RCS and DAP development

[SiameseCat]

This thread is for development of the RCS system and attitude autopilot.

Does anyone know how the P and Y angles in UNIV PTG are used to specify a body vector? I'm guessing the P angles is between the vector and the XZ-plane, and the Y angles is between the vector and the YZ-plane, but I'm not sure.

 

[Urwumpe]

Yes, sounds about right to me. You basically rotate the shuttle coordinate system that way.

 

[SiameseCat]

Here's another question: one of the BODY_VECT axis options is described as -Y ST, which (I think) will point the start tracker at the specified target. Does anyone know what the appropriate P and Y angles (as described above) will be for this axis?

 

[Donamy]

Shouldn't there be two startracker fixes ?

 

[tblaxland]

There are two star trackers, roughly on the -Y and -Z axis. The diagram at the bottom of page 6 of this document shows the offsets. I assume from these diagrams that these offsets are in the YZ plane.

With regard to body vector definition, the usual method is to use Tait-Bryan rotations with the order typically pitch-yaw-roll. Under this system, the yaw angle is not the angle between the body vector and the XZ plane, it is the angle between the body vector and the pitch vector. The pitch angle is the angle of the pitch vector above the YZ plane. The pitch vector lies in the XZ plane.

On this basis, the body vector angles for the star trackers are as follows:

-Y tracker: pitch=+90,yaw=-79.433
-Z tracker: pitch=+90,yaw=-3

 

[SiameseCat]

Thanks for the star tracker angles.

Assuming the Y rotation is about an axis perpendicular to the pitch axis, wouldn't the angle between the body vector and the pitch vector be the same as the angle between the body vector and the XZ-plane?

 

[tblaxland]

Assuming the Y rotation is about an axis perpendicular to the pitch axis, wouldn't the angle between the body vector and the pitch vector be the same as the angle between the body vector and the XZ-plane?

No. To help explain this I've attached a sketch. The top half shows the scheme proposed in your OP (also known as alt-azimuth), the bottom shows Tait-Bryan rotations. Both are for pitch=45, yaw=60 and the vectors are unit vectors.

In the alt-azimuth case, the locus of a unit vector with pitch=45 is a circle of radius=cos(45)=0.707 located in the plane Z=-sin(45)=-0.707. In the Tait-Bryan case, the locus of a unit vector with pitch=45 is a circle of radius=1 located in a plane inclined 45° to the XY plane and intersecting that plane along the Y-axis. These two cases are only equal for yaw=0.

Order in Tait-Bryan rotations is very important but it is irrelevant for alt-azimuth systems. This is one of the advantages of alt-azimuth. The advantage of Tait-Bryan for aerospace applications is that the rotations are defined in frames that are aligned with the control surfaces/RCS systems.

 

[SiameseCat]

Thanks. I've updated the code to use the Tait-Bryan rotations for P and Y.

 

[Donamy]

Any chance to use the star trackers in the sim ?

 

[SiameseCat]

I'm starting work on the DAP pushbuttons. I'm planning to have a single class to handle bothe sets of PBIs. It will respond to mouse events and return the status of each light in the PBIs.

 

[SiameseCat]

Problem with DAP controls

I've found a problem with the DAP controls currently used; the labels on the buttons are different from the ones currently in use. I've attached screenshots of the current Orbiter version and what it should look like (picture copied from the SCOM).

 

[Donamy]

I have the .psd file for that panel, if you really need it changed.

 

[DaveS]

I have the .psd file for that panel, if you really need it changed.

We do need it changed. I believe that there has been two versions of the Orbital DAP, the one you have here and the one used now illustrated by the SCOM graphic here.

As you see, you're missing several important PBIs, like High Z and and Low Z, which enables/disables upward firing RCS jets(in the -Z direction) to avoid plume impingement.

Another set of PBIs missing is the PRI and VERN PBIs which selects either the primary jets or the smaller vernier jets.

 

[tblaxland]

OK, you've got me curious now. What does the "FIRE HOLE" do?

 

[DaveS]

OK, you've got me curious now. What does the "FIRE HOLE" do?

In the event of fire behind the panel, a fire extinguisher nozzle is put in front of it putting out the fire. Alot faster than manually removing the many screws that holds the panels togheter.

 

[tblaxland]

Thanks.

 

[SiameseCat]

We do need it changed. I believe that there has been two versions of the Orbital DAP, the one you have here and the one used now illustrated by the SCOM graphic here.

As you see, you're missing several important PBIs, like High Z and and Low Z, which enables/disables upward firing RCS jets(in the -Z direction) to avoid plume impingement.

Another set of PBIs missing is the PRI and VERN PBIs which selects either the primary jets or the smaller vernier jets.

I think parts of the VC mesh are modelling old panels. The PanelR2 used in the real shuttle is slightly different from what we have, which represents an older version of the panel.

 

[DaveS]

I think parts of the VC mesh are modelling old panels. The PanelR2 used in the real shuttle is slightly different from what we have, which represents an older version of the panel.

Speaking of older panels, take a look on this photo from STS-114: http://spaceflight.nasa.gov/gallery/images/shuttle/sts-114/hires/s114e5185.jpg

Notice that the talkbacks on the A8L panel is different from what we have? Like DPY instead of DEP? And the different talkback backgrounds?

 

[SiameseCat]

Do you have any screenshots of the ET Umbilical door talkbacks on R2? I'm guessing those would have the same white background for the LAT talkback, but I'd like to make sure.

 

[DaveS]

Do you have any screenshots of the ET Umbilical door talkbacks on R2? I'm guessing those would have the same white background for the LAT talkback, but I'd like to make sure.

Sorry, no photos of the ET talkbacks. But my guess would they're the same.