V8 Release Work Thread

indy91

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The update I was talking about in the last post is now released. The CSM now has a center of gravity that shifts depending on (mainly) SPS propellant mass being burned. That means that for all SPS burns you now need to use SPS trim gimbal angles that are non-zero. The MCC and RTCC MFD should be able to provide the right numbers in all cases. The same applies to docked DPS burns. The trim angles are in all cases very close to the actual numbers from the transcript. I guess that makes sense as the SPS propellant makes up such a large part of the CSM and the CG of the SPS tanks are well known, so this wasn't difficult to simulate.

What also behaves a little bit different now is transposition and docking. Previously the CG of the CSM was always in front of the SM RCS quads. That means a translation up was causing a small pitch down moment. So the advanced technique was to thrust in one direction and then wait until the attitude rate has settled before judging how much of a translation the RCS firing actually caused. Now the effect is the other way around, as the CG is now in most cases behind the SM RCS quads. Also, the moments of inertia are updated dynamically, too, based on mass. The mass normalized principal moments of inertia (PMI) are smaller for a heavy CSM now (about 3.6 instead of 4.6 in pitch and yaw), although for a light CSM there shouldn't be a big difference. But the smaller PMI make the rotation caused by a translation effect during TD&E a bit stronger than before. So TD&E is a little different now, just something to get used to.

As part of this update I discovered that the empty masses of the Apollo 8 and 10 CM and SM included the SM RCS and CM RCS. That made the CSM about 700 kg too heavy at launch for those missions, which is now fixed. Old mission scenarios have been edited to implement this, too, although the CMC might still have the old mass loaded. The SPS trim gimbal angles have been correctly loaded in the CMC in the mission scenarios though.
 
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