Centaur G/G Prime High Energy Upper Stage

[DaveS]

Yeah I'd try 3 first, and if that costs too much performance try 2, and 1 would be my last choice.
Going back to the trunk, as it looks like something is not right with the MFD button labeling... :facepalm:

---------- Post added 03-04-15 at 12:29 AM ---------- Previous post was 03-03-15 at 04:46 PM ----------

DaveS, any reason why you when back on the Centaur and CISS code in r1981?

Had some problems checking some fixes and the only thing that resolved it was going back. As far as I can tell, nothing major was lost and was overwritten with newer data any way.

 

[GLS]

If the conflicts don't allow you to commit, first save a copy of the file(s), then do whatever it takes for tortoise to be happy (normally revert) and then just replace the reverted file with the one you saved.
This branch switching is really a PITA, some modified files always get conflicts and others in a similar state don't :S

---------- Post added at 12:47 AM ---------- Previous post was at 12:45 AM ----------

Heads-up, I'll try to correct r1981 (using the new numbers).

---------- Post added at 02:06 AM ---------- Previous post was at 12:47 AM ----------

Done. Everything looks +/- in the right place, just missing the fine tuning of the relative positions when the meshes are complete.

---------- Post added at 11:51 AM ---------- Previous post was at 02:06 AM ----------

Last night I had an idea for a workaround to the SSU performance deficit regarding the Centaur. We could apply what I call the "SSU Performance Factor" to all the Centaur/CISS masses. That factor, smaller than 1, would lower those masses, thus allowing the shuttle to make into orbit, but at the same time would keep the Centaur dV intact because the ratio of masses in the "rocket equation" is the same. Yes, it would have a smaller burn time and higher acceleration, but same dV. Correct?
A factor of 0.95 would decrease the Centaur/CISS mass by about 3000 lbs, which might just be enough to launch Galileo (the most mass critical case ATM).
I haven't tested anything yet, just wanted to put this up for discussion first.

 

[DaveS]

I know that some Centaur propellant would have been offloaded for STS-61G as a full propellant load would have put the Centaur over the 65k lbs mass budget. How much of prop offloaded are you flying with?

 

[Urwumpe]

Last night I had an idea for a workaround to the SSU performance deficit regarding the Centaur. We could apply what I call the "SSU Performance Factor" to all the Centaur/CISS masses. That factor, smaller than 1, would lower those masses, thus allowing the shuttle to make into orbit, but at the same time would keep the Centaur dV intact because the ratio of masses in the "rocket equation" is the same. Yes, it would have a smaller burn time and higher acceleration, but same dV. Correct?
A factor of 0.95 would decrease the Centaur/CISS mass by about 3000 lbs, which might just be enough to launch Galileo (the most mass critical case ATM).

I haven't tested anything yet, just wanted to put this up for discussion first.

I disagree against it, because it is largely against what SSU was initially about. We should better look at more realistic ways to improve performance for such missions - off-loading propellant, correct Orbiter dry weight.

I am not sure if we also calculate the mass of the cryogen storage tanks for the fuel cells correctly, possible that we have a heavier Orbiter because we are assuming longer missions.

Also, are we correctly using pre-challenger masses or post-challenger masses?

Just calculated: Alone by the ICES pole (248 lb) and the ACES suits (70 lb per crew), the "empty weight" of the Shuttle orbiter is now 738 lb heavier than it was supposed to be for the Centaur missions.

 

[DaveS]

I took a look in ParameterValues.h and it reports an orbiter dry mass of 81100 kg (178 794.895 lbs) which is in Columbia territory. I think we all can agree on that an orbiter with the mass of Columbia could not have done the STS-61G mission.

As a comparison, Atlantis reported in at 77463 kg (171 000 lbs) at Palmdale rollout. That was taking in account the mass of the three SSMEs. Without the engines, the dry mass was reported as 68545.695 kg (151 315 lbs).

Remember, this was the reason why Atlantis got STS-61G and not Challenger. Challenger did have the performance for a fully loaded Centaur G Prime at 104. This was due to the lighter Ulysses being the payload instead of the heavier Galileo which lugged around on plenty of propellant for the JOI burn as well as the atmospheric entry probe.

Ulysses in contrast only had propellant for the attitude thrusters which also pulled double duty as course correction thrusters and no secondary probe. This got the total mass below 500 kg, which is very light.

 

[Urwumpe]

I think we need a better knowledge of the mass properties of the orbiters, regarding everything that was changed by modifications or configured for a mission - the historic changes are significant enough for making the difference between orbit and a not-converging guidance.

Also, we maybe need a parameter for IVA payload mass, not sure if we simply don't add it now or have it in the dry mass already somewhere.

 

[GLS]

Looking at the OV mass first makes sense. How about, for this release, we add a system to choose the mass of the orbiter based on the "Orbiter" parameter in the mission file? It's not perfect as the masses changed over time, but it would allow us to tell Columbia apart from Endeavour.
And for the next release put these configuration issues to bed.

 

[DaveS]

Looking at the OV mass first makes sense. How about, for this release, we add a system to choose the mass of the orbiter based on the "Orbiter" parameter in the mission file? It's not perfect as the masses changed over time, but it would allow us to tell Columbia apart from Endeavour.
And for the next release put these configuration issues to bed.

This is something much better than a unrealistic "fudge factor". Also, something that is also unknown is just how much OMS/RCS propellant was included into the ability of an orbiter to reach that 65k lbs payload mass to orbit. That is also several thousand lbs of potentially unnecessary mass to take into orbit.

 

[GLS]

Just looked at a partial list of OMS prop loads, and the minimum load I found was ~49.6%. So let's say that in these missions they only loaded 50% OMS prop, that would mean less ~12000lbs. :jawdrops: To quote a well known TV show: "Well, there's your problem". :lol: Of course it would be nice to know if they were going to offload OMS by that amount.
Anyway, if we could agree on a list of average OV masses to use, I could squeeze some time this afternoon to add the code to link OV mass to the OV name in the mission file.

 

[DaveS]

Just looked at a partial list of OMS prop loads, and the minimum load I found was ~49.6%. So let's say that in these missions they only loaded 50% OMS prop, that would mean less ~12000lbs. To quote a well known TV show: "Well, there's your problem". :lol: Of course it would be nice to know if they were going to offload OMS by that amount.
Anyway, if we could agree on a list of average OV masses to use, I could squeeze some time this afternoon to add the code to link OV mass to the OV name in the mission file.

These are the rollout masses I have tracked down (all with main engines installed)

OV-102: 80634 kg (178k lbs)
OV-099: 79325.283 kg (175111 lbs)
OV-103: 77463 kg (171k lbs)
OV-104: Same as OV-103
OV-105: 77916 kg (172k lbs)

Without SSMEs:
OV-102: 71704.917 kg (158, 289 lbs)
OV-099: 70396.2 kg (155, 400 lbs)
OV-103: 68592.807 kg (151, 419 lbs)
OV-104: 68545.695 kg (151, 315 lbs)
OV-105: 68495.865 kg (151, 205 lbs)

---------- Post added at 03:40 PM ---------- Previous post was at 02:49 PM ----------

The Centaur G CISS is now sufficiently complete to allow animations to be added. Once that is done, I'll make the Centaur G Prime CISS and finish the work on the Centaur Mission Kit. The animation ready CISS have been checked in.

 

[Urwumpe]

The Centaur G CISS is now sufficiently complete to allow animations to be added. Once that is done, I'll make the Centaur G Prime CISS and finish the work on the Centaur Mission Kit. The animation ready CISS have been checked in.

Are the reference points for the animations still the same?

And you have some small reference drawing how things should be moving?

 

[DaveS]

Are the reference points for the animations still the same?

And you have some small reference drawing how things should be moving?

CISS Deployment Adapter rotation point: 0, -0.354937, -2.21002
CISS Deployment Adapter rotation arm rotation point: 0, 0.9954, -2.2926
CISS Deployment Adapter rotation link rotation point(where it meets the arm): 0, 0.8580, -2.7548
CISS Deployment Adapter rotation link rotation point(where it meets the CISS): 0, 0.56, -3.3501

LH2 F/D segment 1: -1.47526, -1.12367, -2.29268
LH2 F/D segment 2: -1.47526, 0.491686, -2.24982
LH2 F/D segment 3: -1.47526, 0.491686, -1.83982

GH2 vent segment 1: -1.77116, -0.793329, -2.22066
GH2 vent segment 2: -1.48555, 0.327039, -2.3239
GH2 vent segment 3: -1.48555, 0.327039, -1.83982

LOX/GOX segments, mirrored X-axis only, Y and Z stay the same

---------- Post added at 06:11 PM ---------- Previous post was at 03:50 PM ----------

I have updated the SSU Centaur reference document with the Flight and Contingency ops from the Centaur G Prime Technical Description. I think they'll be useful later once more detailed systems are implemented.

 

[GLS]

These are the rollout masses I have tracked down (all with main engines installed)

OV-102: 80634 kg (178k lbs)
OV-099: 79325.283 kg (175111 lbs)
OV-103: 77463 kg (171k lbs)
OV-104: Same as OV-103
OV-105: 77916 kg (172k lbs)

Without SSMEs:
OV-102: 71704.917 kg (158, 289 lbs)
OV-099: 70396.2 kg (155, 400 lbs)
OV-103: 68592.807 kg (151, 419 lbs)
OV-104: 68545.695 kg (151, 315 lbs)
OV-105: 68495.865 kg (151, 205 lbs)

The source of those numbers is pounds right? Because they don't match...
I'll use the mass with SSMEs, as they are not defining their masses in the subsystem ATM.

 

[DaveS]

The source of those numbers is pounds right? Because they don't match.

Yes, the source was lbs.

 

[GLS]

The new orbiter mass definition is up.

 

[DaveS]

I think I have discovered a bug with the payload adapter code in the Centaur. If the offset is exactly 0, the adapter mesh doesn't show up. But if you add just a tiny bit of offset, it shows up without problems. I have tried this several times now and have replicated it every time, no exceptions.

---------- Post added at 10:37 PM ---------- Previous post was at 10:17 PM ----------

Checked in a simple adapter that allows the default Carina to properly interface with the Centaur G. It should fit nicely on the Centaur G Prime as well but I haven't tested it.

 

[GLS]

I think I have discovered a bug with the payload adapter code in the Centaur. If the offset is exactly 0, the adapter mesh doesn't show up. But if you add just a tiny bit of offset, it shows up without problems. I have tried this several times now and have replicated it every time, no exceptions.

It isn't a bug, but a feature . If there's an adapter, the payload attachment has to be further forward, and that is the reason why there's the "adapter offset" parameter. The adapter will not be loaded at all if there isn't a mass parameter or an adapter offset parameter (which is just the height of the adapter). Also, I see you changed the SSU_GenericPayload attachment, and that's not needed because of the adapter offset.
If we have a correct payload attachment point in the Centaur, at the "top plane" of that section with stringers, I think this system will work.

I'm going to put an error message for when there's something wrong, and the adapter doesn't show, the user gets informed. Sorry for this oversight.

 

[Urwumpe]

I'm going to put an error message for when there's something wrong, and the adapter doesn't show, the user gets informed. Sorry for this oversight.

If possible, we should maybe crash orbiter in a controlled way with a log message, should a simulation not run at all.

 

[GLS]

If possible, we should maybe crash orbiter in a controlled way with a log message, should a simulation not run at all.

I see the need for that in some areas (don't remember any now...), but for this case it isn't needed.

 

[DaveS]

If we have a correct payload attachment point in the Centaur, at the "top plane" of that section with stringers, I think this system will work.

That's where it is. The change was necessary due to the fact that without it, the Carina would be buried in the Centaur. The adapter zero point is located where it interfaces with the Centaur. The screenshot below shows the layout. The Centaur I/F is where the two intersecting lines meet (zero point) and the Carina I/F is at the narrow cone end.