Search the Community

Hi guys, I'm doing some sat contracts (in RSS) and need some advice. I'm talking, of course, about launching into the appropriate inclination. I know there have been threads about this topic before, but I did pretty extensive searching and couldn't find what I was looking for, so here goes. Since I'm using RSS, I'm launching from Cape Canaveral AFS in Florida, which is at 28.6 degrees. The orbit I'm going for is a tundra orbit 71,000x460km, inclined at 110 degrees. The orbit appears to cross the equator about half way between Ap and Pe. I've noticed though, that the ascending/descending nodes slide around and change value as I time warp on the pad. As a full day passes on the pad, the nodes swing back and forth along the target orbit (~45 degrees), and vary between 88 and 145 degrees. I looked up a launch azimuth calculator and it gave me ~202.9 as a heading, which sounds right to me. I rotated the rocket in the VAB 115 degrees so I'd only have to do a little yaw correction achieve the proper heading. Does all this sound right? I assumed it would make sense to launch when the nodes read 110/-110, but when I tried it, I was off by more than 15 degrees. I then tried launching when they read 138/-138 (110+28.6), but I was off by 40 degrees. So does anyone know when I should actually launch? Am I not taking travel distance during launch into account? How should I calculate this?

Hello word! Have you ever ask yourself how to spend the minimal amount of ΔV for matching planes? If so this is the guide for you. I know that in the 99% you launch rocket toward east but if you are using mod like RSS or you need to rendezvous with a target in an inclined orbit you want to know what is the azimuth that save you to do the most inefficent burn in the spaceflight, the matching planes burns or inclination change burns. First of all a precisation launch azimuth=launch heading :-) So you need timewarp until the target orbit cross your launch site so you are directly under the ascending or descending node of your target so when you will launch is like you are doing a plane change manouvre but you are starting from a velocity equals to zero, so for the oberth effect is free! PS: For a precise alignment you can set the camera to the planet and move it until you see the target orbit as a line. Now you know when launch, for know at what heading launch there is a bit of trigonometry. For the spherical trigonometry we can calculte the azimuth for any inclinaton that is smaller than our latitude with this formula: Cos(Inc) = Cos(Lat)*Cos() Where is our launch azimuth, inc the target inclination and Lat is the our latitude. Now we have only to single out : = arcos[cos(inc)/cos(Lat)] But this formula is not 100% precise because it consider a non rotating planet, for example for the ISS from cape canaveral give us 44.98° or 135.02° If you want a more precise azimuth you need to take account of the rotating velocity of the planet and the math involed start to being a bit more complicated If you are a true masochist here can find the dimostration: http://www.orbiterwiki.org/wiki/Launch_Azimuth#Rotation_of_the_Earth If not this is the final formula: sqrt(VTarget*sin() - VChaser*Cos(Lat))2+(VOrbit*Cos())2) Where VTarget is the orbital velocity of your target and VChaser is your orbital velocity at launchpad Using this formula instead of the previous one you save 284 m/s for a launch to the ISS from Cape Canaveral.