OHM Delta IV Launch Vehicles 3.0

[I Come in Peace]

Looks nice.

 

[Jarod]

That was not my problem, I was tired :rofl:

So your suggesting recalculate heading every once in a while?
Ive tryed so many ways of reaching the desired inclination and what I have now seems to work but, try launching to the ISS. You will get the same inclination but the orbital plane is off. I still don't fully understand the relationship between inclination and orbital plane [...] Also from what I understood, was the launch azmuth is the heading you need to hold.

You could recalculate heading once in a while, but if everything is good the result will be the actual prograde direction.
The problem with physical targets, like ISS, is that you're not only targeting an equatorial inclination but also a precise LAN.
For the launch window, we wait for ISS to pass over the launch pad, in theory you would be in the same orbital plane after launch.
In practice, ISS doesn't strictly pass over the launchpad but a few kms away. This result in a different orbital plane.
The course correction you implemented is good but it takes the wrong reference, if you're targeting a precise inclination and LAN, you need to reduce RInc for the ecliptic plane, that will adjust the LAN to the same as ISS.
And you must not hold the heading, look at the MapMFD, the ISS track is like a sine wave, your launch azimuth depend on your launchpad latitude.
Say there is another launchpad 500 km away, it will have a different launch azimuth, so at the moment you'll pass over the second launchpad, the second rocket will go in a direction while the first would go in another one because you presently hold the heading. And still both rockets want to go to the same destination.
While if you don't hold the heading, both rockets will go in the same direction.
I'm very bad at explaining, I hope it helps a little.

---------- Post added at 09:50 PM ---------- Previous post was at 09:31 PM ----------

I forgot one thing, you say that you're adjusting heading depending on the payload mass, while the heading is not dependant on it.
You say it is better like that, I'm gonna guess it is because you're yawing (holding the heading) , that would be why suddenly adjusting for mass as an effect. If you're launching a Delta 4 or a SpaceX vehicle, both will have different total mass, payload mass and still would launch to the same heading at the same launchpad.

 

[virii2k]

That was not my problem, I was tired :rofl:

Say there is another launchpad 500 km away, it will have a different launch azimuth, so at the moment you'll pass over the second launchpad, the second rocket will go in a direction while the first would go in another one because you presently hold the heading. And still both rockets want to go to the same destination.
While if you don't hold the heading, both rockets will go in the same direction.
I'm very bad at explaining, I hope it helps a little.

---------- Post added at 09:50 PM ---------- Previous post was at 09:31 PM ----------

I forgot one thing, you say that you're adjusting heading depending on the payload mass, while the heading is not dependant on it.
You say it is better like that, I'm gonna guess it is because you're yawing (holding the heading) , that would be why suddenly adjusting for mass as an effect.

Switching to the launch azmuth of a base Im passing over 500km away would put the vessel way off course. I wouldnt be at ground level.

The current autopilot has less the 0.01 slip angle for most of the first half of ascent. So changing the heading 0.01 during the ascent stage wouldnt make much difference.


More mass means more time to reach the desired apoapsis, meaning a longer burn. The launch azmuth is a formula that "predicts" your inclination when you reach the desired apoapsis. When your no longer rasing your apoapsis
you can burn prograde because until you reach the desired apoapsis you inclination is changing.

---------- Post added at 11:57 PM ---------- Previous post was at 11:53 PM ----------

I also tried SpaceX Falcon Heavy at 51.57 degrees and 350 KM, It ends up at 51.69.

---------- Post added 03-27-12 at 12:22 AM ---------- Previous post was 03-26-12 at 11:57 PM ----------

Adjusting the heading for payload mass is done before launch to makeup for the longer or shorter burntime.

 

[Jarod]

The current autopilot has less the 0.01 slip angle for most of the first half of ascent. So changing the heading 0.01 during the ascent stage wouldnt make much difference.

Well it adds up very fast, look at the "sine wave", in the middle of it this is like a straight line and why by not holding the heading vs holding it, it doesn't make a big difference.
But as you approach the maximum/minimum of the "sine wave", your prograde direction becomes 90° east versus 42° if you're holding the heading.
There is no way a rocket in the air would go to 42° east to target an orbital plane while a rocket on the ground is heading 90° for the same target, even accounting all errors relative to heading on ground levels.

More mass means more time to reach the desired apoapsis, meaning a longer burn. The launch azmuth is a formula that "predicts" your inclination when you reach the desired apoapsis. When your no longer rasing your apoapsis
you can burn prograde because until you reach the desired apoapsis you inclination is changing.

Are you 100% sure about that ? Yes more mass means more time to reach the apoapsis, that will play a part in your relative inclination (ecliptic) and LAN, but your equatorial inclination will be the good one whatever the duration as long as you're taking at launch the right heading and don't hold it.

I also tried SpaceX Falcon Heavy at 51.57 degrees and 350 KM, It ends up at 51.69.

Which is very small compared to the first delta4 default scenario.

I don't know your code but if this is something you can change easily, why don't you test ? Not holding the heading and don't change the heading with the mass and look where the rocket ends its course.
There is no mass involved in the launch azimuth wiki page at all.

---------- Post added at 09:40 AM ---------- Previous post was at 09:38 AM ----------

Right now you overshoot your desired inclination, because you're holding the heading, if you don't hold it, the rocket will approach the correct inclination during the full course of its burn.

 

[boogabooga]

Now compare to 28.6 degree orbits from Canaveral.
Delta IV is off by over a degree...

 

[Enjo]

You could write a pitch program in Launch MFD for your launcher, that would solve many of the problems that you describe here, but the launcher doesn't react to pitch commands until MET = 270s.

 

[Jarod]

The pitch program is not the problem here, the pitch program is really good compared to others and make a circular orbit. Just a few quirks to make Delta4 the best autopiloted launcher for Orbiter

 

[Enjo]

Yes, but I'm not talking about the pitch being the problem, but all the rest. Therefore the pitch information already gathered could be used as input to the Launch MFD program.

 

[boogabooga]

Enjo, perhaps you could offer your expertise.

Does one hold launch azimuth, or prograde direction through launch?

 

[Enjo]

Neither. The heading should be continuously recalculated (notice the latitude in the equation), and the target 2D velocity vector should be substracted by the current 2D velocity vector. This way you take not only the planet rotation into account but generally your current situation.

Have fun then

 

[Jarod]

That should not be too far from prograde direction :lol: while correcting for any error in initial heading.

 

[Enjo]

That's far away, believe me. You're at the very beginning of the work that I've been doing for 6 years now, along with many experienced developers, including Kwan and Agentgonzo. You have to take into account the current velocity vector, as well as on-the-fly LAN correction, that I haven't mentioned until now.

This is why I proposed simply writing a pitch program for Launch MFD, that does all the magick for you. It will surely be faster this way, and after this is done you could experiment with your own autopilot if you can take the challange. Otherwise you'll waste a lot of time trying to make the laucher usable.
First though, the launcher needs to react on the MFD control. It's probably overriden somehow, or an appropriate attitude thruster group for pitch hasn't been defined in the module. Wouldn't it be better to fix this small bug first?

 

[Jarod]

deleted, I'm too stubborn sometimes.

 

[virii2k]

Ok, Ive changed the code to constantly recalculate the launch azimuth.....
Seems to be alot better. Still a slight mis-calculation somewhere but I think recalculating
is the way to go.

 

[Jarod]

Ok, Ive changed the code to constantly recalculate the launch azimuth.....
Seems to be alot better. Still a slight mis-calculation somewhere but I think recalculating
is the way to go.

Do you mean that we can redownload the addon or that you'll update it later ?

 

[virii2k]

It will be in the next version. Its still off slightly, so its going to take some more work.

 

[flyingkorolevR7]

it won't install into Orbiter

 

[AdamR]

How to you add custom payload from the orbiter file
:idk:

 

[virii2k]

Its explaned in the Delta IV Launch Vehicles PDF in the add-on docs folder.

 

[boogabooga]

I'm using this add-on in a project that I am working on.

I'm noticing that the M+ 5.4 vastly over-performs from published literature, and the add-on documentation. (I can get 12,000 kg to GTO, almost twice what it should). I haven't tested too much yet but the Delta IV M 4 (no SRMs) doesn't seem to have as much as a problem. I'm suspecting the performance of the solids is a little exaggerated.

I wouldn't harp on this sort of thing too much, but I need this to be accurate for something. Or, at least I need to know what exactly is exaggerated. Any ideas?