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Author Topic: LM Landing questions/report  (Read 130566 times)
LazyD
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« Reply #675 on: January 12, 2006, 07:49:49 PM »

Hi Toadtal,

I think you have a good idea - it would be easy to make the initial targeting randomize the landing site by some distance, then you have to use redesignation in P64 to try to get as close to the actual landing site as you can.

For now you can mess up the EMEM addresses containing the landing lon and lat, and see if you can get to the site anyway.

It might be fun to add a variable for mis-targeting that does something like this.  Also when we get Meshland integrated the guidance will have to deal with terrain in doesn't know about in advance - should be fun!

If you have suggestions, I'm happy to listen.  If your complaint is that the landing guidance is too accurate, I will take that as a compliment!

Cheers!

D.
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Toadtal
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« Reply #676 on: January 13, 2006, 01:16:24 PM »

No my complaint about accuracy in not a complaint  Very Happy . Just the reason i mentioned it is that NASSP is supposed to be about making it as realistic as possible and i kno that almost 40 years ago nasa wasnt that accurate. Very Happy  Very Happy  Very Happy

but anyway i think that having a DSKY (allbeit a far to accurate one Wink ) that will get me from orbit to tranquility base is great to have
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movieman
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« Reply #677 on: January 13, 2006, 01:33:01 PM »

Quote
i kno that almost 40 years ago nasa wasnt that accurate.


Yes, but it puts you on the exact spot where the real Apollo landed, every time: what could be more accurate than that Happy ?

I'd just put a random offset into the AGC which is added to the landing location, then aim for that location.. the value could vary based on the REALISM setting so that at 0 it would land precisely in the right place, and at 10 it could be maybe a few tens of meters away and rely on you hand-flying the last part of the approach.
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LazyD
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« Reply #678 on: January 17, 2006, 01:04:17 PM »

Here it is, all in one place.  I would appreciate feedback if anything doesn't make sense.




The REALISM variable:

The REALISM variable is used to specify the extent of DSKY interaction the user wishes.  If REALISM is set to zero, it is only necessary to start a program (i.e. V37N63E) and everything is automatic.  If REALISM is > zero, the DSKY interactions are as described below.

Programs available for Orbit, Landing, Ascent and Rendezvous:
P12 - LM Ascent
P16 - LOI: Lunar Orbit Insertion
P17 - DOI: Descent Orbit Insertion
P18 - Orbit Plane/Surface Alignment
P19 - Orbit Adjustment- In Plane
P32 - CSI: Coelliptic Sequence Initiation
P33 - CDH: Constant Delta Height
P34 - TPI: Transfer Phase Initiation
P35 - TPM: Transfer Phase Midcourse
P36 - Rendezvous Braking and station keeping
P40 - DPS: Descent Propulsion System Burn
P41 - RCS: RCS Burn
P42 - APS: Ascent Propulsion System Burn
P63 - LM PDI Braking
P64 - LM Approach
P65 - LM Auto Landing
P66 - LM Manual landing
P70 - LM DPS Abort
P71 - LM APS Abort


Landing the LM on the moon  and returning to the CSM with Project Apollo:

Prior to initiating a descent to the moon, the orbit plane needs to come fairly close (<24 km) to the landing site (see P18), and have a periapsis altitude of between 10 and 20 km which is roughly above the landing site (see P17). This translates to radius from moon center of 1748 to 1758 km. When your orbit is correct and the LM is approaching the base about 1000 km away, you can start P63:

On the DSKY:

PRO

Verb 37 Noun 63 Enter

Noun 89:
   R1=landing latitude    XX.XXX
   R2=longitude/2       XX.XXX  

PRO

Noun 61:
   R1=time-to-go
   R2=Time from Ignition
   R3=crossrange       XXXX.X km
(you can adjust crossrange with this display if you need to)

PRO

Noun 33: Ignition MET
   R1=HH
   R2=MM
   R3=SS.SS

PRO

Verb 50 Noun 18: PDI Orientation angle
   R1=pitch
   R2=roll
   R3=yaw
(verb 50=Please perform - ask the AGC to orient the LM)

PRO

Noun 18 monitors attitude for PDI

At Ignition-35 seconds, DSKY blanks
At Ignition-30 seconds, DSKY displays:

Noun 62:
   R1=Velocity
   R2=Time from ignition (seconds)
   R3=DeltaV

At Ignition-5 seconds, Verb 99 Noun 62 flashes,

PRO (make sure you hit PRO before the count gets to zero!!)

At ignition, the display is:

Noun 63:
   R1=Delta Altitude
   R2=Alt. rate
   R3=Altitude. Just watch.


At about 3 minutes into powered descent, the yaw maneuver rolls the LM into heads-up oriention. Now the display will be:

Verb 16 Noun 68:
   R1=Downrange distance
   R2=Time-to-go in braking phase (mm ss)
   R3=velocity

At this point our landing radar would measure altitude and this information would be incorporated into guidance.

At around 2 minutes to go in P63, throttledown will occur. You will notice a slight pitchover.

At Zero time-to-go, P64 will begin, displaying:

Noun 64:
   R1=LPD time (seconds) LPD angle(degrees) SS DD
   R2=Altitude rate
   R3=Altitude

The LPD is the "down-angle" to the landing site, which matches the scribe marks on the window. The CDR could move the landing point closer, further, left or right with the attitude controller. Currently the keys for target redesignation are:

<comma> = left 2 degrees
<period> = right 2 degrees
<home> = 1/2 degree further
<end> = 1/2 degree closer

At the beginning of Approach phase, each key hit moves the target about 160 meters. As the LM gets closer to the target, the redesignations move the target smaller distances. Left/right redesignations will cause the LM yaw 2 degree to the direction of redesignation so the LPD reticle always points directly to the target. Left/right redesignations will also cause the LM to roll slightly - this is normal and necessary.
At any time during Approach Phase, one can assume manual control and enter P66 using either the <minus> or <equals> key.

When the Approach phase is complete, P65 will take over and the display will change to:

Noun 60:
   R1=Forward velocity
   R2=Altitude rate
   R3=Altitude

At any time during Landing Phase, one can assume manual control and enter P66 using either the <minus> or <equals> key.

P66 allows one to control the attitude of the LM using the keypad 2, 4, 6, and 8 keys in the same manner as for RCS attitude control. Attitude will change only while a key is held down, and after key release attitude will remain constant until further control input. Rate of descent is controller using the <minus> or <equals> keys. The first <minus> or <equals> hit used to enter P66 does not increment or decrement the descent rate, but sets the current descent rate as default. Each <minus> or <equals> key hit will increase/decrease the descent rate by 0.3077 m/s. WARNING! P66 displays:

Noun 60:
   R1=forward velocity*10 (m/s)
   R2=rate of descent*10 (m/s)   
   R3=altitude (m)

At contact, the engine will shut down automatically and P68 will be run.

After you land, P68 will start and tell you your landing lat and lon.




Ascent and Rendezvous with ProjectApollo - Apollo 11 Example


Start the Apollo 11 - Lunar Liftoff scenario. The LM is almost prepared for liftoff, and the CSM is about 4 minutes away from passing overhead.

Start P12:

V37N12E

Noun 33 will display the MET of liftoff. Write it on your flight plan, then:

PRO

Noun 76 will display:
   R1=Desired downrange velocity
   R2=Desired radial velocity
   R3=Crossrange distance

PRO

Noun 74:
   R1=Time from ignition
   R2=Yaw after vertical rise DEG.hh
   R3=Pitch after vertical rise DEG.hh

The countdown will proceed in R1. At t-35 seconds, the DSKY will blank. Press

ABORT STAGE

At T-5 seconds, Verb 99 Noun 74 will flash. Press:

PRO

For the next 7 1/2 minutes, enjoy the ride - guidance will put you into an elliptical orbit about 18 X 82 kms, and close to coplanar with the CSM. From now on you don't have to do anything but watch. You can use 10X time acceleration except for the burns themselves.

Apollo 11 and 12 used the coelliptic rendezvous procedure.  Later missions userd direct rendezvous, which lift off a littler sooner and skip P32 and P33, and go directly to TPI using P34.  

For coelliptic rendezvous, after cutoff, P32 will start and the LM will orient with windows (and rendezvous radar) facing the CSM. Noun 39 will display the time to CSI burn, which occurs at apoapsis and will circularize the LM orbit. The burn is done using RCS, so 120 seconds before the burn P41 will start, orient the LM, and do the burn.

After the CSI burn is complete, P33 will start and calculate the CDH burn, which tries to maintain a constant altitude difference between the LM and CSM. Since the CSM orbit is nearly circular, this will be a small burn about 40 minutes after the CSI burn.

Next, P34 will start and calculate the TPI burn, which takes us to the rendezvous point in about 45 minutes (130 degrees of a 360 degree orbit). Again, P34 will start P41 to do the burn.

Next P35 will do the two TPM burns, which will be very small. The first will be 30 minutes to rendezvous, and the next will be 15 minutes to rendezvous. Time to rendezvous will be displayed with Noun 39 (fictitious).

Next P36 (a fictitious program) starts and takes care of final braking and station keeping. If you would rather do this manually, simply V37N00E and take over.  As you approach the CSM, watch the -V and position indicator on the docking HUD. They should be fairly close. At 1.8 km distance, TPF begins, and the closing speed is reduced in stages as was done manually on the LM. The LM will come to a stop with windows facing the CSM at a distance of 10 m. When velocities are damped, the LM will pitch forward to present the docking port to the CSM. Let the attitude stabilize, then V37N00E, kit KILLROT and transfer to the CSM to dock. If you don't terminate P36, you'll have quite a time trying to dock - try it and see!


P17 - DOI: Descent Orbit Insertion

P17 will run either on the LM or CSM computer, for the LM, CSM, or docked pair. Start the program with V37N17E. The display will show noun 23, which is:

Noun 23:
   R1=Number of passes BEFORE landing
   R2=MM SS minutes and seconds to plane change burn, or seconds if more than -99 minutes
   R3=Burn dv m/s MM.M

The program will calculate a time-to-burn for the next possible periapsis 15 degrees before the landing site. If you want to Wait until a later time, use V21E to enter in R1 the number of passes over the landing site BEFORE the landing. P17 will will figure out the timings, orientation and dV and do the burn. You can enter V16E to get a countdown to the burn.

P17 doesn't attempt to get the apoapsis to be 110 km. It simply does a burn 195 degrees away from where the landing site will be after the number of passes entered, so as to make the flight path angle zero and have the proper periapsis 15 degrees before the landing site. Since we're going to land, the apoapsis doesn't matter too much.

After running P17, you can run P18 to correct offplane errors.



P18 - Alignment of Orbit with Landing site

P18 will run either on the LM or CSM computer. Start the program with V37N18E. The display will show noun 23, which is:

Noun 23:
   R1=Number of passes
   R2=MM SS minutes and seconds to plane change burn, or seconds if more than -99 minutes
   R3=Burn dv m/s MM.M

The program first calculates an orbit alignment for the next possible alignment. If R1=0, that means the alignment is for the next pass over the PDI point (about 500 km uprange of the landing site) BRFORE a landing or liftoff. You can increase the number of passes using V21E, then enter some number larger than the current value of R1. P17 will now calculate alignment for the site after the designated number of passes, but will execute the burn at the next opportunity.

You can monitor noun 23 with V16E - now you can see the countdown to the burn. When the burn is complete, P18 starts P00.


P16 - LOI


All you need to do is P37N16E. It will display a new noun, (19) which is:

Noun 19:
   R1=time to ignition(before ignition)/time to cutoff(after ignition)
   R2=altitude xxx.x km
   R3=offplane distance xxx.x km



P19 - Orbit Change Program

P19 is a fictious AGC program to change orbits in a general way. It uses non-Hohman transfers to change orbits rapidly at the expense of fuel efficiency, and can usually change your orbit to the desired one in 1/2 orbit. If the current and desired orbits intersect, a single burn is used, otherwise a transfer burn is done to make the orbits intersect, then a correction burn is done at the intersection.

Run P19 using V37N19E. Noun 30 will be displayed:
Noun 30:
   R1=Current Apoapsis XXXX.x km above surface
   R2=Current Periapsis XXXX.x km above surface
   R3=Phase angle XXX.XX degrees

You can change these values using V21E, V22E and V23E, then enter PRO to make the change The phase angle determines the location of the new pariapsis relative to the current one. It can have a value of +180 degrees to -180 degrees. A positive angle will move the periapsis earlier in the orbit than the current periapsis.

When Noun 30 is PROceeded, Noun 50 will be monitored (display only):

Noun 50:
   R1=Time until next burn MM SS
   R2=Burn Delta v in m/s xxxx.x
   R3=Burn Duration, seconds xxxx.x

The single-burn orbit changes use some interesting attitudes. One example to try is for an orbit with very different apo and per, simply V23E and enter +18000. The burn will reverse the location of the apo and per. The downside of these transfers is they use more fuel than Hohman transfer burns done at apo and per, but they get you where you want to be much faster. I think this might be useful in a LM rescue situation where the LM has only 11 hours of oxygen aboard, and the CSM has to get to the LM before it runs out.


There it is,

D.
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Coussini
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« Reply #679 on: January 17, 2006, 01:09:43 PM »

WOW... great comment....

Thanks  Shocked
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movieman
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« Reply #680 on: January 17, 2006, 02:18:54 PM »

Great... looks like we're getting close to something releasable once the important parts of the LEM panel are working.
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slaintemaith
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« Reply #681 on: January 22, 2006, 12:59:18 AM »

Silly question, but, ah, can LazyD's last post there be dropped in the documentation folder in the next (or even the current!) release?  That post there covers very well a lot of stuff that I'm not sure is in the current release docs/notes/etc.
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LazyD
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« Reply #682 on: January 22, 2006, 10:19:46 AM »

Hi Slaintemaith,

I'll do that, and try to keep it up-to-date.  My file is LMdoc.txt.

D.
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LazyD
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« Reply #683 on: January 29, 2006, 03:37:50 PM »

movieman or Tschachim,

Moonwalker made bitmaps for the LM DSKY ALT and VEL lights, but they still don't light up for me.  I can verify that I am calling LightAlt and LightVel.  If I am doing something wrong please let me know.

Also, if anyone knows a good documentation source describing how the landing (and rendezvous) radar are operated and what the instruments should be reading, I'd like to make both work as realistically as possible, and make the LR look at the mesh terrain as we descend to a landing site.

D.
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Apassi
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« Reply #684 on: February 05, 2006, 10:10:35 PM »

Hi

LazyD or Tschachim.

Question:
If Im trying land to Tranquillity base (Apollo Historical missions: 10 Mins to Pdi). The P64 doesnt allow me to adjust rate of descent when Im pressing the minus or equals key.
The whole LPD stuff just stops there including the X-pointer, number of the LPD angle/time, rate of descent and foward velocity.
It just shuts down the DPS engine and I have to do the landing manually.
Though it works perfectly using quick missions scenario: Apollo 14 landing to Fra Mauro, which is fun Very Happy

Whats the difference between Tran-base and Mauro.
Does this meshland stuff work only with Fra Mauro, but not with Tranquillity landing site yet ?
I might be doing something wrong here. Rolling Eyes

Cheers.

Apassi
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LazyD
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« Reply #685 on: February 06, 2006, 06:12:21 PM »

Hi Apassi,

You are completely right.  I did a stupid thing in P64 so if you try to go to P66 before the LM is over the landing mesh, it shuts down the engine and goes directly to P68.

I fixed it, and commited a new lemautoland.cpp.

I appreciate you finding this!

Have fun!

D.
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Apassi
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« Reply #686 on: February 06, 2006, 07:35:46 PM »

Hi LazyD

I compiled lemautoland.cpp. Landing using P66 works perfectly now in Tranquillity base scenario.

Thanks Very Happy

Apassi
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LazyD
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« Reply #687 on: February 06, 2006, 08:47:44 PM »

Hi again Apassi,

One problem I noticed but forgot to mention is that if you go to P66 manual control early in P64, it can be impossible to hit the "+" key enough to reduce your descent rate enough not to crash.

Although this authentic - ( the ROD switch changed descent rate by 1 ft/sec)  it doesn't work out well if you have a big descent rate.

Tschachim mentioned this issue earlier, and I am happy to make a change if anyone thinks it would be good.  An additional problem is that the key handling is pretty slow and you are limited in how often you can hit a "+" and have it be detected.

Any advice will be apprecated.

D.
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Apassi
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« Reply #688 on: February 07, 2006, 11:37:38 AM »

Hi LazyD.

Hi I enjoy flying LM as it is and at least for me ROD changes ok for now.
And more autenthic, more the better.  
Sometimes in future it would be nice to have FDAI, DSKY,  those ROD and fwd velocity tape meters on side of the LPD window.

Apassi
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legion
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« Reply #689 on: August 11, 2006, 06:57:11 AM »

ok lazy ds manual for using the lm descent autopilot is great. i have been looking a long time for this......
...i hope it will work.

lunar landing is so hard...there is not much doc to find...
PLZ how the hell do i deploy the landing gear?(didnt find lls-switch on beta20060731)

-hope one day i will make it-

legion
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