RCS Best practice Apollo

sw34669

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I have, with some help from indy and a few others now managed to get 69 hours in to Apollo 11/MCC. Houston, I think i've been an idiot again.

Long story short, I fired the SM helium RCS SEC some time ago and now i've almost run out of propellant and helium on all 4. I'm not 100% sure how these are simulated but have read a few articles online about the systems in real life and how this has been coded. I had a play around with Orbiter Prop Tanks 2/3/4/5 that seem to be a blended mix of the materials for RCS.

This brings me to a wider realization .... and question of what did I do wrong, all my moves have been done for 1xTLI/3xMCC burns or putting the ship into PTC. I have noticed when rotating or translating i'm using a good chunk of He+Prop so the consumption rate is high and I can watch the needle move.

1)Am I in some sort or Orbiter RCS mode that has a higher consumption when moving ? I found the joystick page on an older version allowed you to turn off Orbiter RCS thats not there now.

2) What is the best practice for optimal RCS fuel consumption when parking in and out of PTC (rates(1/2/Accel/Rate/Min), modes (CMC/SCS/Hold) and overall manual control of ship with keyboard)

3) 69 hours in, what should be my RCS fuel and He levels

4) Can I cross bleed from any of my other He tanks to top up (probably not having looked at Nasa docs)

I had been trying to do the mission not using any cheat/god/uberMFD modes........Shouldn't have had that party with all those baloons !

Help/advice very much appreciated.

thanks.
 

indy91

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Are you using Orbiter 2016 or the Orbiter Beta? NASSP should be run with the Orbiter Beta, although it does mostly work with Orbiter 2016. The relevance of this is a change that was done in Orbiter concerning the calculation of the moments of inertia of docked vehicles. Basically, in Orbiter 2016 and before it takes a lot more RCS to maneuver around with the docked CSM+LM. I remember running low on RCS early in lunar orbit because of this. In the Orbiter Beta this was fixed and I never had issues anymore with RCS.

With the docked CSM+LM you should do slow maneuvers to conserve fuel. Usually the 0.2°/s DAP setting for auto maneuvers. Other than that it shouldn't really be critical what you do. No higher RCS consumption mode or so. You can't move propellant around betwen the tanks. The best you can do is check which quads have the most RCS remaining and use those for roll control, both in the DAP and for manual control (disable the other 4 Auto RCS switches for roll).
 

sw34669

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Thanks Indy understood. I have just downloaded SVN and am updating
I think I updated NASSP, last week, not long into my journey...........
The issue I found was my RCS tanks shrank from 150 to 50kg; this and the consumption issue you note above, i've done well, i should know better about configuration management and switching code in the middle of nowhere.
 

sw34669

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ok, got oribter beta (90) installed and NASSP 1200 from github

Prop tanks now 150k but consumption even when moving manually is high. 10 Mins of some gentle manuavers took the prop on 1 tank to 50%.

This was on my original save and I used one of the new Apollo 11 - 06 - Before MCC-2 T+26h30min scenarios. I'm not seeing any difference in consumption between my Beta and my stock 2016 instances like you did.

Any clues or what I could look at. What is the rcs fuel burn rate / sec in the broken and then in the fixed version. These numbers may help me track where the issue is.

Thanks.
 

indy91

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NASSP release 1200 from Github is almost 3 years old. The most recent one is 1600 from here: https://github.com/orbiternassp/NASSP/releases Direct link to the latest release file: https://github.com/orbiternassp/NAS...016-1600/NASSP-V8.0-Beta-Orbiter2016-1600.zip

From the other thread:

Looking at Orbiter 2016 prop tanks 2-3-4-5 they are all just about empty 69 hours in and showing as 50kg tanks. is 50kg the correct ammount for He+Prop ? I think they should be 150kg

Where does it show as 50kg tanks. In the scenario editor? That would be very weird, as the tanks are hardcoded to 152.5 kg. There also are the two CM RCS tanks which have 55.5kg each.

10 Mins of some gentle manuavers took the prop on 1 tank to 50%.

Define "gentle". Nearly sustained firing for that time will of course do that, but during an attitude maneuver it should mainly fire the RCS to initiate the attitude rate and then maybe a short burst every few seconds to keep it on the desired path, that's how the DAP of the AGC would do it. Actually the exact math results in: 1 thruster firing can deplete one of the RCS tanks in 982 seconds. That is sustained firing. Of course if more than one thruster is firing then it can be much quicker.

What is the rcs fuel burn rate / sec in the broken and then in the fixed version

What was fixed was the moments of inertia of docked vehicles. So in the fixed version you get a larger angular acceleration for e.g. 1 second of firing a pair of thrusters to rotate the vehicles. Before, docked vehicles were more inert, you needed to spend more RCS to get up to a desired attitude rate. And over a long mission that accumulates as there is a lot of start and stop concerning the attitude rate.
 

sw34669

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the 50kg tanks were on my orginal save prior to me updating to orbiter beta (when looking at tanks 2-5 in edit scenario ctrl-F4) very very strange they were exactly the same size as tanks 6 and 7. When I ran out of prop it's the first thing I looked at. They are now back at 152.50 each and i've updated both my beta and 2016 orbiter instances with the latest version of NASSP. I spent sat and sunday loding up many pre-saved and template scn files comparing what was in the .scn with what I could see in the scenario editor. Loading my save gave the 50kg tanks, loading a pre-defined newer .scn from NASSP gave 4 x152kg tanks. I think this occured after I released the rcs sec prop on all 4 chans. I updated versions 1/2 way through this trip so this also may be the source of the wrong 50kg tanks. I remember reading how the RCS prop/ox/fuel simulation was changed. Maybe I had a very old version of the code to start with.

Thanks understand the inertia part now. Fewer (but correct) pulses to move. I will have a play.

The burn side I get and i'm seeing what you say ~15-16kg/min from the RCS units. A doc i found showed .117lb/sec burn for the RCS thrusters which is around 6.5kg/sec. Could these be smaller thrusters on the LM and the SM has larger units ?

My learning from this is dont update the NASSP code mid flight.

Thanks again for your help the sim is superb :) Have a good week.
 
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Just to observe: in real life, RCS usage was always a topic of high interest to the crew and controllers. I’m fairly certain each manoeuvre was contemplated in advance to account for its RCS usage. For example, following transposition and docking, the crews were generally keen for an assessment of their RCS usage from the ground, to see how their actual manoeuvres compared with pre flight calculations. From my own NASSP experience, I know that TD&E and P23s can be quite notorious on RCS usage, if one is not careful. Finally, doing small things such as switching from CMC to SCS while mid-manoeuvre can sometimes cause excessive thruster firings if switches aren’t properly set. All in all, these things add up to quite a bit of potentially excess usage over the course of a mission.
 

indy91

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The burn side I get and i'm seeing what you say ~15-16kg/min from the RCS units. A doc i found showed .117lb/sec burn for the RCS thrusters which is around 6.5kg/sec. Could these be smaller thrusters on the LM and the SM has larger units ?

SM and LM RCS had identical thrusters. You are very rarely only firing a single thruster with the RCS, your consumption rate is slightly low, but about right for 2 thrusters. That's probably what you tested.
 

sw34669

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hey hey "i has pads" , a hat trick of pads LOI-1, TEI-1 and TEI-4

All going well for lunar arrival

quick couple of questions

1) Are these pads saved anywhere for recall in RTC MFD ?
2) Are they dumped out anywhere for easy text printing ? Would be a cool addition to the mission control menu just throw to default lpq print pad
3) Whats the diff between TEI-1 and 4 are they different returns (Free etc)

You're right, of course, much less energy in Orbiter Beta for moving the docked ship around. That's all good now thank you Indy.
 

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I’m not tracking any method of saving PADs or generating dumps. Maybe Indy has more on that. As some others appear to do, I take a photo. High tech solution to a low tech problem.

3) I believe TEI 1 and 4 are contingency PADs, in the event you need to abort and get back to earth without landing, or at least prior to the scheduled TEI. They refer to the orbit in which the TEI burn is conducted (in this case, 1 or 4). So, unless I am mistaken, they are not technically free returns so much as they are just the usual TEI burn, brought forward.
 

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Just to observe: in real life, RCS usage was always a topic of high interest to the crew and controllers. I’m fairly certain each manoeuvre was contemplated in advance to account for its RCS usage. For example, following transposition and docking, the crews were generally keen for an assessment of their RCS usage from the ground, to see how their actual manoeuvres compared with pre flight calculations. From my own NASSP experience, I know that TD&E and P23s can be quite notorious on RCS usage, if one is not careful. Finally, doing small things such as switching from CMC to SCS while mid-manoeuvre can sometimes cause excessive thruster firings if switches aren’t properly set. All in all, these things add up to quite a bit of potentially excess usage over the course of a mission.
Thanks, understood. I'm sure I did a little too much fiddling and had a large borkborkbork with my tank qty on RCS prop. I need to do some more reading of the different nav modes and their impact as you say.
What would switching from cmc to scs cause ? does each have a different default/home position. i.e cmc uses v49, what does scs use?
 

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doh ! of course 2 thrusters firing so actually simulated perfectly :)
SM and LM RCS had identical thrusters. You are very rarely only firing a single thruster with the RCS, your consumption rate is slightly low, but about right for 2 thrusters. That's probably what you tested.
 

indy91

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Well my suggested method for PADs, if you want to do it realistically, is to get this Apollo 11 Flight Plan and print out the forms from section 2 a bunch of times and fill out the numbers when the MCC is showing the PADs. The PADs in that reformatted document look really nice and clean. But I will take the idea into consideration of saving the PAD data somewhere, maybe with this PAD but filled out automatically.
 

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What would switching from cmc to scs cause ? does each have a different default/home position. i.e cmc uses v49, what does scs use?
I’m thinking of the situation where a V49 wants to take you through gimbal lock. There are two ways you can take over: taking manual control while under DAP (eg just move the RHC while 06 18 is displayed) or switching to SCS. The former shouldn’t cause excessive RCS firings. The latter might if your BMAGs have been uncaged (namely, they’re in Att1/Rate2). Generally, they should be in Rate 2 if you’re moving around. That’s about the only “default” setting I’m aware of, outside of the steps you take to prep the spacecraft for a burn.
 

sw34669

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No joy (tried 4 times) with the LOI-1. Gets right down to 0 and the engine doesnt fire. Checked and re-checked all the correct switches hadn't been missed by the automatic checklist. Just doesn't fire @ 0 . I've done 3 prev burns (P40) all ok.

Is there anything obvious im missing here.
1611615338187.png
 

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Always a deflating feeling... we’ve all been there. Did you hit PRO at T-5 seconds, when the V99 is flashing?
 

sw34669

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yup its a timing thang you're right; thank you. Using the checklist makes it harder possibly.
I also dont get why DET isn't set to count down to TIG this would help with timing.
I'm inserted now and having an issue with V64 antenna it says to wait for Rev 2 AOS but that would be a long time round. when the second V64E is used the comp gives an OPR ERR.
Time for bed !
thanks all.
 

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sw34669

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I’m thinking of the situation where a V49 wants to take you through gimbal lock. There are two ways you can take over: taking manual control while under DAP (eg just move the RHC while 06 18 is displayed) or switching to SCS. The former shouldn’t cause excessive RCS firings. The latter might if your BMAGs have been uncaged (namely, they’re in Att1/Rate2). Generally, they should be in Rate 2 if you’re moving around. That’s about the only “default” setting I’m aware of, outside of the steps you take to prep the spacecraft for a burn.
rate 2 now set . Jeez, this thing's like a lump of 1960s technology.
the other horror of Orbiter beta is that my fave old MFD lunarxfer MFD crashes. I only use it for monitoring though have gone back to the std orbit mfd.
 

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Well done.
DET counting up is helpful, once you get used to it (and assuming you’ve set it correctly, not completely intuitive at the outset). The fact that it counts up from 0 at Tig helps to cross-check predicted BT with actual BT.
Interesting you’re having issues with V64 - it sounds like you’ve got another extended Verb running already, which is usually the reason why you’ll get an OPR ERR light. Did you go to P00 and then try V64?
 

sw34669

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Well my suggested method for PADs, if you want to do it realistically, is to get this Apollo 11 Flight Plan and print out the forms from section 2 a bunch of times and fill out the numbers when the MCC is showing the PADs. The PADs in that reformatted document look really nice and clean. But I will take the idea into consideration of saving the PAD data somewhere, maybe with this PAD but filled out automatically.
:) Printed on my laser looks great. I get the realism thing.
dumping them out to either a print q or directory would be great but of course not urgent. I know it's a hobby :)
Just for my interest, who owns NASSP ?
 
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