J Mission Work-Around (Apollo 15-16-17)


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Aug 11, 2008
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The J-missions are not officially supported by NASSP 8.0, but they are fully functional provided the following work-around is performed with regards to the ECS and EPS systems in the CSM/LM:

Note 1: The real J missions LM included a fifth battery in the descent stage that permitted the extended-duration stay on the moon for Apollo 15-17. This battery is not yet implemented in NASSP and the only work-around as of now is to increase the 4 LM batteries to the combined capacity of 5 batteries. The CSM had an extra O2 & H2 tank but these are also not yet implemented so the 2 tanks for both O2 and H2 are increased to the capacity of 3 equivalent tanks.

Note 2: These steps must be preformed before running a fresh launch scenario, any previous quicksaves will not read the modified configuration.

1. Navigate to the .../Config/ProjectApollo folder & find these 2 files:


Backup these files!

2. Open SaturnSystems.cfg with a text editor:

- At the top you will see 2 sets of the following: <TANK> O2TANK1, <TANK> O2TANK2, <TANK> H2TANK1 and <TANK> H2TANK2.

- The 1st is the the normal set and the 2nd commented set is the J version. Remove or comment the 1st set and un-comment (remove the #) on each line of the 2nd set.

3. Open LEMSystems.cfg with a text editor:

- Find <TANK> DESO2TANK (near the top) and <TANK> DESH2OTANK (further down)

- Replace them with the J versions of those tanks which are underneath of each tank in the same way that was done in SaturnSystems.cfg.

- Scroll down to the bottom of the file to find the <ELECTRIC> section.

- Do not use the "415AH Batteries for J Missions" version but rather, find the "400AH Batteries" below it.

- Replace the 4 <BATTERY> lines with these:

<BATTERY> DSC_BATTERY_A 56025000 37.2 0.23 NOPOWER
<BATTERY> DSC_BATTERY_B 56025000 37.2 0.23 NOPOWER
<BATTERY> DSC_BATTERY_C 56025000 37.2 0.23 NOPOWER
<BATTERY> DSC_BATTERY_D 56025000 37.2 0.23 NOPOWER

4. Save both files. Remember to switch back to the original files to fly any pre-Apollo 15 mission.

Note: The O2 and H2 gauges in the CSM, O2 & H2O in the LM will indicate full until many hours into the mission. This is unfortunately because the gauges are still scaled in code for the lower capacity. If you desire to have proper gauge readings, there is an optional work-around for this detailed below.

5. (This step is optional and is for advanced users. You will need to edit the source-code and build modules yourself) There are comments in the source-code indicating what values to use for the proper scaling of the J-mission ECS gauges in the LM & CSM

- In MS Visual Studio, open nasspdef.h and find #define CSM_H2TANK_CAPACITY & #define CSM_O2TANK_CAPACITY, below them are the commented J-mission versions. Un-comment those and comment the old ones.

- Further down you will find #define LM_DES_H2O_CAPACITY and below the J-mission version of it, apply the same procedure as above.

- Open lemswitches.cpp and find "return (lem->ecs.DescentOxyTankQuantityLBS()/(48.0))*100;", below it is the commented J-mission version, remove the comments on the lines starting with "case 1" and "return" and comment the old ones above.

- Rebuild modules. To revert back just follow the same procedure in reverse.
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LM Junky
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Jun 4, 2016
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Adding to this, I have created a branch on my git repo with the J mission changes, if anyone is interested and is used to git building for NASSP you can pull and build from this branch and it will include all the above J mission changes.