NASSP Apollo Reentry, or lack thereof....

Wedge313

Well-known member
Joined
Apr 18, 2020
Messages
488
Reaction score
118
Points
58
Location
Boston
After six failed attempts I've decided to plead for assistance. I'm running the Apollo 8 mission. All seemed OK, MCC6 and 7 were scrubbed, leading me into a false sense of security. The first inkling I had that something was amiss was with the horizon check. If I understand the procedure, at the designated time and at the designated pitch (268 deg from the PAD), I should see the horizon, correct? I've had to pitch to 285 deg before I see the earth, and that's more than the 5 deg error the checklist mentions. Every effort proceeding from that point results in wild gyrations and bodily harm that weren't in the original flight plan. Also the checklist has me compare my P61 RTGO, VI0 and TFE values with the PAD for a go/no go decision. What are the limits here? What constitutes a "no go", and what could I do about it? I'm trying to find some guidance for this phase of the mission but I'm struggling. I'm also wondering if the Project Apollo checklist is leading me astray, after completing the Entry Preparation section it jumps back to the TLI checklist, and I've had to navigate back to the next section CM-SM Separation. I'm wondering if I'm skipping over some important procedure? So I'm running out of altitude, time and ideas. Any help getting me pointed in the right direction would be appreciated. Is there a good point I can go back to and correct this? I'd like to end up bobbing in the Pacific, and not having my ashes fluttering down over China. Thanks.
 

indy91

Addon Developer
Addon Developer
Joined
Oct 26, 2011
Messages
1,224
Reaction score
582
Points
128
The horizon check is for the 31.7° line on the left rendezvous window. That's the long line on the window that you can see when you go up from the main panel. And the line there is not correctly aligned at 31.7°, so there is a zoomed in version of that view to the left. So on the 2D panel up from the main panel and all the way to the left. If you used that and the check failed then there could be a problem.

About the P61 check, the AGC assumes an ellipsoid Earth, while Orbiter has a spherical Earth. So the AGC will come up with different numbers for reentry than the MCC would. The best numbers to use are the ones from the Entry PAD as they use the actual shape of the Earth in Orbiter.

And about the checklists, sometimes when you have gone to the main menu of the Checklist MFD to start a checklist then it can lead to problems. You shouldn't ever have to do that. Sometimes the Checklist MFD will say it has run out of checklists to do, that will have been the case after Entry Preparations. So I think you did the right thing, the Entry Preparations end with switching the Main Bus Ties on. When it does bad things there you can go to CM/SM Separation and proceed. You might also have to switch manually to the splashdown checklist just before splashing down.

I don't know about your wild gyrations, must be some weird control mode you ended up in. That is still before CM/SM sep, right?
 
Last edited:

Wedge313

Well-known member
Joined
Apr 18, 2020
Messages
488
Reaction score
118
Points
58
Location
Boston
The instability occurs after .05G. To further troubleshoot I pulled up one of the "canned" scenarios (Apollo 8 Entry Interface T+146h40m) and I'm getting the same unstable results, the spacecraft spins and tumbles shortly after the G's start to build. Out of curiosity I "crawled" down into the LEB to stare at nothing during the initial phase, and didn't die! But, the capsule skipped out of the atmosphere and won't come back down for a little bit, I noticed it never rolled to change the lift vector. I'm wondering if this issue goes back to the computationally challenged laptop I'm using, or some video or parameter setting I've got wrong (I do have Complex Flight Model, Limited Fuel, Gravity Gradient Torque and Nonspherical Gravity Sources checked). I saw a previous thread where people were discussing frame rates, is there something I can do to tweak that? Anyway I thought it possibly informative that the correctly set up "canned" scenario gave me similar results as my (possibly?) incorrectly configured scenario.
 

indy91

Addon Developer
Addon Developer
Joined
Oct 26, 2011
Messages
1,224
Reaction score
582
Points
128
Oh that scenario is quite old, hasn't been replaced since the NASSP 7 release. You might have to switch RCS CMD to on and RCS TRNFR to CM to allow the CMC and SCS to use the RCS. I updated some Apollo 8 mission scenarios early in the mission due to Saturn V updates that would have completely broken the scenarios. That entry interface scenario at least loads so it hasn't been replaced quite yet, even if it has some issues (you can notice those old scenarios by seeing the mission and event timers being 0).

For better performance you could even use the virtual cockpit of the CM. Only the main panel works so far but it has better performance than the 2D main panel, at least for me. Also, if you haven't done so, you can split up the main panel in three parts which also will help. Open Orbiter, go to Extras, Vessel configuration, Project Apollo Configuration, Visuals and use the "Multiple, split panels" option for the CSM main panel.
 

Wedge313

Well-known member
Joined
Apr 18, 2020
Messages
488
Reaction score
118
Points
58
Location
Boston
OK! Almost there....Your suggestion to use split panels helped. When the .05G light comes on, if I hit F1 and go to external view, and turn off the Ext MFD, the spacecraft rolls as necessary to control the reentry. If I hit F1 to "re-enter" the cockpit, after a second the RCS starts firing wildly and the gyrations begin. Hit F1 again, and from exterior view the craft settles back down. Once the craft slows down I was able to go back into the cockpit view. The "canned" scenario splashed down fine. I went back to my Apollo 8 scenario, and using the same procedure survived the reentry. So I'd guess the problem is with my computer, it can't handle the addition of the EMS or something.
Sadly, the drogue and main chutes did not deploy, and I suspect I know why....on panel 229 there are two yellow-collared CBs, BAT BUS A(B) TO PYRO BUS TIE. Should those be open or closed? Earlier in the flight while checking the electrical system the Pyro Bat voltage was reading zero, and I closed these breakers to "fix" that. I fear I might have done damage to some circuit. Also the checklist refers to a Main Deploy push button, but the only "button" I see that's labeled "Main Deploy" has no function. So I "splashed" down a bit firmly, and you can cancel the carrier pickup. Any suggestions how I can go back in time and configure so the chutes open? Thanks.
 
Last edited:

indy91

Addon Developer
Addon Developer
Joined
Oct 26, 2011
Messages
1,224
Reaction score
582
Points
128
The Apollo 8 checklists like to open two circuit breakers for the pyros, on panel 250, Pyro Seq A and Pyro Seq B. It's the only mission opening those breakers and I guess it's possible that the Checklist MFD isn't accounting in all cases for those being open. Even in the real Apollo 8 CMP Checklist it's only a handwritten note to close those for a pyro voltage check:


There is no damage simulated to anything in the EPS, so powering the pyro buses from the battery buses should be fine, even if that is just the backup method.

I don't know why your ELS wasn't working right. Did you have ELS logic on and ELS switch to Auto? That should be done no later than passing 24,000 feet. The main chutes button doesn't work if the previous steps in the ELS haven't been done manually or automatically. So that would be apex cover jettison and drogue chute deployment.
 

Wedge313

Well-known member
Joined
Apr 18, 2020
Messages
488
Reaction score
118
Points
58
Location
Boston
OK, it was not an electrical issue, it was an operator issue. After the spacecraft slowed and I "reentered" the cockpit, I opened the checklist MFD and turned Auto on. Maybe because I closed the checklist MFD at .05G, and didn't re-open it until around 90,000 ft or so, the checklist hung up at the Program 67 section. If I switch auto off and skip ahead to the 90,000 ft point, I get to the ELS steps. When the chutes didn't open, I started to press two buttons, DROGUE DEPLOY and MAIN DEPLOY. No matter how hard or often I mashed them during my plummet they didn't do anything. It wasn't until after splashdown I figured out these were guarded switches. So I'm bobbing around serenely watching the sun come up, which is much better than slamming into the ocean at high speed regretting my poor mission decisions. Hey, thanks for the help! You and others here on the forum got me through this, It's truly an amazing simulation. I look forward to working with the LM, and eventually actually landing on the moon. Thank you.
 
Top