Apollo 15: Lunar Ascent Preparation and RTCC Procedures?

[rcflyinghokie]

After the shape burn, when I go to P00 (V37E 00E) I have a steady COMP ACTY light. V96 will get rid of the light, but if I go back to P00 the COMP ACTY comes back on. I don't know what routine might be running, but how do I stop it? Thanks.

Was this a P00 immediately after the burn? Sounds like your state vector is still integrating. Did you set the surface flag for the LM after jettison (V44)?

You reset it before the shape burn but only after a V66 to put the CSM SV in both slots. If your LM SV was still in there it can cause problems. You can check your SV time with V16 N38 and see where it is compared to your CMC time. If it is far off the easy fix is a V96 and uplinking a new CM SV and V66 and V45 to make sure the surface flag is reset.

 

[Wedge313]

W-matrix. At 236:20 on the flight plan there are some V67 values, position and velocity errors, to load. Is this something I should be calculating with the RTCC somehow, or can we load the flight plan values? (I guess the overall learning opportunity here is : What is the W-matrix, and how is it determined?)

 

[indy91]

Flight plan values. The W-Matrix is the uncertainty matrix of your current state vector. With V67 you give it initial uncertainties. Every good mark makes the uncertainty of your state vector better, bad marks made it worse.

 

[Wedge313]

I've tried to figure out how to calculate MCC-5 on my own, but no luck. The RTCC Input Reference Guide (under TEMCC) refers to steps TAR>ENT>RTE>TIG but on the RTE page I don't see any way to enter the TIG. Also it indicates I should select TYP> Corridor Control, and I couldn't find that either. And I can't find much guidance in the RTCC Manual. I'm going to have to ask for help again. Could you walk me through the MCC calculation process? I'll need help calculating the three MCCs and the re-entry.

Also, while maneuvering for the P23s my SM RCS B and C lights came on. I turned on the SEC PRPLNT, but is it normal for these lights to come on?

Thanks.

 

[indy91]

The input guide hasn't been updated yet for a change in the calculation procedures for the Return-to-Earth maneuvers. The RTCC MFD manual has been updated though, read through the whole Return-to-Earth Targeting section (you can skip the part about the tradeoff display) and you will already have a much better clue. It's mainly a change in terminology and workflow and not really of the way things are calculated. Corridor control is now called the Fuel Critical, Unspecified Area (FCUA) mode. That's what you will want to use for MCC-5 through 7. What is still missing is an example calculation in the manual, but at least all displays and buttons you need are explained.

Yeah I think it's pretty normal for the SEC PRPLNT to be necessary. I'm not sure when it happened on the actual missions, but as you are already on your way home there shouldn't be any danger of running out of propellant.

 

[Wedge313]

OK. Printed out the Return-to-Earth Targeting section, did the highlight and underline thing, dove into the RTCC and came up with some results. But not sure if they're good results.

Starting with TAR>ENT>AST, under TYP I'm using "Unspecified", SIT is FCUA, entered my MCC5 burn time (I used 238:45:00) and estimated splashdown time (295:11:46) . Then AST>CLC and I get the table with the AST results. It gave me a total dV of 0.98, an INCL of A25.76, the GEI (flight path angle) is -6.49. The TEI and splashdown times make sense, and the LAT/LONG is about where I hoped to be (somewhere in the Pacific). (Should the INCL be ascending?)

From the AST I select RTE, used my CUR REFSMMAT and CSUX, then DIS>CLC. The burn time comes up 0:0.6 sec, VC and VT both 0.0.

So based on that I would skip the MCC.

This being my first run-through where I used the RTCC to calculate my TEI burn, I expected some major course correction here. I'm very skeptical of these numbers.

Here's a .scn where I'm at. Could you calculate the MCC and check this for me, and let me know where I'm going wrong? Thanks.

 

[rcflyinghokie]

Just ran the numbers and attached are my results.

If TEI went well and you aren't changing your landing site, you should expect very low dV as it is corridor control and your trajectory hasn't been perturbed much post TEI.

EDIT: Also, for fun, you can see what your MCC-7 would be also, I would wager it will be something worth an RCS burn. Just put MCC-7 time into the AST instead of MCC-5 and see what it spits out.

 

[Wedge313]

Thanks for checking.

 

[indy91]

The RTE Digitals will try to simulate the burn properly, so it probably had a few difficulties to perform your 0.9 ft/s maneuver with the SPS. That's way too short of a burn for a light CSM after TEI, that is why it showed it as zero DV. Not sure about the 0.6, but that can't be the actual burn time. Minimum burn time with the SPS normally is 0.5 seconds, which is probably almost 10 ft/s in Delta V. So instead of the code "CSUX" you want "CRUX". At least for all the post TEI maneuvers it is very unlikely that you would ever need the SPS.

 

[Wedge313]

At least for all the post TEI maneuvers it is very unlikely that you would ever need the SPS.

I fully expected to be making a big burn here. This being my first time calculating the TEI with the RTCC, I had some doubts that the TEI had me headed towards Earth, so I'm glad to know I'm headed in the right direction.

 

[rcflyinghokie]

I fully expected to be making a big burn here. This being my first time calculating the TEI with the RTCC, I had some doubts that the TEI had me headed towards Earth, so I'm glad to know I'm headed in the right direction.

Haha means you did the TEI properly! Just remember for TEI and TEMCC's you do the retrofire uplink so your entry targeting gets uplinked with it.

 

[Wedge313]

Could you walk me through using the RTCC to generate the Entry REFSMMAT? My reentry SXTS check and HORZ check are not close, and I suspect I uplinked a bad REFSMMAT. Thanks.

 

[rcflyinghokie]

You should just be able to choose "lunar entry" from the REFSMMAT selection page and hit CLC and uplink a desired REFSMMAT as usual.

Where did you get your numbers for SXTS/HORIZ checks?

 

[Wedge313]

You should just be able to choose "lunar entry" from the REFSMMAT selection page and hit CLC and uplink a desired REFSMMAT as usual.

Hmmm.....ok, that's what I did.

Where did you get your numbers for SXTS/HORIZ checks?

I probably don't understand the procedure. At about 293:38 on the flight plan we're supposed to maneuver to the "horizon check attitude". The Entry PAD HORZ check pitch is 268 degrees, so I V49'd to 000, 268, 000. But the PAD time of the check is 294:40:37, about 18 minutes before EI. The SXTS star is 11 SFT +02849 TRN +12867. But my attitude (RPY 000, 268, 000) at 293:38 has me nowhere near these checks. Out of curiosity I maneuvered the ship's pitch until I found the SXTS star, and the pitch was 152 (the entry pitch). But I thought we weren't supposed to maneuver to 000, 152, 000 until after CM/SM SEP. So confusion reigns.

 

[rcflyinghokie]

Hmmm.....ok, that's what I did.

I probably don't understand the procedure. At about 293:38 on the flight plan we're supposed to maneuver to the "horizon check attitude". The Entry PAD HORZ check pitch is 268 degrees, so I V49'd to 000, 268, 000. But the PAD time of the check is 294:40:37, about 18 minutes before EI. The SXTS star is 11 SFT +02849 TRN +12867. But my attitude (RPY 000, 268, 000) at 293:38 has me nowhere near these checks. Out of curiosity I maneuvered the ship's pitch until I found the SXTS star, and the pitch was 152 (the entry pitch). But I thought we weren't supposed to maneuver to 000, 152, 000 until after CM/SM SEP. So confusion reigns.

Assuming you are getting these from the entry pad, I will defer to @indy91 as it seems to be some discrepancy on those.

 

[indy91]

Seems like they changed the order of things starting with Apollo 15. From the mission techniques document:

The high-speed entry procedures are updated as follows:
a) The SXT star and boresight star checks which were previously scheduled at EI - 2 hours are now performed at EI - 1:35 (after the P52). To conserve CSM maneuvering, these star checks (to verify the IMU) are performed in the horizon check/separation (no yaw) attitude instead of the entry attitude.
b) For the nominal case, the CM is maneuvered to the entry attitude after CM/SM separation instead of tracking the horizon. Again, this is done to reduce CM maneuvering. In the event of no communication, the horizon Is tracked from separation to entry as on previous missions.
c) The spacecraft control is switched from SCS to CMC DAP at 0.05 g rather than EI - 2 minutes (crew preference).

So on previous missions you maneuvered very early to the entry attitude and did the sextant and boresight star checks in that attitude. Only shortly before CM/SM sep you maneuver to the horizon check attitude, do the check, and then yaw 45° for separation. And this procedure is what our current Lunar Entry PAD calculation assumes, so it doesn't work 100% yet for Apollo 15 and later.

 

[Wedge313]

I've run three re-entries, each with it's own varying levels of success and failure. The first attempt started ok, but the CM started to lift and initially tried to roll, but then abandoned the roll for some reason and ended up with a huge skip, and splashdown was off the west coast of Mexico south of Baha. The second doesn't count, because when the skip began I took over manually and rolled as necessary to avoid the skip, this time ended up north and east of Hawaii. The third attempt I finally figured out that when you start P61 and get F 06 61, you can manually change the LAT/LONG to your desired land point. For some reason my F 06 61 initially showed as 26.28N 171.50W, which was close to my EI LAT/LONG. I changed that to the Entry PAD values 25.48N 157.78W, and this time the CM rolled as necessary to control the path, and ended up north of Oahu at 25.35N 157.76W.

I still have no understanding of the SXTS check and Horizon check, but even though those don't appear to be correct the re-entry seems to go ok (or at least the last one did). And what should I be doing with P27? I don't see any auto uplink going on and I have no idea if I should be manually inputting anything here.

I also have a few procedural questions, such as: on AOH pg. 4-549 the procedure refers to "Auto RCS CM 1 (6) - MNA or MNB, Auto RCS CM 2 (6) - OFF".
Not sure what I was supposed to do here, I just left the Auto RCS configured the way it was per AOH pg. 4-546.

 

[indy91]

The splashdown coordinates would have been uplinked together with the P30 data for TEI and your transearth midcourse correction. Which target did you use there? I would assume that's the 157.78° W one. Which uplink did you use for those burns? Not the Retrofire External DV uplink? Because that uplinks TIG, DV and the splashdown latitude and longitude together. The normal External DV uplink just puts the TIG and DV into the computer. Or did you just manually enter the TIG and DV into P30? Then maybe you never got your splashdown coordinates. But changing them manually in P61 to the PAD coordinates works fine, after all you are supposed to check that the numbers are correct in the Entry Checklist.

The sextant star check simply works as in the entry checklist. You put the trunnion and shaft angles into the computer with V41 N91E and of course you need to configure the optics so that the CMC can drive the sextant. And then it should move the sextant to the star on the PAD. As I said before, the attitude which you are in for the sextant star check is different for Apollo 15 and later but the Entry PAD in the RTCC MFD doesn't account for that yet. So you have to be in the entry attitude, not the horizon check attitude, for the check to work right.

The horizon check requires the use of a window marking on the left rendezvous window. That is the 31.7° line. In the 2D panel you can get the correct view by going left from the left rendezvous panel. Not sure it can be properly done yet in the VC. So at the right time in the right attitude you would then have that line close to the horizon.

I don't understand your question about P27. That is just the uplink program. All uplinks from the RTCC MFD (or the MCC for mission that are supported) go through P27. You can also manually enter P27 and input data, but I don't know where you would get the numbers for that. What is your issue with P27?

For the Auto RCS configuration, the CM RCS has 12 thrusters, divided into 2 systems with separate propellant supply of 6 thrusters each. This procedure basically switches off system 2 and you are only using the 6 thrusters of system 1. As the remark on the right side of that AOH page says, "Electrically isolates CM RCS system 2 for entry. If a problem develops in system 1, disable affected channel and use direct RCS control." So switch off 6 thrusters of system 2, and switch the 6 thrusters of system 1 either to MNA or MNB power. The thruster IDs of the CM RCS thrusters are just below the Auto RCS switches. For example where it says "+Z/11" it is system 1, thruster 1. "25" would be system 2, thruster 5. So that's how you know which thruster belongs to which CM RCS system.

 

[Wedge313]

The splashdown coordinates would have been uplinked together with the P30 data for TEI and your transearth midcourse correction.

Which uplink did you use for those burns? Not the Retrofire External DV uplink?

I may have messed this up, this P30 was for MCC 7? I think I did External dV, not Retrofire. I'll re-check that.

The horizon check requires the use of a window marking on the left rendezvous window. That is the 31.7° line

Yes, I'm looking at the correct line. My confusion is still when I should be seeing the horizon (In spite of your good explanation). The entry checklist has us look at this about 25 minutes before EI. At that point I see nothing, I have to pitch to 345 to get the horizon on the 31.7 line. Later at EI at pitch 152 the line and horizon are ok. So I guess that's OK? I think that's what you're saying. Must be, I don't burn up.

The SXTS check I did was back at 293:40, so I wasn't at the entry attitude yet. I turned the Optics PWR off about 1+15 before EI; I might leave it on next time and see what happens with V41 N91 at the entry attitude approaching EI.

What is your issue with P27?

I don't really have an issue, I'm sure it's a very nice program , just another area I don't know much about. I just saw the Entry Checklist line at EI - 00:45 "P27 & Entry PAD Update" and didn't know what I was supposed to do there.

The thruster IDs of the CM RCS thrusters are just below the Auto RCS switches. For example where it says "+Z/11" it is system 1, thruster 1. "25" would be system 2, thruster 5. So that's how you know which thruster belongs to which CM RCS system.

OK! Another piece of knowledge gained. I didn't understand that.

I'm going to run through the re-entry again a few times to get the kinks out (like re-doing MCC 7 with the Retrofire uplink). But thanks for all the help throughout the whole flight. You guys did all the heavy lifting, and talking me through the RTCC was an added burden on you. But thanks for all the help.

 

[indy91]

I may have messed this up, this P30 was for MCC 7? I think I did External dV, not Retrofire. I'll re-check that.

The return-to-Earth and deorbit targeting always calculate splashdown coordinates for uplink, too. You could say they go together with the P30 data, so when the RTE is the source of the P30 data then it's probably best to uplink Retrofire External DV.

Yes, I'm looking at the correct line. My confusion is still when I should be seeing the horizon (In spite of your good explanation). The entry checklist has us look at this about 25 minutes before EI. At that point I see nothing, I have to pitch to 345 to get the horizon on the 31.7 line. Later at EI at pitch 152 the line and horizon are ok. So I guess that's OK? I think that's what you're saying. Must be, I don't burn up.

I'm only seeing entry interface minus 17 minutes in the checklists for the check. Was there a mission that used 25 minutes? The Apollo 15 Entry Checklist has it at EI-17.

The SXTS check I did was back at 293:40, so I wasn't at the entry attitude yet. I turned the Optics PWR off about 1+15 before EI; I might leave it on next time and see what happens with V41 N91 at the entry attitude approaching EI.

Yeah, this is just the Lunar Entry PAD calculation not accounting yet for the changed procedures on Apollo 15. I'll add that some time.

I don't really have an issue, I'm sure it's a very nice program , just another area I don't know much about. I just saw the Entry Checklist line at EI - 00:45 "P27 & Entry PAD Update" and didn't know what I was supposed to do there.

Ah, that's the last state vector uplink before reentry. As it says in the flight plan at that time, "CSM SV and V66".

I'm going to run through the re-entry again a few times to get the kinks out (like re-doing MCC 7 with the Retrofire uplink). But thanks for all the help throughout the whole flight. You guys did all the heavy lifting, and talking me through the RTCC was an added burden on you. But thanks for all the help.

We are just making up for the fact that doing this all manually instead of with the MCC isn't very well documented or user friendly yet. It helps me figuring that out, too, next time you fly a mission you can probably avoid using the MPT entirely, as I've already done some changes there.