Spacelog Apollo 13

Okay. We're going to stop the PTC for LM entry at roll 285, and high gain angles are pitch 23 and yaw 267.

That's correct, Jim. And, 13, Houston. The computer is yours.

The computer is ours. We're in BLOCK, and exactly when do you want the TV to be cranked up?

You can crank it up sometime prior to 55 hours at your convenience just to set it up. We'll be expecting transmission at 55 hours.

Okay.

And, Houston, Apollo 13. One thing I missed about the O₂ fuel cell purge and waste and water dump.

Roger. We'd like the the O₂ fuel cell purge and waste water dump at 54:50.

Roger. We'll pick up those items at 54:50.

Apollo 13, Houston.

Go ahead, Joe.

All right, Jack. One thing we'd like to have done sometime soon is to have you cycle the cryo fans in O₂ tank 2 one more time. We'd like to see if we can get that sensor back.

Okay. O₂ tank 2 fan on now.

Roger.

Houston, 13.

Go, 13.

We—We have just one question, the LM tunnel vent valve. We're questioning why we're venting until the DELTA-V is greater than 1.7 if we are going to open up the tunnel, then pressurize the LM usually.

Right. Stand by on that.

13, Houston.

Go ahead.

Roger. The word on that, Jim, is that they want to insure the proper O₂ concentration in the LM when you get to the surface, and this is a method of doing that by bleeding out additional nitrogen.

Okay. Thank you.

And, 13, Houston. If Jack is up, I'd like to talk to him about the P52, briefly.

Okay. He's here.

Go ahead, Joe.

Okay, Jack. What they'd like you to do on this P52 at 49 hours, they've been observing a slight jitter in the optics shaft angle of about 0.2 of a degree plus or minus. Before you come out of the OPTICS ZERO position, at the start of this P52, they'd like you to just observe the shaft readout, and see if the jitter occurs on your direct readout there, and also they'd like you to briefly call up a VERB 16, NOUN 91 so we can look at the shaft and trunnion angles.

Okay. Let's see if I got it right. On the P52 at 49 hours, before coming out of ZERO on the OPTICS, observe the shaft and also call up 16, 91 and let you look at the shaft and trunnion angles to observe a possible jitter. See whether it occurs in the ZERO position as well as out of ZERO.

Roger, Jack. That's correct; and if you have time, now, I've got a flight plan update for you on looking for the Comet Bennett.

Okay. Stand by 1, Joe. And the commander's going off the air briefly.

Roger that.

Okay, Joe. I'm ready to copy the … now.

Okay, Jack. I'm going to read it to you, and then add some comments and we'll talk about it a little. This should occur sometime after 49:30. After the P52 realine at 49 hours, if time permits we would like the crew to investigate while in PTC if there is a roll angle in which the comet can be observed for photos. If there is, record the optimum roll angle for possible photography, prior to reinitiating PTC at 56:30 or so, whenever the guys are done in the LM, use P52 planet option, and the following half-unit vectors for tracking Comet Bennett at about 49:46. Are you ready to copy half-unit vectors? Over.

Okay. Go ahead, Joe.

Okay. R₁ plus 0.34202, R₂ minus 0.07374, R₃ plus 0.35719. Read back.

Okay. Copy R₁ plus 0.34202, R₂ minus 0.07374, R₃ plus 0.35719.

Okay. That's correct and the last sentence on the update is that you can expect AOS of the comet at a roll of 45 degrees and LOS at a roll of 155 degrees. Now, the deal here, Jack, according to the plots they showed me is, the comet appears to be about 10 degrees away from the Sun, and due to the geometry of the LM there shadowing the Sun, it would appear that you will be able to see the comet through the sextant without getting Sun shafting between roll angles of about 45 degrees and 75 degrees. It appears that as your roll gets higher than 75 degrees, although the comet is still in the field of view, the Sun is also in the field of view, and you probably will not have any success between 75 and 155 if you haven't got it from 45 to 75. If you do find that you can see the comet somewhere between 45 and 75 or 80 degrees, just note that roll angle and then if it's feasible we'd like you to photograph it after the LM entry part of the checklist. Over.

Okay, Joe. Let me give it back to you and see if I've got it here. After the P52, during our PTC you want us to use P52 and observe Bennett's Comet through the sextant; note a roll angle if we can find it visible. It would be visible somewhere between—ideally between 45 and 75 degrees, and we should lose it about 155 roll, and if we do see it, make an observation of whether it is photographable, note the roll angle for photographs to be taken after or prior to initiation of PTC at 56:30.

That's exactly right, Jack.

Apollo 13, Houston.

Go ahead, Joe.