General Question Launch Azimuth

[wdjohnson2]

Everything I've read says you can't launch at an inclination below the launch latitude. I understand the math behind this (sort of), however for the GEOS-T launch on 1 Mar, the Telemetry in Flight Club says the inclination is 27.55 from Canaveral. Can anyone explain?

 

[BrianJ]

Hi,
and welcome to the forum!

you can't launch at an inclination below the launch latitude

This is true if your rocket simply "follows its nose" and keeps pointing along its velocity vector after launching.
However, to launch to the minimum inclination from a given latitude you would launch due East (90deg launch azimuth),
and you can see that if you do that, the first part of your orbit will gradually curve down towards the equator - so your latitude is decreasing (you can try it in Orbiter).
Once you get to a lower latitude, you can "yaw" your rocket to point a little to one side of the velocity vector.
This will change the inclination slightly - if you yaw a little to the North after launching from KSC, you will decrease the inclination.
Of course, this uses up some of the rocket's energy just changing the orbit inclination, so you pay a penalty with regard to how much payload you can lift or how fast your final velocity is.

Hope this helps!
Cheers,
Brian

 

[GLS]

Because Earth is not a perfect sphere, there is also Geodectic Latitude and Geocentric Latitude to take into account.

 

[BrianJ]

Because Earth is not a perfect sphere, there is also Geodectic Latitude and Geocentric Latitude to take into account.

I always forget about that! This is what happens when ones thinking becomes embedded in a simulation rather than the "real world"!
So, I'm guessing you might end up at 27.55 inclination if you launch due East from SLC-41 and just keep going straight ahead?

 

[GLS]

I always forget about that! This is what happens when ones thinking becomes embedded in a simulation rather than the "real world"!
So, I'm guessing you might end up at 27.55 inclination if you launch due East from SLC-41 and just keep going straight ahead?

KSC is ~28.45º geocentric latitude (the one that matters for orbits as it is the angle to the center of the Earth) and ~28.6º geodetic latitude, so launches heading East end up in a 28.45º orbit. The 27.55º might be possible, with a yaw North late in the ascent, like you posted above.
FYI, in Orbiter the Earth is a sphere, so KSC is in the "wrong place" in relation to the center of the Earth, so East launches end up in a 28.6º orbit.