Scenario Atlantis Launch into Sunrise

[markopolo5437]

It took a couple of weeks, but I'm comfortable manually launching the DG into orbit, docking w/ISS, and landing. Tex's tutorials really helped understand what was going on. Now I'm working on flying Atlantis into orbit on the Launch into Sunrise scenario.

First problem: the sim won't work with the default configuration. I had to go into the settings (not really knowing what I was doing) using the Scenario Editor to set the dx/dt, dy/dt, and dz/dt values to zero. They all read -1.J#, which seemed odd to me. Sitting on the launchpad, there should be no velocity in x, y, and z. After setting those values to 0.0, the sim works.

By using the Ascent MFD AP to get to orbit, and documenting the various attitudes and thrust vectors during the autoflight, I can manually achieve orbit at various heights. Not as well as the AP, but I can git 'er done.

Next problem: I've tried a wide variety of launch azimuths, recording the RInc outcomes on the Align Planes MFD, in order to eventually dock with ISS and/or Mir. The closest I can get for ISS is an RInc of 22.01 degrees at a launch Az =100 degrees, and for Mir, RInc = 55.51 also at Az = 100. I'm using the Ascent MFD to input the launch Az.

I'm mystified. There is a setting below the launch Az in the Ascent MFD for Orbit inc., Shouldn't I be able to enter an Az value which drives the Orbit inc. to the posted value in the information screen, i.e. 74.27 degrees for ISS, and 3.93 degrees for Mir?

Scrolling the AZ+ and AZ- keys yields a minimum Orbit inc. value of 28.6 degrees in the range from 88.8 degrees to 91.2 degrees Az. It's not possible, from what I'm doing, to achieve a Orbit inc. of 3.9 for Mir, and when I set the launch Az to drive the Orbit inc. to 74.3 for ISS (either to the NE or the SE), the resultant RInc turns out horribly.

Any help with the Ascent MFD, or any other ideas, would be appreciated.

 

[BrianJ]

Hi,
I'm not a great Shuttle pilot but maybe I can help a little...

First problem: the sim won't work with the default configuration. I had to go into the settings (not really knowing what I was doing) using the Scenario Editor to set the dx/dt, dy/dt, and dz/dt values to zero. They all read -1.J#, which seemed odd to me. Sitting on the launchpad, there should be no velocity in x, y, and z. After setting those values to 0.0, the sim works.

I'm not quite sure what the problem is you're describing - but my Atlantis takes a couple of seconds to "settle down" to "Landed" status after I open the scenario. Everything works fine after that.

Next problem: I've tried a wide variety of launch azimuths, recording the RInc outcomes on the Align Planes MFD, in order to eventually dock with ISS and/or Mir. The closest I can get for ISS is an RInc of 22.01 degrees at a launch Az =100 degrees, and for Mir, RInc = 55.51 also at Az = 100. I'm using the Ascent MFD to input the launch Az.

I'm mystified. There is a setting below the launch Az in the Ascent MFD for Orbit inc., Shouldn't I be able to enter an Az value which drives the Orbit inc. to the posted value in the information screen, i.e. 74.27 degrees for ISS, and 3.93 degrees for Mir?

First thing, AscentAP works in the Equatorial reference frame but you are looking at figures for ISS and MIR in Ecliptic frame - on your OrbitMFD, click the FRM button to change to equatorial frame and check inclination figures.


Now you can set your AscentAP launch azimuth to the correct value for the target inclination(Equatorial frame).


Wait until your target flight path passes overhead at your location(see MapMFD) and launch.


NOTE Since MIR is in a lower inclination orbit than your latitude, you won't be able to go directly to MIR's orbit plane, best you can do is a couple of degrees RInc, then do a plane change correction on orbit.


Hope this helps,
BrianJ

 

[markopolo5437]

Thanks for replying, Brian. I get the same results in AscentAPMFD in either setting (ECL or EQU) in OrbitMFD...a minimum INC of 28.6 in the range of AZ from 88.8 to 91.2 degrees. I even did an uninstall/install to get a clean version, with the same results.

Any other ideas?

BTW, what does the OMS2 setting do?

 

[DaveS]

Thanks for replying, Brian. I get the same results in AscentAPMFD in either setting (ECL or EQU) in OrbitMFD...a minimum INC of 28.6 in the range of AZ from 88.8 to 91.2 degrees. I even did an uninstall/install to get a clean version, with the same results.

Any other ideas?

You need to wait for the ground track to pass over the launch site. The shuttle carries a very small propellant margin so there's only a very small "launch window" available each day. For ISS it's only around 10 minutes long and the best time to launch is very second the ground track passes over the actual launch pad. This time is called the "in-plane" launch time and usually occurs 3-5 minutes into the launch window.


Once the launch window has closed, the shuttle doesn't have enough propellant to make up the relative inclination difference any more. So you just to have to wait until the launch window opens if the scenario isn't set up to be near the time it opens.

 

[markopolo5437]

The results are the same for either ECL or EQU setting in the Orbit MFD - I can't get an INC less than 28.6 degrees on the AscentAP MFD.

 

[Thorsten]

Inclination can't be smaller than launch site latitude (unless you have huge propellant reserves to burn and fly a rather curved launch path).

It isn't possible for a Shuttle launching from KSC to achieve a 3.9 degree inclination- so you can give up trying.

 

[Urwumpe]

Yes, for getting into an equatorial inclination that is lower than the latitude of the launch site, you need a so called "dog leg maneuver". First you point more towards the equator than usual, then when you are approaching the target orbit plane, you accelerate eastwards or even away from the equator a bit to do a sharp turn into the target orbit.

As you can imagine, this costs a lot of fuel, but can still be better than correcting inclination afterwards at higher speeds.

 

[GLS]

The results are the same for either ECL or EQU setting in the Orbit MFD - I can't get an INC less than 28.6 degrees on the AscentAP MFD.

This is the result of the Earth being a sphere in Orbiter and not the spheroid it is in reality. So, while the rockets launching from Florida are launched from a ~28.45º latitude, in Orbiter that ends up being ~28.6º. :facepalm: The only thing we can do to reach a 28.45º inclination orbit from Florida is a "dog-leg" during launch. The rest is in Martin's hands. :shrug:

 

[Thorsten]

Yes, for getting into an equatorial inclination that is lower than the latitude of the launch site, you need a so called "dog leg maneuver". First you point more towards the equator than usual, then when you are approaching the target orbit plane, you accelerate eastwards or even away from the equator a bit to do a sharp turn into the target orbit.

Heh, this is actually an interesting guidance problem - I'm currently sitting down and devising a scheme to target offsets to the longitude of the ascending node in the final orbit (which is kind of similar in targeting a plane that does not intersect the launch site).

 

[GLS]

Heh, this is actually an interesting guidance problem - I'm currently sitting down and devising a scheme to target offsets to the longitude of the ascending node in the final orbit (which is kind of similar in targeting a plane that does not intersect the launch site).

AFAIK, the real shuttle targeted a "IY vector", which is the normal vector of the orbital plane.

 

[Thorsten]

The interesting part is not so much in how you parametrize the target plane (I've settled on the orbital elements, but the normal is admittedly more clever), it's in the fact that for pretty much most of the ascent you can't really compute a usable error to it, because due to the non-zero inertial speed of the launch site, you're constantly converging to it right until MECO.

It resembles RTLS guidance in being a fuzzy problem - there's more than one way to skin the cat, and initially you only need to do 'better', only in the end you need to do 'good'.

 

[Thorsten]

Today I've made some headway automatically steering Atlantis to a plane about 10 miles displaced from the 'natural' plane you launch into by fixing inclination only.

It's a surprisingly nasty problem, because the turn onto the actual launch azimuth needs to happen relatively early for performance reasons, but lots of things are happening at this stage, and the vectoring of course also affects ascent performance.

And needless to say, a rocket at Mach 5+ isn't really a very nimble object to turn into a different course, the controller has to work decisively, but without causing oscillations or long delays (which deteriorate the inclination precision).

So the ingredients are there, but it still needs some tuning...