Apollo 15 Post Orbital Insertion Procedures Question

[rcflyinghokie]

I need to look at Apollo 15's descent targeting, but 50000 ft is 8.22 nautical miles. I am curious if they targeted a higher perilune? I think I need @indy91 to weigh in here as it seems a bit odd. 15's PDI started at 50000ft above LLS, so I wonder if our LLS radius is incorrect?

Oh and pericynthion is closest point of approach and perilune is lowest point in lunar orbit, which is why we use PC before entering orbit, hope that helps clear it up!

 

[indy91]

The answer is the lunar gravity. One effect that we get in Orbiter and one we don't get. The effect we don't have is the mascons changing the HA and HP of a lunar orbit over time. That's why DOI has a planned HP of 9.6 NM but over the next hours that altitude becomes lower, the 50,000 ft (or about 8.23 NM) that is desirable for PDI. Because we don't have this effect in Orbiter, our HP is already targeted for the desired number at PDI.

The effect that we do get is the gravity asymmetry as a function of latitude, which is something that Orbiter simulates. In lunar orbit that isn't as strong as in Earth orbit, but if you take the DOI cutoff state vector and calculate HA and HP with it and then numerically integrate the trajectory to the actual perilune you get two different numbers. They only differ by a few tenths of a nautical mile, but that is probably the explanation for a 8.6 NM altitude on the Maneuver PAD, but then the actual perilune altitude is 8.23 NM. The DOI (trim) targeting achieves the actually desired perilune altitude.

 

[Wedge313]

Thanks for that explanation.

Setting up for the burn the flight plan shows they uplinked a "DOI Trim Orient" and later did a P52 opt 1. My current REFSMMAT is the landing site, and I couldn't see a "DOI Trim" REFSMMAT choice in the RTCC. If I stay with my current REFSMATT, won't the RTCC calculate the burn using that and orient the spacecraft accordingly?

And an unrelated question: Where would I find the mission planned fuel usage? A sort of "HOWGOZIT" chart so you can check how well (or poorly) you were managing your fuel consumption (or other consumables)? I've been searching for it (I know I've seen something like that) but can't find it.

 

[indy91]

094:49:21 Parker: Roger. And at 95:43, we will delete the "P52 option 1," because we will be staying on [the] landing site REFSMMAT.

Seems like they simply stayed on the landing site REFSMMAT for the burn. I guess if the burn was larger, maybe with the SPS, they could have changed to the preferred REFSMMAT (P30 in the RTCC MFD), which gives you 0,0,0 IMU angles at ignition. Which REFSMMAT you use for a burn doesn't really matter, as long as you have a good IMU alignment with P52 and the burn doesn't happen in gimbal lock.

The Flight Plan has a section called consumables analysis with the numbers you are looking for. But often copies of the flight plan are missing that section, including the Apollo 15 Flight Plan that can be found on the AFJ. But the Honeysuckle Creek website has a version of the flight plan that has the section, just look for pages 4-1 and later: https://honeysucklecreek.net/msfn_missions/Apollo_15_mission/index.html

 

[Wedge313]

Plodding along, bouncing back and forth between the CSM, LM and RTCC, and just completed the CSM Circularization burn.

One problem I had was with the LM RR Checkout, the LM RR locks on to Endeavour OK, but I couldn't figure out how to get the VHF Ranging to work. I dug into the AOH and believe I have all the VHF switches and the EMS configured correctly, but the EMS reading is stuck on zero. Any thoughts on where I might be going wrong, a "VHF Ranging for Dummies" link? Thanks.

 

[Thespacer]

Not sure if applicable to Apollo 15 (or whether there were any hardware changes meaning the switches should vary) but have you tried cross-checking the Apollo 11 Operations Checklist, page F10-20? https://history.nasa.gov/afj/ap11fj/a11-csmocindex.html

Also, the Apollo 15 CSM G&C Checklist has a procedure to display VHF RNG display on the DSKY (although it assumes all switches are set correctly and P20 running): V87E, V16 N20E, 3703E… R1 will display range (XXX.XX nm) at a max range of 163nm. Not strictly helpful if the switches are not set properly but theoretically a backup display mechanism if the EMS was not set up properly (or failed).

 

[thermocalc]

dear Wedge313, I tried to understand how to "see" the VHF range while inside the CSM and the LM coasting to do the DOI burn (inside the LM I have the RR locked on to the CSM and the Range / range rate values from the display are more or less aligned with the ones from the LGC V83 and the AGS addresses) but I was curious to understand how Collins came to know the range of the LM in the CSM locking at what? which instrument?
I "thought" that there must be a sort of "scale" to convert the DC Volt read on the voltmeter in the panel 100 into NM ... but I didn't go on to investigate further.
I also thought to use the EMS set to VHF RANGE but i got Zero.
if I do the same procedure mentioned in the link above with P20 and B87E i also got R1 00000 .... while according the LM I am at around 11nm ....
BUT at this point I am not sure if i set the "switches" correctly inti the CSM....as you mentioned.
could you please tell me or direct me somewhere were i can find the correct procedure to set the CSM switches to can do VHF ranging ?
(maybe I do something wrong here? I set the VHF A to DUPLEX, VHF RANGE to ON, and CHF B to SIMPLEX).
thanks for your guidance and good luck for your A15 mission, you are a source of inspiration for us (at least for me).

 

[Wedge313]

Hi Thermocalc,

could you please tell me or direct me somewhere were i can find the correct procedure to set the CSM switches to can do VHF ranging ?

I'm still digging, but for switch configurations this is all I have so far (see attached) from the flight plan, LM Timeline, and AOH. It looks to me that it should work whether you have P20 running or not, you should still get a reading on the EMS, but I don't know.

thanks for your guidance and good luck for your A15 mission, you are a source of inspiration for us (at least for me).

Haha! I'm learning as I go, relying on the help of people on this forum who really know this stuff. I glean a lot from reading other people's threads, many times others working with NASSP have asked the same questions and I can learn from their experiences (I know I've picked stuff up from some of your threads).

I'm remembered of a comment a friend of mine once made while filling out an evaluation for one of the men in his division: Under the topic of "Leadership Ability" he said "I can't imagine anyone following this man, unless it was out of idle curiosity."

 

[rcflyinghokie]

Walk us through your setup in the LM and CSM to try to get ranging.

 

[Wedge313]

I went through the sequence a few times this morning, still couldn't get the VHF ranging to work.

As for how I'm configuring, starting on the CSM flight plan at T 100+00 there's an Undocking Checklist, after undocking I'm setting up the EMS and VHF per this checklist. Later, on the LM Timeline Checklist at T 100+46 during the Rendezvous Radar Checkout I'm placing the LM VHF A XMTR to VOICE/RNG. And then when directed I'm back in the CSM, and going to RESET with the VHF RNG switch. My EMS shows 00 (two zeros, no decimal point displayed).

(FWIW I do show a good lock, tracking in the LGC position, N78 and tapemeters agree)

In the Apollo 15 Flight Journal, during this test they had the CSM "go to Simplex A". I think that's because they had lost comm prior to that, but I played around with the VHF AM switch, going from OFF (where the CSM Flight Plan Undock Checklist has it) to Simplex A, and it had no effect on the VHF range on the EMS. I then tried different comm switch positions, VHF antenna positions, playing around with different configurations to see if I could get some reading on the EMS, no joy.

A couple of additional questions/comments: A while back when I ran the CSM RR Activation I couldn't find the "decal" so I used the procedure in the AOH 4.5.6.9. The last step shows in test position B a reading for "RRT AGC SIG", if that's referring to the VHF ranging system (?) I'm showing a reading of about 0.9 when locked on. And when I first started the test my LM HTR CONT TEMP gauge showed a RNDZ radar temp of about zero. After running it for a while the temp comes up, but on panel 11 the HEATERS/RNDZ RDR/STBY circuit breaker is out per the LM Activation Checklist Undocking CB Chart, and I can't find anywhere where I was supposed to push it in (if it's supposed to be in?)

I don't want to beat this to death, but if I'm messing this up I'd like to get it right. Thanks.

 

[indy91]

In terms of switch configuration, it comes down to this:

LM:

VHF A XMTR sw - VOICE/RNG
VHF A RCVR sw - OFF
VHF B XMTR sw - OFF
VHF B RCVR sw - ON

CSM:

EMS FUNC and MODE to VHF RNG
VHF AM A - OFF
VHF AM B - DUPLEX
VHF RANGING - RANGING
VHF AM RCV ONLY - OFF (not sure if strictly required)
VHF RNG - RESET

wait 13 seconds.

It also is attitude dependent, but I think it's very unlikely that you have selected a wrong antenna.

 

[rcflyinghokie]

I went through the sequence a few times this morning, still couldn't get the VHF ranging to work.

As for how I'm configuring, starting on the CSM flight plan at T 100+00 there's an Undocking Checklist, after undocking I'm setting up the EMS and VHF per this checklist. Later, on the LM Timeline Checklist at T 100+46 during the Rendezvous Radar Checkout I'm placing the LM VHF A XMTR to VOICE/RNG. And then when directed I'm back in the CSM, and going to RESET with the VHF RNG switch. My EMS shows 00 (two zeros, no decimal point displayed).

(FWIW I do show a good lock, tracking in the LGC position, N78 and tapemeters agree)

In the Apollo 15 Flight Journal, during this test they had the CSM "go to Simplex A". I think that's because they had lost comm prior to that, but I played around with the VHF AM switch, going from OFF (where the CSM Flight Plan Undock Checklist has it) to Simplex A, and it had no effect on the VHF range on the EMS. I then tried different comm switch positions, VHF antenna positions, playing around with different configurations to see if I could get some reading on the EMS, no joy.

So here is your VHF Ranging configuration (per the AOH)

LM:
COMM VHF A XMTR - VOICE/RNG
COMM VHF B RCVR - RCV

AUDIO VHF A (both) - OFF

CM
VHF AM A - OFF
VHF AM B - DUPLEX
VHF RNG - ON
EMS FUNC - VHF RNG
EMS MODE - VHF RNG

VHF RNG - RSET (hold for at least 1 second)

This should begin range readings within 1 minute on the EMS.

A couple of additional questions/comments: A while back when I ran the CSM RR Activation I couldn't find the "decal" so I used the procedure in the AOH 4.5.6.9. The last step shows in test position B a reading for "RRT AGC SIG", if that's referring to the VHF ranging system (?) I'm showing a reading of about 0.9 when locked on. And when I first started the test my LM HTR CONT TEMP gauge showed a RNDZ radar temp of about zero. After running it for a while the temp comes up, but on panel 11 the HEATERS/RNDZ RDR/STBY circuit breaker is out per the LM Activation Checklist Undocking CB Chart, and I can't find anywhere where I was supposed to push it in (if it's supposed to be in?)

All of those "decals" will be in your systems checklist as well, there is a page for it in the CSM Systems Checklist you can use.
RRT AGC SIG is on the systems test meter.

Regarding your RR, you should have the STBY heater breaker out and the OPR heater breaker in. Do you have both of those out? The OPR breaker heats the RR to about 10F as the normal operating range is 10-50F.

I don't want to beat this to death, but if I'm messing this up I'd like to get it right. Thanks.

Beating this to death is how we learn!

EDIT: I see @indy91 swooped in and beat me

 

[Wedge313]

Placing the LM VHF A RCVR switch to OFF resolved my problem, I got a good reading on the EMS.

I missed something somewhere. I'm looking at the LM AOH, and under the VHF Ranging Check 4.13.2.10 I don't see where the VHF A RCVR gets turned off. And the Comm Basic setup on 4.13.2.1 shows the VHF A RCVR should normally be on.

Not sure where I went wrong here, but hey it's working (thanks to you) and I'll dig around the checklist and try to find how I missed that switch.

Thanks

 

[rcflyinghokie]

Placing the LM VHF A RCVR switch to OFF resolved my problem, I got a good reading on the EMS.

I missed something somewhere. I'm looking at the LM AOH, and under the VHF Ranging Check 4.13.2.10 I don't see where the VHF A RCVR gets turned off. And the Comm Basic setup on 4.13.2.1 shows the VHF A RCVR should normally be on.

Not sure where I went wrong here, but hey it's working (thanks to you) and I'll dig around the checklist and try to find how I missed that switch.

Thanks

Good question. My kneejerk reaction is typically you don't have both VHF A and B receivers running at the same time. But I am diving into the actual system to see if there is a more concrete answer than that haha.

 

[Wedge313]

Plowing ahead.... attempting the undocked P52 and struggling a bit. I'd like to try to figure it out on my own, but one quick question: after sighting the second star and looking at V06N05, what is the accept/reject sighting angle difference? 00003? Thanks.

 

[rcflyinghokie]

Plowing ahead.... attempting the undocked P52 and struggling a bit. I'd like to try to figure it out on my own, but one quick question: after sighting the second star and looking at V06N05, what is the accept/reject sighting angle difference? 00003? Thanks.

Best way I have found for the P52 (assuming using the numpad for RCS) is to turn off the hardover switch it gives you finer pulses so you can mark when the star crosses the axis and do your 4 marks on each. And the rejection angle for the AOT is anything > .12 (00012) but you can get them < 0.03 (00003) with practice.

Also, the procedure for the different ways Apollo 15 uses P52 are in the G&N Checklist, and this includes that rejection angle you asked about.

 

[thermocalc]

sorry to interfere, but i was asking similar question to Wedge313, and I also confirm putting the sw as Indy and rcfly... said I also got the range reading working in the CSM in my A11 mission. Thanks.

@ rcfly:
when you mention to "turn off the hardover switch" to can use pulse mode in the LM for doing P52 more accuratly .... do you mean set the two sw of ACA/4 jets to DISABLE on the left and right of the DSKY?

 

[rcflyinghokie]

@ rcfly:
when you mention to "turn off the hardover switch" to can use pulse mode in the LM for doing P52 more accuratly .... do you mean set the two sw of ACA/4 jets to DISABLE on the left and right of the DSKY?

Yep exactly. If memory serves, that switch in "enable" allows full deflection or "hardover" on the ACA which overrides any auto attitude control and fires the secondary RCS coils.

Since our numpad essentially is full deflection, with that switch enabled it will fire secondary coils. If you switch it off, it will not fire the secondary coils giving you better control with the numpad.

 

[Wedge313]

OK, I give up. I've done this P52 about twelve times and cant figure out what I'm doing wrong.

The maneuver/mark part seems to go ok (after twelve attempts I'm getting the hang of it I think ) , my last try gave me a F 06 05 of +00000 with F 06 93 of +00119, -00074, and +00091. But the LPD check is leaving me with doubts. I set up for NUNKI (037 per the timeline), but after the maneuver NUNKI is nowhere near the COAS and in the expanded LPD view it's sitting on the line but at the 40 mark, so I'm not sure what I should see here. I tried another check using the AOT and NUNKI, after the maneuver NUNKI is not quite centered in the AOT, it's a bit above center. Again, not sure what I should see here.

So I'm not sure if the alignment is correct.

Side Note: The other thing that was driving me nuts was (I forget why) I tried a V49, and input the RPY values I wanted, and after the maneuver my FDAI was nowhere near what I wanted. I checked my gimbal angles with V06N20 and couldn't figure out why the FDAI didn't match. That cost me about seven P52s trying to fix my alignment. Finally figured out that in the CSM V49 F 06 22 you're looking at R,P,Y, but in the LM V49 F 06 22 is Y,P,R. Never noticed that before. (I hope you're laughing with me, not at me).

EDIT: looking at the LM Timeline, I just noticed this (see attached, I had been ignoring it because I didn't know what it was for). So maybe I'm OK?

 

[rcflyinghokie]

It seems that you are in good shape based on what I am seeing. Did you do a AOT star check with P52 (PRO on 00014) and see if it centers your chosen star in the AOT?