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| | | |-+  AGC++ reentry help
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Author Topic: AGC++ reentry help  (Read 24624 times)
movieman
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« Reply #45 on: January 15, 2007, 05:25:19 PM »

Do the SM thrusters point in the right direction now? I know when I first moved them to match the new mesh they were pointing a few degrees out from where they should have been... I don't know whether anyone ever fixed that.
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dseagrav
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« Reply #46 on: January 15, 2007, 07:21:59 PM »

I worked on both the CM and SM (and the LM), because I'm the one who originally split and repositioned the CM RCS. I never did AIM them in the right direction though. They're wired through the RJ/EC, but if I remember right tschachim has a hack that shuts off part of the RJ/EC logic for the AGC++.

For whoever makes the scrolling tape images, please use US units first, so we can confirm operation with the NASA documents and vAGC, and then make metric versions later. The logic shouldn't change at all, just the scroll tape images.

I would like for someone else to please look at the SCS 0.5G switch, or tell me how to do it. The doc says it "modifies the roll-rate gyro output by the tangent 21 degrees and sums with the yaw rate". I don't know what this means. The idea is to make the yaw rate zero when the CM is rolled about the stability axis. (I never went past algebra in school, I spent more time in electronics and computer stuffs! ^_^)
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Tschachim
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« Reply #47 on: January 16, 2007, 07:30:15 AM »

About the EMS: Chode, you did a great job with the AGC++ entry autopilot, I think you should continue with the EMS. Please use the historical (US) units, except some AGC++ outputs all displays and controls use the historically correct units and I would like to stay with that. Are you also going to do the dV/range display and the dV mode we need for the SPS SCS dV mode? If not, perhaps Dseagrav could take a look at that part of the EMS? Happy

About the CM/entry: Thanks for explaining! It seems to look like the VAGC is working better with the new CM RCS thruster positions/directions, but I (we) need to do more tests, I'll post if I have some results.

About the SM RCS: Dseagrav, I think you did the last modifications of the SM RCS thrusters a few months ago? I don't know if they are really correct, but they seem to work fine with the VAGC and the SCS. Anyway, perhaps you or chode could take a look at that just to have "that issue closed"? Swatch, I don't know the RCS thrusters very well, I plan to stick to the SPS until that's ready.

The hack I introduced is the CSMcomputer::SetAttitudeRotLevel(VECTOR3 level) function, which sets the RCS thrusters with Orbiter's SetAttitudeRotLevel function and disables the RJ/EC for 2s (AGC++ control loop is 2s). But this is only used by some of LazyD's AGC++ programs (mainly LOI and the rendezvous programs) and not by the VAGC or the SCS and should be modified sooner or later to use the I/O channels.

Cheers
Tschachim

EDIT: I modified this post a couple of times, I hope it's finished now (and not to weird)... Happy
« Last Edit: January 16, 2007, 08:02:29 AM by Tschachim » Logged

Swatch
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« Reply #48 on: January 16, 2007, 08:51:35 AM »

alrighty, sounds cool  Cool

Hey Chode, do you think you can get me everything you have on the scrolls?  I'll look into replicating them.
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My Project Apollo Work:
CM Visual
 -VC (~75% complete: texture work beginning again; mesh-78%; texture-70%)
Propulsion Particle Improvements (Focused on S1B right now, BETA 1.0 has been commited)
New Docking Method (~50% complete: research complete; coding partially completed, testing not underway)

Future Work:  (if it's here, it's deemed unnecessary to upcoming release)

Older Work:  (if it's here, it's fair game to whoever wants to improve)
EMS Implementation (committed: minor flaws, but groundwork is there, needs extensive testing)
EMS scrolls (committed: not refined, but usable)
SM Visual (committed: mesh-finished, texture-60%; possibly revisited in future)
J2 Texture (commited: room for improvement)
LRV (committed: mesh-finished, texture-90%; in future a ground up rebuild may be in order, but not on my plans)
dseagrav
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« Reply #49 on: January 16, 2007, 09:35:57 AM »

I'll go along with that as well; chode can do the EMS. I can re-check the CM RCS if you like, probably this afternoon. I'll probably go back to my primary project after that, about which another thread will be posted in a few minutes. (The AC inverter stuff was a diversion from that project, just because I stumbled across the efficiency data while doing some spelunking at NTRS ^_^)



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Tschachim
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« Reply #50 on: January 16, 2007, 09:41:26 AM »

I can re-check the CM RCS if you like, probably this afternoon.

Cool, perhaps you could also check the SM RCS as movieman requested? The CM RCS seems to be better since chodes modifications, but re-checking can't hurt... Happy
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dseagrav
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« Reply #51 on: January 16, 2007, 10:12:39 AM »

Meh, that was a thinko. I meant SM.
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chode
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« Reply #52 on: January 16, 2007, 11:54:35 AM »

As it stands now, the only thing that I would suggest correcting in the CM RCS system is to have the thruster positions coincide with the mesh. The pitch and yaw thrusters look to be only an inch or two off, but the roll thrusters look to be off by a larger amount. This re-positioning shouldn't have much effect on the performance.

The reason for the rate gyro summing during the entry is because the CM is not rolling along the z axis of the spacecraft, the angle of rotation is off by about 21-25 degrees. What you really want to measure is the roll angle relative to the rotation axis, so you need to geometrically sum the roll and yaw rates to arrive at the "true" roll angle. I'll see if I can come up with a more mathematical explanation that would be useful in practice.

The AGC in P61 - P67 presently uses metric units in all the displays. It sounds like people prefer English (historical) units, so I'll look at making English the standard and leave the option to show metric. Would the best thing be to have a line in the scenario file, something like UNITS METRIC/ENGLISH?

The Delta V display is not at the top of my list of things to work on, so feel free to work on it.

Swatch, I'm away from home for the next week at least, and that is where most of my Apollo data resides. I'll see if I can find links to the documentation with pictures of the EMS scroll.

Regards


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Tschachim
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« Reply #53 on: January 16, 2007, 12:00:21 PM »

Would the best thing be to have a line in the scenario file, something like UNITS METRIC/ENGLISH?

A setting like this already exists (at least partially), please check ApolloGuidance::DisplayUnits.
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dseagrav
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« Reply #54 on: January 16, 2007, 12:21:35 PM »

It sounds like people prefer English (historical) units, so I'll look at making English the standard and leave the option to show metric.

It's actually the opposite - We have to use US measurements initially, so we can check against NASA's documentation, but Orbiter and the majority of the people want metric measurements.

As I understand it, this is primarily a European project, Americans are a minority here.
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Tschachim
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« Reply #55 on: January 16, 2007, 12:33:01 PM »

Well, despite the fact that I'm used to metric units (and an European, but I would characterize Project Apollo - NASSP more an international project Happy), I would prefer to have the historically correct (i.e. imperial) units, just because this is the way it was. But of course I've no problem to show metric units optionally for user's convenience.

Cheers
Tschachim
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dseagrav
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« Reply #56 on: January 16, 2007, 12:57:28 PM »

Well, in other projects I've been involved in, I usually catch some flak for being too Americentric, so I'm trying to be more considerate this time around. Not everyone is a big fan of Americans, and on the prior Apollo project I even was asked by a potential user if it would be possible to remove the NASA and USA marks from the equipment so the user could pretend that another "more civilized" nation had done the landing instead. I ignored the request, did not forward it to the others in the project, and quite frankly was insulted by it. In retrospect, that's incredibly close-minded, to be insulted by the idea that someone else should have done something rather than you. I'm trying to do better this time.
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movieman
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« Reply #57 on: January 16, 2007, 01:34:40 PM »

Given that all the MFDs output metric units, it's almost certainly better for the AGC default to be metric Happy.

Also, while the flag exists to distinguish between imperial and metric units, most of the code ignores it, so making it work will take a fair amount of work. At one point in the distant past all the altitude, velocity, etc displays did use the correct macros to convert values appropriately but many values have been added since which don't.
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chode
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« Reply #58 on: January 16, 2007, 07:20:01 PM »

I'll take a look at making the metric/english flag work for the AGC display, and maybe then we can move on from there.

Swatch,

Here are links to a few of the best drawings and descriptions of the EMS scroll I've come across:

Graphics of scrolls:

Apollo Operations Handbook, Stabilization and Control System (12.8 MB) at
http://history.nasa.gov/afj/aohindex.htm
 pp. 58-64

Apollo 7 scroll, post-flight:

Apollo 7 Mission Report at 
http://www.hq.nasa.gov/alsj/alsj-mrs.html
p. 201

Shows the G scale on the left of the scroll:

Command/Service Module Systems Handbook at http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730060780_1973060780.pdf
p. 41

The main problem would seem to be that the numbers and letters on the scroll are going to be awfully small, and it will be difficult to make them readable.

Regards
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Swatch
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jasonims
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« Reply #59 on: January 17, 2007, 02:01:04 AM »

alright, I definately have a good handle on what was on the scroll now, as well as the dimensions....if I make one big realistic scroll the bitmap will be upwards of 6100 x 150 or so pixels  if memory serves me.  That's pretty big, but I'm going to look into what it would take to make it work with smaller ones.  I might make a big one first though, and then just chop from there.


I also think I understand the usage and what exactly its showing if there are any questions...
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My Project Apollo Work:
CM Visual
 -VC (~75% complete: texture work beginning again; mesh-78%; texture-70%)
Propulsion Particle Improvements (Focused on S1B right now, BETA 1.0 has been commited)
New Docking Method (~50% complete: research complete; coding partially completed, testing not underway)

Future Work:  (if it's here, it's deemed unnecessary to upcoming release)

Older Work:  (if it's here, it's fair game to whoever wants to improve)
EMS Implementation (committed: minor flaws, but groundwork is there, needs extensive testing)
EMS scrolls (committed: not refined, but usable)
SM Visual (committed: mesh-finished, texture-60%; possibly revisited in future)
J2 Texture (commited: room for improvement)
LRV (committed: mesh-finished, texture-90%; in future a ground up rebuild may be in order, but not on my plans)
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