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, Jack. I'm looking at your burn pad and I see that the … total gimbal … 19.3 feet per second.

Okay, Jim. We verify 19.3 feet per second for 39 seconds.

The old midcourse technique sounds like something that we came up with on Apollo 8.