Flight Question Launch Heading and Window help

[Southwell]

Hey, I have just got the whole launch to orbit align plane and then synch orbit with ISS, I am a bit confused with the DGIV scenario KSC to ISS in which it says to use the auto pilot wiht a heading of 42 degrees, but if u use the calculator with the latitue at 28.5 and the desired inclination orbit at 74.5 degrees you get a heading of 17.7 degrees for launch. One other aspect I have not been able to figure out is how to wait for the correct launch windows so that my LAN is the same as the ISS. At the moment I can only make it to the ISS with about 5% fuel remaining, very inneficient.

Thanks

 

[Tommy]

Check the DGIV's manual for the instructions on calculating launch headings, you are doing something wrong somewhere. Correct launch headings for the ISS from the Cape are 42 or 138 degrees, depending.

As for the window, a rough but effective method is to use AlignPlanesMFD, and launch when Tn is about 300. This gets me within one degree RInc every time (mind you I my launch profile may be a bit different, but with practice you'll get the hang of it.)

 

[Southwell]

Hey Tommy thanks for that, I had no idea how to line the launch window up, a rough but effective method will do for now cheers. I had looked in the documentation for the launch heading before so i checked again

"« NN » stand for the launch heading you want, it depend of the Orbital inclinaison of the target orbit you want to
reach. For mir for example it would be 90° while for ISS it would be 42°.
The formula to calculate a launch heading is :​

Launch Azimuth = arcsin (cos (desired_orbital_inclination) / cos (launch_ latitude)) "

So from KSC with the lattitude of 28.5 and ISS is orbiting at 74.5, gives me a launch azimuth of 17.7, the scenario and the documentation say to use 42. This is real simple math, I must be using a wrong value somewhere???

 

[Tommy]

Not sure where you're going wrong on the heading, but the DGIV's manual has a "Keypress by Keypress" method for finding it - just follow that strictly and you should get something a few minutes over 42 degrees. Also, the manual gives an "easy" way and a "better", more advanced method - use the more advanced (takes planet's rotation into account, this can mean a difference of a few degrees in some cases).

Or, you could do it the easy/lazy/smart way and use LaunchMFD, which will give you heading, time, and even pitch information to get a launch very close to in plane.

BTW, as I recall, MIR's inclination is a bit less than Canaveral's latitude, so Tn may not ever get down to 300. Just launch when it's (Tn) about as low as it it wants to go, and you should be OK.

 

[Southwell]

Thanks for the help Tommy, I really rate the waiting for Tn down to 300 method is pretty accurate for what it is.

 

[Moach]

i usually just time-warp until i get a "good enough" intersection on the map MFD.. then i fly up and head roughly to the same direction the target orbit is going, whilst keeping a eye out on the MFD to see if i'm not too bad off course...

past the first thousand m/s - i just leave the map and proceed normally making sure i don't toss around to the sides too much.... once i get up there... RInc is usually 1~2 degrees, which can be corrected with a few seconds worth of engine


or, for more precision, on comes LaunchMFD and it's wonderful flight director thingy:thumbup:

 

[Fabri91]

ISS inclination is 51,6 degrees. Are you using equatorial or ecliptic reference?
When calculating launch azimuth/heading use equatorial: press FRM on the orbit MFD to display inclination relative to the equator.

 

[Southwell]

wow cant beleive that got me, thanks Fabri91!