>
So I think I can dead reckon the burnout velocity, assuming a constant thrust and some other things.
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<schnobs>
Anyhoo, repeat question: is it even conceivable that this thing may return without melting?
<schnobs>
von Braun assumed that everything would be fine as long as you were taking your time...
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<soundnfury>
schnobs: depends on too many factors to predict. So just try it and report back ;)
<schnobs>
lost control. It's spinning.
<awang>
ferram4: Is there a difference between obtaining dynamic pressure from FARAPI.VesselDynPres vs vessel.dynamicPressurekPa?
<schnobs>
I have no idea how this vessel can ever be in any doubt as to which way it should be going.
<ferram4>
There should not be, though I believe that FARAPI does account for differences when in water.
<awang>
...Interesting
<awang>
How'd that come about?
<awang>
Can't imagine that coming up that frequently
<schnobs>
soundnfury: see above. As to heat, it doesn't quite seem to work with stock parts in RSS. If I was sane, I'd just turn it off completely....
<schnobs>
That reentry attempt took me 40 minutes to get to 5km/s @50km. Even if I can figure out a way to make it work, there's no way I'll do that on a regular basis.
<soundnfury>
schnobs: my spessplane once did a re-entry that did, indeed, complete an entire orbit after hitting the atmosphere, taking over an hour.
<soundnfury>
and yes, this is tedious and another reason I hate spessplanes
<soundnfury>
but hey, they're way cheaper than capsules in rp-1 and don't require R&D-centre upgrades, so v0v
<schnobs>
How does one control them, by the way?
<schnobs>
Used to be that you could use any kind of RCS thruster, as long as it was the one particular model approved for reentry.
<soundnfury>
schnobs: oh, I just put all my RCS thrusters in the shock shadow
<schnobs>
didn't work for me, way back when. Upside of wing, 40deg AoA -- poof!
* soundnfury
shrugs
<schnobs>
Anyway, I think I'll call it a day. That plane needs MOAR tailfins, it seems.
<schnobs>
I also needs to become shorther for proper proportions. No idea where shall i put my payload then, half of the fuselage is tanks -- that's what I get for recreating some artists' vision.
<BadRocketsCo>
How do y'all like my main work horse?
<BadRocketsCo>
It's an R-7 with a cryogenic upper stage :D
<wb99999999>
I have literally came up with the same idea before lol
<ProjectThoth>
BadRocketsCo: I'd give it an R-7/10.
<soundnfury>
ProjectThoth: not a perfect R-5/R-7?
<wb99999999>
R-7 has so much thrust it's almost a waste to not put a cryo upper stage on it
<BadRocketsCo>
wb99999999: it works bloody great though, doesn't it?
<soundnfury>
BadRocketsCo: that just sounds _wrong_
<soundnfury>
wait, what kind of cryo stage
<soundnfury>
hydrolox, or just kerolox?
<BadRocketsCo>
hydrolox, ye
<wb99999999>
I think someone actually plugged in some numbers for me and it turns out
<soundnfury>
then yeah, _wrong_
<wb99999999>
Block I is about the same mass as a Centaur
<BadRocketsCo>
soundnfury: slapped an RL10 on there
<wb99999999>
it's a perfect match, almost
<ProjectThoth>
Is the actual R-7 export limited?
<wb99999999>
problem is nobody really want it anymore
<ProjectThoth>
Seems like it could be a good foundation for an aspiring rocket company.
<soundnfury>
like, I don't care how well it works. It offends my sense of justice :/
<wb99999999>
it's really old and shabby
<BadRocketsCo>
soundnfury: huh?
<BadRocketsCo>
What's wrong with that? :D
<ProjectThoth>
wb99999999: s/old and shabby/reliable
<Qboid>
ProjectThoth thinks wb99999999 meant to say: it's really reliable
<soundnfury>
BadRocketsCo: probably just because hydrogen and soviet rockets do not belong together in my headcanon
<BadRocketsCo>
Heh, true
<BadRocketsCo>
The russians really missed a lot with that
<BadRocketsCo>
But oh well
<ProjectThoth>
I consider peroxide turbopumps to be a good starting point for reuse, actually.
<BadRocketsCo>
Their rockets are still great
<soundnfury>
ehhhh, hydrogen's not that great
<wb99999999>
my worry is the hardware is so old it's very costly to build infrastructure around it
<ProjectThoth>
Low temps on the turbines, longer MTF... could be pretty handy.
<wb99999999>
so even if someone buys it, it wouldn't worth it
<soundnfury>
except specifically for high-energy applications like outer-planets probes
<soundnfury>
ProjectThoth: go team peroxide \o/
<ProjectThoth>
soundnfury: Peroxide turbos are awesome!
<BadRocketsCo>
soundnfury: i mostly use her for that indeed
<BadRocketsCo>
and geosats
<wb99999999>
I want to ask a few questions about Merlin engines
<wb99999999>
they're pretty nice engines right?
<ProjectThoth>
wb99999999: They're pretty decent, as engines go.
<wb99999999>
I wander if it is the broad progress of technology or spaceX's intentional effort made the performance
<ProjectThoth>
Bit of both.
<wb99999999>
maybe I should rephrase my question in English Otz
<ProjectThoth>
Tech advancement makes the engine cycle more efficient, and SpaceX basically pushed kerelox to its (Western) limit.
<ProjectThoth>
Russia still has better OSRC tech.
<wb99999999>
if someone else were to make a new engine, would it be easy to make an engine with such low structural weight and decent Isp?
<BadRocketsCo>
wb99999999: i mean, easy is a pretty subjective term, isn't it? :P
<ProjectThoth>
Yeah, define "easy."
<wb99999999>
you are right.
<BadRocketsCo>
K
<soundnfury>
wb99999999: I think the SpaceX team were competent and disciplined (in the engineering sense) but not unreplicable genius
<wb99999999>
so may I say that modern technology made it possible, but spaceX made it good
<soundnfury>
so yes, if you have a team of good engineers with adequate resources and a clear focus on what to optimise for, I think you could make a roughly-as-good engine
<soundnfury>
it's achieving those preconditions that's the hard bit ;)
<BadRocketsCo>
I wonder how open space-x actualy is with their tech
<ProjectThoth>
BadRocketsCo: Not very.
<BadRocketsCo>
actualy that's a dumb question too...
<ProjectThoth>
But I'm not industry... yet.
<BadRocketsCo>
It's not like they can go give anyone blueprints of their engines...
<BadRocketsCo>
Some countries with rather unfriendly leaders may not use it for good thinga
<BadRocketsCo>
things*
<wb99999999>
so talking about Russia being big on OSRC
<soundnfury>
wb99999999: s/SR/RS
<Qboid>
soundnfury thinks wb99999999 meant to say: so talking about Russia being big on ORSC
<wb99999999>
I kinda got the impressions that for main engines, they did not make many engines that's not staged combustion after the R-7 at all
<ProjectThoth>
R7 wasn't staged combustion.
<ProjectThoth>
(I swear, I may be wrong)
<wb99999999>
I did say after the R-7
<wb99999999>
they made many ballistic missiles and as far as I remember most of them uses hypergols with some form of staged combustion cycle
<BadRocketsCo>
Russians didn't make a lot of new engines to begin with
<wb99999999>
they did, for missiles
<wb99999999>
not many for space rocket of course
<BadRocketsCo>
I mean, most of their tech is based on stuff from 1960s, even still having the same name
<BadRocketsCo>
wb99999999: ah yeah, fair enough
<wb99999999>
and when they decided to make big space rocket they went straight into staged combustion with kerolox
<wb99999999>
it almost feels like for them it's a staged combustion main engine or it's not a main engine
<wb99999999>
I mean a lot of literature goes like "they decided to go with high efficient close cycle engine..." for the N-1
<wb99999999>
but for me it feels more like a natural evolution
<wb99999999>
nobody decided to go staged combustion for the main engines, it's just what main engines always has been for them
<wb99999999>
and for the R-7, it's more of a V-2 derivative in terms of powerplants
<BadRocketsCo>
I mean, closed cycle engines are more complicated so it makes sense not to use them on missiles that you want to be as reliable as possible
<wb99999999>
actually I think performance outweights reliability a little bit on missiles when compared to space rocket...
<wb99999999>
since you'll be launching many of them in a short period of times
<BadRocketsCo>
Yeah but the question is what the russian goverment thinks :P
<BadRocketsCo>
Or the soviet union thought, respectively.
<BadRocketsCo>
Soooo
<BadRocketsCo>
Has anyone here actualy completed a legit Mars mission?
<BadRocketsCo>
Err, manned that is.
<BadRocketsCo>
soundnfury?
<wb99999999>
btw I just really like RD-253 in RO
<wb99999999>
one of the best booster engines there
<wb99999999>
upgraded version is insanely powerful
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<ProjectThoth>
BadRocketsCo: Give me a few weeks. :P
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<soundnfury>
!tell BadRocketsCo no mars here, I usually restart before getting to lunar flaggage. Think I might have done a venus fly-by once, not sure.
<Qboid>
soundnfury: I'll redirect this as soon as they are around.