SSU Development Thread (2.0 to 3.0)

[SiameseCat]

I'm currently working on the Centaur stuff, and I have come across a launch anomaly. It is that ascent events, especially second stage events, occur too early. I have logged the events to consistently occur 30 seconds too early. This the 3G throttling and MECO zero thrust.

This is simulating the STS-61G mission. This is with a historically mass accurate Centaur, CISS and a Galileo mass simulator. And I'm using 109% thrust level with maxed out FRCS and OMS/ARCS propellant levels.

According to everything I have read on the STS-61G mission, this mass combination should leave me well short of the MECO apogee of 240.76 km (130 n.mi) planned for the Centaur missions. Yet, the vehicle is able to reach it and well beyond!

I'm not sure what is going on here.

---------- Post added at 11:20 PM ---------- Previous post was at 08:59 PM ----------

Another data point discovered: The hard coded empty mass is set to that of Columbia, the heaviest orbiter in the fleet, at 81100 kg. There is no way Columbia would have been able to fly STS-61G with that mass as it required Atlantis, the lightest orbiter and the engines at 109% FPL.

For comparison's sake the dry mass of Atlantis as of 2 October 2000 was recorded at 79382.25 kg.

Can you check the ET/SRB masses?

---------- Post added at 09:10 PM ---------- Previous post was at 09:04 PM ----------

Also, I think the SSME specifications (thrust & ISP) changed a bit over time. This might have some effect on the Centaur missions.

It might be a good idea to test one of the ISS missions and see if there is still significant overperformance.

 

[GLS]

Well, I think it's a 2 part problem:
> the orbiters back then were heavier (had more "structural stuff" that was changed/removed in the late 90s "diet" for ISS, but had only 3 cryo tank sets (or 4 in Atlantis and Discovery? :idk; there was only the LWT (I don't think we do the differentiation between ET versions); not sure we have the mass of the SSMEs included; and also there was more weight due to the Centaur piping in the aft.
> the SSMEs had slightly different performance, (don't remember exactly at this time of the night but) as the SSME upgrades went along, the engines got heavier and (slighty) less efficient.

 

[DaveS]

Well, I think it's a 2 part problem:
> the orbiters back then were heavier (had more "structural stuff" that was changed/removed in the late 90s "diet" for ISS, but had only 3 cryo tank sets (or 4 in Atlantis and Discovery? :idk; there was only the LWT (I don't think we do the differentiation between ET versions); not sure we have the mass of the SSMEs included; and also there was more weight due to the Centaur piping in the aft.
> the SSMEs had slightly different performance, (don't remember exactly at this time of the night but) as the SSME upgrades went along, the engines got heavier and (slighty) less efficient.

The different ETs are simulated properly in terms of dry masses.

Centaur plumbing mass would have been around 135 kg (not much at all due to the smallness of the plumbing).

The hard-coded empty mass seems to be with everything optional included (RMS, Ku band DA, Orbiter docking equipment (airlock/ODS)).

The three lightweight orbiters all clocked in at an generic weight of 67950 kg at rollout from final assembly in Palmdale.

 

[GLS]

Had a couple of slow days and decided to take another look into my idea for vehicle configuration (in this post). So I basically moved most of the code from the Atlantis constructor, and placed it just after the loading of the mission file. Fired up a scenario and got into orbit just fine (yes, not much of a test :lol.
One easy-to-spot bug is if the configuration file line in the .scn is somewhere in the middle of the other entries, it will probably CTD, because most systems would still not have been created. A possible fix for that would be: 1) reading the .scn file lines into a buffer; 2) finding the configuration file line in the buffer and load it; 3) load appropriate subsystems and stuff; 4) give the rest of the lines in the buffer to the subsystems or back to orbiter.
So, it's a different way of loading the systems, I don't see any drawbacks from it, and we gain more capability in vehicle configuration.

What does everybody else think?

 

[DaveS]

When I was testing and working out the ascent data for STS-61G I noted an issue with the ET post-SRB sep, namely that its texture changes to that of the SLWT instead of maintaining it's LWT texture. I suspect the same is true for the SWT.

 

[DaveS]

Just to give an update on what I'm currently working on:

While going over the current LC-39 element meshes, I discovered size flaws in just about everything, except for the orbiter.

Just to give an example: The ET LH2 tank too long. According to the schematics in the SLWT Systems Definition Handbook (SDH) the length of the LH2 from the intertank flange to the aft dome is 22.8 m. Currently it sits at 23.65m. Not only that the LH2/LOX tanks don't have the same diameter!

And the intertank door as well as the ETCA are located in the wrong areas of the intertank.

I haven't checked the SRB segments yet for any issues. I'm still working on the SLWT mesh.

 

[DaveS]

I have now checked the SRBs, they're good. And the redone ET is coming along nicely.

 

[SiameseCat]

When I was testing and working out the ascent data for STS-61G I noted an issue with the ET post-SRB sep, namely that its texture changes to that of the SLWT instead of maintaining it's LWT texture. I suspect the same is true for the SWT.

I can add a scenario file entry (BURNT_TEX_NAME) to specify the texture to be used after SRB sep.

 

[DaveS]

I can add a scenario file entry (BURNT_TEX_NAME) to specify the texture to be used after SRB sep.

That would be great. Another ET tex issue is that currently there's no way to make STS-1/2 fly with the white FRL coated ETs. I'm not sure how to handle that.

 

[Urwumpe]

That would be great. Another ET tex issue is that currently there's no way to make STS-1/2 fly with the white FRL coated ETs. I'm not sure how to handle that.

What about letting the ET vessel handle this and use special code for the 5 ET versions around?

 

[SiameseCat]

That would be great. Another ET tex issue is that currently there's no way to make STS-1/2 fly with the white FRL coated ETs. I'm not sure how to handle that.

There's already a ET_TEX_NAME scenario file entry which specifies the (unburnt) ET texture. This should work for STS-1/2.

 

[DaveS]

There's already a ET_TEX_NAME scenario file entry which specifies the (unburnt) ET texture. This should work for STS-1/2.

That parameter seems to be in-operational at the moment. It just won't apply to the mesh. I checked it all over to make sure that it isn't being applied to the wrong parts (like the cable trays) but that's not the case.

 

[SiameseCat]

That parameter seems to be in-operational at the moment. It just won't apply to the mesh. I checked it all over to make sure that it isn't being applied to the wrong parts (like the cable trays) but that's not the case.

The texture name is probably incomplete. It should look like

ET_TEX_NAME SSU\SLWT_ETtex.dds

Both the SSU\ folder and the .dds extension are required, otherwise the texture won't be found.

 

[DaveS]

The texture name is probably incomplete. It should look like

ET_TEX_NAME SSU\SLWT_ETtex.dds

Both the SSU\ folder and the .dds extension are required, otherwise the texture won't be found.

Thanks. I think it should be updated to work like the OrbiterTexture parameter in the mission files, to ensure consistency.

 

[SiameseCat]

Thanks. I think it should be updated to work like the OrbiterTexture parameter in the mission files, to ensure consistency.

Done. I've also added the BURNT_TEX_NAME parameter.

 

[GLS]

So, I'm back in development chair again!
I'm planning on finishing some small things, improve the ET sep (and possibly the SRB sep as well) and adding the TRANS DAP, before I ask for a merger of the mps branch. For that I need the panel C3 ETSEP switches (and the SRBSEP if possible).

There's a "bug" in the Main Engine Shutdown PBs from day 1: once you click to move the cover, the PB below is also activated. Don't know if it's possible to improve the cover operation... maybe use right click to open the cover and left click to push the PB?

I know I'm late but I want to give my 2 cents on the ET texture discussion above. Basically every ET type has a default (normal) texture and a burnt texture, differentiated by the addition of "_BURN" (or something) to the name. So the ET texture files would consist of a pair of textures. If the user wants to specify a different texture set, there should be 1 parameter passed to SSU (thru mission file or scn) specifying the desired texture name. From that name (ex. "myETtexture.dds") we would search
that file and the burnt texture "myETtexture_BURN.dds". Any problems -> use default textures for the current ET type. This way it works properly without any "user inputs" (aside from the ET type), and there's a simple way to specify another texture (1 parameter only).

And finally, any comments about this idea?

 

[DaveS]

So, I'm back in development chair again!
I'm planning on finishing some small things, improve the ET sep (and possibly the SRB sep as well) and adding the TRANS DAP, before I ask for a merger of the mps branch. For that I need the panel C3 ETSEP switches (and the SRBSEP if possible).

Here you:

ET sep switch: -0.083, 1.7, 14.075
SRB sep switch: 0.006, 1.7, 14.079

There's a "bug" in the Main Engine Shutdown PBs from day 1: once you click to move the cover, the PB below is also activated. Don't know if it's possible to improve the cover operation... maybe use right click to open the cover and left click to push the PB?

Check out the code for the A8 panels, they have working covers.

 

[GLS]

Here you:

ET sep switch: -0.083, 1.7, 14.075
SRB sep switch: 0.006, 1.7, 14.079

Check out the code for the A8 panels, they have working covers.

OK, I'll see what I can do, thanks! (are those coordinates for the PBs or for the MAN/AUTO switches? need both...)

BTW still on the ET textures: about the STS-1/2 painted ET, I think there's more than just the textures to worry about, because the paint added weight. So I think we should consider 2 SWT types: painted and "natural". That way there is no problem choosing the correct textures.

 

[DaveS]

OK, I'll see what I can do, thanks! (are those coordinates for the PBs or for the MAN/AUTO switches? need both...)

They're for the actual switches, not the PBs.

ET sep cover: -0.119, 1.734, 14.096
SRB sep cover: -0.031, 1.734, 14.096

 

[GLS]

OK, got the switches, the covers and the PBs to work, but the coordinates for the switches are not exactly correct as the switches are slightly above the panel. DaveS, if you want I can upload the panel and you fine tune the numbers.
On the covers also activating the PBs: I checked the code on panels A8 and O6 and I don't see anything "special" aside from the coordinates for the cover and the switch being the same (tried that and it did not work). Both those cases there's a switch below the cover, not a PB, so the "mechanics" are probably different.

One way to solve this is to place the cover open zone just on the bottom of the cover (in the little "bulge"), so that there's no overlap between that and the PBs click zone.