Trouble calculating launch azimuth

[johan]

OK so I've done some reading and searching, but reliably calculating launch azimuth still escapes me.

I've set up a scenario on Europa as attached - two DeltaGliders, one in orbit the other on the ground at (0,0).

I get into the DG on the ground, set up OrbitMFD with the other DG as target, make sure it's "From" is set to EQU and read off the target inclination: 40.18.

So my calculation (from here: http://www.orbiterwiki.org/wiki/Launch_Azimuth), is:

B = arcsin(cos(40.18)/cos(0))
  = arcsin(0.76402...)
  = 49.82

Yet, if I launch at that heading (i.e. just a hair under 50 deg), I get to an orbit with 80 deg relative inclination to my target.

What am I missing here?

 

[GLS]

OK so I've done some reading and searching, but reliably calculating launch azimuth still escapes me.

I've set up a scenario on Europa as attached - two DeltaGliders, one in orbit the other on the ground at (0,0).

I get into the DG on the ground, set up OrbitMFD with the other DG as target, make sure it's "From" is set to EQU and read off the target inclination: 40.18.

So my calculation (from here: http://www.orbiterwiki.org/wiki/Launch_Azimuth), is:

B = arcsin(cos(40.18)/cos(0))
  = arcsin(0.76402...)
  = 49.82

Yet, if I launch at that heading (i.e. just a hair under 50 deg), I get to an orbit with 80 deg relative inclination to my target.

What am I missing here?

But your orbital inclination is correct, right?
The difference between your target and you is because you are not launching into the target's orbital plane.
That formula gives the heading to reach an orbital plane with a certain inclination to the equatorial plane. But, a launch now vs a launch in 1 hour, although both will produce orbits with the same inclination in relation to the equator, they will not be aligned because the planet rotates. For rendezvous to happen, not only must the orbital inclination be the same, but the LAN ( longitude of the ascending node) angle must also match.
To launch from the surface of a planet/moon/whatever and to reach a target in orbit, not only must you launch in the correct direction (using that formula), but you must launch at a time when the target's track is +/- over the launch site, i.e., the launcher is "inside" the target's orbital plane.

 

[johan]

Aaaah!

Of course, you are right. Thank you.

 

[Ripley]

...i.e., the launcher is "inside" the target's orbital plane.

This actually "visualizes" quite well when to launch (given that orbital planes are no more than thin slices).

 

[johan]

I'm happy to say that I'm now nailing it. I got to within 2.7 degrees RInc of the ISS just now.

 

[Ripley]

Now you have to shave those few degrees off by banking right or left during ascent.

 

[Thorsten]

That's why spaceflight isn't nearly as entertaining as aerial flight - you have to pre-compute everything, wait for the right moment to do anything - no spur of the moment decisions, you just make your plan and then follow it to the end.

If you've done it right, you don't actually need to launch any more, because you know what'll happen anyway.

:lol:

 

[boogabooga]

That's why spaceflight isn't nearly as entertaining as aerial flight

You are in the wrong place, my friend...:dry:

FlightGear...is somewhere else.

 

[C3PO]

Kerbal Space Program is kinda here. And it is entertaining.

 

[Thorsten]

You are in the wrong place, my friend.

Hint: This:

:lol:

means the preceding text is not meant too seriously.

FlightGear...is somewhere else.

Doesn't have much bearing on the question now, does it, because Flightgear also happens to be an excellent space simulator and there seem to be Orbiter addons for aircraft carrier ops.

(Oh, and there's plenty of Virtual Airline pilots who program the flight computer of their favourite airliner, take off in the evening, switch to Autopilot and go to sleep, wake up in the morning, have breakfast, land their plane and go to work...).

 

[johan]

Hey, I fly to the moon by the seat of my pants all the time.

Sure, sometimes I end up just barely grazing its sphere of influence, and have to spend a lot of fuel to get into a proper orbit, but hey. All fun comes at a price!

At least I've started to remember to check life support levels before takeoff. It sucks to get nearly there and have all the crew pass out due to hypoxia.

 

[boogabooga]

Hint: This:

:lol:

means the preceding text is not meant too seriously.

Funny- for you- but came across to me as a bit condescending of the Orbiter community.

I've been insulted many times by people who thought it was funny.

 

[Thorsten]

Personally I don't see any reason why I can't be part of two communities and participate in discussions here - especially since I am interested in spaceflight and believe I have accumulated a reasonable body of knowledge about how to operate spacecraft by now which I try to share. The same goes for discussions of physics questions.

In the post which offended you so very much, in addition to the smiley marking this as not so serious there was also zero mention of a simulator other than Orbiter. Neither does my signature advertize any other simulator. I am very consciously trying to contribute to this community here and by and large keep my non-Orbiter activities in its own thread (unless there's a specific reason not to). There's also plenty of people in the Orbiter community who enjoy flying Digital Combat Simulator - does that make them less worthy?

I'm sorry, but I feel it's you who wants to erect fences here and reacts in a needlessly hostile way with 'go elsewhere' to a harmless joke. If you want to frame this in an 'us vs. them' scheme, be assured I do not.

Oh, and I don't think I have a habit of insulting people online - feel free to skim through my post history and try to dig up examples, I think that'll go blank.

---------- Post added at 05:26 AM ---------- Previous post was at 05:19 AM ----------

Hey, I fly to the moon by the seat of my pants all the time.

I don't remember what novel this was in, but there was the sentence 'Navigation is only for people who don't have enough thrust - if you have enough, you just point and burn away.'

Sort of sums it up :lol:

 

[Enjo]

Oh, and I don't think I have a habit of insulting people online - feel free to skim through my post history and try to dig up examples, I think that'll go blank.

I think you do. You just try to cover up the insults with some concrete information, or you just don't know how to be diplomatic, which is equally wrong.
Don't be surprised of his reaction. Sometimes insults return to the source in various, seemingly unrelated forms.

 

[Thorsten]

I don't think taking posted information as indicative for a desire to insult people is a particularly fruitful attitude in a technology and science-based forum.

But that's just my two cents...

 

[Enjo]

We're still people with feelings.

 

[jroly]

You better repent

 

[Thorsten]

We're still people with feelings.

If you make it an inclusive 'we', you'll immediately see why one should not tell people to go elsewhere for making a joke.

Look, I honestly don't know what put you off. I remember a technical conversation about the merits of different burn targeting algorithms, I remember you telling me you were not interested in what I had to say, and I remember me quitting posting in a thread I was interested in as a result to let you work out in peace whatever you want without having to read what I think about it.

It's kinda hard for me to be less offensive than that (short of just not posting anywhere), but for some reason you still seem to have taken something as a serious insult.

I can't control what you read into what I write - if me posting information is really insulting for you because you suspect I'm really doing it to cleverly mask that I wan to affront people, or if a harmless joke marked as such looks condescending for boogabooga, then maybe the problem isn't actually with what I write (I have, on occasion, being accused of being disrespectful to a community for using no avatar picture - frankly this here seems similar).

I can tell you that I don't mean you or boogabooga any harm (largely I don't know either of you very well, and I have no reason to be offended by either of you - so why on Earth would I even want to?).

Maybe you come from a very different cultural context. Maybe you don't like me personally, maybe you don't like my involvement in OpenSource development, maybe you want to be the only guy who ever talks about burn targeting in this forum - I don't know and I have no way of knowing.

None of this should matter - we should be able to exchange information in a polite, technical manner here and not hold every post of the other under suspicion that despite nice words he really means evil. And that's really all I'm asking.

Anyway, I am sorry if I have offended any of you, it was not my intention.

 

[Enjo]

Oh TL;DR. I have a life.

 

[Thorsten]

Such much for politeness and respect then.