Problem problem with Space Shuttle Ultra 3.0

[conradsm]

Hi Guys
I'm an Italian Orbiter fan. I have a problem. I have done just few days ago a new fresh installation of orbiter than I have installed the addon SSU 3.0

My problem starts when I have the Shuttle at MECO and I have to wait to arrive to apoapsis to engage OMS burn. Well, now In this situation I have not the possibility to operate OMS burn, prograde orientation , kill rotation. The only things I have able to do are rotation.

Seems I have not propeller to do that. So I check the Shuttle propeller with the panel (CTRL F4 ) and I have always 18 tanks but always three of them empty. Than I fill these three tanks but I have the same problem.Than I think the problem is something else. Seems that

What I have to do ? someone could you help me?
Thanks
Corrado

 

[Thorsten]

I guess this works like the real thing, which means you have to program the OMS-1 or OMS-2 burn via OPS 104/ OPS 105 (the MNVR display) by entering suitable PEG-4 or PEG-7 burn targets. You can't just point and punch throttle.

Another wild guess is that the three empty tanks would be 2 SRBs and one ET.

I'm sure some SSU developer will refine that assessment.

 

[GLS]

If you used one of the included launch scenarios, then you will have OMS propellant for many burns.
Like Thorson said, to use the OMS you need to call the OMS MNVR display in one of the displays to tell the computers how much delta-v you want, in which direction, and when ignition should take place. For the OMS-2 burn, you have to manually transition from OPS 104 to OPS 105, maybe 20 minutes (?) into the mission. Then you have to set the ignition time using ITEM 10, which should be targeted to the apogee of your current orbit, and then set the delta-v using ITEM 19 in feet per second (positive is prograde, negative is retrograde), ITEM 22 loads that info, ITEM 23 starts the timer in the top right of the display, ITEM 27 tells the computers to orient the orbiter to the burn attitude (the ORBITAL DAP has to be in AUTO, which you can tell by checking the buttons with the yellow lights on panel C3), and then you wait until 15 seconds before ignition and a yellow "EXEC" will start flashing in the display, telling you to enable the burn by hitting the EXEC key and if all is correct the OMS should ignite when the clock hits zero.
The real NASA checklists are a good source for the steps needed to do something, and the SCOM has tons of "background" information.

 

[conradsm]

Hi GLS, two questions:
1) there is a manual to follow these steps you mean because I don't understand how I have to do that. It's not enough clear for me how to put these command. I tryied to digit them but I can't see any action after and It's not clear the sequence.
2) If I want, could I skip these command ad procede manually to OMS burn etc. after MECO and ET separation ?
thanks

 

[DaveS]

Hi GLS, two questions:
1) there is a manual to follow these steps you mean because I don't understand how I have to do that. It's not enough clear for me how to put these command. I tryied to digit them but I can't see any action after and It's not clear the sequence.
2) If I want, could I skip these command ad procede manually to OMS burn etc. after MECO and ET separation ?
thanks

1) You input the commands through one of the two keyboards on panel C2, that's the angled section of the center panel console. Here's a command example for an OMS-2 burn done at an MET of 37 minutes and 36 seconds which has a delta V of 195 fps:

ITEM 7-5.7+5.7 EXEC // This will angle the OMS engines properly for the burn (TRIM ANGLES)
ITEM 10+0+0+37+36 EXEC // MET timing of burn ignition. The first zero is days, the second is hours while 37 is minutes and 36 is seconds
ITEM 19+195 EXEC //This is a posigrade delta V in the orbiter's X-axis of 195 fps
ITEM 22 EXEC // This will load the entered burn targets
ITEM 23 EXEC // This will enable the burn countdown timer which will appear beneath the MET counter on the DPS screens

At burn ignition -2 minutes, take the two OMS ENG switches on panel C3 to ARM/PRESS.

2)No. SSU is all about the highest commitment to realism. This includes doing away with "cheats" like manual OMS ignitions. On the real shuttle OMS burns were done by the onboard computers called the General Purpose Computers or GPCs.

The procedure is the same for any OMS burn. Just follow the actual NASA checklists and you'll be fine.

 

[Thorsten]

2) If I want, could I skip these command ad procede manually to OMS burn etc. after MECO and ET separation ?

I suppose if you really wanted, you could orient the Shuttle properly and do the burn with an RCS translational DAP (attitude hold would make it easier).

Note that this may gobble a lot of RCS propellant, so likely you need to have an OMS to RCS crossfeed set up, otherwise you'll empty the RCS tanks too early. It also takes quite a bit longer that way...

I can't recall having come across any procedure to ignite the OMS outside of programming a burn.

 

[GLS]

I suppose if you really wanted, you could orient the Shuttle properly and do the burn with an RCS translational DAP (attitude hold would make it easier).

Note that this may gobble a lot of RCS propellant, so likely you need to have an OMS to RCS crossfeed set up, otherwise you'll empty the RCS tanks too early. It also takes quite a bit longer that way...

I can't recall having come across any procedure to ignite the OMS outside of programming a burn.

Yes, I'm pretty sure the OMS are GPC-controlled only. But the RCS are always available for manual translational (and rotational) maneuvers... but we don't have the OMS/RCS interconnect working, so RCS prop is pretty limited at the moment. :facepalm:

 

[DaveS]

Yes, I'm pretty sure the OMS are GPC-controlled only. But the RCS are always available for manual translational (and rotational) maneuvers... but we don't have the OMS/RCS interconnect working, so RCS prop is pretty limited at the moment. :facepalm:

Not really. The ARCS currently shares its propellant with the OMS so it has a hefty delta V budget. Only the FRCS is properly implemented with it's own dedicated propellant resource.

 

[GLS]

Not really. The ARCS currently shares its propellant with the OMS so it has a hefty delta V budget. Only the FRCS is properly implemented with it's own dedicated propellant resource.

Not sure that is always the case since Urwumpe changed the RCS last year or so.

 

[DaveS]

Not sure that is always the case since Urwumpe changed the RCS last year or so.

It's still the case:

th_att_rcs[1] = CreateThruster(_V(0, 0, -15.5), _V(0, -1, 0), ORBITER_RCS_THRUST, ph_oms, ORBITER_RCS_ISP0, ORBITER_RCS_ISP1)

Note the "ph_oms", this is the propellant handle for the OMS propellant resource. That leads to this mass definition:

const double ORBITER_MAX_PROPELLANT_MASS = 11284.23 + 2162.622;
// Per SODB Vol 1, 3.4.3.3, maximum propellant load in the OMS tanks is 4711.5 lbs (2134.3095 kg) of fuel and 7743.5 lbs (3507.8055 kg) of oxidizer per pod. Min load is 2038 (923.214 kg) lbs of fuel and 3362 lbs (1522.986 kg) of oxidizer per pod.
// This parameter for now includes the propellant mass of the Aft RCS fuel and oxidizer

 

[GLS]

I didn't check the code to see where the thrusters were plugged in, but the ARCS tanks sometimes show up with some prop so...

 

[DaveS]

I didn't check the code to see where the thrusters were plugged in, but the ARCS tanks sometimes show up with some prop so...

My guess is that they're defined and loaded but not used. The RCS is still using the idealized setup. See these tickets: https://sourceforge.net/p/shuttleultra/tickets/102/
https://sourceforge.net/p/shuttleultra/tickets/18/

 

[Thorsten]

Actually, I've been wondering about that one

ITEM 7-5.7+5.7 EXEC // This will angle the OMS engines properly for the burn (TRIM ANGLES)

because it wasn't compatible with my understanding of how OMS TVC works internally. So I've tried to do some research, and it seems what this will do is make sure the ADI error needles are showing correct during the burn.

Crew Operations Manual 7.3-2 contrasts the two ways of operating:

OMS TVC gimbals the OMS engines to null vehicle rates and point sensed thrust in the desired ΔVTOT direction.

ADI error needles display vehicle attitude error from the attitude that would point the net thrust through the c.g., as defined by the trim angles, and in the desired ΔVTOT direction. If trim angles are incorrect or flight control does not recognize an engine failure, the ADI error needles will not display correct error information.

My understanding is that OMS TVC runs internally on a PID, which due to the integrator is able to trim itself and hence can maintain zero attitude rates (biased by whatever comes from the RHC during manual) - just the ADI doesn't have access to the internal workings of the controller but it does sense gimbal angles, so it needs to know what the angles pointing through the center of gravity are. Hence the need for trim angles.