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Author Topic: LM Landing questions/report  (Read 130567 times)
gimp1992
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« Reply #15 on: May 20, 2005, 03:56:59 PM »

Sounds like your "going right down US 1" I think it's great what your doing. Plese keep up the good work.
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Joe Brown
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« Reply #16 on: May 21, 2005, 07:26:28 AM »

Quote from: LazyD
Sorry for the big post, but I'm about to wire the guidance into this, and it's easier to make major changes now than it will be later. Also I'd like some feedback - I am trying to do this as authentically as I reasonably can, but do think this is too much work for the Orbiter users?

Hey, don't worry about your big post, you asked very good and very interesting questions. I'll try to figure out a few things, but this will take some time...

About the authenticity: There's an ongoing discussion about introducing different "complexity levels" ( http://www.ibiblio.org/mscorbit/phpBB2/viewtopic.php?t=46 ), but at the moment all NASSP AGC programs seem to try to be realistic as possible so I think you are on "the right way"!  Happy

Cheers
Tschachim
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LazyD
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« Reply #17 on: May 21, 2005, 09:11:40 AM »

Thanks gimp and Tschachim,

That discussion was useful to read, and I think I have an idea how to proceed.  movieman pointed out the REALISM variable, and I think I'll code the landing so if REALISM=0, all the displays are the same, but the user doesn't have to enter PRO to go on to the next step, it just happens.  Otherwise if REALISM>0 the interaction is just like the real thing.

This way if a user can figure out V37N63E, he can land on the moon.  And we can even distribute scenarios with P63 already running, if that's too complicated.

This way the addon can appeal to newbies while still being interesting for "button-pushers" who want to learn the actual procedures the Apollo astronauts went through.

I had an idea about how to implement target redesignation.  If we can define a camera position and angle so it looks through the LM window so the LPD markings line up currectly, the user could pick a landing site.  I know the DSKY wouldn't be visible in this view, but I could put a DebugString in the screen lower left with LPD time remaining, LPD angle, altitude rate and altitude.  I'm not sure if this is possible but if we could go to this view automatically when P64 starts it could be quite realistic.

What do you think?

P63 currently acts correctly through engine throttleup at +26 seconds.  Next, guidance.  I'm going to do this with a 2 second interval, just like the real thing.

D.
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movieman
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« Reply #18 on: May 21, 2005, 11:08:45 AM »

I just realised last week that the REALISM setting is broken for the LEM at the moment Happy. I'll check in changes shortly to pass it through properly from the CSM to the LEM.

That said, I think we should have a config file somewhere that lets people globally set defaults for things like realism and audio language rather than have to set them in every scenario file.
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Tschachim
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« Reply #19 on: May 21, 2005, 11:50:47 AM »

Quote from: LazyD
Here's how P63 is set up at present - I welcome any input or suggestions.

V37N63E  Loads P63

Flashing V06N89
Displays:
R1=Latitude in degrees*1000
R2=Longitude/2 in degrees*1000
R3=Landing Altitude (zero for now)

PRO to accept and proceed

Flashing V06N61
Displays:
R1=Braking phase burn time
R2=Time from Ignition mm ss
R3=Crossrange distance km*10

PRO to accept and proceed

Flashing V06N33
Displays:
R1=Ignition hour hh
R2=Ignition minute mm
R3=Ignition second*100 ss.ss

PRO to accept and proceed (instead of Key Rel)

Flashing V50N18
Displays:
R1=Pitch for PDI degrees*100
R2=Roll for PDI
R3=Yaw for PDI


I'm not sure if this is correct. If I look into A15Delco, there seems to be no V06N89 and it seems to work a little bit different:
Code:

V37N63E
        F 06 61

The user can (but not have to) key in:
N33E
        F 06 33, KEY REL light on, because the user overrided 06 61
In that case the user can (but not have to) key in:
KEY REL
        back to F 06 61, KEY REL light off

In both cases PRO is next:
PRO
        F 50 18    

But I'm not perfectly sure about this, the Guidance System Operations Plan is difficult to read and understand. The best way would be to try with Ron Burkey's Virtual AGC, but I fear P63 is not working at the moment...  Wink

Cheers
Tschachim
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LazyD
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« Reply #20 on: May 21, 2005, 01:29:52 PM »

Hi Tschachim,

You are completely correct - I didn't understand what the KEY REL was for or how to detect it, so I used a PRO 'cause I know how to detect it.

You may be answering one of my other questions from before.  After ignition, I have a V06N63 up, not flashing.  It seems the astronauts could key in other nouns to display during the descent, but I don't know how to code this - right now I have SetVerbNoun getting called each time Prog63 gets called - otherwise the DSKY doesn't update, even though I am updating the noun variables every 2 sec in my guidance calcs.

For the pre-ignition phase, P63 is setting up verb and noun, and flashing and waiting for the PRO - can you point to to an example of how to let the user pick a noun to display and have it update.  Sorry, I'm still pretty ignorant about the DSKY.

Anyway, progress is good - attitude and engine control works, and I'm adding the guidance routine now.  For now, for simplicity, I plan to do the 180 degree yaw maneuver at +3 minutes automatically instead of allowing manual yaw.  So getting down to high gate should be easy.  Since for this project I'm only having to fly a LM, I'm going to experiment with acceleration targets that will yield a realistic pitchover when P64 starts - my MFD version actually pitches up a bit at high gate.

I appreciate everyone's input and help on this!

D.
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movieman
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« Reply #21 on: May 21, 2005, 02:08:37 PM »

Quote
otherwise the DSKY doesn't update, even though I am updating the noun variables every 2 sec in my guidance calcs.


If you want them to update, you need VERB 16 rather than VERB 06: that updates twice a second.

Personally I'd do something that works and makes sense initially, and then we can see how it _really_ worked once we have yaagc fully integrated Happy.
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chode
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« Reply #22 on: May 21, 2005, 02:11:21 PM »

Quote from: LazyD
Here's how P63 is set up at present - I welcome any input or suggestions.

V37N63E  Loads P63

Flashing V06N89
Displays:
R1=Latitude in degrees*1000
R2=Longitude/2 in degrees*1000
R3=Landing Altitude (zero for now)

PRO to accept and proceed

Flashing V06N61
Displays:
R1=Braking phase burn time
R2=Time from Ignition mm ss
R3=Crossrange distance km*10

PRO to accept and proceed

Flashing V06N33
Displays:
R1=Ignition hour hh
R2=Ignition minute mm
R3=Ignition second*100 ss.ss

PRO to accept and proceed (instead of Key Rel)

Flashing V50N18
Displays:
R1=Pitch for PDI degrees*100
R2=Roll for PDI
R3=Yaw for PDI

PRO to perform automaneuver to this attitude

V06N18
Displays:
R1=current pitch
R2=current roll
R3=current yaw

When attitude is achieved:

Flashing V50N18
Display: same as above

PRO to accept retrograde face-down attitude

V06N62
Displays:
R1=Absolute value of velocity
R2=Time from ignition mm ss
R3=Delta V accumulated (zero until ignition)

At t-35 seconds, the DSKY blanks, then resumes above display

At t-5 seconds,

Flashing V99N62
Displays same as above

PRO to proceed with ignition

Flashing V06N63
Displays:
R1=Delta Altitude
R2=Altitude rate
R3=Computed Altitude

Does anyone know what Delta Altitude and Computed Altitude are?  And is there a PRO I'm supposed to be waiting for and quit flashing?

I'm skipping the V57E for accepting landing radar data for now.  This is the point where A15Delco runs out of information.  It was my impression that the astronauts could have the DSKY display a variety of nouns related to their descent.

Also, when I blank the DSKY at t-35, when I call SetVerbNounAndFlash, the display doesn't show program 63 any more.  How can I fix that?

Looking down the road a bit, I'm going to need to select some keys for P64 and P66 to use.  

For P64 target redesignation,  I plan to use keypad 2, 4, 6 and 8 for closer, left, right and further respectively.  We also need a pair of keys for P66 rate-of-descent control - maybe + and -.

I know less than nothing about panels, but it would be really nice for P66 if the velocity cross-pointers could be made to work!

Sorry for the big post, but I'm about to wire the guidance into this, and it's easier to make major changes now than it will be later.  Also I'd like some feedback - I am trying to do this as authentically as I reasonably can, but do think this is too much work for the Orbiter users?  It would be easier for me to just P63 PRO and land the damn thing without any further interaction but it seems to me NASSP appeals to those who are fascinated with the details of the missions.  Please advise if you think I'm going down the wrong road.

D.


This looks very good. The only suggestion I would have is that it would streamline the process a bit (and be closer to the real operation) if you eliminated the N33 stage, since as far as I can tell, it just shows the MET of the burn, and you really don't need that info, since you get a countdown while waiting for the burn.

Also,  the DAP automatically starts P64 when high gate is reached.
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chode
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« Reply #23 on: May 21, 2005, 02:17:39 PM »

What are you using for your attitude control algorithm?

I'm developing a reentry autopilot,  and maybe you can help me out, since I'm not happy with what I've got right now. The thing tends to overshoot and gets into modes where it is continuously thrusting.
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LazyD
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« Reply #24 on: May 21, 2005, 03:36:40 PM »

Hi Chode,

My attitude control is something I adapted from Chris Knestrick's control.cpp.  It differs in that it computes desired rotational rates as a linear function of actual-desired attitude, and does all three axes at once.  I will be happy to email the code to you, it is self-contained - the only thing you may have to change is establishing a vessel handle - though it's pretty easy when you ARE a vessel!  Doing this an MFD is a lot more complicated.

Any of my stuff is yours for the asking.

And movieman, I agree.  I will just get on and get the guidance working and landing properly, then the DSKY details can be worked out with time.

D.
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LazyD
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« Reply #25 on: May 22, 2005, 06:12:50 PM »

Hi Tschachim,

You are correct about P63 not starting out with a V06N89 - that is what P63 did already when I began working on it.  I think movieman wrote that.  I think the actual place it can be changed is P57 but for now it made sense to me to verify the landing site first, I need to know that before P63 can do very much.  This would be very easy to change later if we want to.

I added quite a bit of code in the last day, and I'm still fighting with it trying to make it work properly, but pretty soon P63 is going to be "driving down the hill" to high gate.

Looking ahead, does anyone have any input for keys to use for P64 target redesignation, or how the astronauts selected P66 instead of P65?  Was it the ROD control or the ACA?  Any suggestions for how to simulate this in NASSP?

Yeah, movieman, I wish I had a working P63 in YAAGC to play with - it would sure answer a lot of questions!  For now, I'll do the best I can figure out.

Thank you all for input!

D.
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LazyD
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« Reply #26 on: May 26, 2005, 03:17:49 PM »

P63 is working properly.  It orients to face-down retrograde, lights the engine and guidance works fine.  At 3 minutes into the descent, I automatically roll to a "face-up" orientation and proceed on down to high gate.

I am playing around with target accelerations for downrange and vertical trying to get an authentic descent profile.  I am realizing that the tolerances were pretty tight.  Apollo 16 was high at PDI, (66000 ft instead of 50000 ft) and they got a bit concerned because guidance set up a rather scary descent rate trying to make it's targets.  If I make this really authentic, your starting orbits will need to be pretty close!  Again, I would appreciate any advice - my worry is making it too difficult for beginners to make a landing from a lousy orbit.

I will get on with P64 now.  Although not mentioned in my documentation, the journal for Apollo 16 and 17 has conversation of someone entering a "PRO" just before P64.  Can anyone enlighten me?  Otherwise I'll just start P64 at high gate, do target redesignation and fly to low gate, the P65 and land.  Then I'll do P66, which is really nothing but  two nouns and getting out of the way.

D.
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movieman
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« Reply #27 on: May 26, 2005, 05:36:47 PM »

It's worth remembering that they used different versions of the software on different missions, so they might have decided it was safer to give the astronaut more control over when the program switched modes.
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Tschachim
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« Reply #28 on: May 27, 2005, 07:24:46 AM »

Hi LazyD,

just a few thoughts regrading your questions:

Quote from: LazyD
If I make this really authentic, your starting orbits will need to be pretty close!  Again, I would appreciate any advice - my worry is making it too difficult for beginners to make a landing from a lousy orbit.

Is the LM orbit in the "h) Apollo 11 - ready for lunar descent.scn" scenario good enough? Assuming this is a quit "good" orbit it's perhaps too difficult if this is not good enough?

Quote from: LazyD
I wish I had a working P63 in YAAGC to play with - it would sure answer a lot of questions!

If I start P63 with the current Virtual AGC version I get an 00220 Bad REFSMMAT error. Experientially it's difficult to get it working because then lot's of pad loaded data is missing... Crying or Very sad

Quote from: LazyD
Looking ahead, does anyone have any input for keys to use for P64 target redesignation, or how the astronauts selected P66 instead of P65? Was it the ROD control or the ACA? Any suggestions for how to simulate this in NASSP?

From R-567:  Guidance System Operations Plan: "P65 does not allow manual control of LM attitude or throttle. If manual attitude control is desired put ATTITUDE CONTROL MODE SWITCH in ATTITUDE HOLD. The LGC will automatically select landing phase (ROD) program (P66) ..."
At the beginning of the description of P64 landing site redesignation is explained. The ACA (joystick) and the markings on the left window are used to change the landing site, but I'm not sure how this is done exactly or if the LM attitude changes during that...

Cheers
Tschachim
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Tschachim
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« Reply #29 on: May 27, 2005, 12:13:14 PM »

I did an "ugly but working" DSKY on the left LM panel in CVS, so you can use the DSKY again for testing and development.
I recommend that you don't wait too long until you use CVS because movieman integrated already RMaia's ascent autopilot in CVS, so the 6.4.1 files and the CVS files begin to differ...
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