Spacelog Apollo 13

What I'm saying, Jim, is the guys who are working on this attitude situation for the burns haven't made their final conclusions yet, but in the interim period, we want to come up with something you can use, in the event that you lose COMM.

Houston, Aquarius. The Earth is going through the 10-degree line or angle of the LPD.

Okay, We copied 10 degrees. Is that Earth or Moon, Jim?

That is Earth.

And, Houston … As we … No! … has an angle of about 24 degrees on the LPD.

Okay. We read 24, Jim.

Jack, … the LPD on the Moon now is 22 degrees.

Okay. I'm reading you better, Jim. Say again, please.

Roger. The LPD now on the Moon is 22 degrees. I missed the Earth last time. I'll get it this time.

Okay. Twenty-two degrees, and looks like we've come up with a procedure for the attitude control on the upcoming burns. Probably the ones that we'll use from here on out.

Okay, Jack. Stand by 1.

It's going to be a few minutes before I'm ready to read it up to you.

Jack, on the first of the LPD angles is about a minus 2 degrees and just slightly above the top line.

Okay. Just went by minus 2 degrees. Is that on the Earth?

That's the Earth. Now, I don't know whether we're oscillating back and forth or not, Jack, or whether it's a continual motion. We'll have to see here.

Okay, Jack. The Moon now has an LPD angle of 10 degrees

Roger. The Moon at 10 degrees.

Okay, Jim. Just as kind of a lead-in to this procedure that we're going to use for the mid-course to use AGS and it's going to be a manual burn. The attitude will be controlled manually; the start/stop on the engine will be controlled manually. So we have a pretty good vector on you now, and it turns out you're coming in a little bit too shallow. So what that means is we're going to make our burn to come in a little more steeply, and we're going to be coming in around the dark side of the Earth. Therefore, to come in more steep, our thrust should be in the direction of the Sun. Does that all make sense to you?

I think so. We're going to use AGS for a burn monitor. The burns are going to be manual, and they're going to be started manually and stopped manually.

Okay. And your reentry is around the dark side of the Earth, and since we're coming in shallow, we're going to have to burn toward the Sun to make it steeper. Do you follow that?

That's affirm. Especially these burns will be perpendicular to our flight path and to the Sun giving a steeper entry angle.

Okay, Jim. I heard you say perpendicular to your flight path, which is affirmative, and I didn't get the rest of your statement.

I understand the technique, Jack. We're burning to give us time to steepen our entry angle, and it will be perpendicular to our flight path for corridor control.

Okay. That's affirmative. So, in general terms, what we're going to have to do is to power up the AGS and bring up the AGS eight-ball, and then to set up your attitude, put the COAS in the front window, and guidance control will be in AGS, of course. But manually orient the spacecraft to place the center of the Earth directly out the Z-axis. Then rotate about the Z-axis to place the point of the crescent on the Y-axis of the COAS. And this will have your plus X-axis in the direction of the Sun as we discussed before. So the crescent will be up with the point down. Copy that?

Okay, Jack. We'll have to go over what again. The COAS will be out front window; we'll place the Earth in the center of the COAS, and, let's see, the center of the Earth right now is parallel to the LPD which is about parallel to our X-axis. And we'll have to rotate about 90 degrees

Okay, Jim. So we want to get the Y-axis of the spacecraft parallel to the terminator by putting the points of the crescent on the Y-axis.

Roger. Understand.

Seriously, Jack, when I stop the spacecraft looking at—at the Earth, I'm going to have to roll—in LM terms, roll the spacecraft 90 degrees to get the tip of the Earth all on the Y-axis.

That's affirmative, Jim. You're going to have to roll 90 degrees to point your plus X-axis at the Sun and put the crescent—the points of the crescent on the Y-axis. The points of the crescent on the Y-axis with the COAS pointed at the center of the Earth will take care of your yaw and your pitch.

Roger.

Okay, Jim. After you get that orientation to come in a little more steeply, we perform an AGS body-axis aline which is at 400 plus 5 on the DEDA. If the AGS ball is up at this time, the AGS ball will go to 000. We can talk more about control modes later, but we'd recommend doing this, of course, in AGS ATTITUDE HOLD—ATTITUDE HOLD. Put your YAW to MODE CONTROL and leave PITCH and ROLL in PULSE, therefore, controlling your attitude with the TTCA. We don't want to use the gimbal, so have ENGINE GIMBAL OFF. We'll make these burns at 10-percent thrust. We'll use a manual start and stop. For ullage, we'll use the PLUS-X TRANSLATIONAL button, and ullage will be for 10 seconds. Over.

Okay. I understand what you're saying, but you'll have to repeat it here.

Okay. We'll perform the burn in GUIDANCE CONTROL to AGS. And MODE CONTROL to ATTITUDE HOLD. Your ATTITUDE CONTROL switches will be ROLL to PULSE, PITCH to PULSE, and YAW to MODE CONTROL. So the AGS will control your yaw and you will use the TTCA to control pitch and roll. ENGINE GIMBAL OFF; 10-percent thrust. Start and stop manual. For ullage, use the plus-X translational button; 10 seconds ullage. Over.

Okay. For the burn there will be go to GUIDANCE CONTROL AGS, MODE CONTROL ATT HOLD, ATTITUDE CONTROL switches will be ROLL PULSE, PITCH PULSE, YAW MODE CONTROL. We'll use TTCA control for pitch and roll. ENGINE GIMBAL will be OFF; we'll be using 10-percent thrust; we'll start and stop manually, the … control ullage will be a PLUS-X TRANSLATIONAL button. And also our thrust will still be, but before that we are going to do an AGS aline … ball …

That's affirmative, Jim. After you get oriented in the attitude you want to burn in, do an AGS aline which is—an AGS body-axis aline which is 400 plus 5. When you get ENTER, this will bring ball up to 000, and I want to confirm that you—that you said ENGINE GIMBAL OFF. O-F-F. Over.

Roger. Confirm that ENGINE GIMBAL will be off.

And, Jack, how long do you estimate the length of the burns will be?

Houston, Aquarius.

Go ahead, Aquarius.

Okay, Jack. Let's just talk over how I'm going to get to the attitude and then do the burn. What I'm talking about is the control techniques. The way it looks now I'll try to stop the spacecraft in yaw with the Earth out my window, then we'll be in GUIDANCE or we'll be AGS CONTROL; we'll be in—yaw will be in MODE CONTROL. Then we'll be using the TTCAs to control the pitch and then control the roll. I don't see another way we can control the combination that we have here without using the TTCAs. Then we will also use the TTCA during engine burn. Do you people concur with that technique?

Jim, that sounds like the one that is best to use to me. Let me talk it over with the rest of the guys here, and we'll advise you.

Jim, in that control mode, that sounds like the best way to go. The only thing you'll have to do is to get ATTITUDE HOLD in the AGS, and so before you start to maneuver, you'll have to bring the AGS up, and get a 400 plus all zeros in there, and then AGS will respond in yaw when you go to MODE CONTROL. That is, AGS will control your yaw in MODE CONTROL and your pitch and roll can be taken care of in PULSE with a TTCA. After you get in attitude, then, you'll have to re-do an AGS body axis aline which is 400 plus 5, then go back to 400 plus all zeros again.

Right, Jack. That was my next question. I don't want to aline the AGS ball 000 until I am in position, so we use that as a primary attitude burn monitor device.

And, Jim, you can do a 400 plus all zeros any time you want to; that just tells the AGS that you want it to control your attitude should you go to ATTITUDE HOLD in MODE CONTROL.

Roger. I understand, but after we get to the attitude, we'll do a 400 plus 5 to get the AGS aline ball, and then we'll do a 400 plus zero.

Affirmative.

Another thing, Jim, is while you're maneuvering to that attitude using AGS to control your yaw, if you find out enroute to that attitude that you didn't quite have the yaw where you wanted it to be, you can use your ACA and tweak up the yaw, and your AGS needles go right back to zero because you zero the attitude errors.

Roger. Sounds good.

Jim, you'll be splashing down about 560 miles southeast of Samoa at about 0800 local time. The weather forecast for the area is good; 1500, scattered, high broken, 10-mile visibility. The seas will be 5-foot waves, 15 knots, and you'll be going to Samoa by boat and/or aircraft. You'll spend either the night on the boat or in Samoa and return to Ellington by 141 on Saturday, the following day.

Roger. Would you tell the people of the LRL to turn it off.

Oh, no. We're going to do the whole bit.

And don't forget my hack at 88 hours, Jack.

Say again, please, Aquarius.

I want to get my time hack at 88 hours.

Roger. That will be in about 6-1/2 more minutes.

Roger.

Jim, we got a couple of news-type items. President Nixon has chosen a judge from Minnesota for the position of Associate Justice in the Supreme Court. A bill giving federal employees a 6-percent pay raise passed the House and went to the President; includes the military. And the air traffic controllers returned to work.

Well, that's great. You think they'll consider this for flight pay?

Well, we might be able to work out some arrangement.

Standing by for the 88-hour time hack.

Say again, Jim.