Flight Question In which direction do I have to start?

[Koloss]

Dear Community,

I did a lot of searching here in the forum but didn't get the answers I need.
Perhaps there is already a thread which covers this topic.

So... Let's say I am in my Delta Glider IV sitting on the Runway at Cape Canaveral. I would like to go to the ISS.
The onboard computer (or the checklists) tell me that the launch heading for the ISS is "42". But how do I know this heading?
It's a complete mystery to me. :facepalm:

Other example: I would like to launch from Wideawake International to the ISS. How do I know in which direction I have to launch and fly?!

At the moment I am complete dependent on the autopilot. Which sucks. A lot.

Sorry for this NOOB-Question

 

[Ripley]

Well, if you want to find "how to know" that heading, just read the DGIV pdf manual (Your_Orbiter_ROOT\Doc\DeltaGliderIV\res).

At page 20-21 you can read the exact formula.

 

[Koloss]

Yeah I saw the thing like "your_latitude COS MR1/M1" and so on.

But... Isn't there a way to know this heading without the Delta Glider onboard Computer?

Or did you mean something else?

 

[statickid]

42 is just the answer, the question was ... Wait a minute!!! The question is "what direction do I launch the delta glider to get to the iss?".

Eh, sorry

OK, 42 is just a couple degrees of Northwest, which is 45. You can read this on the surface MFD or on the surface HUD, except on the surface HUD its just midway between 4 and 5, closer to 4. You can also look at the map MFD and draw orbital plane. Or use launch mfd for a specialized approach

 

[garyw]

There is a mathematical forumla behind it and you can work it out yourself of you can just use this tool [ame="http://orbithangar.com/searchid.php?ID=2464"]Azimuth calculator v. 1.5 - GUI[/ame] or this [ame="http://orbithangar.com/searchid.php?ID=2802"]Launch MFD - v. 1.5.9 for Orbiter 2010[/ame]

 

[statickid]

OR AM I TOTALY WRONG??? I NEVER USED IT BEFORE I THOUGHT IT WAS JUST A HEADING!!!

 

[Koloss]

42 is just the answer, the question was ... Wait a minute!!!

:lol:
Guess what... I thought exactly the same :lol:

Thanks garyw!
I'll try out the MFD you mentioned! :tiphat:

 

[Urwumpe]

At page 20-21 you can read the exact formula.

It is not exact (rotation of Earth is not included), but approximately right.

Essentially, the direction you want to launch to is simple spherical trigonometry - if such a thing as simple spherical trigometry exists. You cut with the orbit plane throught the sphere of Earth and your launch site. The launch azimuth is simply the angle between true North and this cut. At the equator, this angle is the same as the equatorial inclination (thus the name of it). At an latitude (north or south) that equals the equatorial azimuth, it is 90° - due east. Unless you aim for a retrograde orbit... well, yes. If your latitude is bigger than the inclination, you can't reach the orbit without plane changes (very pittoresque called "dog-leg maneuvers").

Now lets construct the formula by stomach feeling: the ISS is in 51.6° inclination and you are at 28°N (about KSC). What is your target azimuth? it has to be made of sinus or cosinus, because we are in spherical trigonometry. And since the case is pretty simple, it should only be multiplication or division, no addition or subtraction or worse needed.

At 0° (sin(0) = 0, cos(0) = 1) latitude we want to get the inclination back.
At latitude = inclination, we want to get 90° (cos(az)=0, sin(az)=1), regardless if we have north or south.


So...

sin(az) = cos(i)/cos(lat)

Simple, isn't it? :lol:

If cos(lat) would be smaller than cos(i), the result is bigger than 1 or smaller than -1 ... no solution possible = no intersection between your orbit and the launch site.

This still doesn't include rotation of earth, but this calculation is also a lot more complex (you need to know the target orbit speed there)

LaunchMFD does very accurate calculations there, I recommend looking at it if you want to avoid too much math at once.

 

[Enjo]

What Gary said, plus if you want to see what equations are used by Launch MFD and the azimuth calculator, have a look at this article:

http://www.orbiterwiki.org/wiki/Launch_Azimuth

and this implementation:

http://sourceforge.net/p/enjomitchsorbit/code/HEAD/tree/lib/Math/AzimuthMath.cpp

 

[Koloss]

It is not exact (rotation of Earth is not included), but approximately right.

Essentially, the direction you want to launch to is simple spherical trigonometry - if such a thing as simple spherical trigometry exists. You cut with the orbit plane throught the sphere of Earth and your launch site. The launch azimuth is simply the angle between true North and this cut. At the equator, this angle is the same as the equatorial inclination (thus the name of it). At an latitude (north or south) that equals the equatorial azimuth, it is 90° - due east. Unless you aim for a retrograde orbit... well, yes. If your latitude is bigger than the inclination, you can't reach the orbit without plane changes (very pittoresque called "dog-leg maneuvers").

Now lets construct the formula by stomach feeling: the ISS is in 51.6° inclination and you are at 28°N (about KSC). What is your target azimuth? it has to be made of sinus or cosinus, because we are in spherical trigonometry. And since the case is pretty simple, it should only be multiplication or division, no addition or subtraction or worse needed.

At 0° (sin(0) = 0, cos(0) = 1) latitude we want to get the inclination back.
At latitude = inclination, we want to get 90° (cos(az)=0, sin(az)=1), regardless if we have north or south.


So...

sin(az) = cos(i)/cos(lat)

Simple, isn't it? :lol:

If cos(lat) would be smaller than cos(i), the result is bigger than 1 or smaller than -1 ... no solution possible = no intersection between your orbit and the launch site.

This still doesn't include rotation of earth, but this calculation is also a lot more complex (you need to know the target orbit speed there)

LaunchMFD does very accurate calculations there, I recommend looking at it if you want to avoid too much math at once.

Holy... ok... well... errr... let's stick with a solution which fits my brain capacity ok? :lol:

 

[george7378]

I can't resist shamelessly throwing this in too:

[ame="http://orbithangar.com/searchid.php?ID=5757"]Space Calculators V2[/ame]

It uses the 'Accurate calculation' as described in the DG-IV manual.

 

[Enjo]

Ah, and while we are here, then since I haven't seen it mentioned anytime, the so called Earth Rotation, is just a specific case of your Current Velocity, effective until you launch. During the flight you have to continuously update the remaining velocity vector, subtracting the current velocity, as you may note in the Launch MFD implementation. You also have to update your latitude.

There's also a need for off-plane correction for final LAN correctness, but Launch MFD does it too.

 

[Koloss]

Update: Yesterday I downloaded The LaunchMFD. First try: RInc of 0.42. Not too bad!

Thanks guys!!!