Limiting factors on Saturn IB launch weight.

[Linguofreak]

I was recently playing around with the Velcro Saturn Ib and AAPO CSM, and found that I could actually get into orbit quite comfortably with a fully fueled SM and about 3 km/s left on the S-IVb. Real-life Saturn Ib missions never flew with a fully fueled SM because of weight restrictions, yet I seem to be reaching orbit with plenty of DV and T/W ratio to spare. Were there any other limiting factors on the Saturn I's launch weight (structural, abort profile, etc)?

 

[Hlynkacg]

It wouldn't surprise me to find out that the aerodynamic modeling is less than accurate. the AAPO CSM's is still a work in progress and I don't know if Velcro is modeling the dv penalties for atmospheric pressure.

ETA
A 10% reduction in exhaust velocity early in the ascent could account for that

 

[sputnik]

That sounds like the Velcro Saturn isn't carrying the weight of the Apollo at ALL for some reason. It works properly for NASSP and AMSO Apollos; you have to offload fuel just to get the thing in orbit at all; you're certainly not doing it with 3 km/s in the tanks.
Could you share your scenario with us? Sounds like a glitch.

 

[Linguofreak]

That sounds like the Velcro Saturn isn't carrying the weight of the Apollo at ALL for some reason. It works properly for NASSP and AMSO Apollos; you have to offload fuel just to get the thing in orbit at all; you're certainly not doing it with 3 km/s in the tanks.
Could you share your scenario with us? Sounds like a glitch.

I did notice that the attachment of the AAPO spacecraft to the stack seems to be a custom method for AAPO, not a typical Velcro payload setup. I'm not on the relevant computer at the moment and have to head off pretty soon, I'll try to remember to post the scenario this evening.

 

[Hlynkacg]

I did notice that the attachment of the AAPO spacecraft to the stack seems to be a custom method for AAPO, not a typical Velcro payload setup. I'm not on the relevant computer at the moment and have to head off pretty soon, I'll try to remember to post the scenario this evening.

This is due to the SLA.

The SLA class vessel is attached to booster and then the CSM is defined as occupying the SLA's forward payload slot. Not significant in solo-ops but becomes important when launch the complete Apollo stack (LM + CSM). The SLA is supposed to gain/lose mass depending on it's defined payloads but something may not be getting updated properly.

 

[sputnik]

It might be. Velcro spends the first Orbiter cycle gluing attachments together, and the second tallying up the masses. If the SLA's mass isn't correct by the 2nd timecycle, it's not going to be counted properly.

Hmm. You could add a dummy payload to ballast the S-IV to the right mass. There's probably a better way, but I'd have to see the scenario. I admit I haven't had the chance to check out AAPO yet.

 

[Linguofreak]

There's a chance I may have screwed something up in converting from the full Apollo Saturn V launch scenario that comes with AAPO to my CSM only Saturn I scenario, as I copy-pasted stuff and don't fully understand the AAPO scenario syntax.

I haven't forgotten about uploading the scenario, but I haven't had an opportunity yet.

---------- Post added at 18:47 ---------- Previous post was at 11:52 ----------

The scenario follows:

BEGIN_DESC

The Saturn-Ib was an improved Saturn-I. 

END_DESC



BEGIN_ENVIRONMENT

  System Sol



END_ENVIRONMENT



BEGIN_FOCUS

  Ship S-Ib

END_FOCUS



BEGIN_CAMERA

  TARGET S-Ib

  MODE Extern

  POS 9.73 -0.51 -123.30

  TRACKMODE TargetRelative

  FOV 50.00

END_CAMERA



BEGIN_HUD

  TYPE Surface

END_HUD



BEGIN_MFD Left

  TYPE Surface

END_MFD



BEGIN_MFD Right

  TYPE Orbit

  PROJ Ship

  REF Earth

END_MFD



BEGIN_SHIPS

ISS:ProjectAlpha_ISS

  STATUS Orbiting Earth

  ELEMENTS 6734918.9 0.00090 74.51300 169.03400 328.27205 361.47656 51982.10678799

  AROT 30.00 0.00 50.00

END

Gumdrop:AAPO\CSM

  STATUS Landed Earth

  POS -80.62090 28.62719

  HEADING 0.00

  ATTACHED 0:0,S-IVb

  AFCMODE 7

  PRPLEVEL 0:1.000000 1:1.000000 3:1.000000 4:1.000000 5:1.000000 6:1.000000 7:0.500000 8:1.000000 9:0.997832 10:1.000000 11:1.000000

  NAVFREQ 0 0

  HATCH 0 0.0000

  LIGHT 0 0.0000

  HGA 0 0.0000

  LES_ATTACHED 1

  SLA_ATTACHED 1

  SM_ATTACHED 1

  SM_BAYOPEN 0

  DOCKING_PROBE 1

  APEX_COVER 1

  DROGUES_DEPLOYED 0 0.0000

  CHUTES_DEPLOYED 0 0.0000

  UMMUCREW Capt-James-40-65-82

  UMMUCREW Crew-Dave-37-65-82

  UMMUCREW Doc-Rusty-34-65-82

  UCGO @@0,0,0,0,@@1,0,0,0,

END

S-IVb:AAPO/Velcro/s4b

  STATUS Landed Earth

  POS -80.62090 28.62719

  HEADING 0.00

  TGT_HEADING 095.0

  FUEL 1.000

  CONFIGURATION 0

END

S-Ib:Velcro/S-1b

  STATUS Landed Earth

  BASE Cape Canaveral:6

  HEADING 0.00

  TGT_HEADING 095.0

  FUEL 1.000

  CONFIGURATION 0

  CAMERA 0 0 55.0

  SERIESBURN 0 S-IVB 0.0 0.0 -8.9  0.0 1.0 0.0 

  PAYLOAD Fins Velcro/Parts/S-1bFins Velcro/Parts/S-1bFins 0 0 0 0.0 0 0.0 1.0

  PAYLOAD Interstage Velcro/Parts/S4b_to_s4b_interstage Velcro/Parts/S4b_to_s4b_interstage 0 0 -37.5 1000.0 0 0.0 1.0

END

END_SHIPS

 

[sputnik]

Well, it looks like the AAPO CSM is just hung onto the side of the Velcro Saturn with the line ATTACHED 0:0,S-IVb
You need to use one of Velcro's methods of attachment; just using the native Orbiter line doesn't let Velcro know it's there.

 

[Linguofreak]

So the question now is, can the AAPO CSM be attached with SERIESBURN without screwing up AAPO?

 

[Linguofreak]

After some investigation, it appears that the using SERIESBURN doesn't cause any serious problems with AAPO itself (though there are one or two more things I want to check), but the S-IVb doesn't end up shedding the mass of the escape tower when AAPO jettisons it, and that or something else is causing the S-IVb/CSM/LM stack to turn up a couple hundred m/s short of the DV necessary for TLI when launched due east from the Cape on a full Saturn V stack.

 

[4throck]

I'm setting up similar launch scenarios using the Saturn IB and AAPO/AMSO. The solution that works is the one used in the Skylab 1973 add-on: create a custom velcro config for the rocket stages and reduce their weight until it simply works as intended...